Friday, August 26, 2011

Primary Sensory Cortices and Consciousness

I just reread Dr. Kaspar Meyer’s recently published paper entitled: “Primary Sensory Cortices, Top-down Projections and Conscious Experience.” It is a great article, published in Progress in Neurobiology, that I highly recommend. In it he covers a lot of ground focusing on the role of primary visual cortex and addressing the role it may play in consciousness. He concludes, insightfully in my estimation, that activity induced in primary visual cortex (and other primary sensory processing areas) from bottom-up signaling originating in the thalamus are not consciously accessible, whereas activity induced in these areas from cortico-cortical top-down signaling can become accessible to consciousness. After reviewing a large amount of pertinent experimental results he says: “Thus, top-down projections, contrary to received opinion, do not merely modulate bottom-up signals but are able, all by themselves, to construct sensory activity patterns of considerable resolution in the earliest cortical sectors.” I agree with this notion wholeheartedly. I think that even my limited imagination is too intense and visually vivid not to be a product of top-down hegemony. Meyer goes on to say: “Interestingly, in a very general sense, the finding that conscious experience relies heavily on top-down signals supports the ideas of those who have argued that perception should be conceptualized as an active interpretive process, in which the element of prediction (sometimes formalized in terms of Bayesian inference) is key.” I like this last quote a lot and it makes me think that neither late associative, nor early visual cortex can identify an abstract concept on its own but instead must work in together in lockstep.
You can find the article, and read the abstract here:
While reading the article I was inspired to jot down the following in the margins:
I can see my computer keyboard in front of me, in its entirety, in early visual cortex. Interestingly though, it is not a keyboard there. In early visual cortex it is only an image of a keyboard. The letters on the keyboard are not true symbols there, they are only arrangements of lines and curves. The keyboard represented in early visual cortex cannot yet be identified as a large, black rectangle, and even though this early cortex holds information about the color of the board, it can’t name that color.  The representation of the keyboard in early visual cortex has keys that are not yet identified as keys, and are certainly not meant to be pressed. Early visual cortex processes the visual imagery, but none of the identities of the board, or the affordances offered by it. This type of higher-order imagery is processed by and appreciated in brain areas, visual and otherwise, higher in the processing hierarchy. These higher-order areas, in the same vein, process more complex and abstracted elements of the keyboard without holding what is held by the earlier visual areas. Different areas of the brain are specialized to handle their own unique processes and they don’t need to represent what is already represented elsewhere. There is no need for redundant representation simply because all of these areas of the cortex are interconnected by vast networks of projections allowing them to share their unique and eccentric knowledge. An important question then is: how does consciousness arise from communicatory yet compartmentalized modules if no one module can see the big picture? This view makes consciousness seem, not only distributed in time, but also decentralized in space.

Thursday, August 25, 2011

If I Developed Schizophrenia, What Would My Delusions Be Like?

