Consciousness, Self, and the Prefrontal Cortex

cartesian-theater

There is a basic question that must be addressed when pondering the nature of consciousness, and that is: why have consciousness at all? The brain processes a great deal of information below the level of conscious awareness, from visual to auditory to tactile, and then the integration of all of these before they can be brought into conscious awareness. Yet conscious awareness itself seems much more limited in the amount of information that it can handle at a time—5 to 9 “chunks” of information, at a time, it would seem. So why rely on conscious awareness as heavily as we do? It certainly seems, at least from this angle, much less able than non-conscious processing—yet, given its apparent efficacy in raising humanity to the heights of culture and insight that we enjoy today, it surely has something essential to offer us.

The prefrontal cortex is the latest structure to appear in the evolution of the brain, and is the structure that shows the greatest development between humans and our closest biological relatives. Furthermore, it is known to mediate a great deal of the abilities considered distinctly human, such as planning, reflection, and empathy, all of which apparently require conscious awareness. Surprisingly, however, a vast abundance of the projections that the prefrontal cortex sends back to more primitive, sub-cortical structures are inhibitory—they function largely to suppress activity in these regions. In fact, this has led several researchers to rethink the concept of free will and, somewhat amusingly, refer to it rather as “free won’t,” in that we are mainly choosing what not to do, of all of the responses recommended by sub-cortical structures. And this is where we might find a reason for conscious awareness.

Consciousness relies on a crucial ingredient for dealing with the world in the way that the prefrontal cortex specializes in doing: it removes behavior from the moment-to-moment sensory perceptions incessantly presenting themselves to sub-cortical brain regions. Instead of constantly responding to each and every stimulus as it comes in, consciousness introduces a disconnect that allows reality apart from oneself to be treated as perceived, and thus distinct from the self and manipulable. Non-conscious responses don’t require perception in the same way that conscious processes do. In order to consciously ponder a course of action while planning, you need a virtual representation to work with, and in order to do that, you need some distance between yourself and the object being represented. Every day perceptions such as the visual field in front of you may function in a very similar manner: a stimulus presents itself, is processed by sub-cortical structures, and then a course of action is offered up to conscious awareness to be chosen or discarded by conscious reflection. There is a whiff of “opponent processing” going on in this narrative, something that comes up a lot in systems biology: two structures working in opposite directions in order to better center around a single desired outcome. Non-conscious, sub-cortical processing is largely reactive, leading to sometimes extreme, reflexive responses; conscious prefrontal processing, on the other hand, divorced from the constant demands of the environment, is more receptive to multiple courses of action, but can sometimes leave us unable to settle on an alternative. With the two of these working with opposing aims, however, behavior that is reactive enough to survive, but receptive enough to be a functioning member of society, can be attained.

This is far from a coherent theory or hypothesis, but the parallels between the roles of sub-cortical and non-conscious processes on the one hand, and prefrontal and conscious processes on the other, along with the connections between the two, are surely going to be important in mapping human consciousness.

In Search of Memory

A few weeks ago, I read Eric Kandel’s In Search of Memory. It was different from the books that I normally post about here, as it is an autobiography with the emergence of modern neurobiology woven in, rather than an argument for this or that perspective. But I am a neurobiologist at heart and an aspiring scientist at the very beginning of my career, so I couldn’t resist:

memory

Eric Kandel won the nobel prize in the year 2000 for his pioneering work on the molecular mechanisms of memory formation and storage. In this book, Kandel lays down the path of his life, professional and otherwise, from his earliest days in Vienna, just before World War II, up through his acceptance of the nobel prize in Stockholm, just a few years ago. His book will be of interest to biologists, philosophers, psychologists and laymen alike. The material is presented in the order that it was first discovered and assumes no prior knowledge, leaving no bars to entry for this exciting journey. All the same, weathered experimentalists will surely enjoy the ride that is the birth of this new science, from single-cell recordings in hippocampal cells, to the neural networks of Aplysia, to the beginnings of the differentiation of  the neural substrates for unconscious vs conscious information processing.

And a fun fact for those who are, like me, still trying to break into this field: What was Eric Kandel, nobel laureate in biology, studying in his Junior year of college? None other than Northern European History. He didn’t set foot in a lab until medical school, when he was entranced by the promises of psychoanalytic theory. I think we’ll be ok.

