CHAPTER OUTLINE
CHAPTER PREVIEW
As we ascend the central nervous system, we get to what most people think of when they think of the brain—the cerebral hemispheres. In this chapter, we will broadly survey the cerebral hemispheres as well as common disorders associated with their damage.
IN THIS CHAPTER
In this chapter, we will . . .
■ Survey how the brain is protected and nourished
■ Describe the anatomical features of the cerebral hemispheres
■ Survey the lobes of the brain and their function
■ Explain the phenomenon of hemispheric specialization
■ Survey some examples of disorders associated with cerebral hemisphere damage
LEARNING OBJECTIVES
■ The learner will list four structures/systems that nourish and protect the brain.
■ The learner will identify important features of the cerebral hemispheres, including the lobes of the brain.
■ The learner will describe the phenomenon of hemispheric specialization, especially how it relates to language.
■ The learner will list and briefly describe causes of damage to the cerebral hemispheres.
■ The learner will describe the phenomenon of brain plasticity and its principles.
■ Introduction
■ The Protection and Nourishment of the Cerebrum
• Protection: The Meninges
• Protection: The Blood-Brain Barrier
• Nourishment: The Cerebral Arteries
• Waste Removal: The Venous System
■ The Cerebrum
• Important Cerebral Landmarks
• Layers of the Cerebral Cortex
• The Lobes of the Brain
■ Hemispheric Specialization and Connections
• Hemispheric Specialization
• Inter- and Intrahemispheric Connections
■ Cerebral Disorders
• Cerebral Vascular Accident
• Traumatic Brain Injury
• Cerebral Palsy
• Stuttering
■ Brain Plasticity
• Use It or Lose It and Use It and Improve It
• Specificity Matters
• Repetition and Intensity Matter
• Time Matters
• Salience Matters
• Age Matters
• Transference Matters
• Interference Matters
■ Conclusion
■ Summary of Learning Objectives
■ Key Terms
■ Draw It to Know It
■ Questions for Deeper Reflection
■ Case Study
■ Suggested Projects
■ References
► Introduction
The human brain weighs approximately 3 pounds, which is about 2% of a human’s body weight, yet it consumes about 20% of the body’s energy. We humans certainly do not have the largest brains on earth in terms of size (think of a whale or elephant brain), but in comparison to our body size, our brains are quite large. Is this the reason for our superior cognitive skills compared to apes, whales, and elephants? Currently, researchers believe it is not brain size that makes a difference in our cognitive abilities, but rather the number and organization of neurons (Herculano- Houzel, 2009).
Our brains really consist of two brains. We have a left hemisphere and a right hemisphere that together account for 82% of the brain’s mass (Herculano- Houzel, 2009). The surface of the brain consists of what is called the cerebral cortex (cortex is Latin for “bark”), which is made up of neuron cell bodies. These cell bodies produce a gray color, hence the term gray matter. Under this layer lies a layer of white matter that consists of neuronal axons. This tissue is white because of the myelin coating on the axons. The purpose of this chapter is to survey the cerebral hemispheres, especially their gray matter, as well as structures that protect and nourish the hemispheres. We will end this chapter by reviewing various disorders associated with them.
► The Protection and Nourishment of the Cerebrum
Protection: The Meninges
The cerebral tissues have a gelatinous consistency and are made of delicate cells and connections. The meninges, a three-layered membrane that surrounds both the brain and the spinal cord, provides a measure of protection for these central nervous system (CNS) structures (FIGURE 7-1). Our skull protects the brain against things that might penetrate brain tissue, but the meninges is an added layer of protection against blows and shocks to the head as well as against bony protrusions on the inside of the skull. A person need only look at the inside of the skull to realize it is not an especially hospitable place for the delicate tissues of the brain (FIGURE 7-2). In addition to providing protection, the meninges also support the brain, as will be seen.
The three layers of the meninges are as follows: dura mater, arachnoid mater, and pia mater. The dura mater (Latin for “tough mother”) is a membrane that adheres to the inside of the skull. It is made of two dense layers of fibrous connective tissue, an external periosteal lining the inside of the skull (absent in the spinal meninges) and an inner meningeal layer. (Note: Periosteum is a membrane that covers the surface of bones.) Under normal circumstances, these two layers are always pressed together, except where they form sinuses. The dura not only surrounds the brain, but it also creates compartments for the cerebral hemispheres and the cerebellum. For example, it plunges down the longitudinal fissure, a deep groove that separates the right and left hemispheres, to form the falx cerebri (falx is Latin for “curved blade”). Additionally, the dura mater separates the occipital lobes of the brain from the cerebellum to form a structure known as the tentorium cerebelli (Latin for “tent of the cerebellum”). It also descends between the hemispheres of the cerebellum to form the falx cerebelli (Latin for “curved blade of the cerebellum”) (FIGURE 7-3).
FIGURE 7-1 The three layers of the meninges are connective tissue covering the brain. The outermost layer is the dura mater, followed by the arachnoid mater and subarachnoid space, and finally the pia mater.
FIGURE 7-2 The inside of the cranial vault. Note the rough inner surface.
© Jones and Bartlett Learning. Specimen courtesy of the Biology Department, Northeastern University.
There is a potential space between the skull and the dura mater called the epidural space and another potential space under the dura called the subdural space. (Note: A potential space refers to a space that could occur between two structures that are normally pressed together.) The epidural space is an actual space at the level of the spinal cord. During childbirth, some mothers receive an epidural, which is a shot of painkillers that temporarily blocks spinal nerve transmission of pain signals. These potential spaces can become actual spaces when a pathology occurs. For example, if a blood vessel is breached, blood can get into the spaces, a condition known as a hematoma. Patients who experience a hematoma often report headache as a main symptom. This pain results because dura is well supplied with sensory nerves from the trigeminal nerve (cranial nerve V).
FIGURE 7-3 The falx cerebri, tentorium cerebelli, and falx cerebelli.
Under the dura mater is the next layer, the arachnoid mater (Latin for “spider mother”). The arachnoid consists of thin and delicate connective tissue (collagen plus elastic fibers). It gets its name from the actual space below it, called the subarachnoid space. Blood vessels and lacey, spider-web-like support structures (i.e., trabeculae) occupy this space as well as cerebrospinal fluid (CSF). The brain is essentially wrapped in a waterbed, and this fluid protects and supports the brain. Floating on this cushion also reduces the weight of the brain on itself.
The final and innermost meningeal layer is the pia mater (Latin for “faithful mother”). It adheres tightly to the hills (gyri) and valleys (sulci) of the brain. It consists of thin, delicate connective tissue made of collagen and elastic fibers. Blood vessels that run on the surface of the brain actually are located on top of the pia mater in the subarachnoid space.