I have lost two friends to schizophrenia in the last few months. Two, savory characters that didn’t know each other, but that I knew well, recently had psychotic episodes where they became totally delusional for several days. Both of my friends had been under a lot of stress (both had lost a parent) and their breakdowns were so severe that they had to be hospitalized for a few weeks. Both experienced a kind of temporary insanity, and now have diagnoses that include schizophrenia. In the weeks before hospitalization, their thinking was so distorted that they began to believe things that were totally irrational. My first friend thought his friends were saints and that he was an angel responsible for preventing an ensuing apocalypse. My other friend thought that every video on was a personal message giving him clues about his future. I wanted to tell myself that there was no way that I would have the same delusions if I had a biologically similar episode. I figured that I couldn’t possibly believe what they believed. Perhaps I am not psychologically wired to have delusions involving the same content as those of my friends, but I would probably believe something else, something equally as delusional. My first friend believed more in the existence of angels and saints than I do and this must be one reason why he had this specific delusion. I stopped believing in supernatural phenomena completely as a child, so my delusions would probably be much less likely to feature superstitious or unscientific conceptions.
Chronic stress usually plays a large role in the onset of schizophrenia. If chronic stress is severe enough, and one has a genetic predisposition for it, the brain’s chemistry can change profoundly. Dopamine transmission to the prefrontal cortex is one the things affected the most and this skews perceptions (causing hallucinations) and also skews conceptions (causing delusions). In a general sense, skewed, psychotic or schizophrenic thinking causes people to take fewer mental representations into account when making decisions. This makes it so that the conclusions that they generate are hasty or poorly informed. For example, I might see a shoebox on the carpet in the corner of my eye and assume that it is my cat. Anybody might make this mistake, but the person with schizophrenia might feel certain that it was their cat, at least for that moment. The same changes that underlie hallucinations are probably also responsible for delusions.
Because our brains are constantly generating automatic conclusions from given assumptions, our minds become accustomed to this. All people tend to rely heavily on the perceptual and even conceptual conclusions that our brains jump to. If we had to consciously test every implicit conclusion that our brain makes, we would never get anything done. We are so used to trusting our snap judgments that we often don’t even question them, especially if they are accompanied by a feeling of certainty. I think that in schizophrenia, the certainty thermostat in the brain is set to a lower level. Delusions are usually caused when someone comes to feel the feeling of certainty even though their belief was based on limited evidence, causing them to feel strongly about superficial conclusions. If my mental abilities were similarly encumbered and if the certainty thermostat in my brain was equally off mark, what would I be delusional about?
The brain changes that accompany schizophrenia fundamentally change the process of generating conclusions. The snap judgments that a psychotic brain makes are less informed than they used to be, but most people don’t have any way of knowing this until their friends tell them that they are acting crazy. Certainty – the tendency to trust one’s judgments – stays the same, but because the judgments are less informed the psychotic person begins believing things that are patently wrong. It seems that in schizophrenia, and with some street drugs, this sense of certainty can be very compelling and falsely reassuring. In a psychotic episode, I might see someone do something vaguely familiar to something I saw in a horror movie. Because I wasn’t thinking on all cylinders, I might implicitly jump to the conclusion that this person was threatening me despite other evidence to the contrary. Because I have almost always been able to trust my sense of certainty in the past, I might fail to question or observe this impulse.
I feel like I have spent a good deal of my life actively avoiding irrational, unscientific and superstitious thinking. When I am not running on all cylinders, I don’t come up with fantastic, imaginative scenarios; instead I become dull and slow because I am not as good at thinking logically deliberately. Perhaps what I would be delusional about might not be quite as socially inappropriate or clinically recognizable as the delusions that my friends were having. Also, my clinical knowledge of schizophrenia and its symptoms might keep me from acting stereotypically schizophrenic. Perhaps people experiencing schizophrenia that are socially considerate and conscientious would simply be off compared to their former selves, but not compared to a social standard.
When your dopamine system is deranged, you are likely to act immature, emotional and to be driven by juvenile notions and goals. Even though I may have been psychologically sane enough not to do anything too out of the ordinary, the biological toll that prolonged stress took on me caused me to do things that I would normally know better than to do. After pronounced stress, I began to take up an obsessive interest in videogames, comics and Legos. I kept going to work, I kept trying to act normal and professional but I began to buy toys and intricately decorate whole rooms with them. I was so caught up with this that I did not question it the way I would have before the stress. At first I just saw it as a fun hobby that wasn’t taking up too much time but now, with hindsight, I believe that I never would have taken the resurgent interest in Legos to the same extent had my brain chemistry, my level of certainty and my judgment not been substantially altered. 

Thursday, August 18, 2011

How Do Hippocampal Memories "Migrate" to the Cortex?

The hippocampus is a finger-shaped brain area that is necessary for a very important kind of memory. You have two, and they extend a couple of inches beneath your cheeks back towards your ears. Your hippocampi serve as the repositories for all of your short term memories. As crazy as it sounds, people cannot form almost any new explicit, contextual or episodic memories without the hippocampus. A few people in recent medical history have had the area removed or badly damaged and their deficits are illuminating. These individuals basically cannot remember anything they have done, any place they have been or anyone they have met since the damage took place.

Much recent research has shown that the hippocampus probably does not actually hold the memories itself. Rather, it has the ability to take snap shots of what is going on in the cerebral cortex. Its unique connectivity allows it to keep track of which cortical association areas are firing together at a certain time. It records the coordinates of these coactivated areas of cortex allowing it to remember patterns of activity. Later when the environment, or a thought, causes a portion of a previous pattern to become active within the cortex, the hippocampus is able to recognize this and reactivate the other areas that were coincident with this portion before. This unique ability of the hippocampus is called "pattern completion" and is thought to underlie the mammalian capability for short term memory. Interestingly though, birds, reptiles, amphibians and even fish have brain areas that are equivalent (or homologous) to our hippocampus.

