Now it is time to explore the anatomy and functions of various cortical areas in more detail. We will begin at the front of the brain and make our way to the back of the brain using a special numbering system developed for this kind of journey.
IN THIS CHAPTER
In this chapter, we will . . .
■ Describe the origins and use of the Brodmann map
■ Survey the cerebral areas and functions using the Brodmann map, especially those functions related to communication and communication disorders
■ The learner will state the main limitation of the Brodmann map.
■ The learner will list the important areas in each lobe of the brain and ascribe at least one function to each area.
■ The Cerebral Cortex
• Frontal Lobe
• Parietal Lobe
• Occipital Lobe: The Visual Cortex
• Temporal Lobe
• Cingulate Cortex
• Insular Cortex
■ Summary of Learning Objectives
■ Key Terms
■ Draw It to Know It
■ Questions for Deeper Reflection
■ Case Study
■ Suggested Projects
At the beginning of the 20th century, a German neurologist named Korbinian Brodmann (1868-1918) developed what is known today as the Brodmann map (FIGURE 8-1). With this map, he divided the human brain into 52 areas based on differences in gross anatomy and cytoarchitecture (i.e., cellular structure) and postulated that each of these areas, either individually or in connection with other areas, is responsible for certain functions. Today this map is a useful way to navigate around the human brain and discuss cerebral functions, with special attention to areas involved in speech, language, hearing, cognition, and swallowing. Instead of moving from area 1 to area 52 numerically, we will move anatomically from frontal to parietal to occipital lobe and, finally, to the temporal lobe.
FIGURE 8-1 A. A lateral view of the left hemisphere with Brodmann numbers indicating cytoarchitecturally distinct areas. B. A medial view of the left hemisphere with Brodmann numbers. The blank white area in the middle would contain the corpus callosum, fornix, thalamus, and other structures.
There is one danger that needs to be mentioned before proceeding. Examining the cerebral cortex in this way could lead one to think that each area is responsible for a certain function and, correspondingly, that this particular function is managed by only that area. For example, is the Wernicke area (Brodmann area [BA] 22) in the superior temporal lobe the only area involved in the comprehension of human speech? The human brain is far more complex than this, with multiple areas in the cortex being involved in various functions, like auditory comprehension, as well as structures in the white matter under the cortex. The Brodmann map is meant to be a simple navigation tool that helps to survey the many complexities of the cerebral hemispheres.
► The Cerebral Cortex
Prefrontal Cortex (Brodmann Areas 9, 10, 11, 12, 46, and 47)
The prefrontal cortex lies in the rostral end of the frontal lobe, with its caudal end being the premotor areas (e.g., BA 6). It is usually defined as areas 8, 44, and 45 in addition to 9, 10, 11, 12, 46, and 47, but for our purposes, we will leave these three areas (BAs 8, 44, 45) for a later discussion (FIGURE 8-2). Overall, the prefrontal cortex is associated with cognition, personality, decision making, and social behavior.
Much is known about the prefrontal cortex through cases of brain damage, the most famous case being that of Phineas Gage from the 19th century. Gage was a 25-year-old man who worked in railroad track installation, clearing rocks from the railroad path. To do this, a hole was drilled in a rock, which was then filled halfway with explosives. Sand was then added on top of the explosive powder to direct the explosion downward, which would split the rock into pieces. A long metal rod, known as a tamping iron, was used to ignite the powder and cause the explosion. On September 13, 1848, Gage became distracted and failed to realize his coworker had not added sand to the hole. When Gage tamped, the powder exploded, sending the metal rod up through Gage’s head, with the entry wound being just under his cheek and the exit wound being at the top of his head where the frontal lobe lies (FIGURE 8-3). The rod fell some 100 yards away, showing the tremendous force of the explosion. Miraculously, Gage survived the tragic accident, but Gage was no longer Gage. Before his accident, Gage was known to be diligent, dependable, and likeable, but after his accident he was bad-tempered, foulmouthed, and antisocial. His injury, though tragic and sad, has taught neuroscientists much about the functioning of the prefrontal cortex.
Brodmann areas are anatomical in nature, being based on cytoarchitecture. These areas in the prefrontal cortex can be regrouped into at least three functional regions (TABLE 8-1).
FIGURE 8-2 The prefrontal cortex occupies Brodmann areas 9, 10, 11, 12, 46, and 47. It sometimes includes areas 8, 44, and 45, which are not shaded but will be discussed later.
FIGURE 8-3 Phineas Gage and his injury.
Courtesy of the National Library of Medicine.
TABLE 8-1 Functional Regions of the Prefrontal Cortex
Dorsolateral prefrontal cortex (DLPFC)
9, 10, 46
Ventrolateral prefrontal cortex (VLPFC)
Orbitofrontal prefrontal cortex (OFC)
Medial Prefrontal Cortex (MPFC)
24, 25, 32
Data from: Bateman, J. R. & Kaufer, D. I. (2018). The dorsolateral and cingulate cortex. In B. L. Miller & J. L. Cummings (Eds.), The human frontal lobes: Functions and disorders (3rd ed., pp. 29-41). New York, NY: Guilford Press.
The dorsolateral prefrontal cortex (DLPFC) region includes BAs 9, 10, and 46. The dorsal DLPFC is involved in working memory, a type of short-term memory used for temporarily holding information needed for different types of cognitive and linguistic processing. The ventral DLPFC is thought to be important for retrieving previously stored information needed to make judgments and decisions. For example, if someone challenged one of your deeply held political views with contradictory evidence, you would search through your stored information on the view and make a decision to either reject or accept the new evidence. You might even change your political view, though deeply held beliefs are difficult to overturn (Kaplan, Gimbel, & Harris, 2016).