The arachnoid mater and the pia mater are sometimes grouped together and called the leptomenin- ges, or “thin meninges.” The dura mater is sometimes referred to as the pachymeninx, or “thick meninges.”
Protection: The Blood-Brain Barrier
Over a century ago, early pioneers in neuroscience discovered that if blue dye were injected into the vascular system, it would stain all the tissues in the body blue with two exceptions—the brain and the spinal cord. To explain this finding, neuroscientists theorized that some sort of barrier must prevent the blue dye from reaching the CNS. Today, this barrier is called the blood-brain barrier (BBB).
FIGURE 7-4 A. The structure of a typical capillary versus a nervous system capillary. B. The structure of the blood-brain barrier.
The BBB is located in the walls of CNS blood vessels (FIGURE 7-4). Endothelial cells are tightly packed together and thus are semipermeable, meaning they let smaller molecules from the bloodstream (e.g., oxygen molecules) in but keep larger substances (e.g., bacteria) out (FIGURE 7-5). Large molecules, such as glucose, that are needed by the brain are actively transported through the vascular walls. Tight junctions hold cells together and tightly regulate which substances can pass through. The BBB protects the brain from foreign invaders, hormones, antibodies, and other substances that might adversely affect it. By doing this, the BBB maintains a constant environment for the brain and makes infections of the brain very rare, but when they do occur, they are very hard to treat. There is an exception: The BBB of fetuses and infants is not fully developed; thus, they are susceptible to drugs and other substances. This is why substance abuse (e.g., alcohol) during pregnancy can be so devastating to fetal brains (BOX 7-1).
FIGURE 7-5 Transport of substances through the bloodbrain barrier.
BOX 7-1 Fetal Alcohol Spectrum Disorder
Fetal alcohol spectrum disorder (FASD) is a spectrum of disorders that occur due to maternal alcohol consumption during pregnancy. Neither the placenta nor the fetus's BBB are impediments to alcohol. The fetal liver cannot metabolize alcohol, and once the fetal brain is exposed to it, the central nervous, peripheral nervous, and autonomic nervous systems can all be affected. More specifically, if the brain is exposed to alcohol during the first trimester, it can interfere with migration and organization of neurons within the nervous system. Microcephaly and intellectual disability are possible outcomes (Clarren, Alvord, Sumi, Streissguth, & Smith, 1978). Other outcomes include learning disabilities and other cognitive deficits (e.g., attention deficit). Some children with FASD also have common facial characteristics, such as a smooth philtrum, a thin upper lip, and small eye openings. Children may be below average in height and weight. The Centers for Disease Control and Prevention (CDC) and other organizations have undertaken public awareness campaigns to warn potential parents of the dangers of alcohol consumption during pregnancy (FIGURE 7-6).
FIGURE 7-6 A poster from the CDC campaign to raise aware about the connection between maternal alcohol consumption and fetal alcohol spectrum disorder.
Centers for Disease Control and Prevention (n.d.). Poster: Pregnancy and alcohol don't mix, Retrieved from www.cdc.gov/ncbddd/fasd/documents/FASD-Poster-Pregnancy-and-Alcohol-Don-t-Mix.pdf. © Centers for Disease Control and Prevention.
There are, of course, challenges to having a BBB. Specifically, it is sometimes difficult to get therapeutic drugs (e.g., antibiotics) to the brain. To overcome the protective function of the BBB, special delivery systems have been developed. On a more negative note, many substances can compromise the BBB and lead to unfavorable effects on the brain, including conditions like meningitis, epilepsy, stroke, and brain tumors.
The body does have its own way around the BBB with circumventricular organs (CVOs). These brain structures are highly vascular and lack the normal BBB. CVOs link the CNS, the vascular system, and the endocrine system, creating an alternative route for neuropeptides and hormones. Microglia stand as guards at CVOs, monitoring for pathogens. Some CVOs are sensory organs that monitor for the presence of salt and toxic substances. For example, the subfornical organ, which is located at the roof of the third ventricle, monitors salt concentration in the blood and relays data to the hypothalamus. Another example is the area postrema located at the posterior end of the fourth ventricle. It monitors the blood for toxins and initiates the vomit response if any are present. Other CVOs are secretory organs that secrete hormones into the bloodstream. Examples of these CVOs include the pituitary and pineal glands.
Nourishment: The Cerebral Arteries
As mentioned in the introduction, the brain is an energy hog, consuming approximately 20% of the oxygen in the body. Oxygen nourishes the brain; without it, the brain starves and quickly begins to die. Because of its oxygen dependency, the brain is less tolerant of ischemia (i.e., a lack of blood flow) than other tissues and organs in the body. In fact, only minutes of reduced blood flow and accompanying oxygen deprivation can lead to brain tissue damage (TABLE 7-1). To avoid oxygen deprivation, the brain has a rich blood supply. Oxygen enters the brain through two routes—the internal carotid arteries and the vertebral arteries (FIGURE 7-7). Arteries bring oxygenated blood from the heart to the brain, and veins carry deoxygenated blood from brain tissues back to the heart. We will first survey the arterial system and then the venous system.
FIGURE 7-7 Major arteries supplying blood to the brain.
The carotid artery system includes the external carotid artery and the internal carotid artery. Both arise from the common carotid arteries (FIGURE 7-8). The external carotid artery supplies blood to the face muscles and to the oral, nasal, and eye (orbital) cavities. The internal carotid artery system is a major supplier of blood to the cerebral hemispheres. This artery, which runs up the anterolateral sides of the neck, bifurcates (i.e., splits) to form the anterior cerebral artery and the middle cerebral artery. The anterior cerebral artery supplies blood to the medial surface of the frontal and parietal lobes as well as the corpus callosum (FIGURE 7-9). The middle cerebral artery supplies the lateral portions of the hemispheres and has branches that supply internal structures, like the basal ganglia and internal capsule. Because many language areas in the brain are in this lateral region, strokes involving the middle cerebral artery can be devastating to language function. Before the anterior and middle cerebral arteries bifurcate, collateral branches course out to supply the following structures: the pituitary gland, the eye and optic tract, the hippocampus, and the globus pallidus.
|
TABLE 7-1 Cerebral Blood Flow and Function |
|
|
Functional Status |
Cerebral Blood Flow |
|
Normal function |
40-55 mL/min per 100 grams brain tissue |
|
Reduced brain function |
20-40 mL/min per 100 grams brain tissue |
|
Temporary loss of function |
15-20 mL/min per 100 grams brain tissue |
|
Brain tissue damage |
<20 mL/min per 100 grams brain tissue over several minutes |
Data from: Castro, A. J., Merchut, M. P., Neafsey, E. J., & Wurster, R. D. (2002). Neuroscience: An outline approach. St. Louis, MO: Mosby.