Scientists know that when you lose your hippocampus you not only lose the ability to remember new things (to complete recent patterns) but you also lose most of what has happened to you in the last two years. For instance, if your hippocampi were removed today you could remember a lot of autobiographical information, but would have trouble remembering most of what happened to you over the prior two years. This finding caused scientists to assume that over the course of two years, memories must migrate out of the hippocampus and into the cortex. When I first read this, I didn't know how to conceptualize this "migratory process." I imagined small, physical objects moving from the hippocampus to the cortex. This is of course absurd because memories are not tangible things, they are made of tiny intricate modifications of existing circuitry. Even knowing this, I didn't know what to replace this conceptualization with until recently.

I no longer think that the brain's memories are physically shuffled around. I think that the hippocampus is constantly recording patterns, and only when it is later stimulated to complete one of these pattern, does it share what it holds. Individual instances of this sharing may underlie the transfer process. I think that the cortex learns plastically, although slowly, every time the hippocampus causes it to retrieve a memory (to reactivate a specific pattern of cortical activity). If this is true, then we should expect that the many memories that the hippocampus holds, that are never reactivated, would never "migrate" to the cortex. In other words, if you never recall a short term memory it will never make it into long term memory. Clearly, the things that we think about the most are the most ingrained in our memory, but does it have to work this way? It is very hard to be sure. I imagine that migration could happen below the threshold of consciousness or perhaps during sleep but I think that migration is a cumulative process where the cortex slowly learns the patterns that are brought up most frequently. This may account for why things that were never recollected become the hardest to recall with time.
Another pertinent question then would be: Once the cortex has learned to code for a memory that was previously held in the hippocampus, does it remain in the hippocampus? Also it is clear that even though the memory is transferred from the hippocampus to the cortex, it changes subtly. The hippocampus holds contextual information whereas the cortex holds a mysterious brand of memory that I would describe as fragments of imagery. Understanding the fundamental differences between cortical and hippocampal memory must involve understanding how they are transferred. Why would the hippocampus interact exclusively with the association cortices and not with sensory cortices? Could it be that taking snapshots of unprocessed stimuli would lead to garbled information or invalid associations? What if the receptive fields of cortical neurons, that were once a part of a specific pattern held together by the hippocampus, change appreciably. Perhaps after two years of cortical remapping, the hippocampus will attempt to complete a pattern, and find that the cortical assemblies that it activates no longer code for the same elementary features that they once did because of cortical plasticity.

This might be a way to create a memory implant: create a specific hippocampal memory and then alter the tuning properties of the cortical neurons involved in the memory to evoke different imagery. As long as you could keep the person from consciously understanding what was done the fabricated memory should feel authentic. But the weights of our cortical maps are changing everyday with experience, and this must make hippocampus-driven coactivations fuzzier with the progression of time. Perhaps this is related to the reason why the hippocampus seems to lose memories after two years.

So, why does the hippocampus exist at all if it is only around to catalogue memories and slowly transfer them to the cortex? Couldn't the brain just as easily increase plasticity in the cortex, allowing it to remember its own patterns of coactivity? Perhaps the cortex cannot trust that new experiences will be valid or interesting. Perhaps it needs the hippocampus to store memories for it temporarily to determine if they are useful. Perhaps it needs the contextual aspect of hippocampal memory because it allows animals to discriminate between semantic and episodic knowledge. This makes me wonder a lot about the nature of the connections between the hippocampus and the cortex. I think understanding how the cortex and the hippocampus interface will be very important in understanding the nature of memory and conscious experience.

Monday, August 15, 2011

My Personal Experience with Chronic Stress: Compromised Cognition

Anxiety or stress leads the brain to process information differently. Basically, stress causes you to think fast, rather than to think comprehensively. Working memory and the ability to carry information through time is adversely affected by acute stress, even if the stressor only lasts for a few minutes. The transient changes are mostly chemical but prolonged stress measured in days or weeks actually creates physical changes to the brain and its neurons. Depending on severity and duration, stress can lead to irreversible modifications in thought and cognitive ability. The stress hormone cortisol is the main culprit and it makes alterations all over the brain particularly in the hippocampus and prefrontal cortex. I have written at length about this here:

I believe that I have personally experienced what it is like to lose mental aptitude to stress. I want to take the opportunity to offer some anecdotes from my experiences because, however subjective, I feel that they may offer insight for the psychotherapist and the philosopher, if not the clinical neuroscientist. I have been fighting severe stress for several years and what follows is a memoir on the cognitive dissolution that I withstood.