The ventrolateral prefrontal cortex (VLPFC) region is BA 47 as well as BA 45. It appears to also be important in working memory as well as episodic memory. Episodic memory is our memory for space-time events, and the VLPFC plays a role in encoding these memories and retrieving relevant memories for goal- directed tasks. A third type of memory that the VLPFC is involved in is autobiographical memory, a personal episodic memory. For example, you have the ability to recall your trip to France, but you also have the ability to insert your personal involvement in the trip into the retelling of those memories (Diamond & Levine, 2018). One additional function of the VLPFC is motor inhibition. For example, if you are walking and suddenly stop because a child ran in front of you, the VLPFC would be inhibiting the motor signals of walking (Aron, Robbins, & Poldrack, 2004). This motor stopping mechanism can be activated by an external signal (e.g., the child suddenly running in front of you) or an internal signal (e.g., you deciding to stop walking because you are tired) (Aron, Robbins, & Poldrack, 2014).
The orbitofrontal cortex (OFC) region, which includes BAs 11 and 12, is involved in learning and decision making. In particular, when you are about to perform an action, the OFC appears to evaluate the possible rewards or punishments associated with that action. In other words, it helps to guess the risks and rewards of certain behaviors. After the behavior is completed, the brain associates the behavior with the resulting reward or punishment, thus learning from the experience (Schoenbaum, Takahashi, Liu, & McDannald, 2011). This process is a type of learning called adaptive learning. Patients with damage to the OFC are often apathetic and irresponsible and demonstrate a lack of facial expression (i.e., flat affect) (Kim, Ogar, & Gorno-Tempini, 2018).
The medial prefrontal cortex (MPFC) region includes BAs 24, 25, and 32. This region is part of the cingulate cortex, which will be discussed later. Functionally, it is involved in working memory, but working memory that is spatial in nature. There are connections to the emotional parts of the brain (e.g., amygdala); thus, the MPFC is involved in emotional memory. Like the VLPFC, the MPFC is involved in autobiographical memory, specifically in one’s ability to integrate a sense of self into episodic memories.
Overall, the prefrontal cortex is responsible for executive control, which involves goal-directed behavior. In other words, humans have the ability to order their cognitive functions to achieve goals, and the prefrontal cortex is the seat of this executive control. Important aspects of this executive control include restraint, initiative, and order (Fuster, 2008). Restraint involves the inhibition of inappropriate behaviors (e.g., sexual urges) due to having foresight (i.e., the ability to predict being rewarded versus being punished), whereas initiative has to do with the pursuit of productive activities (e.g., motivation, creativity). Order is the capacity to sequence information and events logically, and this task involves specific functions like reasoning, working memory, planning, insight, and organization.
Two distinct profiles can emerge after prefrontal cortex damage (TABLE 8-2). A depressive profile emerges with damage to the lateral prefrontal cortex regions, whereas a manic profile materializes with damage to the more anterior and medial regions (Fuster, 2008; Gazzaley & D’Esposito, 2007; Keeley, 2003). A person who fits the depressive profile will be apathetic and indifferent to people and situations, seemingly with a lack of will (abulia) to accomplish goals in life. The result is a lack of movement (akinesia) or talking (mutism), a virtual couch potato. When there is interest in something, it is a perseverative interest (i.e., getting stuck on one an idea). The person may be depressed and have little interest in sex, which can create tension in marital situations. In contrast, people who fit the manic profile will be explosively emotional, with seemingly small incidents triggering major explosions of anger. They will be distractible and unable to maintain motor acts (i.e., impersistence). Because of their distractedness and impersistence, they will appear frenzied (i.e., manic), moving from one task to another without completing the tasks. They will also confabulate or make up memories, often to compensate for memory gaps. Unlike people in the depressive profile, people with a manic profile often are obsessed with the topic of sex, which can create awkward social situations for those who interact with them. Having reviewed these two profiles, which one do you think better describes Phineas Gage after his injury?
TABLE 8-2 The Two Profiles Resulting From Prefrontal Cortex Damage
Profile 1: Depressive
Profile 2: Manic
Explosive emotional lability
Data from: Blumenfeld, H. (2010). Neuroanatomy through clinical cases. Sunderland, MA: Sinauer Associates.
Frontal Lobe: Frontal Eye Fields (Brodmann Area 8)
Area 8, known as the frontal eye fields, is an area located just anterior to the premotor cortex (BA 6) that controls left, right, up, and down eye movements (FIGURE 8-4). Typically, when damaged, a patient’s eyes will deviate or look toward the side of injury. This area is more than a motor area for the eyes, though, as it appears to play a role in the management of uncertainty. Volz, Schubotz, and von Cramon (2005) demonstrated that when test subjects experienced increasing uncertainty, there was increased activation in this area. This area may also be involved in the experience of hope, the feeling that events will turn out for the best (Chew & Ho, 1994).
FIGURE 8-4 Brodmann area 8, the frontal eye fields.
As can be seen by looking at the Brodmann map in Figure 8-4, area 8 is adjacent to the prefrontal cortex and, as mentioned earlier, is sometimes included as part of the prefrontal cortex. This makes sense given this area’s role in uncertainty and hope, which could be thought of as part of the goal-directed behavior associated with executive control. In other words, as we plan a motor behavior, there is a certain amount of hope that the behavior will be successful, but also an uncertainty of its success.
