In the preceding chapters we have described the many parts of the brain that contribute to the self. The diversity of the brain, however, stands in stark contrast to the subjective unity of the mind. In this chapter, I explore the belief that the essence of a mind, and a conscious and self-conscious self, extends beyond or is “more than the sum of the parts” of the material brain. This is the claim that the immaterial mind emerges from the many parts of the material brain.
Emergence and the Brain
In order to understand the claim that the self and the mind emerge from the brain, there are three key interrelated concepts to consider. The first concept is the idea of emergence itself. The doctrine of emergence, according to philosopher Jaegwon Kim, holds that
although the fundamental entities of this world and their properties are material, when material processes reach a certain level of complexity, genuinely novel and unpredictable properties emerge, and that this process of emergence is cumulative, generating a hierarchy of increasingly more complex novel properties. Thus, emergentism presents the world not only as an evolutionary process but also as a layered structure—a hierarchically organized system of levels of properties, each level emergent from and dependent on the one below.1
One popular example of an emergent system is water, for which it is noted that the properties of liquidity, wetness, and transparency do not apply to a single water molecule, but to the aggregate “water.” In biology, emergent properties are viewed as the result of hierarchicallyordered living things. A hierarchy, in the general sense of the term, refers to an organized system composed of multiple parts arranged in a graded series of levels. In accord with Kim's definition, emergence in living things occurs as the product of a hierarchically organized system—the organism—in which each level of complexity of the organism produces novel
emergent features from the levels below it. Emergent properties are also said to be unpredictable in that complete knowledge of the parts at a lower level of a hierarchy would not allow the prediction of the appearance of the emergent property at the higher level. In this way, the emergent feature is said to be “greater than the sum of its parts.”
A second key concept of emergence theory is the notion of constraint. Although the term emergence connotes the way that the parts in a hierarchy combine to form wholes, constraint is the process by which higher levels in the hierarchy impose control over the lower levels. Campbell coined the term “downward causation” to refer to the control that a higher level of a hierarchy exerts on its contributing parts.2 The biologist H. H. Pattee pointed out the importance of constraint in biological systems:
If there is to be any theory of general biology, it must explain the origin and operation (including the reliability and persistence) of the hierarchical constraints which harness matter to perform coherent functions. This is not just the problem of why certain amino acids are strung together to catalyze a specific reaction. The problem is universal and characteristic of all living matter. It occurs at every level of biological organization, from the molecule to the brain. It is the central problem of the origin of life, when aggregations of matter obeying only elementary physical laws first began to constrain individual molecules to a functional, collective behavior. It is the central problem of development where collections of cells control the growth or genetic expression of individual cells. It is the central problem of biological evolution in which groups of cells form larger and larger organizations by generating hierarchical constraints on subgroups. It is the central problem of the brain where there appears to be an unlimited possibility for new hierarchical levels of description. These are all problems of hierarchical organization. Theoretical biology must face this problem as fundamental, since hierarchical control is the essential and distinguishing characteristic of life.3
It is through constraint that hierarchical systems operate. In biological systems such as a person, the individual cells of the human body constrain the microscopic organelles of the cell to perform cellular metabolism; the organs of the body constrain the cells so that they secrete enzymes; the entire body of the person constrains the organs to digest, breathe, and perform all the macroscopic functions necessary for the life of the body.4
There is often a reciprocal relationship between emergence and constraint in hierarchical systems. If you were to look at a single cell from the
human lung, for example, under a high-powered microscope, you would see the thousands of miniscule organelles within the cell. Among these organelles would be found the mitochondria, the organelles responsible for generating energy from the oxygen we breathe via a process known as cellular respiration. These tiny organelles are a part of the cell that along with other cells make up the tissues that eventually give rise to the lung. The mitochondria contribute to the structure of the lung and therefore to the emergence of the lung at a higher level of the hierarchy of the body. The lung, at a higher level on the hierarchy, displays emergent features not possessed by mitochondria, such as the capacity to move air in and out of the body. If the lung did not breathe, the body would not have oxygen, and if we did not have oxygen, the mitochondria would not be able to carry on cellular respiration. In this manner the higher level property of breathing constrains the activity of the mitochondria. When the system is considered as a whole, the mitochondria contribute to the emergence of the lung, and the lung in turn constrains the mitochondria.