FIGURE 7-8 The internal and external carotid arteries arise from the common carotid artery. The right common carotid artery arises from the brachiocephalic artery, and the left common artery arises from aortic arch.
FIGURE 7-9 The cerebral cortex territory covered by the anterior, middle, and posterior cerebral arteries.
The vertebral artery system arises from the subclavian arteries and supplies the brainstem, cerebellum, occipital lobe, and temporal lobe. The vertebral arteries course up the spinal column and the back of the neck to join and form the basilar artery. Several arteries branch off the basilar artery and supply brainstem and cerebellar structures. The basilar artery bifurcates into the posterior cerebral artery, which supplies the occipital lobe and the inferior portion of the temporal lobe.
The vertebral-basilar system, along with the carotid arteries, feeds a circular array of blood vessels called the circle of Willis (FIGURE 7-10). The ingenious design of the circle of Willis helps promote equal blood pressure and blood flow to all areas of the brain. For example, if one of the carotid arteries becomes occluded, blood will continue to supply the circle of Willis from the remaining carotid and basilar arteries. As people grow older, plaque deposits sometimes form on the carotid arteries, which can become almost completely or completely occluded. Even if this happens, blood will still feed the circle of Willis from the vertebral arteries.
FIGURE 7-10 A ventral view of the brain showing the blood supply to the brain via the internal carotid arteries and the vertebral arteries to the circle of Willis.
© Alila Medical Media/ShutterStock.
FIGURE 7-11 A. The venous system of the brain. B. The superior sagittal sinus.
Waste Removal: The Venous System
The arterial system brings oxygenated blood to brain tissue, whereas the venous system (Figure 7-11A in FIGURE 7-11) acts as a waste disposal system, moving deoxygenated blood away from the brain and moving used CSF away from the ventricular system. Small veins called venules collect deoxygenated blood from capillaries in the brain and dump it into veins. There are two main sets of cerebral veins: the superficial cerebral veins and the deep cerebral veins. The superficial cerebral veins collect blood from the cerebral cortex and subcortical white matter; the deep cerebral veins collect blood from subcortical gray matter structures, like the thalamus and hippocampus.
As mentioned in the section on the meninges, the dura mater has two layers. These two layers are tightly fused through most of the brain; however, there are areas where they are separated. These separated areas are called sinuses; a sinus is a cavity or channel (Figure 7-11B). Inside a sinus is a structure called the arachnoid granulation (or villi). These structures act as drains for deoxygenated blood and CSF, routing these fluids into the brain’s venous system. From there, these fluids drain into the internal jugular veins and return to the heart.
► The Cerebrum
Important Cerebral Landmarks
The cerebral cortex has several notable landmarks. First, there are deep grooves called fissures, shallower grooves called sulci (singular = sulcus), and hills called gyri (singular = gyrus) (FIGURE 7-12). This hill and valley structure is a simple way to increase the surface area of the brain as well as the number of neurons, but also a way to keep the size of the brain relatively small and compact. The surface area of the human brain differs based on sex but generally is around 2.5 square feet (Bhatnagar, 2008; Jones & Peters, 1984), or the size of an unfolded newspaper, which is obviously too large to fit in the skull without crumpling. Cortical surface area and the high degree of folding in the human brain distinguish it from the brains of other primates (Toro et al., 2008).
There are a number of prominent gyri, sulci, and fissures in the human brain (FIGURE 7-13). The frontal lobe has four prominent gyri—the superior frontal gyrus, the middle frontal gyrus, the inferior frontal gyrus, and the precentral gyrus. The parietal lobe also contains four gyri, named the postcentral gyrus, superior parietal gyrus, supramarginal gyrus, and angular gyrus. The temporal and occipital lobes each contain three large gyri. The occipital lobe contains the lateral, superior, and inferior occipital gyri, and the temporal lobe is made up of the superior, middle, and inferior temporal gyri. If the two cerebral hemispheres are pulled apart and the medial portions of the cerebral hemisphere are brought into view, additional gyri can be seen (Figure 7-13B). These include the cingulate, hippocampal, lingual, and fusiform gyri.
FIGURE 7-12 Gyri (hills) and sulci (valleys) of the cerebral cortex.
FIGURE 7-13 A. Prominent gyri of the lateral left hemisphere. B. Prominent gyri of the medial left hemisphere.
FIGURE 7-14 A. Prominent sulci of the lateral left hemisphere. B. Prominent sulci of the medial left hemisphere.
Where there are hills, there are valleys, and various sulci mark the boundaries between the gyri just noted (FIGURE 7-14). The prominent sulci of the lateral frontal lobe include the superior frontal, inferior frontal, and precentral sulci. The parietal lobe contains two notable sulci: the postcentral and the intraparietal sulci. The parieto-occipital sulcus separates the parietal lobe from the occipital lobe. The occipital lobe itself has one major sulcus, the lateral occipital sulcus. The superior and middle temporal sulci are found in the temporal lobe. Again, if the two hemispheres are pulled apart, additional sulci can be observed in the medial portion of the hemispheres (Figure 7-14B). The cingulate sulcus separates the frontal and parietal lobes from the cingulate gyrus. The collateral sulcus separates the hippocampal gyrus from the fusiform gyrus, and the inferior temporal sulcus separates the fusiform gyrus from the inferior temporal lobe. The parieto-occipital and calcarine sulci run through the occipital lobe and eventually meet, separating the cingulate and lingual gyri.
In terms of deep brain valleys, there are three prominent fissures in the human brain. The longitudinal fissure runs from front to back and separates the two hemispheres (FIGURE 7-15). The central fissure, also known as the Rolandic fissure, separates the frontal lobe from the parietal lobe. Finally, the lateral fissure, or Sylvian fissure, separates the frontal and parietal lobes from the temporal lobe (see Figure 7-14A).
All healthy human brains have these hills and valleys; however, in some people, the cerebral cortex is smooth in appearance (FIGURE 7-16). This condition, known as agyria (a = “without”; gyria = gyri) or lissencephaly
FIGURE 7-15 The longitudinal fissure is a deep groove that separates the left and right hemispheres.
FIGURE 7-16 Imaging scan of a normal brain compared to a lissencephalic (LIS) brain.
Courtesy of Dr. Joseph G. Gleeson, University of California, San Diego.
(“smooth brain”), causes severe motor, intellectual, and psychological disability (National Institute of Neurological Disorders and Stroke, 2018). Most people with this condition die before the age of 10 years, though there is at least one case of a person living into adulthood (Hooper, 2013).