Frontal Lobe: Broca's Area (Brodmann Areas 44 and 45)
The Broca's area is located in the inferior frontal gyrus of the frontal lobe and is sandwiched between the premotor cortex (BA 6) and the prefrontal cortex. It is involved in language processing and speech production. This area is named after the French physician Paul Broca (FIGURE 8-5), who first described it in 1861. Broca had a mysterious speech-impaired patient known only by his last name (Leborgne) and his nickname “Tan.” He received this nickname because “tan” was the only word he could say. Tan suffered from language loss without loss of intellect. Tan’s identity has only recently been discovered as Louis Victor Lebor- gne, an artisan in the shoe trade who suffered from epilepsy since his youth (Domanski, 2013). Leborgne died under Broca’s care; after conducting a postmortem examination, Broca had the evidence to support his theory that the human speech center is located in the inferior frontal gyrus of the frontal lobe, because this is where Tan’s brain damage was (FIGURE 8-6).
FIGURE 8-5 Paul Broca.
Courtesy of the National Library of Medicine.
FIGURE 8-6 The brain of Mr. Leborgne (Tan).
Reproduced from Marie, P (1906). Essai de critique historique sur la genese de la doctrine de Broca. Semaine Medkale, 26, 565-571.
There are two main parts of Broca’s area (FIGURE 8-7), an anterior portion called the pars triangularis (BA 45; Latin for the “triangular portion”) and a posterior portion called pars opercularis (BA 44; Latin for the “lid portion”). As a whole, Broca’s area has an important role in both the comprehension and production of language. For example, pars triangularis (BA 45) in the left hemisphere is thought to support the interpretation of language, especially syntax and the planning and programming of verbal responses. Since BA 45 is also considered to be part of the VLPFC, it may have a role in stopping motor speech processes as well. Pars opercularis (BA 44) in the left hemisphere is thought to initiate and coordinate the speech organs for the actual production of language, which makes sense given its close proximity to a motor-related area called the premotor cortex (BA 6). Area 44 also contains mirror neurons, neurons that not only fire when a subject acts, but also when the subject observes someone else acting. Mirror neurons in area 44 fire in response to others’ hand or mouth movements, and these cells appear important in our ability to imitate the hand and mouth movements of others (Rajmohan & Mohandas, 2007; Rizzolatti & Craighero, 2004). Damage to these neurons can impair a person’s ability to read lips and imitate mouth movements, two strategies often employed in both speech-language pathology and audiology. More generally, the left hemisphere’s Broca area appears to be involved in the ability to retrieve and say verbs and the ability to spell words correctly in writing. Nouns appear to be activated in more posterior brain areas (Gonzalez-Fernandez & Hillis, 2018).
FIGURE 8-7 Brodmann areas 44 and 45, collectively known as the Broca's area.
Broca’s area is thought to be part of a larger dorsal stream of language that is strongly left hemisphere dominant. This is compared to a bilateral ventral stream of language that makes meaning out of heard sound. In short, the ventral stream maps meaning to sound while the dorsal stream maps sound to action (i.e., articulatory action). As already mentioned, the dorsal stream of language is more than Broca’s area; it is theorized to also include the premotor cortex, the anterior insula, and the supramarginal gyrus in the parietal lobe, which acts as an interface between motor and sensory information (Hickok & Poeppel, 2007).
Broca’s area in the right hemisphere is complementary to Broca’s area in the left hemisphere and appears involved in the expression of emotional intonation (or prosody) in our expressive speech as well as the interpretation of intonation, especially the emotional content of others’ prosody (Wildgruber, Ackermann, Kreifelts, & Ethofer, 2006). In addition, both right and left Broca areas seem to play some role in the phonological processing of heard speech (Hartwigsen et al., 2010).
Damage to Broca’s area can cause what is called Broca aphasia, a condition in which people have limited verbal output that is agrammatic in nature. Agrammatism is a symptom of some aphasia types in which patients are not completely grammatical in their speaking. For example, a person with this symptom might say, “Dog . . . walk . . . park” instead of “I walked the dog to the park.” The substantial words (nouns, verbs) are present, but the function words (“to” and “the”) are absent. Patients can also have a cooccurring motor speech disorder called apraxia of speech (AOS), which is difficulty planning or programming the articulators for speech. Patients with this condition experience great effort in speaking but have intact language functions (in pure forms of AOS). AOS leads to searching and groping for articulatory placement as well as random sound substitutions.
FIGURE 8-8 compares the language disorder aphasia to some other communication impairments. This figure divides communication into three processes: input of information (sensation and recognition), central processing of that information (language), and output of a response (planning and execution). Various dysfunctions or breakdowns in these processes are also listed. For example, if there were a breakdown in central processing, the person would then have aphasia. In comparison, if there is a breakdown in planning, a person would have apraxia of speech. This illustration is a helpful tool in summarizing neurogenic communication disorders and seeing the basic differences between them.
FIGURE 8-8 Comparison of different communication impairments.
Data from Davis, G. A. (2000). Aphasiology: Disorders and clinical practice. Needham Heights, MA: Allyn & Bacon.
FIGURE 8-9 Brodmann area 6, the premotor cortex.
Frontal Lobe: Premotor Cortex (Brodmann Area 6)
The premotor cortex is anterior to the primary motor cortex (BA 4) and runs down the length of the frontal lobe to the lateral fissure (FIGURE 8-9). It is involved in selecting, planning, and sequencing of complex voluntary motor movements of the opposite side of the body in the absence of muscular weakness. When it comes to speech, it would appear that this area and area 44 (pars opercularis) have some relationship, because both are involved in motor movement planning and both contain mirror neurons. Damage to the premotor cortex can cause various forms of apraxia (TABLE 8-3). In other words, patients will have difficulty completing motor commands and tasks because they cannot pull up the appropriate motor plan to execute the request. For example, an examiner might ask a patient to show him or her how to salute. The patient would comprehend the command, but then might move his or her hand in strange ways, trying to figure out the motor plan for saluting. This type of apraxia is known as limb-kinetic apraxia.