The third key concept of emergence theory that I wish to discuss is perhaps its most controversial. This concept is the notion ofnonreducibility, the claim that the wholes created by an emergent system cannot be explained simply by or reduced to the properties of its constituent parts. According to Medawar and Medawar, in their book The Life Science the nonreducibility of a higher level to a lower level in a hierarchical system is a key characteristic of an emergent property.5 They define emergence as the “philosophical doctrine opposed toreducibility which declares that in a hierarchical system each level may have properties and modes of behavior peculiar to itself and not fully explicable by analytic reduction.”6 According to the Medawars, if a property is emergent, it is not reducible to those parts. It follows that if a property in a hierarchy is reducible to the properties of things at lower levels of the hierarchy, it is not emergent.
According to philosopher John Searle, the basic idea underlying the principle of reduction was the notion that “certain things might be shown to be nothing but certain other sorts of things.”7 Searle also pointed out that a satisfactory scientific reduction involves a form of identity relation that he calls a “nothing-but” relation: a property A is said to be reducible to property B if it can be shown that A “is nothing but” B. In other words, we do not need to invoke a new or novel property to explain A over and above those principles by which we understand B. Searle identified several subtypes of reduction in his writings, but what Searle called ontological reduction is the form of reduction most relevant to emergence theory:
The most important form of reduction is ontological reduction. It is the form in which objects of certain types can be shown to consist in nothing but objects of other types. For example, chairs are shown to be nothing but collections of molecules. This form is clearly important in the history of science. For example, material objects in general can be shown to be nothing but collections of molecules, genes can be shown to consist in nothing but DNA molecules.8
Examples of successful ontological reductions in neuroscience include the identification of the manner in which motor action can be reduced to the physiology of the nerve and muscle, or the determination that paralysis can be reduced to a lesion of the motor system. These processes at one time considered mysterious and beyond the reach of natural science can now be explained in purely biological terms. Similarly, there currently is no “seizure-brain enigma” because we understand how the observable epileptic fit can be reduced to abnormal electrical discharges of cortical neurons in a particular brain region.
The three key aspects of emergence theory that I have enumerated are emergence, constraint, and nonreducibility. Keeping these general principles in mind, we now are ready to consider theories that view the mind as an emergent feature of the brain. The brain is generally thought of as a hierarchically organized system, and the concept of hierarchical organization is central to those theories that view the mind and the self as emergent phenomena. According to emergence theories of the mind, the self“emerges” from the complex interactions of the hierarchically organized parts of the brain. C. Lloyd Morgan was a leader of the school of emergentism. He viewed the emergence of mental phenomenon in terms of a hierarchical model of the brain. He wrote:
In the foregoing lecture the notion of a pyramid with ascending levels was put forward. Near its base is a swarm of atoms with relational structure and the quality we may call atomicity. Above this level, atoms combine to form new units, the distinguishing quality of which is molecularity; higher up, on one line of advance, are, let us say, crystals wherein atoms and molecules are grouped in new relations of which the expression is crystalline form; on another line of advance are organisms with a different kind of natural relations which give the quality of vitality; yet higher, a new kind of natural relatedness supervenes and to its expression the word “mentality” may be applied.9
Morgan views the mind as emerging at the summit of the brain, just like the eye that sits atop the pyramid in Figure 1-2. According to emergentist theory, the “cyclopean eye” is an emergent phenomenon as well. As you will recall from the last chapter, the problem of the cyclopean eye refers to the question of how visual unity is possible with both eyes when either eye alone is capable of a complete and independent visual image. Why do we not see two of everything, one image coming from each eye? According to the principles of emergence theory, the images from each eye are components of the lower level of the visual hierarchy. These components are combined to create a single and unified cyclopean eye that “emerges” in consciousness as a single cyclopean image. It is this cyclopean eye that sits atop the visual hierarchy, just like the eye poised on top of the pyramid. The whole of the cyclopean eye is greater than the sum of the parts that are contributed by each eye alone. When we view with one eye open, we lack depth perception. When we view our environment with both eyes open, due to the differences between the images generated by each eye, the cyclopean eye possesses depth perception for the integrated image. Depth perception is an emergent property of vision not present when viewing with either eye alone.10
Roger Sperry Argues for the Emergence of an Immaterial Mind
