Brief Lecture Notes for Unit 3 (revised 09/08/06)
The mind-brain problem (see text pages 17-18, 140-145)
This unit will again (as with Unit 2) begin with a philosophical issue, the so-called "mind-brain problem". If we're going to learn in detail about the operation of the brain (the main topic of Unit 3), we'd better ask ourselves why, as students of the mind, we bother. How are the brain (a physical, and presumably deterministic, system) and the mind (a nonphysical, and potentially nondeterministic, system) related?
What no one disputes
All psychologists agree that understanding the structure, functions, and activity of the physical brain is an important part of understanding human conscious experience (how the mind works), including perception and cognition. That is a universal given (at least among Western thinkers who accept the basic assumptions and values of the scientific method and the scientific enterprise). If this were not a given -- one of the few principles about which all contemporary psychologists agree -- there would be no point to studying Unit 3 at all! In fact, the practical implications of understanding the biology of the brain -- for both normal (nonclinical) and abnormal psychology -- are many and profound. They have revolutionized the world of psychiatry, for instance, and have rendered treatable many forms of mental illness that would have been seen as "hopeless" only two generations ago.
What is disputed
What is a source of ongoing disagreement among psychologists (and within the wider culture generally) is the exact nature of the relationship between the brain and the mind. This is a "watershed" philosophical issue that is central and determinative with regard to a wide variety of other metaphysical, ethical, legal, and public policy issues that at times threaten to divide our society into warring camps.
It's important to understand that this dispute is not one that can (at least in my view) ever be resolved scientifically. It is not a matter of observation; empirical analysis is of little or no help in addressing it one way or the other. It is a matter for the philosopher (or the theologian), not the scientist as such. In other words, using terms we've discussed earlier in the course, it is outside the "universe of discourse" of the scientific method and the scientific enterprise; alternative "ways of knowing" (in Chapman's sense) are needed to addess these issues. That doesn't mean that individual scientists don't have defined points of view about the question! They do, of course: because (like the rest of us) they are human beings, and these kinds of questions are universal and inescapable. But to pass judgment on these questions is to abandon the mantle of scientific expertise. When a scientist (no matter how prominent) offers his or her opinion on such issues, he or she is no more expert than anyone else, though still worth listening to respectfully (as one might anyone else). But his or her point of view can never be, in the nature of things, "scientifically proven". The disputed issues are simply not empirical and observational in character.
In our1 culture, there are two major ways that people think about the mind-brain relationship. Common terms for them, which I will use here, are "epiphenomenalism" and "dualism", though other writers use different terms. Because debates about terminology generate more heat than light, I'll try to avoid them. And, because whoever controls the language controls the debate, I've tried to pick neutral terms that don't favor either side, though that's hard to do.
The scheme below is inevitably an oversimplification. For a more complex model, see F. F. Centore's book, Persons: A Comparative Account of the Six Possible Views, which I strongly recommend. The first two views in his model ("reductionistic materialism" and "nonreductionistic materialism") are subtypes of what I'm here calling epiphenomenalism. The second two views ("first-order psychosomaticism" and "second-order psychosomaticism") are subtypes of what I'm calling dualism. His last two views ("vitalism" and "reductionistic immaterialism") do not fit into either category and, until recently, were very rare within Western thought, though they have strongly influenced and informed the thinking of many non-Western cultures.
By the way, I don't care -- at least for the purposes of your earning a grade in this class! -- which point of view you take, or whether you agree or disagree with my own conclusions on these issues. I do care that you understand the issues so that you can make up your own mind! I happen to be a dualist, but as the saying goes, some of my best friends are epiphenomenalists.
Epiphenomenalism
The epiphenomenalist point of view is that, ultimately, the brain is all there is. (Note that -- and with apologies to Centore, whose terminology appears somewhat to contradict this -- this is inherently a reductionistic point of view. The mind is "simply" the brain in action and nothing more.) Human consciousness, in this view, is a by-product of the functioning brain, just as the glow from a light bulb is a by-product of the functioning bulb. It is not a "thing" in itself, but a process that depends entirely on the underlying physical system that produces it. As a result, chains of cause and effect can only run in one direction (from the brain to the mind); physical changes in the brain can result in changes in conscious experience, but never the other way around. Brain events are always the "cause", conscious experiences always the "result".
Because, in the epiphenomenalist view, there is nothing "special" about consciousness -- in theory it could be fully explained in physical, materialistic terms, though in fact no one has even the first glimmers of a clue about how one might actually do so -- it need not be restricted to human beings or even to biological systems. If we only knew how, we could construct a computer that could actually think (that is, be conscious of itself). In that event, pressing Ctrl-Alt-Del would actually be a form of murder (bringing the conscious life of our computer to an end). Consciousness, in this view, is a sort of evolutionary accident; nice if you happen to have it, but hardly inevitable.