At the top of area 6 is another area without its own Brodmann number called the supplementary motor area (SMA). This area is thought to be involved with the sequencing of motor movements (Lee & Quessy, 2003), maintaining one’s posture while walking (Penfield & Welch, 1951), initiating internally driven movement (Halsband, Matsuzaka, & Tanji, 1994), and using both hands to complete a task (i.e., bimanual coordination), such as tying a shoe (Serrien, Strens, Oliviero, & Brown, 2002). The SMA is thought to extend from BA 6 into the frontal eye fields (BA 8) (Schlag & Schlag-Rey, 1987).
TABLE 8-3 Different Types of Apraxia
Loss of the idea of how to interact with an object because the knowledge and purpose of the object have been lost. Difficulty seen in sequencing multistep tasks due to this loss.
Loss of ability to voluntarily carry out a motor action though the knowledge and purpose of the object have been retained.
Loss of ability to voluntarily move the limbs (e.g., wave "hello”).
Loss of ability to voluntarily use the dominant hand in drawing figures (e.g., drawing a square).
Loss of ability to voluntarily move and coordinate the lower limbs in a walking motion.
Loss of ability to voluntarily coordinate the limbs in the movements necessary to dress (e.g., button a shirt).
Loss of ability to voluntarily move the eyes.
Oral (or buccofacial) apraxia
Loss of ability to voluntarily move the oral structures in nonspeech movements (e.g., sticking the tongue out).
Apraxia of speech
Loss of ability to voluntarily execute the movements of speech.
Data from: Wertz, R. T., LaPointe, L. L., & Rosenbek, J. C. (1991). Apraxia of speech in adults: The disorder and its management. San Diego, CA: Singular Publishing.
Frontal Lobe: Primary Motor Cortex (Brodmann Area 4)
The primary motor cortex is located on the precentral gyrus just anterior to the central fissure and posterior to the premotor cortex (FIGURE 8-10). In terms of function, it activates the motor plans from areas 44 and 6 by sending motor signals to muscles on the opposite side of the body to move. It has the form of a homunculus (Latin for “little man”), meaning certain areas of this cortex control the motor movements of certain body structures (Figure 8-11A in FIGURE 8-11). For example, the knee is controlled near the top of the primary motor cortex, while the tongue is near the bottom with other speech structures. The homunculus is exaggerated, though, with more motor fibers going to structures that are involved in fine motor movement, such as the tongue and the hands, and fewer fibers to gross motor structures, such as the knee (Figure 8-11B). Damage to the primary motor cortex can result in contralateral hemiplegia or hemiparesis. In terms of speech, damage to this region can result in dysarthria, a motor speech disorder where there is significant weakness in the speech musculature and thus difficulty in executing the movements of speech.
Primary Sensory Cortex (Brodmann Areas 1,2, and 3)
The primary sensory cortex’s anterior border is the central fissure, and its posterior border is made up of BAs 5, 7, and 40 (FIGURE 8-12). From anterior to posterior, the areas are organized 3, 1, and then 2.
Functionally, the primary sensory cortex is similar to the primary motor cortex in that a homunculus can be mapped on it, but instead of activating motor plans, it receives and perceives sensory information from the body (i.e., somatosensory information) (Figure 8-13A in FIGURE 8-13). Sensory fibers from the body project up through somatosensory tracts and are routed through the thalamus to the primary sensory cortex. The primary sensory cortex processes somatosensory information such as touch, temperature, vibration, proprioception (i.e., the body’s eyes for itself), and stereognosia (i.e., tactile knowledge of three-dimensional forms). As mentioned earlier, the primary sensory cortex can be viewed as a homunculus that has exaggerated features corresponding to the amount of sensory fibers a structure requires (Figure 8-13B). For example, the lips of the homunculus are exaggerated because the lips are extremely sensitive structures as compared to the knee, which is less sensitive in comparison. The ears are exaggerated also because of their special sensory abilities.
FIGURE 8-10 Brodmann area 4, the primary motor cortex.
FIGURE 8-11 A. A coronal view of the left primary motor cortex with the homunculus mapped onto it. B. A motor homunculus.
FIGURE 8-12 Brodmann areas 1,2, and 3, the primary sensory cortex (or somatosensory cortex).
Damage to the primary sensory cortex can result in decreased sensory abilities in touch (hemihypes- thesia), temperature (thermoception), and pain (nociception), and in vibration on one side of the body. Damage can also result in an inability to discriminate the tactile characteristics of objects and an inability to identify objects via touch. Phantom limb syndrome, a condition in which amputees continue to sense their missing limb (e.g., feel pain in it), may be associated with this area (Ramachan- dran & Hirstein, 1998). Finally, the primary sensory cortex is remarkably plastic. For example, if a finger is amputated, the primary sensory cortex tissue assigned to that finger will be reassigned to other nearby body parts.
Somatosensory Association Cortex (Brodmann Areas 5 and 7)
BAs 5 and 7 are collectively known as the somatosensory association cortex. These areas lie on the dorsal part of the parietal lobe and are bordered by the primary sensory cortex anteriorly, the visual cortex posteriorly (BA 19), and the supramarginal gyrus (BA 40) ventrally (FIGURE 8-14).
Motor and sensory information are both important to speech. The motor system provides the basic movements needed, but the sensory system provides feedback to refine those movements. For example, if a person holds a paper cup of water, the sensory system influences the motor system so that the person does not hold the cup too loosely so as to drop it or too tightly so as to crush it. Speech is similarly controlled, and the somatosensory association cortex plays a role in influencing the fine movements needed for fluent speech (Dhanjal, Handunnetthi, Patel, & Wise, 2008; Premji, Rai, & Nelson, 2011). In addition, a writing circuit has been identified in the somatosensory association cortex through functional magnetic resonance imaging (Harrington, Farias, Davis, & Buonocore, 2007). Astereognosis, the inability to recognize three-dimensional forms via touch, is associated with damage to area 5 (Endo, Miya- saka, Makishita, & Yanagisawa, 1992; Nakamura, Endo, Sumida, & Hasegawa, 1998).