The psychologist Roger Sperry, who received the Nobel Prize for his work on the split brain, argued that the mind constitutes an emergentphenomenon deriving from diverse parts of the material brain. Sperry claimed that the mind is “more than the sum of the parts” of the material brain and that the mind goes above and beyond the brain's physical limitations in important and sometimes mysterious ways. In Sperry's words: “conscious phenomena are different from, more than, and not reducible to, neural events. . ..”11 All the features of emergence theory were present in his formulation of the relationship between the mind and the brain. Like most emergence theorists, Sperry viewed the mind-brain relationship in hierarchical terms and supposed that the neural elements of the brain combine in increasingly complex configuations until at the summit of organization, the mind emerges. Just as the unified cyclopean eye sits atop the visual hierarchy, Sperry argued the unified “I” sits atop the neural hierarchy of the entire brain. But Sperry took this idea further. He argued that since the mind was an emergent feature of the brain, the mind, therefore, could not be reduced to the brain. Since the mind could not be reduced to the physical brain, it was not a material substance like the brain. Lastly, another result of Sperry's formulation was the view that
emergent mental forces or properties, while not material, can nonetheless influence the material body. Even though the mind is not material, it can cause material events to happen in the brain. In this way, Sperry suggested that the immaterial mind has causal properties over the material brain and constrains the brain. Sperry articulated his thoughts on the nature of consciousness as follows:
consciousness was conceived to be a dynamic emergent of brain activity, neither identical with, nor reducible to, the neural events of which it is mainly composed. Further, consciousness was not conceived as an epiphenomenon, inner aspect, or other passive correlate of brain processing, but rather to be an active integral part of the cerebral process itself, exerting potent causal effects in the interplay of cerebral operations. In a position of top command at the highest levels in the hierarchy of brain organization, the subjective properties were seen to exert control over the biophysical and chemical activities at subordinate levels. It was described initially as a brain model that puts “conscious mind back into the brain of objective science in a position of top command . . .a brain model in which conscious, mental, psychic forces are recognized to be the crowning achievement . . .of evolution.”12
The causal power attributed to the subjective properties is nothing mystical. It is seen to reside in the hierarchical organization of the nervous system combined with the universal power of any whole over its parts. Any system that coheres as a whole, acting, reacting, and interacting as a unit, has systemic organizational properties of the system as a whole that determine its behavior as an entity, and control thereby at the same time the course and fate of its components. The whole has properties as a system that are not reducible to the properties of the parts, and the properties at higher levels exert causal control over those at lower levels. In the case of brain function, the conscious properties of high-order brain activity determine the course of the neural events at lower levels.13
More recently, mathematician Alwyn Scott in his book Stairway to the Mind14 expresses a point of view similar to that of Sperry. Like Sperry, Scott suggests that consciousness “emerges” at the top of a hierarchically ordered nervous system. Scott compares the hierarchy of the nervous system to a flight of stairs or the rungs of a ladder. In this scheme, as in the model proposed by Sperry, consciousness emerges at the highest and
most complex neural levels. According to Scott, “Just as life emerges from cycles of cycles of cycles of biochemical activity, consciousness seems to emerge from assemblies of assemblies of . . .of assemblies of neurons” and “as life emerges from several of the lower levels of the hierarchy, consciousness emerges from several of the upper levels.” Scott calls this point of view hierarchical or emergent dualism.
There are problems with Sperry's account of the mind-brain relationship in my view. First, Sperry claimed that the mind emerges at the summit of a hierarchically ordered brain. But, as I described in chapter 7, there is no material summit of the brain or the self. There is no basis for the idea that the mind appears at the pinnacle of the brain because there is no place in the brain where all the brain's activity physically “conies together.” Additionally, we are left with the Cartesian dilemma. If the brain is material, and the mind is immaterial, how does a nonmaterial mind control a material brain? There must be another way to reconcile the divisible brain with our internal sense of ourselves as unified and whole beings.
Non-Nested and Nested Hierarchies
The difficulty with Sperry's account lies in the way that he viewed the hierarchy of the brain. Sperry viewed the brain and the mind as parts of a particular type of hierarchy known as a non-nested hierarchy.15 A non-nested hierarchy has a pyramidal structure with a clear-cut top and bottom in which higher levels control the operation of lower levels. A common example of a non-nested hierarchy is a military command. There is a general at the top who controls the lieutenants, who control their sergeants, and so on, down the chain of command until we finally reach the level of the individual troops. This would seem to be what Sperry had in mind when he spoke of a “top command” that subordinated lower levels of a hierarchy (Figure 8-1).