Dualism
In contrast, the dualist view is that both the mind and the brain are equally "real", or to use more formal philosophical language, both have a "noncontingent ontological status" (try saying that five times fast). Though the brain and mind clearly interact and are inextricably linked, neither is directly dependent on the other. Chains of cause and effect can run in either direction: from brain to mind (as when drinking alcohol makes you feel tipsy), or from mind to brain (as when choosing to think a certain thought causes the activation of various brain centers). In some sense or another, the mind is a "thing" in itself, a separate domain of reality that is just as real as the physical, but not itself a physical reality.
In this view, consciousness -- regardless of how or why it arose -- can never be thought of as a mere accident. In consequence, because it is not a physical property or quality, it is not something we can "make happen" in physical systems (such as computers) of our own making.
Ramifications and implications
Though it is not absolutely necessary for a dualist to believe in the reality of free will (authentic human choice), most dualists probably do so. Conversely, it is difficult (at least for me) to see how epiphenomenalists can make room for the idea of genuine human freedom (though some attempt to do so, in a fashion that I happen to find singularly unconvincing -- but you may disagree), since physical systems are by definition either random or deterministic (low information content), but the mind gives every appearance of being rational and free (high information content). Most epiphenomenalists -- the consistent ones, anyway, in my view -- argue that while we perceive ourselves to be free to think as we please and (within limits) act as we choose, this is actually a delusion; our thoughts and acts are as strictly determined as anything else in the universe. What this says about the validity of human thought and the merits of the intellectual enterprise, I leave to your own judgment (the assumption being that you are capable of making trustworthy judgments, an assumption that I happen to think requires dualism to be valid and defensible).
Students sometimes ask me about the relationship between the epiphenomenalist-dualist debate and "religious" versus "secular" views of reality. Again the issues are complex, but in general, many (though not all) dualists have a religious or spiritual view of reality (the ultimate reality is a Mind or minds), while most (though not all) epiphenomenalists have a materialistic or secular view of reality (the ultimate reality is impersonal matter). To some extent this reflects the greater reductionism of the epiphenomenalist view. Research indicates that the epiphenomenalist view may tend to be associated more with "left-hemisphere", the dualist view more with "right-hemisphere", ways of thinking: about this distinction, more later in this unit.
1 I'm never quite certain, in our multicultural society, how to handle pronouns like "we", "us", "our", and "ours" that -- to some extent -- wrongly imply that everyone in my audience has the same cultural background. What I mean -- with no bias or harm intended -- is that, despite increasing diversity (a good and healthy thing indeed), American society is still, for better or worse, predominantly oriented around a certain consensual or mainstream point of view -- what Lillard calls the "European-American Social Science Model" (EASSM) of reality. Most (though not all) Americans either share this view or else (consciously or unconsciously) defer to it. Nothing more is meant by my choice of pronouns than that. Among other things, the EASSM assumes that individual personality is real and important, that science is a worthwhile and valuable enterprise, and so forth. The EASSM appears, at least to me, to be about equally influenced by epiphenomenalistic and dualistic views of the person, which is why this issue remains a debated one in our society.
As we move into the technical aspects of Unit 3, note that I'm keeping my promise in Unit 1 to start at the boundary between biology and psychology (the most reductionistic aspect of the field of psychology) and move gradually toward less and less reductionistic concepts as we go along, ending in Unit 12 at the boundary between psychology and sociology (the least reductionistic aspect). Pay attention to the unfolding of this process as we progress through the course.
Neural structure and functioning (see text pages 88-96, 129-132)
Three parts of the neuron or individual nerve cell are the soma, the dendrites, and the axon (including the axon terminal endings). The soma, as with all cells of the body, is responsible for processes like respiration that keep the cell alive. The dendrites are receptors that receive incoming information from other neurons; the axon is a conductor and transmitter of information that sends information on to other neurons. Thus, neural information thus always flows (within a neuron) in a single direction, from dendrites to axon terminal endings.
There are two different processes by which information is transmitted within the nervous system. Within an individual neuron, intraneural transmission, an electrical process, is involved. However, to transmit information from one neuron to another, a different, chemical process, synaptic transmission, is involved. This fact explains many observable phenomena about the nervous system and about our behavior and our conscious experience. Intraneural transmission is a much faster and more efficient process as compared to synaptic transmission.