Layers of the Cerebral Cortex
In addition to these hill and valley landmarks, the cerebral cortex consists of six distinguishable layers of tissue made up of pyramidal and nonpyramidal neuron cells (FIGURE 7-17). Pyramidal cells take their name from their pyramid shape and are motor in nature. Nonpyra- midal cells are smaller, often star shaped (“stellate”), and are involved in sensory function as well as communication between different parts of the brain. In terms of this communication, there are four basic fiber connections in the cerebral hemispheres (Figure 7-17). First, there are projection fibers that project from the cerebral cortex to subcortical structures. Second, there are callosal fibers that connect the cortex of one hemisphere to the cortex of the other hemisphere. Third, there are association fibers that connect cortical structures in the same hemisphere. Fourth, there are thalamocortical fibers that connect the cerebral cortex to the thalamus.
In terms of cerebral cortex layers, layer I is called the molecular layer, and it consists of glial cells and axons. This layer of cortext is just underneath the pia mater. Layer II is the external granular layer, which is made up of small pyramidal cells and other neurons called granule cells. Small to medium pyramidal cells make up layer III, which is known as the external pyramidal layer. Layer IV is known as the internal granular layer. It consists of nonpyramidal cells (stellate neurons) and receives sensory input from the thalamus. The internal pyramidal layer (layer V) has medium to large pyramidal cells that project to motor areas such as the basal ganglia, brainstem, and spinal cord. This layer is where the primary motor cortex has its pyramidal cells known as Betz cells, which are the largest type of pyramidal neurons. These neurons send their long axons directly down the spinal cord through the corticobulbar and corticospinal tracts, where they synapse with cranial nerve nuclei or spinal cord ventral horn cells that, in turn, directly synapse to their intended muscle. The final layer, layer VI, is called the multiform layer, and it sends excitatory and inhibitory motor fibers to the thalamus. Layer IV and VI form a nice interconnection between the cerebral cortex and the thalamus. Below layer VI is the white matter of the brain (i.e., myelin-coated axons).
The Lobes of the Brain
As mentioned previously, there are four brain lobes (lobe = roundish projection) (FIGURE 7-18 and TABLE 7-2). The frontal lobe lies at the front of the brain, just above the eyes. The posterior border of this lobe is the central fissure. Overall, its main functions include reasoning, planning, and voluntary motor movement. The frontal lobe is important for expressive language and the planning and execution of speech. Lying just posterior to the central fissure and superior to the lateral fissure is the parietal lobe, which functions in touch sensory perception, interpretation, and integration. Lying inferior to the parietal lobe is the temporal lobe, in which the processing of auditory information, including speech, takes place as well as some memory functions (e.g., long-term memory). Lastly, the occipital lobe lies posterior to the parietal and temporal lobes and makes up the very back part of the brain. Its main function is visual processing.
FIGURE 7-17 A coronal section of the brain showing the major types of fibers to and from the cerebral cortex (left) and the six layers of the cerebral cortex (right).
TABLE 7-2 The Lobes of the Brain and Their Major Functions
|
Frontal lobe |
Cognitive functions (e.g., reasoning), speech, and expressive language |
|
Parietal lobe |
Touch perception and interpretation |
|
Temporal lobe |
Receptive language and long-term memory |
|
Occipital lobe |
Visual perception and interpretation |
FIGURE 7-18 The lobes of the brain.
There is also what could be called a fifth lobe located underneath the four lobes just described, called the limbic lobe. It involves the cingulate gyrus and other brain structures (see Figure 7-13B).
► Hemispheric Specialization and Connections
Hemispheric Specialization
The two hemispheres of the brain do look like each other anatomically. The term hemispheric specialization captures the fact that, in terms of function, each hemisphere is not a mirror image of the other; rather, the two hemispheres function uniquely (FIGURE 7-19). The clearest example of hemispheric specialization is language. Ninety-six percent of right-handed people have their language functions lateralized to the left hemisphere, and we would say that these people are left brain dominant for both motor and language functions. In ambidextrous people, that figure drops to 85%, and the percentage drops further in left-handed people to 73%. Reading this the opposite way, about 4% of right-handed, 15% of ambidextrous, and 27% of left-handed people have their language functions localized bilaterally or just in the right hemisphere (Knecht et al., 2000). Extra-linguistic features, such as intonation and stress, are lateralized to the right hemisphere rather than the left hemisphere (George et al., 1996; Ross & Monnot, 2008).
FIGURE 7-19 The function of the left hemisphere compared to the function of the right hemisphere.
Inter- and Intrahemispheric Connections
Interhemispheric Connections
Although the cerebral hemispheres have specialized functions, they do communicate with each other. The corpus callosum is a band of axonal callosal fibers that connects the two cerebral hemispheres (Figure 7-13B and FIGURE 7-20). It has three major parts. The anterior part is called the genu, the middle part is the isthmus, and the posterior section is the splenium.
Functionally, the corpus callosum allows the cerebral hemispheres to communicate with one another. For example, a printed word presented in the left visual field passes to the right hemisphere and then to the left hemisphere via the corpus callosum for written language to be decoded by the language-dominant left hemisphere.
FIGURE 7-20 Coronal section of brain showing the corpus callosum.
Corpus callosum
In patients who have undergone a surgical procedure called a commissurotomy to cut the corpus callosum (i.e., split-brain patients; see BOX 7-2), reading a word flashed in the left visual field is not possible, because the information cannot travel from the right hemisphere to the language-dominant left hemisphere (FIGURE 7-21).
The corpus callosum can be absent at birth (agenesis), thin and underdeveloped (hypoplasia), partially formed (hypogenesis), or malformed (dysgenesis). Kim Peek (1951-2009), a savant who was the inspiration for Raymond Babbitt in the movie Rain Main, had agenesis of the corpus callosum. Some believe that this abnormality, which leads to unique intrahemispheric connections, was involved in Peek’s incredible memory skills. In an examination of Albert Einstein’s brain, examiners found that he had more interhemispheric connections through a thicker corpus callosum than did people in control groups (Men et al., 2014).
Intrahemispheric Connections
Large bundles of neurons make connections within the cerebral hemispheres (FIGURE 7-22). One large notable bundle is the superior longitudinal fasciculus (SLF), an association fiber tract. This bundle is bidirectional and connects the back and front of the cerebrum and the four brain lobes so all can communicate with one another. The SLF is made up of four parts: SLF I, SLF II, SLF III, and the arcuate fasciculus (AF). The AF (FIGURE 7-23) has received much attention because it connects two important speech and language areas— Broca’s area in the inferior frontal gyrus with Wernicke’s area in the superior temporal gyrus. Damage to the AF can sometimes result in a condition called conduction aphasia, in which patients have difficulty repeating words said to them but have preserved speech fluency and auditory comprehension (Catani & Jones, 2005).