Angular Gyrus (Brodmann Area 39)
The angular gyrus lies in the parietal lobe, situated between BAs 19, 40, 22, and 37 (FIGURE 8-15). It wraps around the posterior end of the middle temporal gyrus.
The angular gyrus is another important language area in the left hemisphere and is associated with reading and math abilities. In terms of reading, it is involved with visual word form processing along with the middle temporal gyrus and ventral occipitotemporal cortex (Ischebeck et al., 2004; Price, 2012).
FIGURE 8-13 A. A coronal view of the left primary sensory cortex with the homunculus mapped onto it. B. A sensory homunculus.
Damage to the angular gyrus can result in alexia (i.e., difficulty reading) and acalculia (i.e., difficulty with math skills). Writing and disorders of writing have traditionally been associated with the angular gyrus, but Katanoda, Yoshikawa, and Sugishita (2001) found no evidence of angular gyrus activation during writing tasks. Hubbard and Ramachandran (2003) have theorized that the angular gyrus is a player in understanding metaphors. Out-of-body experiences, or the experience of floating outside one’s body, have also been induced through stimulation of the angular gyrus (Blanke, Ortigue, Landis, & Seeck, 2002). Lastly, Gerstmann syndrome is associated with damage to this area. The symptoms of Gerstmann syndrome include agraphia, alexia, finger agnosia (i.e., difficulty identifying fingers), and right-left disorientation (Vallar, 2007).
The right hemisphere’s angular gyrus is important for visuospatial processing, and damage to it can result in a condition called hemispatial neglect (Mort et al., 2003). In this condition, a person technically “sees” information from both left and right visual fields, but neglects or ignores visual information from one of the visual fields. Sacks (1999) tells the story of a woman with this kind of deficit who, when she ate her meal, would eat only food on the right side of the plate. She would also put makeup on only one side of her face, ignoring the opposite side.
Supramarginal Gyrus (Brodmann Area 40)
The supramarginal gyrus (SMG) is just anterior to the angular gyrus in the parietal lobe and wraps around the posterior end of the lateral fissure (FIGURE 8-16). It is surrounded by the primary sensory cortex (anteriorly), the somatosensory association cortex (superiorly), the angular gyrus (posteriorly), and the temporal lobe (inferiorly). The SMG appears to have a close connection to the angular gyrus. These two areas together are known as the inferior parietal lobe.
FIGURE 8-14 Brodmann areas 5 and 7, the somatosensory association cortex.
FIGURE 8-15 Brodmann area 39, the angular gyrus.
Functionally, the SMG appears to be involved with our phonological system, specifically in storing auditory representations of phonemes and phoneme combinations. Because of this role, it is thought to be a part of the dorsal stream of language mentioned earlier. It appears that when we see a written word, the SMG helps us form an auditory image (as opposed to a visual image) of the word, which would also be important in speaking. In other words, when we see a printed word, our SMG helps form the “sound of the word.” Phonological dyslexia is a type of central dyslexia, which is a relatively mild form of dyslexia. It usually does not affect the reading of real words. The real difficulty comes in reading/sounding out new words or nonwords (i.e., pseudowords). For example, a nonword such as phope might be read as phone. Unfamiliar or new words can often be misperceived as being other known words (Stoeckel, Gough, Watkins, & Devlin, 2009). The SMG is also involved in our ability to write single letters (Rektor, Rektorova, Mikl, Brazdil, & Krupa, 2006).
FIGURE 8-16 Brodmann area 40, the supramarginal gyrus.
FIGURE 8-17 Brodmann areas 17, 18, and 19, the visual cortices.
Occipital Lobe: The Visual Cortex
(Brodmann Areas 17, 18, and 19)
BA 17 is the primary visual cortex, and BAs 18 and 19 make up the associative visual cortex. These three areas occupy the entire occipital lobe, the most posterior part of the brain (FIGURE 8-17).
The primary visual cortex (BA 17) is where visual information from the eyes is received via the optic tracts and processed. This cortex area is found in both hemispheres, with information from the left visual field traveling to the right visual cortex and information from the right visual field going to the left visual cortex. Damage to this area from a stroke, brain injury, or other mechanism can result in Anton syndrome (also called cortical blindness), a rare condition in which patients have visual loss along with visual anosognosia (i.e., denial of visual deficits). With the lack of sight, patients with this condition often confabulate about things they are “seeing” (McDaniel & McDaniel, 1991).
Taking into consideration the associative visual cortex (BAs 18, 19) along with primary visual cortex (BA 17), it has been hypothesized that there are two streams of visual function (FIGURE 8-18) (Goodale & Milner, 1992). First, there is a dorsal stream beginning in BA 17 and extending into BAs 18, 19, 7, and perhaps 39. This dorsal stream is responsible for the where of vision. In other words, this stream analyzes motion and the spatial relationships between objects. Second, there is the ventral stream of vision, which also begins in BA 17 and involves BAs 18 and 19 along with BA 37. This is the what of vision, meaning this area analyzes forms, colors, faces, and other details, helping us identify objects and people visually.
FIGURE 8-18 The two streams of vision. The dorsal stream is responsible for the where of vision while the ventral stream is responsible for the what of vision.