Over the past five years, I have endured several month-long bouts of chronic stress. In the morning I would wake up feeling anxious, and after just a few social encounters, my heart would be racing and my adrenaline overpowering. Many friends and acquaintances were often surprised by the way I appeared to behave like someone who was panicking for no apparent reason. I tried to compose myself, but struggled because my anxiety was extreme and excessive. Despite concerted attempts to combat stress I would often feel overwhelmed by it for days at a time. I believe that early on I was not fully aware of (I was anosagnosic of) some of the psychological changes that were taking place. After noticing that I was having memory lapses of unprecedented magnitude I began to carefully observe my mental handicaps and measure my performance relative to my premorbid state. Doing this, I believe, allowed me to identify and analyze many of the neuropsychological corollaries of my predicament. I am convinced that, to an extent that is objective of hypochondriacal concern, my attention-span, working memory, declarative memory, and my ability to learn and exercise discipline declined gradually over a period of a few years.

My ability to concentrate was one of the first faculties adversely affected by stress. Prolonged concentration is impossible if the train of thought is persistently derailed. After days of intense anxiety I felt like it actually became harder and harder to remember what it was that I was just thinking. It was the same with reading. I could not conceptualize long complicated sentences because, before I finished the sentence, I had already become oblivious to the first few phrases. My reading comprehension became worse and worse because previous sentences and paragraphs were not immediately available. Reading erudite academic texts was previously challenging and rewarding, but the chronic stress made it prohibitively difficult. When I tried to concentrate on, or grapple with, a question that I posed to myself, I found that within a few seconds, I lost the train of thought. Before I could pin down one concept and evaluate a second concept relative to it, I had already lost attentive command of so many of the relevant features that the effort was useless. I could not collect my ideas on subjects that I was reading about or even wondering about unless I was intensely intrinsically motivated. It was a state of constant intellectual exhaustion.

Because I could no longer pose difficult questions to myself and systematically identify the avenues that would help me answer them, I had fewer interesting insights. The conclusions I reached were trivial and insubstantial. In fact, most of my interesting ideas were accidental, and made through snap judgments instead of earned through inductive reasoning. When I tried to apply rationale, I returned quickly to zero - returned to my physical senses. Instead of being able to become “lost in thought,” I was grounded in physical immediacy. At first it felt as if each new thought was powerful and interesting, but I soon realized that it only seemed this way because previous thoughts faded prematurely. I was distractible precisely because previous thoughts abandoned me before they could perform their function of keeping me on track. Rather than being able to find my mental considerations captivating, I found myself looking around at my surroundings and thinking about how I could attain cheap, quick stimulation. Dedicated and disciplined work became too difficult to persevere through, but I didn’t lose my drive, it was simply refocused towards endeavors with short-term payoffs. The things that would capture my interest appeared important at the time, but it didn’t take long for them to be revealed as shortsighted impracticalities. As I became increasingly shallow and capricious, my activities became unproductive, foolhardy, and even self-defeating.

Epiphenomenally, it felt like the window through which I brought the immediate past had become narrower. Only the very salient or heavily familiar concepts could make it through the gap. I had trouble recalling my last notions, sometimes, even if they were mildly promising or exciting. It seemed that even things that I had been exposed to a few seconds prior, had little or no bearing on my subsequent responses and perceptions. My behavior began to hold similarities to hypofrontality syndromes or with the “environmental dependency” of patients with PFC injury in the sense that I acted as if I had fewer internal representations and an exaggerated dependency on the external environment for behavioral cues. The internally driven perceptions that I experienced lingered only briefly before they were irretrievable. It was as if my mind’s ability to juggle activated engrams was compromised and now an engram that was just present in the volley, would disappear before it could make its proper contribution to thought.

I would come to a point in my thought process where I would try to recall a recent event. I had a couple of cues, enough to assume that, based on past experience, these cues would be sufficient to recruit the rest of the memory. A second would pass… a few more seconds pass… then nothing, no recollection at all, as if the mechanism normally responsible was utterly broken. It seemed like my memory worked either instantaneously, or not at all. If I could not recall something I was trying to remember right away, it would be useless to spend more time trying to refresh the memory. This reminded me of the condition common in prefrontal brain injuries where the patient cannot voluntarily cue up memories from the hippocampus using their PFC, but the hippocampal memoires can be jogged from environmental cues (from the sensory cortex) rendering recollections superficial and rendering associations loose. I realized that my working memory deficit probably led to the recall deficit: Because previous thoughts vanished quickly over time, related concepts could not accumulate to the point where they are able to coactivate or converge upon the associated memory in question. This may be related to the fact that I could either recollect something all at once, or not at all.