Finally, for those of you who wonder what I am doing when I am not reading or writing about consciousness (or wonder why I post so scarcely now!), I am now excitedly spending the majority of my time in the BRAIN Lab at Washington University in St. Louis on a summer research fellowship studying up on neurogenetics (i.e., how genetic variation influences how our brains respond to our environment and modulates risk for psychopathology). Check us out!

The Problem, continued

John Tyndall, 1868:

The passage from the physics of the brain to the corresponding facts of consciousness is unthinkable as a result of mechanics. Granted that a definite thought, and a definite molecular action in the brain, occur simultaneously; we do not possess the intellectual organ, nor apparently any rudiment of the organ, which would enable us to pass, by a process of reasoning, from the one phenomenon to the other. They appear together, but we do not know why. Were our minds and senses so expanded, strengthened, and illuminated, as to enable us to see and feel the very molecules of the brain; were we capable of following all their motions, all their groupings, all their electric discharges, if such there be; and were we intimately acquainted  with the corresponding states of thought and feeling, we should be as far as ever from the solution of the problem, “How are these physical processes connected with the facts of consciousness?” The chasm between the two classes of phenomena would still remain intellectually impassable. Let the consciousness for love, for example, be associated with a right-handed spiral motion of the molecules of the brain, and the consciousness of hate with a left-handed spiral motion. We should then know, when we love, that the motion is in one direction, and, when we hate, that the motion is in the other; but the “WHY?” would remain as unanswerable as before.

Minds and Computers

In everyday conversation, brains are often equivocated to “computers.” This intellectual laziness, as it were, has led to almost an entire generation of academics asserting that minds are nothing more than programs, run on the machinery of the brain. In this post, I hope to clear up a few confusions and oversights related to this position. I do not claim to be the first to say these things, but I’d like to round up a few of these disconnected views and add my own personal thoughts as they seem useful.

The issue is that to claim that the brain is like something—say, a computer—is to assert that we have any idea as to how the brain really works. This is utterly and completely false. We certainly know a lot about the brain, but most of this is in terms of small, isolated events (action potentials) or very coarsely-grained images (e.g., fMRI), so anyone who claims to have a complete view of how the brain processes, integrates, and distributes information is very misguided, to say the least.

There is certainly a lot more about the brain that we’ve learned since these equivocations were first put forth in the literature. We have learned more about how networks of neurons function coherently to produce meaningful representations. We have learned about oscillations in the brain that help unify otherwise disjoint brain functions (gamma-waves are especially exciting in this regard). We have learned about local field potentials, such as those recorded by EEG, and how they help modulate neighborhoods of neurons. In this sense, the brain is still a kind of information processor, albeit much more complex than we once thought it to be, and this is where the equivocation breaks down.

Computers are designed with distinct functional units that attempt to minimize interference from surrounding units. Neurons, the functional units of the brain, certainly do this to an extent—if they did not, the careful modulation of membrane potentials necessary for coherent communication would be impossible to maintain. They are nevertheless heavily influenced by every single signal and associated field potential that passes through any region of the brain they occupy. Neurons could not function properly in isolation (by function, I mean in a way that is conducive to conscious experience), they require complex interactions among themselves—and with the body they represent—the likes of which we do not see in their silicon counterparts. The most complex relation required is that which is often referred to as “dynamic constancy” in chemical terms. The brain is not a static system. It is constantly changing: in order to understand a single word, much less a sentence, it must alter synaptic connections. Sometimes this involves strengthening a handful due to the accumulation of calcium ions in pre- or post-synaptic terminals*. Other times this involves the generation of entirely new synapses through complex genetic regulatory mechanisms. It is astounding to realize that many everyday actions require synchronous activation and deactivation of entire networks of genes with perfect precision, often several times over. Nonetheless, all of this constant modification leaves, at the end of the day, more or less the same brain that started the day, thus dynamic constancy.

We may one day be able to “create” something that is capable of conscious reflection, and we may even call it a computer when the time comes, but it will not be anything that is recognizably a computer according to today’s standards. Likely, it will incorporate some aspects of biological matter, perhaps some actual living cells will be the only solution. The point of all of this is that minds are not merely computer programs, the distinction between program and hardware is nonexistent. The mind is the brain, and the brain is the mind, and nothing more.

*It is especially exciting to learn that the durations of various synaptic modulating processes correlate almost perfectly with discoveries made quite independently in cognitive psychology. For example, estimates of the durations of mono-synaptic facilitation, which can rely on the accumulation of calcium ions as mentioned above, tend to match up almost perfectly with estimates of the durations of various forms of working memory.