The non-nested hierarchy that Sperry envisioned is considered non-nested because, while the successive levels of the hierarchy interact, each level of the hierarchy is physically independent from all higher and lower levels. The various levels of a non-nested hierarchy are notcomposed of each other. Let me now reconsider our example of the military command that represents a non-nested hierarchy. The general commands and controls the lieutenants, but the general is not “made up of” the lieutenants.
An alternative framework for viewing the mind-brain relationship is another type of hierarchy known as a compositional or nested hierarchy.We refer to this type of hierarchy as nested because the elements composing
Figure 8–1. An army is a good example of a non-nested hierarchy. The general, at the top of the pyramid, controls all lower levels down to the privates. Each level of a non-nested hierarchy is physically separate from all other levels.
the lower levels of the hierarchy are physically combined or nested within higher levels to create increasingly complex wholes. The important distinction between non-nested and nested hierarchies is the relationship between the lower and higher levels of the hierarchy. A non-nested hierarchy has a clear top and bottom, and the control of the hierarchy comes from the top. A nested hierarchy has no top or bottom, and the control or constraint of the hierarchy is embodied within the entire hierarchical system.16
All living things, including ourselves, are nested hierarchies (Figure 8-2). We are physically composed of minute organelles that are hierarchically organized to create a human being. In the hierarchy of a living person, it is the complete person who sits at the top of the hierarchy, and that person is not separate from the parts of which he or she is composed. Individual elements of the body that make up the person simultaneously contribute to the life of that person. The “parts” of the person in this way are nested within the totality of the human being.
I return to the example of the lung. The mitochondria make a contribution to the emergence of the lung, but this does not mean the lung is independent of the mitochondria. Indeed, the lung is totally dependent on the mitochondria for its life and, without the mitochondria, the lung, and the person along with it, would die. In this way, both the mitochondria
Figure 8–2. Organisms are nested hierarchies. Lower order elements, such as cellular organelles, combine to create higher order elements, such as organs. In this way, all higher level entities are physically composed of lower order elements. Even though the higher levels of the nested hierarchy display “emergent”features not present in lower levels, all entities at all levels continue to make a contribution to the life and operation of the entire organism.
and the lung independently and interdependently make an essential contribution to the life of the person. Both are part of the nested hierarchy constituting the person.
The Nested Hierarchy of the Brain
With these considerations about hierarchies in mind, I present an alternative model to explain the relationship between the brain and the unified mind. I propose that the brain functions as a nested hierarchy, as do all biological systems, and that the proper model for the integration of the mind and the brain is that of a nested hierarchy. Consider again the face cells that were addressed in the last chapter. How is the mental representation of a face unified in awareness if so many areas of the brain are involved in its production? The convergence of neural pathways makes possible a cell so specific that it will only fire to face. This process might lead one to think that asingle “grandmother” cell, at the top of the perceptual hierarchy, embodies the representation of an entire face in consciousness (Figure 7-4).
We have considered why this logic would be a mistake, and why, in reality, no single neuron embodies the experience of seeing a face. A “grandmother cell” might respond quite selectively to certain stimuli, such as faces. However, the awareness in consciousness of the face of one's actual grandmother requires the representation of an enormous variety of information about the lines of Granny's nose, the location of
her mouth, the color and shape of her eyes, and so on. All this information is not contained in a single cell. Further, this information does not end up in the Cartesian Theater for simultaneous viewing because no such place exists. Rather, the entire nested system of the brain functions interdependently to create the visual image of the face. In the same way that mitochondria and the lung contribute to the life of the person, in the nested hierarchy of the mind, all the lower order elements—every line, shape, and patch of color that make up our awareness of the face—continue to make a contribution to consciousness.