BOX 7-2 Split-Brain Research
Some people suffer from severe epilepsy, a condition in which uncontrollable, violent electrical storms arise in one hemisphere and migrate to the opposite hemisphere. Often, these storms can be managed with medications, but when this treatment option fails, patients may benefit from a commissurotomy. In this procedure, the corpus callosum is surgically severed, leaving the two hemispheres to work independently. In other words, the hemispheres no longer communicate with each other (and the epileptic electrical storms no longer pass from one hemisphere to the other, giving patients relief). In essence, it is like the patient now has two brains. It was through research on these patients in the 1950s and 1960s by Roger Sperry and Michael Gazzaniga that the idea of hemispheric specialization was explored. After the surgical procedure, patients had intact consciousness, intelligence, and emotions as well as the same personalities as before the surgery. However, testing showed that each hemisphere indeed had its own abilities (see Figure 7-19).
FIGURE 7-21 An illustration of a commissurotomy, a procedure that affects communication between the left and right hemispheres.
FIGURE 7-22 The superior longitudinal fasciculus.
FIGURE 7-23 The arcuate fasciculus.
► Cerebral Disorders
There are various neurological conditions involving damage to the cerebral hemispheres. Those conditions that speech-language pathologists (SLPs) and audiologists are most likely to encounter are discussed here.
Cerebral Vascular Accident
A cerebral vascular accident (CVA), commonly known as a stroke, is the fifth leading cause of death in the United States. The CDC estimates that about 795,000 Americans suffer a stroke each year, about one person every 40 seconds. Of these people, 610,000 are experiencing a stroke for the first time, and the remaining 185,000 have had a previous stroke. Many people think that strokes happen only to older adults, but about 34% of stroke victims are younger than 65 years of age. Strokes cost the United States approximately $34 billion each year (CDC, 2017).
CVAs involve some kind of interruption to the brain’s blood supply. There are two types of CVA, ischemic CVA and hemorrhagic CVA (FIGURE 7-24). An ischemic CVA involves loss of blood flow to the brain, usually due to a blockage. The blockage originates in either the blood vessel itself (a thrombus) or somewhere else and lodges in a blood vessel (an embolus). A third type of ischemic event is a transient ischemic attack (TIA). In a TIA, there is a loss of blood flow to the brain, but the loss is temporary and CVA symptoms resolve in a matter of minutes or within 24 hours. An ischemic event that lasts longer than 24 hours but less than 72 hours is called a reversible ischemic neurological deficit (Easton et al., 2009; Ferro et al., 1996).
Ischemic stroke damage is focal in nature. The area deprived of oxygen dies in about 1 hour or less (a process known as tissue necrosis); this dead tissue is called an infarct or an ischemic core (FIGURE 7-25). Surrounding the infarct is the ischemic penumbra (Latin for “almost shadow”), an area of traumatized brain tissue that has lost some level of blood flow but has retained enough to stay alive. Though the infarct is lost through necrosis, there is hope the penumbra can be saved within 2 to 4 hours with appropriate medical treatment.
FIGURE 7-24 A. Ischemic cerebral vascular accident (CVA). B. Hemorrhagic CVA.
Modified from © Alila Medical Media/ShutterStock.
FIGURE 7-25 An ischemic infarct or core and ischemic penumbra.
FIGURE 7-26 A large intracerebral hemorrhage.
A hemorrhagic CVA is a bleeding type of CVA and is divided into two types, intra-axial hemorrhage and extra-axial hemorrhage. The term axial refers to what is central in the human body; thus anything inside the brain is intra-axial, and anything outside the brain is extra-axial. An intra-axial hemorrhage involves blood from a ruptured blood vessel inside the brain (an intraventricular hemorrhage would be in the brain ventricles), whereas an extra-axial hemorrhage involves blood in or around the meninges. Intra-axial hemorrhages are also known as intracerebral hemorrhages (FIGURE 7-26). In an extra-axial hemorrhage, the blood is inside the skull but outside the brain. Both intra- and extra-axial hemorrhages result in a hematoma, a collection of blood in a tissue or space. Extra-axial hemorrhages can result in three different kinds of hematomas (FIGURE 7-27).
FIGURE 7-27 Comparison between subdural and epidural hematomas.
First, epidural hematomas occur between the skull and the outer layer of the meninges (dura mater). Second, subdural hematomas occur between the dura mater and the middle layer of the meninges (arachnoid mater). Third, subarachnoid hematomas occur in the arachnoid space, the space below the arachnoid mater.
One mechanism of hemorrhagic CVA is an aneurysm, an abnormal ballooning of an artery’s wall (Figure 7-24B and FIGURE 7-28). There are several different types, but the most common type is a saccular aneurysm, which is also known as a “berry” aneurysm. This type accounts for 80% to 90% of most aneurysms. Aneurysms are ticking time bombs; some people can live for years and never have issues with them, while others can experience a rupture of the aneurysm. Smoking and high blood pressure can further weaken the aneurysm’s wall, leading to a rupture and a rapid flow of blood into the brain (FIGURE 7-29). When this happens, the victim will experience a severe headache, nausea and vomiting, a loss of consciousness, and possibly death if treatment is not immediate.
Because most strokes are ischemic in nature and this damage is typically focal, various communication disorders may or may not be present. If there is left hemisphere damage, many patients will experience receptive and/or expressive aphasia, apraxia of speech, dysarthria, alexia, dysgraphia, and/or acalculia. In right hemisphere damage, patients will exhibit signs of right hemisphere syndrome, including neuromuscular, perceptional, and/or cognitive-communicative issues. They may also experience dysarthria just as patients with left hemisphere damage sometimes do.
FIGURE 7-28 An angiogram showing a saccular aneurysm of the middle cerebral artery.
FIGURE 7-29 A ruptured aneurysm leading to severe bleeding in the brain.
Stroke is diagnosed through a combination of clinical presentation and neuroimaging data via computed tomography (CT) or magnetic resonance imaging (MRI). In the case of hemorrhagic stroke, emergency surgery may be needed. A medication known as tissue plasminogen activator (tPA) has been shown to be effective in reducing disability in case of ischemic stroke if given within 4 hours of onset. This medication involves a protein enzyme that catalyzes the transformation of plasminogen to plasmin. Plasmin is the major enzyme for clot breakdowns in the human body.
After patients stabilize, recovery can involve months of hard work. This is accomplished through a rehabilitation team made up of occupational, physical, and speech therapists.