I was able to recall a much smaller proportion of the new things that I had learned and could only remember things if the recall cues were numerous. For instance, if I forgot a grocery list, I would not remember the items unless I actually saw them in the market (recognition without recall). Another difficulty that was very foreign to me: after I learned the meaning of a new word it wouldn’t stick, although the word itself might appear more familiar. Instead of assimilating the semantic features immediately, I required many encounters with a new word for the content to consolidate into long term memory. My working vocabulary, the repertoire of words that I can access in the middle of a conversation, was vastly reduced. At first I began to wonder if this might reflect the fact that I wasn’t reading as broadly or working hard enough to maintain my working vocabulary, but it became painfully clear from the shear extent of the loss that it must be due to the stress. I felt like my condition was very similar to what I have read about anterograde hypomnesia. When I was trying to remember something that I had read about or had been exposed to I often could remember how I felt about it emotionally, but many of the episodic and contextual features were irretrievable. Often I could remember something that was said, but I could not remember who said it, or where I was when I heard it. This phenomenon was striking.

This absence of contextual features effectively made it very difficult to do reality testing. I would have a recollection of something, but I would not be sure if it really happened because I could not recall details about the situation. I could not recall whether this event actually took place, was a dream, or was a hypothetical scenario that I had imagined. It became particularly disconcerting when I realized that my reduced capacity for reality testing began to lead to delusional thinking. I would catch myself devising absurd and unrealistic explanations for my actions – confabulations of a degree and severity that were previously foreign to me. I would act in ways that might seem reasonable to someone who cannot see the whole picture, using associations that are applicable in one respect but irrelevant in others. Such superficial associations would cause me to act before I noticed that my action disregarded or flouted more important concerns and norms. I believe this process probably lies at the heart of psychotic impulsivity. I noticed that I would begin to feel an impelling brand of certainty after reaching absurdly premature conclusions. Mere chance coincidences felt ominously significant. When this happened I would have to use reason and patience to fight the overwhelmingly convincing sham certitude. This quasipsychosis, most pronounced during stressful days, was even accompanied by minor auditory and visual hallucinations. Imagined sounds and sights felt exquisitely real momentarily in ways that they never had in the past. Moreover, I would analyze misperceptions, as if they were correct, for inordinately long periods before I recognized them for what they were.

The stress started to become so bad that I began to experience perceptual errors. I continually thought that I was seeing my cat in the corner of my eye but every time I looked it was really a shoe or some dark object on the light carpet. I actually mistook normal household or neighborhood noises to be human voices. At its worst, on days when caffeine greatly exacerbated my stress, sometimes I was totally immersed in my sensory experience to a point where it felt like I didn’t have thoughts of my own. It felt like because I had lost much of my internal monologue, that I had become one with my environment (this sensation probably involved hypofrontality). If I felt this way during an interaction with others I would struggle to hold a reasonable conversation and much of what I would say would be non-sequiturs. I still cannot drink caffeine because if I do, I practically begin to panic (caffeine is a central nervous system stimulant that acts through the effects of the stress hormone system). 

Before experiencing chronic stress I could analyze and evaluate a hypothesis in my head alone, now I have to write about it. I must work an idea out on paper in order to get a feeling for whether it is right or not. Before the stress, most of my thinking used to be visual, it was rarely verbal. Using language was an impediment in the sense that the time needed to form words into sentences slowed down my thought processes. Now I have to put all of my formal thoughts into words because I need the crutch of language and the phonological (articulatory) loop to act as memory buffers to be able to hold concepts in mind. I also feel like my actions, behaviors and speech come out very quickly as if preformed, especially for familiar actions. In the past a single action was broken down into many separate elements, each of which I had some attentive control of or acknowledgement of before they were issued. Now I look back after acting and wonder how all of those elements came together without planning. Interestingly, this only happens in areas I am experienced in. When I am forced to act in an unfamiliar environment or with novel conceptual constructs, I either falter and struggle or speed through it in a crude, poorly integrated way. Because I notice myself doing things without contemplating first I know that I have lost degrees of personal free will and have experienced an accelerated disintegration of self. In many ways I feel as if the person that I was previously is now gone.

My working memory was lacking terribly, but implicit (habitual and procedural) responses actually filled in many gaps quite well. For instance, trying to learn or interact with new systems (such as a new computer operating system, a new bicycle, or a new supermarket) was very difficult and frustrating, but interacting with familiar systems was effortless. Because of this, I eschewed novelty. As long as I stuck with familiar territory I was able to get along well without other people noticing my deficits. My spatial ability, which works somewhat independently of implicit and habitual memory, was one of the faculties that deteriorated most noticeably. I used to be able to walk deep into the journal stacks in the university library basement, absorbed in articles, while at all times keeping my spatial and temporal bearings. No matter how many turns I had taken down windowless corridors I always knew where I was and which direction the compass would point. Today, only a few years later, I can quickly lose my sense of direction and orientation, even outdoors and even in the presence of salient landmarks.