We also can use the model of a nested hierarchy of consciousness to explain our conscious experience of the speeding red Corvette with its horn blasting that we considered in chapter 7. A complex stimulus of this nature is composed of so many elements that its neurological representation covers great areas of the brain and each part of the brain must make a contribution to its unified emergence into consciousness. In a brief review of the visual system (chapter 7) we saw how individual line segments are formed. A “line” of simple cells converges simultaneously onto the single complex cell that represents “a line.” This process of convergence occurs for every line that appears in any image. In the scene with the speeding red Corvette, the roof and trunk of the car are composed of tens of thousands of individual line segments. These individual line segments of the car's outline then are combined into longer segments that produce the car's overall shape and form. The lower order features, for instance, the exact position of a small line sequence in space, emerge in awareness as “part of” something else, such as the outline of the car. A short line segment is “bound” to a longer segment to create the outline of the car, just as a small patch of red is “bound” to a larger red patch that is part of the door. The redness of the Corvette is “bound” to its shape that is bound to its movement that is bound to the honking horn, until all representations are “bound together” to create the entire image. The color, shape, and movement of the car are nested together within the image of the car and this image in turn is nested within the entire scene.
To say an element is bound to another is simply another way of saying that they are represented in awareness dependently and are nested together. It follows from this framework that the extent to which lower order features are bound into a higher order feature is the extent to which the lower order features lose their independence from each other. For example, the neurons responding to the redness of the Corvette are tightly bound to each other. These neurons make their contributions to awareness as a nested whole. Every single neuron in a red patch of the car
makes a unique contribution to consciousness, but it becomes a “patch” of color because all the neurons that represent redness make their contribution to awareness in an entirely dependent, bound, and nested fashion. The binding concept also can be applied to the relationship between the redness and shape of the car. Color and shape are represented in awareness as a nested totality. We do not experience the color of the car independently from the experience of its shape. On the other hand, the experience of the dog that the car passes is bound to the car within the entire visual experience, but is not tightly bound to the color or shape of the car. The higher level or complex neurons that code for car and dog as entities make greater independent contributions to conscious awareness within the nested hierarchy of consciousness than do the simple neurons that code for the specific color or shape of the car.17
If there is no top or bottom to the nested hierarchy of the mind, what provides the topmost constraint that guides and controls our whole brain? What is the physical reality of the “inner I” that pulls together the mind and controls our actions? What keeps the millions of neurons in our brains from all going off in their own directions? How can we exist as single minds and unified selves?
Meaning and the “Inner I”
In the hierarchy of our conscious awareness, it is meaning that provides the constraint that “pulls” the mind together to form the “inner I” of the self. Think once again about our example of the nested hierarchy described by cyclopean perception and the mind's eye. In this example, the two visual images, one from each eye, do not, as Descartes had supposed, “physically” merge. There is no one place in the brain at which the images physically come together. Rather, the two images create a mental condition where their meanings are conjointly represented in awareness to produce a higher level of meaning. In the example of the cyclopean eye, the higher level of meaning is that of a single image now seen in depth. It is the higher meaning of the combined images that produces the “top-down” constraint on the individual elements. This constraint or control of the whole on the parts does not suggest the elimination of these individual parts from the mind because the image from each eye continues to make a contribution to the unified cyclopean eye. Instead, constraint leads to the elimination of the independence of each part from each other when operating within the framework of the nested hierarchy of consciousness. By saying that these parts are represented dependently I also am saying that they are represented meaningfully in
consciousness. Thus, the unified subjective experience that we experience as the integrated self is the result of the nested hierarchy of meaning created by the brain.
Purpose Is the “Ghost in the Machine”
When the control of action or the nature of volition is considered as a nested hierarchy, it is purpose that provides the constraint and guiding force of the self. It is purpose that is the “ghost in the machine.” Neurological theories usually do not make reference to purpose. There is little room for ideas like “free will” or “human purpose” in discussions of the neurological basis of behavior. Invoking purpose in an explanation of a neurological phenomenon is seen as a form of teleological thinking— an effort to invoke the end result of a process as its cause, which is a logical impossibility.18 We cannot say, for example, that we possess the corneal reflex—the reflexive blink when something comes in contact with the cornea—in order to protect the eye. This form of teleological reasoning does not constitute a neurological explanation for the mechanism of the reflex. A neurological explanation of the corneal reflex entails a description of the nerves that provide sensation to the eye and the nerves that blink the eye, and the neurologist does not need to invoke the purpose of the reflex to explain its action. On the other hand, the corneal reflex does serve a purpose in that it protects the eye.