The American Heart Association, National Stroke Association, and CDC have all created campaigns to raise public awareness of strokes as well as awareness of the risk factors for the disease. In fact, the month of May is National Stroke Awareness Month. During this month, there is a push to raise awareness of the signs and symptoms of stroke. One specific educational campaign is Act FAST. This acronym highlights some of the key considerations in recognizing and responding to a stroke: F = face, A = arms, S = speech, and T = time (FIGURE 7-30). The hope of this campaign and others like it is for people to recognize when someone is having a stroke and to get the person to the hospital as soon as possible so he or she may benefit from newer treatments, such as tPA.
FIGURE 7-30 The Act FAST campaign.
Traumatic Brain Injury
Traumatic brain injury (TBI) is defined as some type of traumatic blow to the brain that impairs the functioning of the brain. It can occur in one of two forms, open head injury and closed head injury. In open head injury, some object (e.g., bullet, shell fragment, rock) penetrates the skull and causes damage to the brain. In contrast, closed head injury involves forces that cause damage to the brain, but without penetrating the skull. There are two subtypes of closed head injury. Acceleration-deceleration closed head injury involves the body (and thus the brain) traveling at a high rate of speed and then suddenly coming to a stop (e.g., a car accident). The second type of closed head injury is impact based. In this situation, the body (and the brain) is stationary, but a moving object impacts the head (FIGURE 7-31). For example, this author once had a patient who had gotten into a verbal altercation in a bar. This patient decided to deescalate the situation and leave the bar but was followed out by the men and was hit in the head with a baseball bat, resulting in a severe impact-based closed head injury.
The CDC reports that around 1.7 million people sustain a TBI each year. In addition, TBI is a contributing factor in 30.5% of all injury-related deaths in the United States. Most TBI cases (75%) are in the form of a concussion or mild TBI. As a result, there are many “walking wounded” in our midst, people we would not immediately identify as having a TBI. Those most susceptible to sustaining a TBI include children, older adolescents, and adults older than 65 years (CDC, 2017; Faul, Xu, Wald, & Coronado, 2010).
FIGURE 7-31 Types and subtypes of traumatic brain injury.
Brain damage due to CVAs tends to be focused to a particular area of the brain (i.e., focal damage). The one exception is in the case of large intra-axial hemorrhages. In contrast, brain damage because of TBI tends to be widespread in nature (i.e., diffuse damage), especially in closed injury. This is because the forces applied to the brain in TBI can lead not only to the brain banging up against the inside of the skull (coup damage) and rebounding to the opposite site of the skull (contrecoup damage) but also to damage from rotational forces (FIGURE 7-32). These rotational forces can cause the brain to twist, resulting in the shearing and tearing of axonal fibers as well as metabolic changes (Garnett, Blamire, Rajagopalan, Styles, & Cadoux-Hudson, 2000; Gennarelli, Thibault, & Graham, 1998). This type of damage typically does not show up on conventional imaging studies, though the results can be devastating to the patient. In terms of communication disorders, aphasia, right hemisphere syndrome, dysarthria, apraxia of speech, and/or dysphagia may be present due to the diffuse nature of damage associated with TBI.
FIGURE 7-32 Coup and contrecoup impact.
The diagnosis of TBI is made through knowledge of the injury mechanism (e.g., motor vehicle accident), clinical presentation, and neuroimaging. Recovery may involve various medications and possibly surgery in some cases. The rehabilitation team will be crucial in a patient’s recovery process.
FIGURE 7-33 A child with cerebral palsy.
Cerebral Palsy
Cerebral palsy (CP) is a nonprogressive brain disorder that affects movement, posture, and balance (FIGURE 7-33). It can also affect speech and swallowing in some cases. Cerebral refers to the brain and palsy refers to paralysis or uncontrolled movements. CP develops before birth (prenatal), during birth (perinatal), or shortly after birth (postnatal) and can be caused by a lack of oxygen, premature birth, infections, brain hemorrhages, jaundice, and head injury (CDC, 2018b). It is the most common childhood motor problem (CDC, 2018a).
There are four types of CP based on movement problems (FIGURE 7-34). Spastic CP is the most common form, occurring in 80% of cases; it involves damage to the cerebral hemispheres. It is characterized by muscle stiffness and rigidity. These issues can occur on one side of the body (hemiplegia), just in the legs (diplegia), or in all four limbs (quadriplegia). Dyskinetic CP involves problems with muscle tone that affect the whole body because of damage to the basal ganglia system. Muscle tone can change from hour to hour or day to day. For example, a child may wake up with stiff, rigid muscle tone, which may normalize later in the day but then decrease at night. Ataxic CP involves discoordination between muscle groups because of cerebellar damage; it results in clumsy movement and difficulty walking. This type of CP is caused by damage to the cerebellum. Finally, mixed CP involves more than one type of motor issue (Pellegrino, 2002). CP can also be described by the body parts involved in the condition. Hemiplegic CP involves the arm and leg on one side of the body. When just the legs are involved, this is called diplegic CP. Quadriplegic CP involves all four extremities.
CP is initially diagnosed at birth through clinical presentation and reevaluated when a child is 18 to 24 months old. Neuroimaging is employed if the etiology of the child’s CP is unknown. Occupational, physical, and speech therapy will be performed to reduce disability and get the child to his or her maximal functional capacity.
FIGURE 7-34 Types of cerebral palsy.
Stuttering
Stuttering (or stammering) may seem like an odd addition to this list of cerebral disorders, but there are probable neurophysiological differences in the brains of those who stutter versus those who do not stutter. Fluency refers to the smoothness with which sound, words, and sentences flow during oral language; disfluency is any interruption in this smoothness. All people are disfluent at one time or another, but stuttering is different from normal disfluency. Normal disflu- ency involves problems with whole words or between words. For example, an interjection (“um”) is a disfluency that occurs between words. In stuttering, the disfluency often occurs within words (though there may be whole-word or between-word disfluencies also). For example, people who stutter will repeat or prolong sounds, or a sound will be blocked.
There is no one cause for stuttering. Genetics are involved in many cases, but the environment also seems to play a role in the condition. Whatever the causes, there may be brain differences between those who stutter and those who do not. For example, the right nonlanguage hemisphere is overactive and the left language hemisphere is underactive in some people who stutter. More specifically, the right frontal operculum, which is in about the same place as Broca’s area in the left hemisphere, is sometimes overactive. Another overactive area in some people who stutter is the right insula, an area of the cerebral cortex folded deep within the lateral fissure (Brown, Ingham, Ingham, Laird, & Fox, 2005; Fox, 2003). In contrast, speech motor areas and auditory areas in the left hemisphere are underactive in some people (Guitar, 2013).