Some key facts about intraneural transmission include the following. The neuron can only respond to incoming signals if they are at or above a minimum cutoff level known as the threshold of the neuron. (In practice, the threshold is not a single fixed level, but can change depending on outward circumstances; see Unit 4 for more. But for now, let's ignore that fact.) If an incoming signal is below the threshold, the neuron remains in a quiescent state (a default condition that involves a slight voltage difference between the inside and the outside of the axon) called the resting potential. But if an incoming signal is at or above the threshold, a momentary reversal of the polarity of the "battery" -- a voltage spike or action potential that represents a nervous signal or nervous impulse, the firing of the neuron -- travels down the length of the axon. In general (avoiding a few complexities that we won't bother with in an introductory course), each neuron obeys the all-or-none-law, which means that the intensity of the action potential does NOT depend on the intensity of the incoming signal, as long as it is at or above the threshold level. (This suggests a paradox: if each neuron can either fire or not fire, with no degrees of responding, how can your nervous system as a whole respond in a gradiated manner? How can you, for instance, tell the difference between a dim and a bright light, if each neuron in your eye can only say "I see it" or "I don't"? See if you can come up with the answer.)
In the chemical process of synaptic transmission, specialized chemical substances called neurotransmitters are released into the physical gap (synapse) between the axon terminal endings of one neuron and the dendrites of the other. This chemical process is why conscious experience can be influenced by pharmacological agents. An understanding of how the process of synaptic transmission works has led to a revolution in psychiatry over the past 15-20 years; many previously "incurable" mental illnesses now respond favorably to targeted drug therapies that correct imbalances in the process of synaptic transmission (see Unit 10 for more).
Structure of the nervous system (text pages 105-108, 120-128)
In the simplest kind of behavior known as a reflex, defined as an automatic or involuntary response to an environmental event or stimulus, as many as five neural links may exist in the chain between stimulus and response. First, specialized neural structures called transducers change the physical stimulus energy into the "language" of action potentials. Second, sensory neurons carry this information toward the central nervous system (CNS), which is comprised of interneurons which, in some but not all cases, integrate or further process the incoming information (this is the third step). Fourth, a signal initiating a motor response is then sent by way of the motor neurons and is finally converted (the fifth step) back into physical energy (a behavioral response) by way of the effectors. The entire neural pathway is sometimes called the reflex arc. (Based on these facts, can you explain why, when your hand touches a hot stove, your arm reflexively jerks away before you consciously feel any heat or pain, even though the length of the neural pathway from your spinal cord to your brain is shorter than that from spinal cord to the muscles of your arm? Think about it.) More about reflexes in Unit 6.
The overall nervous system can be subdivided into the CNS (interneurons) and the peripheral nervous system or PNS (sensory and motor neurons). The PNS can further be subdivided into two branches, the somatic and the autonomic. On the sensory side, the somatic system is associated with information of which you eventually become consciously aware, while the autonomic sensory neurons convey sensory information to brain centers that are not associated with conscious awareness (this is a bit of an oversimplification, but is about 90% accurate; a few exceptions exist). On the motor side, the somatic system conveys signals that govern voluntary or deliberate behavior; the autonomic system, involuntary or automatic behavior (again, with some exceptions). Thus, the somatic system as a whole has primarily to do with regulation of, or responding to, the external environment. In contrast, the autonomic system involves regulation of, or responding to, the internal (bodily) environment, and the maintenance of so-called homeostasis.
The autonomic system can further be subdivided into two sub-branches, the parasympathetic and the sympathetic. With again some exceptions, the parasympathetic system is concerned with the conservation of energy (has a so-called vegetative function), while the sympathetic system is concerned with the rapid expenditure of energy in "fight or flight" situations (has a so-called activating function).
The CNS is comprised of the brain and the spinal cord. The two major functions of the spinal cord are to regulate many of the simple reflexes (entirely apart from the brain), and to serve as a way-station between the brain and the PNS.
The brain can be divided into three general regions: the hindbrain, midbrain, and forebrain. (See the diagrams in the text and as presented in lecture, though I do own a scanner and am working on this... maybe, by the time you are reading this, I will have the pictures imbedded, but maybe not.) The hindbrain contains such structures as the medulla, which regulates physiological processes vital to moment-by-moment physical life such as heartbeat and respiration, and the cerebellum, which coordinates automated (overlearned) voluntary behaviors (complex motor sequences that can be performed apart from direct detailed conscious attention). The midbrain includes the reticular formation, which regulates brain activity levels associated with sleep/waking (diurnal) cycles, and the colliculi, responsible for visual and auditory localization. The forebrain includes the thalamus, an important sensory switching or routing station; the hypothalamus, which regulates most autonomic functions including those associated with primary biological drives like hunger, thirst, and sex (see also Unit 5); the limbic system, a loosely coordinated group of structures associated with emotionality, particularly strong unlearned emotions like rage and fear; and the cerebral cortex (see below), associated with higher mental functions.