As pointed out at the beginning of this chapter, all living things are hierarchically organized such that its parts are constrained to perform certain goal-directed actions that serve a purpose for the organism. In a nested hierarchy, constraint is the means through which organisms achieve their goals. Another example of this relationship between constraint and purpose is demonstrated by the absorption of water by a plant via its roots. Parts of the plant (i.e., the roots) are constrained to perform the actions necessary for this vital function. This does not mean that the plant “knows” the purpose of this function or that the plant performs the actions of absorption “in order to” bring water to its leaves. It would be teleological thinking to explain the mechanism of water absorption on the basis of the plant having the purpose of absorbing water. Similarly, a human being's beating heart, which promotes the circulation of blood throughout the body, has a structure and biological design that enables it to perform the functions necessary to maintain the life of the organism. But the heart does not purposefully set out to perform the pumping of blood any more than the plant purposefully sets out to absorb water. Nonetheless, the roots of the plant and the beating
heart have within their structures the biological organization to perform the actions that ensure the organism's survival.19
These examples demonstrate that it is difficult to describe biological functions that serve the purpose of ensuring the organism's survival in non-teleological terms. Theoretical biologist Ernst Mayr suggested that one approach might be to view biological systems as teleonomic, a word derived from the Greek word telos, meaning “goal” or “endpoint.” According to Mayr, “a teleonomic process or behavior is one which owes its goal-directedness to the operation of a program.”20 Evolutionary processes produce living things that are teleonomic. Genetically programmed biological processes, such as the respiration of the mitochondria, are teleonomic. An organism can perform a process that is teleonomic in that the process serves an adaptive purpose for an organism, yet the organism does not have to anticipate or “know” the endpoint of that process.
It is fairly clear that plants and beating hearts do not anticipate the consequences of their actions. But what about a cat stalking its prey? This example is also an instance of a teleonomic process. The cat's stalking behavior is guided by a biological program (in this case we call it an instinct), and it has a clear endpoint, which is to catch and eat its prey. Let us consider if the beating heart has the same teleonomy as a cat chasing a mouse according to Mayr's conception of teleonomy. Does the beating heart have the same teleonomy as the early man who made the first stone tool?
Mayr wished to regard teleonomic processes as those that are end-directed, but not deliberately or intentionally so. Teleonomic phrases such as “the function of the heart's beating” or “the heart beats in order to” are acceptable as long as one realizes the metaphorical use of such language. But if teleonomic processes are not necessarily deliberate, purposive, intentional acts, then the question remains as to whether there is a biological and even philosophical distinction between the beating heart and the thinking and purposive brain of the toolmaker. And if there is a difference between the heart and the brain, how are we to describe the difference in scientific terms?
Although hierarchical constraint produces integrated teleonomic functions in all life, only certain teleonomic systems, events, acts, and so on are also purposeful. It is the degree of conscious purpose that distinguishes intentional from nonintentional teleonomic behaviors. Beating hearts do not have purpose in their actions; toolmakers do. Some neurological phenomena in humans also are teleonomic yet entirely nonpurposeful. The corneal reflex, which consists of the blink of the eye when
it is touched, serves to protect the eye and is therefore a teleonomic behavior. However, this reflex can be invoked in someone in coma and the reflex is largely involuntary. While the corneal reflex is teleonomic in that it serves a purpose for the organism, it is not purposeful. The question is at what point do we consider a behavior purposeful? For example, Braithwaite had no problem attributing purposeful action to his cat:
My cat's behaviour in pawing at the closed door, it may be said, is sufficiently similar to a man's behaviour in knocking at a locked door for it to be reasonable to infer that the cat, like the man, is acting as it does because of a conscious intention, or at least a conscious desire, to be let through the door.21
We can agree that the cat's behavior is to some extent intentional and goal directed. We may additionally agree that the man's behavior is a hierarchically more advanced, or at least more evolved, form of intentionality. For instance, animals including nonhuman primates have very limited voluntary control over their vocalizations. Primate researchers have no difficulty training a rhesus monkey to perform a bar press to obtain a reward, yet they have found it vastly more difficult to train these animals to produce a vocalization in the same way.22 The monkey can control its limbs but not its vocalizations. While the brain regions controlling limb movement must have cortical representation, the brain structures that control vocalization and facial expression in the monkey are in the limbic system, a subcortical phylogenetically older area of the brain that is responsible for emotional, social, and self-preservative behaviors. A major difference, therefore, between the monkey and human vocalization is that humans can control their vocal apparatus. The human can constrain the many parts of the body that are required to produce speech.