The most interesting part of all of this is how normal I seem after a tremendous loss. The other brain areas, programmed by the cortex, allow me to move, act, speak, even hold a conversation and to an outsider, nothing seems to be missing. Externally it is very hard to recognize, but internally I feel that I am missing an entire world of planning, insight and foresight. I have lost the mental leverage that helps me to make complex and unique associations that are different from other associations that I have made in the past. A few years ago, I felt that my conscious life was mostly planning actions and envisioning the future. Today it is mostly having fleeting insights about the repercussions of my actions – automatic, mostly unplanned actions mediated more and more by lower brain systems.

Once my higher-order intellectual faculties were diminished, I could not will them back. I couldn’t do anything to revert back to the old me. This insight dispelled the last dualistic inclinations within me and proved that my previous mental abilities were materialistic and not at all voluntary. PFC mediated thought is as involuntary, transient, fleeting and insubstantial as lower-order cognitive faculties are. Executive processes could be taken away by the stress cascade because they were not inherent in who I was, but were on a fundamental level automatic and reliant upon their neural substrates.  This made me realize that my previous intellect was never earned or willed, it was simply biological chattel.

Before the stress, I was socially inept in many ways; I came across as spacey, stilted, abstract and neurotic. I used to think very hard before I spoke in virtually every social situation. I would even formulate nearly every sentence in my mind before I spoke it. I cannot do this anymore. Now I have to start a sentence before I know how I am going to finish it. It got so bad that I began to frequently lose my train of thought in the middle of conversation. Every time I strayed too far from my topic I would, embarrassingly, not be able to come back to my main point. Formulating long, descriptive sentences could be agitatingly difficult. Now when speaking, I am forced toward brevity and simplicity and made to relinquish hope that I will be able to recall unique technical terms that lack substitutes. Often I know that there is a specific word that I am looking for but that I will not be able to cue it up on the spot. Sometimes it seems like the only words that I can trust to fall into place are those common and habitually ingrained ones that I have been using since childhood.

After awhile, I learned to simplify my discourse and to stop trying to set up complicated arrangements of sentences. I say things that I have already said before, retell the same stories to different people, employ melodic contour, use trite expressions and more emotionality and never veer off too far from the main point, for fear of losing my train of thought. Ironically people responded better to this, and I noticed that I quickly became more socially facile. I was more affectively congruent (a largely implicit ability), and instead of being stilted and detached during conversation, I was able to maintain a high level of emotional fluency which at times helped me build rapport with other people better than I had ever been able to prior. Instead of seeming suppressed, excessively conscientious and calculating, I came across as more emotionally impelled and thus more authentic. Instead of being informed by thoughtful analyses a very large proportion of my speech was simply composed of “dominant responses” which consisted of the easiest thing to say in each situation – the first thing that comes to mind. My newfound ability to be spontaneous, to improvise and to respond without really thinking much made my social interactions much more comfortable and easy. It also made simple motor movements perceivably easier.

Many but not all of the effects of stress on cognition are reversible. The altered dopaminergic response to stress can reverse within a few hours of the stressor; the dendritic retraction appears to reverse after several weeks but the death of hippocampal neurons may not be reversible at all (Sapolsky, 1996). How can we determine the extent of irreversible damage? It seems to me that I have recovered some lost function, and I credit many sources. Mindful meditation, heavy cardiovascular exercise, caffeine and cigarette cessation, abstention from violent video games, yoga, Buddhism, ego-restraint, positive psychology, biofeedback, and efforts at increasing my social support network have all seemed to help me tremendously in my efforts to reduce and recover from stress.

Monday, August 8, 2011

My Personal Experience with Chronic Stress: Facilitated Movement

Chronic stress changes the brain. It reprograms certain brain areas to become more active and other brain areas to become less active. Studies looking at soldiers being deployed for war, a major stressor for most soldiers, have documented that stressed individuals have lower cognitive performance on difficult and abstract thinking tasks but have facilitated reflexes and faster response times on tests of simple muscular responses. The same effects have been shown by animal studies. I personally have allowed stressors to influence me to a clinically significant extent and what follows is my recounting of the behavioral changes. After months of particularly acute, chronic stress I realized that I could do things physically that I could not do before. During these bouts of chronic stress my reflexes were potentiated so much that even other people were able to notice the changes.