For the exam, you will be expected to be able to identify regions and functional areas of the cortex on a diagram (either side view or top view). Again, I'll try to imbed the diagrams here, but don't hold your breath, since anoxia is generally fatal. You are also expected to know the likely effect of a brain lesion (physical injury or stroke) located in various cortical regions, as a way of testing your understanding the functioning of these areas.
The cortex (outer surface of the forebrain) is divided into two symmetrical hemispheres, the left hemisphere (LH) and right hemisphere (RH). Each hemisphere is divided into four lobes: the frontal, temporal, parietal, and occipital, which can be located with respect to two indentations known as the central fissure and the lateral fissure. The two hemispheres can share information by way of a bundle of connecting fibers called the corpus callosum.
Areas in the cortex can generally be classified as either projection areas or association areas. Projection areas deal with the individual building blocks of sensory experience or with individual motor responses. Association areas combine these individual components to yield higher, more complex, coordinated functions such as perception, cognition, and sequenced purposive behavior. (See also Unit 4.) About 75% to 80% of the cortex is made up of association areas.
Projection areas include the motor projection, somatosensory projection, visual projection, and auditory projection areas. Three general principles govern the functioning of the projection areas (with, again, some exceptions or complications). First, the crossing over principle states that information from one side of the body (or from one perceptual field) is associated with the opposite side of the cortex (e.g., if a brick falls on your left foot, the sensation registers in the right somatosensory projection area). Second, cortical areas are mapped upside down on the brain (e.g., the brick falling on your foot registers at the top of the projection area, closest to the central fissure). Third, the amount of cortical space (number of neurons) devoted to a given part of the body (or part of the perceptual field) is a function of the importance, sensitivity, or dexterity of that part, not its physical size (hence, for instance, many more neurons are devoted to the thumb than to the small of the back).
The geographic principle states that association areas are, for the most part, located next to the projection area(s) from which they obtain information or to which they pass information. Key association areas include the premotor area, which integrates individual motor responses into meaningful sequences; the secondary visual area, which integrates individual visual inputs (sensations) into perceptual wholes; and two language areas, Broca's and Wernicke's areas.
Unlike the other cortical areas mentioned above, the language areas of the brain are normally located only on the LH, with no corresponding structures in the RH. Broca's is a language production (output or generation) area, while Wernicke's is a language comprehension (input or reception) area. Thus, roughly speaking, one might assign vocabulary to Wernicke's area and grammar/syntax to Broca's area.
Hemispheric lateralization and the split brain (text pages 137-140)
In general, the LH and RH process information in distinctly different ways and have different specialized functions, a fact known as hemispheric lateralization. Hemispheric lateralization is only fragmentary in infants and develops gradually throughout childhood and early adolescence; it also proceeds in a somewhat different fashion in boys than in girls, partly explaining some of the more innate gender differences in cognition and personality. The LH is the primarily verbal hemisphere, reasoning analytically and sequentially (step by step). The RH is the primarily nonverbal hemisphere, reasoning synthetically and wholistically (big-picture creative insights). (Harkening back to the start of Unit 2, one can now see that some of Chapman's ways of knowing -- such as deduction -- are primarily LH forms of thinking, while others -- like intuition -- primarily involve RH thought. This helps explain why intuitive conclusions are hard to put into words or to justify verbally; do you see why?) These differences have important implications for the understanding of such applied psychology topics as career counseling, educational practices, gender differences, and media effects. (See Unit 5 for a discussion of hemispheric laterallization, motivation, and temperament differences.)
The fact of hemispheric lateralization can be demonstrated by means of research with split-brain subjects, individuals without a functioning corpus callosum. In such persons, the two hemispheres function more or less independently, as can be shown by providing each hemisphere with different information and then asking each hemisphere what it knows. Because of the technical complexities associated with this procedure, I won't summarize it here (you'll have to attend lecture!), but it is fair game for the exam.
Study Guide
1. What is the mind-brain problem? How do epiphenomenalism and dualism differ?
2. What are three parts of the neuron? How do their functions differ?
3. Explain the process of intraneural transmission and contrast it with synaptic transmission. What is a neural threshold? The all-or-none law? In light of these facts, explain how the nervous system can respond in a gradiated manner.
4. What is a reflex? Summarize the steps in the reflex arc. Why are reflex responses usually faster than a person's conscious experience of the eliciting stimulus?
5. How can the overall nervous system be categorized or subdivided? How do sensory neurons, interneurons, and motor neurons differ? How do the somatic and autonomic systems differ? The parasympathetic and the sympathetic?
6. Locate important brain structures on a diagram and summarize their functioning. How do projection and association areas differ? What is the crossing-over principle?
7. What is hemispheric lateralization? Summarize some practical implications of this fact.
8. Summarize split-brain research and its implications for an understanding of normal brain functioning.