Damage to the dorsal stream can result in simultanagnosia, a condition in which a patient cannot put the parts of a visual scene together into a comprehensive whole; optic ataxia, which is difficulty visually guiding the hand to touch an object; and ocular apraxia, which is difficulty voluntarily directing one’s gaze to a certain object. Damage to the ventral stream can lead to prosopagnosia (inability to recognize familiar faces), color blindness, micropsia (where things look abnormally small), macropsia (where things look abnormally large), palinopsia (a reoccurring ghost image), and diplopia (double vision). It is obvious that damage to the visual cortices will significantly impair reading and writing.
Inferior Temporal Area (Brodmann Areas 20 and 21)
The inferior temporal area takes up a majority of the inferior middle gyrus and middle temporal gyrus (FIGURE 8-19). It is involved in the processing of auditory information and language and may be best grouped as part of the Wernicke area (BA 22) due to this functioning. McGuire, Murray, and Shah (1993) have theorized that auditory hallucinations may be associated with dysfunction in this area. It may also play a role in reading facial emotions in conjunction with other areas (Sprengelmeyer et al., 1998).
Parahippocampal Gyrus (Brodmann Areas 27, 28, 34, 35, and 36)
The parahippocampal gyrus is located on the medial surface of the temporal lobe (FIGURE 8-20). There are eight components of this region:
■ Piriform cortex (BA 27)
■ Periamygdaloid cortex
■ Presubicular cortex
■ Parasubicular cortex
■ Entorhinal cortex (BAs 28, 34)
■ Prorhinal cortex
■ Perirhinal cortex (BA 35)
■ Parahippocampal cortex (BA 36)
Superior and medial to the parahippocampal cortex is the hippocampal formation (FIGURE 8-21). It is made up of the following three structures:
■ Dentate gyrus
■ Subiculum (BA 48)
FIGURE 8-19 Brodmann areas 20 and 21, the inferior temporal area.
FIGURE 8-20 The parahippocampal gyrus.
The term hippocampus means “seahorse,” and it was named this because of its compact S shape, like a seahorse’s body. The hippocampus is a key structure for a type of long-term memory called declarative memory, which is our memory for facts (semantic memory) and space-time events (episodic memory) in our lives. The actual storage of memories is thought to take place not in the medial temporal lobe but in the whole of the cerebral cortex itself. The hippocampus is key to storing these memories as well as triggering their release when needed. One of the most important areas for memory in the parahippocampal cortex is the entorhinal cortex (BAs 28, 34), which is a major input/output relay between the cerebral cortex and the hippocampus (Bear, Connors, & Paradiso, 2007; Blumenfeld, 2010).
Fusiform Gyrus (Brodmann Area 37)
The fusiform gyrus (FG) is also known as the occipitotemporal gyrus. It is part of the temporal and occipital lobes (FIGURE 8-22). This area is important for naming objects as well as recognizing and remembering visual objects that have been seen (Tanaka, 1997). In other words, the FG functions as a lexicon; studies have shown that lesions can cause anomia and lexical agraphia (Foundas, Daniels, & Vasterling, 1998; Rapc- sak, Rubens, & Laguna, 1990; Raymer et al., 1997; Saku- rai et al., 2000; Soma, Sugishita, Kitmura, Maruyama, & Imanaga, 1989). Neurofibrillary tangles in the FG may be responsible for naming and object recognition problems (i.e., visual agnosia) that patients with Alzheimer disease face (Thangavel, Sahu, Van Hoesen, & Zaheer, 2008). The FG is also important for facial recognition (Blonder et al., 2004). It has the ability to draw the distinct features of a face into a specific identity. Difficulty recognizing faces is called prosopagnosia, or face blindness (TABLE 8-4). This condition can be developmental or acquired. Sacks (1999) named his book The Man Who Mistook His Wife for a Hat after a case of a music professor who developed prosopagnosia and could not recognize his own wife’s face (and mistook it for a hat). People with this condition usually compensate by using people’s distinct voices to identify them or by using a distinctive physical characteristic, like a scar or a tattoo.
FIGURE 8-21 The hippocampal formation, which lies just superior and medial to the parahippocampal formation.
FIGURE 8-22 Brodmann area 37, the fusiform gyrus.
The Temporal Pole (Brodmann Area 38)
The temporal pole is located on the anterior end of the temporal lobe (FIGURE 8-23). Its functions are many and complex, but only a few will be surveyed here. The left temporal pole is highly involved in language, including semantic processing, speech comprehension, and the comprehension of narratives (Collins et al., 2017; Giraud et al., 2004; Maguire, Frith, & Morris, 1999; Vandenberghe, Nobre, & Price, 2002). The right temporal pole plays a role in identifying familiar voices as well as integrating emotional content of language into narratives (Dupont, 2002; Nakamura et al. 2001). Both temporal poles appear involved in theory of mind (ToM) and empathy (Vollm et al., 2006). ToM is the ability to know you have a mind, that others have a mind, and that their perspectives are different than your own. Empathy, which is related to ToM, describes a person’s attempts to identify with another person’s mental state.
TABLE 8-4 Select Types of Agnosia
Prosopagnosia—inability to recognize previously known faces Simultanagnosia—inability to synthesize all elements of a scene
Pure word deafness—inability to recognize speech
Auditory sound agnosia—inability to recognize environmental sounds Phonagnosia—inability to recognize familiar voices
Astereognosis—inability to recognize objects through touch
Note: Agnosia of taste (gustatory agnosia) and of smell (olfactory agnosia) are also possible.
FIGURE 8-23 Brodmann area 38, the temporal pole.
FIGURE 8-24 Brodmann areas 41 and 42, the primary and secondary auditory cortices.