I always wanted to be good at catching things that were falling, and I liked to think that I was good at it. After the acute stress though, I was very good at it. As long as I did not hesitate, I could even catch things that other people dropped. Many friends and acquaintances put their surprise into words, commenting on my quick, nimble reactions. The best way to describe it would be to say that it felt like my body was on autopilot and my dexterity linked sequences of movements together without me having to preside over the selection process. Playing a familiar sport seemed unconstrained and effortless. Trying to learn the strategies of a new sport was very difficult, however, as I had a hard time trying to systemize new rules and agendas.

In the past, I liked to think that I was decent at dancing, but truth be told, I would lose a beat pattern after just a few beats. Back then, I would try to concentrate on the timing of the music, but the simple act of paying attention to it caused me to lose the beat – I would expect it too early or too late – as if the act of trying to attend to it pulled me out of my sensory world. I would continue to attempt to execute dance moves without being able to synchronize them with the music. After the acute stress, it was impossible to lose cadence. My estimation of when the next beat would strike was much more precise. It felt very natural to coordinate my movements to a repeating rhythm, as if I had practiced doing it my entire life. In fact, I could smoothly alternate from a certain beat-per-second, into half-time or double-time, and then back again, something I had never even conceptualized before. Moreover, I seemed to be faster at familiar activities, my balance was better and my ability to gesticulate had taken on a smoother, more wholesome quality.

Growing up my personality was repressive and stoic and you could hear this in my speech, feel it in my demeanor and see it in my movements. In the past my movements were reserved, deliberate and discrete but stress made it so that they became spontaneous, relatively autonomous and it caused what would have been discrete motions to blend together seamlessly without cognitive guidance. I would notice that I would act or speak without deliberating beforehand. It was frightening at first because it felt like I lost the filter between thought and action. I would do something without first modeling the outcome. I would skip the normal checking, double-checking and planning that used to accompany the initiation of every move. In the past, I would veto every other imagined action before it had a chance to come out. Because of this, I didn’t move or act half as much especially in social situations. After the stress, I felt like a roving automaton that was in a state of constant impromptu activity. Before the stress I felt like I was a creature that, like a chess player, can only make one premeditated move at a time. After the stress I felt like I had become a flurry of well-coordinated but unplanned motions. This had the general effect of giving my behavior the unsupervised quality of punch drunkenness or slaphappiness and led to irreverent, impulsive, unprioritized and unproductive self-management. Interestingly, even though I feel that I have partially recovered from some of the cognitive deficits associated with chronic stress, I feel that I have retained much of the coordination and motoric adroitness.    

How did my motor control and procedural activities become effortless and how did my movements take on a life of their own? It is generally thought that there are three forms of movement: reflex, rhythm, and voluntary movement (Kandel et al., 2000). The prefrontal cortex, an area that is widely disturbed by chronic stress, mediates voluntary movement. Once its dominion over behavior is weakened, brain areas responsible for more automatic behaviors are given free reign. It is clear that the cortex, via the corticospinal tract, puts a great deal of inhibitory pressure on central pattern generators in the spinal cord which are responsible for reflexes and rhythmicity. For example, all healthy infants are born with certain reflexes, such as the Babinski reflex, which disappear within the first year of life. The reason that they disappear is because many axons in the corticospinal tract become myelinated during the first 12 months of life, and they allow the frontal cortex to tonically inhibit certain spinal reflexes which can be unmasked if this tract is damaged or if certain reflexes are highly practiced (Afifi & Bergman, 2005). Frontal brain damage has also been known to unmask motoric patterns that ordinarily would necessitate higher neural activation energy to surface (to overcome the neural inhibitory energy). I imagine that the release of inhibition, not just of the spinal cord but of the basal ganglia, extrapyramidal system, or other early motor centers might be responsible for my physical fluency. It is known that after motoric motions are sequenced consciously in the premotor and supplementary motor areas, implicit knowledge of this sequencing migrates to the basal ganglia and other lower motor centers.  