My purpose in elaborating at some length on this topic is to point out that purposeful action can be distinguished from teleonomic (but non-purposeful) behavior by its greater degree of constraint over a multitude of nested parts. Both birds and certain people fly south for the winter, yet only man has awareness that he is leaving to seek warmer weather in Boca Raton. The simple motor acts of both species are constrained by the highest levels of the nested action hierarchy; but, in the case of the bird, the highest level is a chain of instinctual behavior, with a minimal degree of either flexibility or foresight. On the other hand, for some human behavior, the extent of the constraint over space and time when traveling is extraordinary—buy clothes, tickets, bathing suits; tell friends and associates one will be out of town; go to the airport, and so on. The kind
of “future directedness,” the number and complexity of necesssary steps that human beings implement in order to purposively attain a goal, reflect an unparalleled degree of constraint when compared to that of any other form of life.23
The manner in which higher brain regions purposely control lower regions is one of the cornerstones of modern neurological thought. John Hughlings Jackson's hierarchical model of the nervous system is perhaps the single most influential model in the history of neurology. For Jackson, the nervous system evolved from simple reflexes that could be found at the lowest hierarchical levels of the nervous system tovoluntary forms of action that are produced by the highest cortical levels of the brain.24
Jackson's hierarchical nervous system views higher cortical regions as controlling and suppressing lower levels. What appears at the top of a Jacksonian action hierarchy is not a pontifical cell. Jackson had no image of a “ghost in the machine” controlling lower levels of the nervous system. For Jackson, it was purposeful action, or what Jackson referred to as voluntary (as opposed to automatic) behavior that sits at the highest levels of the nervous system. Voluntary behaviors were the most complex, most specialized, least automatic, involved the greatest degree of consciousness, and had the greatest degree of independence from other movements. Voluntary action was also the most conscious form of action. It was voluntary or purposeful action that constrains the lower elements in the motor hierarchy, not a single cell or brain region.
The act of speaking further illustrates the constraint of purpose over a nested system of parts. When we speak, we do not will a particular muscle of the mouth to move in a specific and conscious way. We do not consciously send a command to the tongue to move left and then right and so on. Indeed, we couldn't do this even if we wanted to. First of all, the average speaker has no idea which particular muscles to move when speaking. We are not consciously aware which muscles of the mouth, tongue, pharynx, larynx, and so on must be called into action to produce a certain sound. Additionally, even if we did know which muscles to move, we lack the fine coordination required to voluntarily move a given muscle “just so” to produce a given speech sound. Finally, even if we were to possess the necessary knowledge and control to voluntarily move each muscle of speech into action, if we were required to do so when speaking, we would lose the overall integration of the speech act. We need to focus on the idea we wish to express, rather than on the way our lips and tongue are moving, or on the way a single fiber in the tongue is firing! The actions of the neurons at these lower levels of the
hierarchy are nested within the higher levels of the hierarchy and the purpose of the act provides the constraint of higher levels on lower levels of the motor hierarchy, and in this case the purpose of speaking is the communication of an idea. When we speak, it is the idea we wish to express, the purpose of our speaking, that sits at the highest level of the action hierarchy. It is this purpose that brings unity to the speech act that constrains all the many muscles that are part of the act of speaking.
Jackson pointed out that proof of the hierarchical control of speech could be found when one considered patients with disease of the nervous system. Jackson studied the patient with aphasia.25 Aphasia is the specific loss of language capacity due to brain dysfunction. Aphasia occurs in most right-handed patients as a result of damage to certain brain areas, which are usually in the left hemisphere in right-handed patients. Some patients with aphasia have problems with expression, so-called Broca's aphasia; while others who have their chief difficulty with comprehension are known as Wernicke's aphasics. Some aphasics may have various combinations of disturbances, sparing some functions, while involving others. Jackson found that the aphasic who could not say a word on command—for instance, in response to “say the word ‘no’ “—might be able to say it in response to a question. And a patient who could not utter “no” in response to a question might be able to say “no” when scolding his children or under states of emotional excitement.