Auditory Cortex (Brodmann Areas 41 and 42)
Situated on the ceiling of the superior temporal gyrus in roughly BA 41 and 42, the auditory cortex is crucial to the special sense of hearing (FIGURE 8-24). The auditory cortex is the initial cortical region that receives auditory information from the auditory pathway. It processes both sound intensity and frequency. In terms of frequency, this auditory cortex is tonotopically organized (FIGURE 8-25), meaning that neurons at one end of the cortex (the base) are sensitive to higher frequencies and neurons at the other end (the apex) are sensitive to lower frequencies.
One condition that can result from damage to the auditory cortex is pure word deafness (or auditory verbal agnosia), a rare type of auditory agnosia. Sufferers of pure word deafness have a pure deficit whereby they cannot understand speech; however, they do not have difficulties with speaking, reading, or writing. Patients report that they can hear the person talking but cannot understand what is being said. They do not have difficulty with nonspeech sounds, though, such as the ringing of a doorbell or the sound of a dog barking. Pure word deafness is produced by bilateral damage to the primary auditory cortex or by left hemisphere damage that destroys the connection of both auditory cortices to Wernicke’s area (Papathana- siou, Coppens, & Potagas, 2013; Wolberg, Temlett, & Fritz, 1990).
FIGURE 8-25 The tonotopic organization of Heschl's gyrus.
Wernicke's Area (Brodmann Area 22)
Named after the 19th-century German neurologist Karl Wernicke, Wernicke's area is traditionally thought to occupy BA 22 (FIGURE 8-26). It is involved in attaching meaning to auditory information, especially speech and language. In other words, it helps us understand what people say to us. Researchers using neuroimaging data suggest that the processing and understanding of speech is a much wider process that involves, in addition to Wernicke’s area, Broca’s area and other temporal areas, like BAs 20, 21, and 38, and perhaps some parietal areas (Hickok & Poeppel, 2007; Poeppel, Idsardi, & Van Wassenhove, 2008). Based on this, some researchers have theorized a ventral stream of language that processes speech for comprehension. In short, this stream maps heard sound to meaning. This dorsal stream is thought to be bilateral because the superior temporal gyrus is activated in both the right and left hemispheres when exposed to human speech (Hickok & Poeppel, 2007).
FIGURE 8-26 Brodmann area 22, Wernicke's area.
Damage to Wernicke’s area and these related cortical areas (BAs 20, 21, 38) can result in Wernicke aphasia, a form of fluent aphasia. Patients with this type of aphasia have trouble comprehending other people’s language. They verbally produce fluent language, but it is filled with jargon and paraphasias (i.e., word and/or sound substitutions), making their language incomprehensible to others. Written language resembles their verbal production, with significant amounts of jargon and paraphasias (Halpern & Goldfarb, 2013).
(Brodmann Areas 23, 24, 25, 26, 29, 30, 31,32, and 33)
The cingulate (Latin for “band that encircles”) cortex is located in the medial surface of the brain between the corpus callosum and the cingulate sulcus (FIGURE 8-27). Above the cingulate sulcus are the frontal and parietal lobes. The cingulate cortex is a part of the limbic system, our emotional processing center. It receives inputs from the anterior thalamic nuclei and projects to the hippocampus via the parahippocampal gyrus; thus it appears to play a role in memory. It also has many back-and-forth connections with the frontal, temporal, and occipital lobes. Overall, it is a very well-connected area of brain tissue.
Based on cell structure, Vogt (2005) divided the cingulate cortex into four areas, each with a main function:
■ Anterior cingulate cortex (ACC): emotional and cognitive processing
■ Midcingulate cortex (MCC): response selection
■ Posterior cingulate cortex (PCC): personal orientation (autobiographical memory)
■ Retrosplenial cortex (RSC): memory formation and access
Other researchers, such as Kozlovskiy, Vartanov, Nikonova, Pyasik, and Velichkovsky (2012), combine the ACC and MCC, resulting in a three-division model. There is disagreement in the literature about how to organize the cingulate cortex and what functions go where (Shackman et al., 2011). Because of this disagreement, the cingulate cortex will be discussed as a functional whole in the following discussion.
Functionally, the cingulate cortex is involved in cognitive control, which given its proximity to the prefrontal cortex is logical. For example, it appears that more anterior areas help in detecting errors when solving problems and the related function of detecting conflicts in information (e.g., uppercase vs. LOWERCASE). The cingulate is also involved in the perception of pain and the negative emotions associated with pain (e.g., fear) (Shackman et al., 2011).
FIGURE 8-27 Brodmann areas 23, 24, 25, 26, 29, 30, 31,32, and 33, the cingulate cortex divided into four regions.
Posterior areas appear involved in autobiographical memory, which is memory about ourselves and the events we have experienced. These areas may also play a role in managing risky behaviors. For example, if I decide to go skydiving, posterior areas might activate and convince me otherwise. Damage to the RSC has been associated with severe retrograde amnesia. Amnesia is a common word to most, meaning memory loss. Retrograde amnesia is a loss of memory before an event occurs, usually memory closer to the traumatic event. For example, many patients with traumatic brain injury after a motor vehicle accident do not remember the events leading up to the accident. The RSC also appears to be involved in emotional processing and in navigating in familiar places. The whole cingulate cortex appears involved in memory, with the ACC working to filter out irrelevant information and the PCC detecting useful information. If true, this filter and focus process would be an important component in our ability to remember things, like all the new terms in this text (Kozlovskiy et al., 2012).