Stuttering is diagnosed by an SLP through clinical presentation. The SLP will then use one of two (or both in some cases) therapy approaches, stuttering modification or fluency shaping. Stuttering modification focuses on the moment of stuttering and training patients to stutter more easily and with less tension. Fluency shaping does not focus on moments of stuttering, but rather on fluency itself and strategies that promote better fluent speech. There is evidence that the brain is changed through these therapies and that the right hemisphere quiets down while the left hemisphere ramps up its activity to more typical levels (Guitar, 2013). This evidence shows the principle of brain plasticity, which will be discussed next.
► Brain Plasticity
Brain plasticity or neuroplasticity refers to the adaptive capacity of the human brain. The brain is always changing, rewiring itself in response to internal and external influences. You are experiencing neuroplasticity right now as you read and study this text. Your brain is changing by the text (external influence) and by your own previous knowledge and experiences with neuroscience and neurological disorders (internal influence). How do our patients recover from some of the devastating conditions outlined in this chapter? The answer is through neuroplasticity.
Use It or Lose It and Use It and Improve It
There are many principles of neuroplasticity (TABLE 7-3). The first principle is “use it or lose it,” which explains that failure to drive certain brain functions leads to loss. For example, a lack of cognitive activity in older adults can contribute to the loss of some cognitive skills (Burda, 2011). Another example is patients on prolonged mechanical ventilation who lose their swallowing ability, in part because of a lack of exercise of the swallowing muscles (Tolep, Getch, & Criner, 1996).
The second principle is the corollary to the first— “use it and improve it.” This principle states that training of a specific brain function leads to improvement (Kleim & Jones, 2008). For example, continued cognitive activity into older adulthood reduces the risk of dementia (Gates & Valenzuela, 2010).
As discussed earlier, some stroke patients experience hemiparesis or hemiplegia. Physical therapists have taken advantage of the “use it or lose it” and “use it and improve it” principles of neuroplasticity through constraint-induced movement therapy (CIMT). In this therapy the patient’s good arm is restrained, forcing the patient to use only the impaired hand in therapy. CIMT has resulted in some substantial functional improvements in many patients, but also imaging data showing increased cerebral metabolism. This same approach has been adapted in speech-language pathology, resulting in a therapy known as constraint- induced language therapy (CILT). In CILT, patients are forced to use verbal language only. In other words,
TABLE 7-3 Principles of Neuroplasticity
|
Principle |
Description |
|
Use it or lose it |
Failure to drive certain functions can lead to loss. |
|
Use it and improve it |
Training of certain brain functions can lead to improvement. |
|
Specificity |
The nature of the training experience dictates the nature of plasticity. |
|
Repetition matters |
Induction of plasticity requires sufficient repetition. |
|
Intensity matters |
Induction of plasticity requires sufficient training intensity. |
|
Time matters |
Different forms of plasticity occur at different times of training. |
|
Salience matters |
The training experience must be important to induce plasticity. |
|
Age matters |
Training-induced plasticity occurs more readily in younger people. |
|
Transference |
Plasticity in response to one training experience can enhance the acquisition of similar behaviors. |
|
Interference |
Plasticity in response to one experience can interfere with the acquisition of other behaviors. |
Data from Kleim, J. A., & Jones, T. A. (2008). Principles of experience-dependent neural plasticity: Implications for rehabilitation after brain damage. Journal of Speech, Language, and Hearing Research, 51, S225-S239.
they cannot use another communication modality or compensatory strategy. Through two additional principles of neuroplasticity (intensity and shaping), patients play games like Go Fish while depending on their verbal skills only. Many patients have experienced gains in their verbal language because of this approach, which taps into the brain’s natural ability to adapt (Pulvermuller et al., 2001).
Specificity Matters
Specificity means that the nature of training experience dictates nature of plasticity. In other words, specific, functional tasks can change the brain more than unspecific, general tasks can. Semantic feature analysis, a word-recall treatment, is an example of a specific treatment targeting a specific skill. In this treatment approach, clinicians help their patients to recall the semantic features of a noun (e.g., lion—fur, king, roars), with the intent of reestablishing semantic connections and improving naming. Identifying the semantic features of target words is a very specific therapy and is more likely to induce changes in the brain than is a less specific treatment.
Repetition and Intensity Matter
Repetition is defined as ongoing practice over time. It is sometimes referred to as dose frequency. For example, a patient’s dose frequency might be 60-minute treatment sessions, three times per week for 12 weeks. This dose frequency would be a lot of repetition of therapy over this period (i.e., 36 total hours of therapy). While repetition refers to the treatment experience more broadly, intensity is focused on the dosage of treatment within individual therapy sessions. In other words, to how many teaching trials or episodes is a patient exposed in a treatment session? Some therapists practice high-intensity dosing, which is also known as massed practice. This practice is focused on teaching a patient a new skill. Other clinicians might choose a low-intensity dose (also called distributed practice) that is more focused on the maintenance of a learned skill. CILT often uses massed practice in the form of 20 to 25 teaching trials in a 1-hour session.
Time Matters
After injury, the brain is more plastic at some times and less plastic at other times. For example, in the acute phase of stroke recovery, the brain is in a state of shock for the first 3 to 4 days and is not very plastic. After 4 days to around 4 months, the brain is more plastic as it recovers. During the chronic phase of recovery (4 months and after), the brain is finding a new normal and is still plastic, but less so than in the post-stroke period (day 4 to 4 months).
Salience Matters
Salience refers to something that is important or meaningful. The principle of salience matters means that the training experience must be important to the patient in order to induce plasticity. A rewarding, functional, motivating therapy task is more like to induce brain plasticity than is a nonrewarding, nonfunctional, boring task. For example, if a patient is a foodie, then therapy tasks that focus on menu reading and recipe following might be more beneficial than tasks focused on automobile maintenance, an area of noninterest for the patient.
Age Matters
This principle states that training-induced plasticity occurs more readily in younger people than in older people. Younger is defined as 50 years of age or younger. This distinction does not mean that plasticity is absent in people older than 50 years, but that it is less dramatic. This principle probably does not shock most readers, as we all remember being children and bouncing back from illness or accidents more quickly than we do now as adults.
Transference Matters
Transference (or generalization) means that plasticity in response to one training experience can enhance the acquisition of similar behaviors. For example, word-retrieval activities for atypical words (e.g., artichoke) may more readily generalize to untrained but related typical words (e.g., carrot). Or, a writing therapy that focuses on correct spelling of words might transfer to better reading ability.