In this instance, the lowest levels of speech, the more emotional and automatic, are the most resistant to—in Jackson's words—“dissolution of function,” while the highest levels, the most voluntary, are more susceptible to disruption as a result of brain damage. An aphasic patient of mine nicely demonstrated this principle. He was a sixty-eight-year-old businessman who had a severe disturbance of speech due to a cortical stroke. As part of his language assessment he was given a series of objects to identify. The patient, who was prior to his stroke quite a raconteur, failed miserably on his ability to name even the simplest items such as a pen or watch. After a few minutes of this, he became noticeably upset and finally blurted out, “Damn it! I'm as smart as you are . . .as any man you'll ever meet!” While his ability to express specific thoughts was limited, he was always capable of producing a string of uninterrupted expletives.
Lesions in certain neocortical regions in the human reliably produce aphasia, a disorder of voluntary speech. But as we have already reviewed, as highlighted by Jackson, some aspects of emotional speech controlled by the limbic system may be preserved. Further, a dissociation between voluntary and nonvoluntary facial expression may occur with a stroke of either side of the brain. A patient with a cortical lesion often has a paralysis
of the lower face on the side opposite the lesion. Thus, if a patient with a lower facial paralysis from a left cortical lesion is asked to “show me your teeth,” the weakness of the opposite lower face becomes evident. However, when the patient is seen to spontaneously smile or laugh, a behavior controlled by the phylogenetically older and more primitive limbic system, the face moves symmetrically and normally. Conversely, neurologists recognize what is known as a “mimetic facial.”26 A patient with a lesion in the limbic system may have no difficulty exposing the teeth on command, but may appear to have a facial paralysis when laughing spontaneously.27
This dissociation of function was made clear to me as a resident when one night I admitted to the hospital a young man who was being evaluated for headaches. I found nothing wrong with him after taking a thorough history and performing a complete neurological examination. Later, as we spoke, we had the opportunity to laugh at something or other, and a noticeable droop on the right side of his face suddenly and somewhat ironically appeared and pointed to the presence of a tumor of the hypothalamus (brainstem). It fortunately was successfully removed.
Another fascinating but sometimes disabling condition called “pseudobulbar palsy” relates to these issues. A patient may develop lesions on both sides of the brain, such that the neocortical regions are disconnected from the lower centers of the brainstem that innervate the facial muscles. Under these conditions, the pathways of voluntary facial expression are severed, the patient losses volitional control over the face, and cannot, for instance, smile or move the mouth on command. If this weren't bad enough, the descending inhibitory pathways from higher brain regions are also damaged, so that the patient also cannot inhibit or suppress spontaneous emotional expression. In these circumstances, the patient is subject to extreme emotional outbursts of laughing or crying that may come over the patient seemingly out of the blue. One patient of mine, a young college-age woman, had a disease of the blood vessels that resulted in two strokes, one on each side of the brain. In my office, and in most social settings, she needed to constantly stifle a smile or laugh regardless of the topic or her mood. Sometimes the drive became too great, and she would burst into a loud prolonged laughing jag to the point of tears. The patient denied that significant emotion except frustration was attached to these occurrences.28
The condition of pseudobulbar palsy nicely demonstrates the principles of hierarchical control of the motor system. In the patient afflicted with this condition, the control of emotional expression at its highest levels is destroyed. This patient cannot smile to show approval or scowl
to demonstrate anger. Yet there are circumstances when emotional expression bursts through without the constraint or control. The neurological underpinnings of emotion are intact, but are no longer under higher level control.
In summary, the self can be understood as a nested hierarchy of meaning and purpose. We do not experience multiple cognitive or conscious representations from each of the brain areas that contribute to the self because these regions serve as lower order elements in the nested hierarchy of the mind. Instead, many brain regions are coordinated into a single nested consciousness. The view that the brain functions as a nested hierarchy appears to have been largely overlooked in the neuroscientific literature. The nested nature of consciousness is not mentioned in the excellent and comprehensive special issue of Consciousness and Cognition29 that is devoted to the topic of temporal binding and consciousness, and Scott30 in his book, Stairway to the Mind, extensively discussed the issue of emergence in hierarchical systems, but the nested nature of the brain/mind in perception and action does not appear as part of his model.31 In contrast, I suggest that the self, the “mind's eye” and our sense of will, is the product of the nested hierarchy of meaning and purpose created by the brain. In the next chapter we will consider how this viewpoint helps up to understand the ultimate nature of the united self.