Folded up and located deep within the lateral fissure is the insular cortex (FIGURE 8-28). It is sometimes referred to as just the insula (insula = “island”). Functionally, it can be divided into two parts, a posteriordorsal portion involved in sensorimotor functions and an anterior part specializing in orofacial programs and emotions. The dorsal-caudal portion is highly connected to the parietal lobe’s somatosensory areas (BAs 5, 7), and its function is similar to these areas’ functions. The anterior part is a way station between the cerebral cortex and the main structures involved in emotions, including the hypothalamus, amygdala, and other subcortical gray areas. It also consists of motor programs for the mouth and face associated with emotion, such as ingestive behaviors (i.e., eating and drinking behaviors), negative food responses (e.g., the look of disgust), and behaviors related to vomiting (Jezzini, Caruana, Stoianov, Gallese, & Rizzolatti, 2012). There is also evidence that this anterior area plays a role in awareness, a state important in consciousness and emotional processing. Awareness includes awareness of body movement, visual images of self, emotions, visual and auditory sensations, and time perception (Craig, 2009).
FIGURE 8-28 The insular cortex.
Clinical data suggest that in addition to these functions, the anterior insula has language functions. Ojemann and Whitaker (1978) concluded that the insula is an additional language area to the language centers located in the frontal lobe. It perhaps plays a role in our ability to pick the appropriate word, a process known as lexical decision making or semantic judgment. In addition, there have been cases of global aphasia reported due to lesions in the insular cortex (Shuren, 1993; Vignolo, Boccardi, & Caverni, 1986), suggesting that the insula does indeed play some important role in our language abilities.
Korbinian Brodmann contributed his mapping of the cerebral cortex to neuroscience, and this system has been a useful tool in navigating it. Several important language areas have been highlighted (e.g., 44, 45) that cluster around the lateral or Sylvian fissure in an area of the left hemisphere known as the perisylvian region.
A word of warning is in order regarding the Brodmann mapping system, however. There is individual variation in the borders of these areas, meaning that every brain has a level of uniqueness. This mapping system is useful to researchers as a kind of shorthand to guide colleagues to general areas of the brain. For example, if one says, “Brodmann areas 44 and 45,” another researcher’s mind will immediately look at the inferior frontal lobe for the Broca area.
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 state the main limitation of the Brodmann map.
• The danger is thinking that each area is responsible for a certain function and that this particular function is managed by only that area.
• The human brain is far more complex than this, with multiple areas in the cortex being involved in various functions as well as structures in the white matter under the cortex.
• The Brodmann map is meant to be a simple navigation tool that helps to survey the cerebral cortex.
2. The learner will list the important areas in each lobe of the brain and ascribe at least one function to each area.
• Frontal lobe areas
□ Prefrontal cortex: Associated with cognition, personality, decision making, and social behavior
□ Frontal eye fields: control of eye movements
□ Broca area: Involved in language processing and speech production
□ Premotor cortex: Involved in selecting and planning complex voluntary motor movements of the body
□ Primary motor cortex: Activates the motor plans from areas 44 and 6 by sending motor signals to muscles to move.
• Parietal lobe areas
□ Primary sensory cortex: Perceives sensory information from the body.
□ Somatosensory association cortex: Plays a role in influencing the fine movements needed for fluent speech.
□ Angular gyrus: Associated with reading and math abilities.
□ Supramarginal gyrus: Involved with our phonological system, specifically in storing auditory representations of phonemes and phoneme combinations.
• Occipital lobe
□ Primary (BA 17) and associative visual cortex (BAs 18, 19): visual processing
• Temporal lobe
□ Inferior temporal area: Involved in the processing of auditory and language information.
□ Parahippocampal gyrus: a key structure for a type of long-term memory called declarative memory, which is our memory for facts (semantic memory) and space-time events (episodic memory) in our lives.
□ Fusiform gyrus: Important for naming objects as well as recognizing and remembering visual objects that have been seen.
□ Temporal pole: Involved in semantic processing, speech comprehension, and the comprehension of narratives.
□ Auditory cortex: Processes both sound intensity and frequency.
□ Wernicke area: Involved in attaching meaning to auditory information, especially speech and language.
□ Cingulate cortex: Involved in cognitive control, perception of pain and negative emotions associated with pain, autobiographical memory, and emotional processing.
□ Insular cortex: Involved in sensorimotor functions and orofacial programs and emotions.
Anton syndrome Apraxia of speech (AOS) Astereognosis Broca aphasia Broca area Brodmann map Cingulate cortex Declarative memory
Entorhinal cortex Hippocampus Insular cortex Macropsia Micropsia Ocular apraxia Optic ataxia Palinopsia
Phineas Gage Phonological dyslexia Prosopagnosia Pure word deafness Simultanagnosia Visual anosognosia Wernicke area
DRAW IT TO KNOW IT
1. Sketch the left hemisphere and label all the important language and speech-related areas with their appropriate Brodmann number.
2. Recreate from memory Figure 8-8.
QUESTIONS FOR DEEPER REFLECTION
1. Given the blank diagram of the left cerebral hemisphere, locate and label all areas possible that were discussed in this chapter.
2. List the important language areas and describe what they contribute to language.
3. Discuss how the functions of the prefrontal cortex are relevant to a student.
Megan is a 32-year-old mother of two young children who reported a sudden loss in the ability to understand speech. Her motor functions were intact as well as her ability to speak, write, and read. She is able to correctly identify environmental sounds (e.g., a dog barking, a door bell ringing, etc.), but could not follow directions given to her auditorily or comprehend
conversation. Megan reports that people’s speech sounds like “gibberish”.
1. What condition do you think Megan suffers from?
2. What brain lobe or lobes have been affected?
3. Can you identify a specific Brodmann area that is likely involved in her case?
1. Research the life of Phineas Gage and write a two- to three-page paper about his life and what his story contributes to our knowledge of the brain.
2. Take one of the specific Brodmann areas discussed in this chapter and perform a Google Scholar search for the most recent information about this area. What are the experts saying?
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