Interference Matters
We are all familiar with bad habits and understand how they can interfere with learning. For example, many students complain that social media can distract them from studying. Interference, as its name suggests, means that as one experience changes the brain, it can interfere with gaining a new and possibly better behavior. Pain, seizures, psychological conditions, and substance abuse are all conditions or behaviors that can change the brain to the detriment of acquiring other behaviors, such as the knowledge and skills for a career in speech-language pathology or audiology.
► Conclusion
This look at the cerebrum surveyed structures that protect and support it, such as the meninges and vascular system. Macroscopic features, like sulci and gyri, were explored next. We discovered that the cerebral hemispheres are not mirror images of each other functionally; each has specialized functions.
Of great importance to those studying communication disorders is the left hemisphere, which is the language-dominant hemisphere for most people. Significant damage can occur to the speech, language, and swallowing systems due to CVAs and TBIs, but some of the effects of this damage can be overcome by applying the principles of neuroplasticity in therapy.
SUMMARY OF LEARNING OBJECTIVES
The following were the main learning objectives of this chapter. The information that should have been learned is below each learning objective.
1. The learner will list four structures/systems that nourish and protect the brain.
• Protection: the meninges and the bloodbrain barrier
• Nourishment: the cerebral arteries
• Waste removal: the venous system
2. The learner will identify important features of the cerebral hemispheres, including the lobes of the brain.
• Fissures: deep grooves in the brain
• Sulci: shallower grooves in the brain
• Gyri: hills in the brain
• Longitudinal fissure: Separates the right and left hemispheres.
• Central fissure: Separates the frontal lobe from the parietal lobe.
• Lateralfissure: Separates the frontal and parietal lobes from the temporal lobe.
• Frontal lobe: Main functions include reasoning, planning, and voluntary motor movement.
• Parietal lobe: Functions in sensory perception and interpretation.
• Temporal lobe: Perception and comprehension of speech takes place as well as some memory functions.
• Occipital lobe: Main function is visual processing.
3. The learner will describe the phenomenon of hemispheric specialization, especially how it relates to language.
• In terms of function, each hemisphere is not a mirror image of the other; rather, the two hemispheres function uniquely. The clearest example of hemispheric specialization is language. Ninety-six percent of right-handed people have their language functions lateral- ized to the left hemisphere.
4. The learner will list and briefly describe causes of damage to the cerebral hemispheres.
• Cerebral vascular accident (CVA): Also known as stroke. A condition caused by an interruption to the brain’s blood supply through either a blockage (ischemia) or bleeding (hemorrhage).
• Traumatic brain injury (TBI): a traumatic blow to the brain that impairs the functioning of the brain. There are two kinds, open and closed head injury. In open, the skull is penetrated by an object; in closed, the skull is not.
• Cerebral palsy (CP): a nonprogressive brain disorder acquired before, during, or shortly after birth that affects movement, posture, and balance.
• Stuttering: a condition characterized by inword interruptions to the free flow of speech.
5. The learner will describe the phenomenon of brain plasticity and its principles.
• Brain plasticity refers to the adaptive capacity of the human brain. The brain is always changing, rewiring itself, in response to internal and external influences. The following are specific principles of neuroplasticity:
□ Use it or lose it: Failure to drive certain functions can lead to loss.
□ Use it and improve it: Training of certain brain functions can lead to improvement.
□ Specificity matters: The nature of the training experience dictates the nature of plasticity.
□ Repetition matters: Induction of plasticity requires sufficient repetition.
□ Intensity matters: Induction of plasticity requires sufficient training intensity.
□ Time matters: Different forms of plasticity occur at different times of training.
□ Salience matters: The training experience must be important to induce plasticity.
□ Age matters: Training-induced plasticity occurs more readily in younger people.
□ Transference: Plasticity in response to one training experience can enhance the acquisition of similar behaviors.
□ Interference: Plasticity in response to one experience can interfere with the acquisition of other behaviors.
KEY TERMS
Agyria Aneurysm Arachnoid mater Arachnoid space Blood-brain barrier (BBB) Carotid artery Central fissure Cerebral palsy (CP) Cerebral vascular accident
(CVA)
Circle of Willis
Circumventricular organs (CVOs)
Closed head injury Commissurotomy Contrecoup damage Corpus callosum Coup damage Deep cerebral veins Diffuse damage Disfluency
Dura mater
Embolus
Epidural hematomas
Epidural space
Extra-axial hemorrhage
Fissures
Fluency
Fluency shaping
Focal damage
Frontal lobe
Gyri (gyrus)
Hematoma
Hemispheric specialization
Hemorrhagic CVA
Infarct
Intra-axial hemorrhage
Ischemic CVA
Lateral fissure
Limbic lobe
Lissencephaly
Longitudinal fissure
Neuroplasticity Occipital lobe Open head injury Parietal lobe Pia mater Stuttering Stuttering modification Subarachnoid hematomas Subarachnoid space Subdural hematomas Subdural space Sulci (sulcus) Superficial cerebral veins Temporal lobe Thrombus Transient ischemic attack (TIA) Traumatic brain injury (TBI) Venous system Vertebral artery
DRAW IT TO KNOW IT
1. Sketch of the meninges, including the brain and skull. Label the following: dura mater, arachnoid mater, subarachnoid space, and pia mater.
2. Sketch of the left hemisphere (see Figures 7-13 and 7-14) and label all the major gyri and sulci as well as the lobes of the brain (see Figure 7-18).
QUESTIONS FOR DEEPER REFLECTION
1. List the four lobes of the brain and one function associated with each.
2. Describe the concept of hemispheric specialization as it relates to language.
3. Describe components of neuroplasticity that might be important to rehabilitation.
CASESTUDY
Ben is a 75-year-old male who suffered a sudden onset of right-sided weakness and aphasia. Upon admission to the hospital a CT scan was completed, which did not show any abnormalities. An MRI was completed later, which reveal a small infarct in the left frontal hemisphere near the lateral fissure. Ben was
administered tPA and both his weakness and language abilities improved.
1. Explain what type of stroke Ben suffered.
2. Why do you think it is this type of stroke?
3. In thinking about the location of the stroke, why were motor and language functions affected?
SUGGESTED PROJECTS
1. Read the article by Kleim and Jones (2008) and give a presentation to the class on how neuroplasticity is important in speech-language therapy.
2. Find two or three sources on split-brain research and write a two- to three-page paper discussing how hemispheric specialization was discovered.
3. Read My Stroke of Insight by Jill Bolte Taylor and write a two- to three-page reflection paper. Half of the paper should be a summary of the book, and the other half should contain your reflections/ reactions to the book.
4. Create a stroke prevention campaign that includes a poster, brochure, and public service announcement.
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