One really interesting example of a facilitated reflex involves recovering from being tripped. When your foot swings forward to take a step, it is very susceptible to being tripped. The foot swings forward briskly and automatically during a step, and if at any time during this movement the foot collides with an object or is caught on something, the person can trip very easily. The only way to keep yourself from stumbling or tripping is to stop the forward movement of the foot (switching quickly from using the quadriceps muscle to the hamstring), and to pull it up or over the obstacle that is impinging on your stride. This is very hard to do, because it requires split-second timing and if it necessitated conscious control, it would probably not occur in time to avoid most stumbles. I was rarely able to avoid tripping by engaging the hamstring quickly enough growing up. However, after the period of chronic stress it became second nature. I am very resistant to tripping over cracks, wires, tree roots or people’s legs now. Friends of mine have even commented on how briskly and effortlessly I have recovered from tripping. The funny thing is that I erroneously thought that the grace and agility required to do this was under my conscious control. In quick movements like this one, consciousness plays a small role if any. The movements controlling recovery of footfall, as in most aspects of walking, are mediated by the spinal cord (Kandel et al., 2000). I realized that I could not give my conscious self credit for the avoidance maneuver, because one day it became obvious to me that consciousness can be fractionated from it: when my foot swings forward sometimes it collides with a flimsy obstacle, one that gives way easily and would not trip me at all.

If the foot maneuver is a conscious one, I should be able to assess whether or not the collision was sufficient to trip me, and if not, I should be able to inhibit it. No such luck. I often find that my hamstring pulls my swinging foot back quickly when the obstacle is as light as a pillow, or as insubstantial as a loose cord. This is a perfect example of the tradeoff between fast inflexible movements and slower adjustable ones. Fast movements are quick enough to accomplish things that conscious ones are too slow to accomplish, but again, are susceptible to pragmatic errors and to being miscued. The effortless coordination of simple motor planning that I experienced was, in my opinion, striking and unmistakable. The effects were interesting and rather entertaining to experience despite the sobering reality that they were actualized by the decline of higher-order brain centers.

Friday, August 5, 2011

Temperature and Metabolism Interact to Create Life

One of the most amazing aspects of cell biology is the chemistry that takes place within the cell walls. The cell takes full advantage of the laws of physics and chemistry to make its living.  A tremendous amount of the work that is done by the cell is accomplished by ambient heat, a property that everything on our planet has an awful lot of. This heat comes from the Earth’s molten (and radioactive) core, from the Sun’s rays and ultimately from the energy released in the big bang. Thermal energy makes the atoms and molecules in everything move and vibrate incredibly fast. Especially in the watery cytosol within the cell membrane, this molecular kinetic energy ceaselessly creates opportunities for molecules to meet and interact. Life takes advantage of this “free energy” by using it to power the work that takes place in our cells. Clearly, we get energy to do work from the food that we eat. Sugars, carbohydrates, proteins and fats are converted to ATP to power work within the cell, but ATP would be worthless if out cells didn’t have molecular kinetic energy, in the form of temperature, complements of the universe (I have never seen this point written out before, so I wanted to do so here).  
The universe is cooling down as it continues to spread out from the force, the explosion, of the big bang.  This cooling will reach absolute zero (-273 degrees Celsius) many billions of years from now at which time the heat will be zero and all atomic and molecular movement will finally cease (even though chemical energy may still be available in the bonds between existing atoms). So the free energy that we enjoy is finite but still it seems amazing how this ubiquitous movement on this tiny scale, can continue for so long, virtually unimpeded.
If you were to place a rock from your backyard in a theoretical, closed system, it would not cool. The momentum of its particles would be conserved despite the billions of collisions that take place every second.  But we all know that in large scale physical systems that are not “closed off,” energy is not well conserved. Imagine putting a number of billiard balls inside of a plastic, transparent box and shaking it vigorously. Physics tells us that the forces and energy that you applied to the box will all be conserved, accounted for in some way, somewhere. Unlike the atoms in a cell though, the kinetic energy of momentum in the balls will be transferred to other forms of energy very rapidly.  The balls will collide with each other and with the walls of the box several times where they will transfer their energy in the form of sounds (energetic vibrations in air), friction against the felt, and heat, heating up the box and the balls.  In this way, momentum is quickly taken out of systems that we observe at our large scale.

On a molecular scale though atoms collide with things and bounce off in an elastic way without losing almost any of their initial momentum.  They can transfer momentum to each other easily but it would take a staggeringly enormous amount of time for the atoms to lose all of their kinetic energy and lay motionless at the bottom of a box.  This is true no matter what phase they are in; liquid, solid or gas. The really cool thing about cells is, they take advantage of the huge number of collisions that take place inside of them due to their temperature alone. Each collision is an event that has the potential of creating an auspicious chemical reaction that will help the cell in its effort to build and thrive.  Fittingly, one of the main things that a cell builds are enzymes, tiny proteins made of thousands of atoms, that help to make the auspicious collisions thousands of times more frequent. Enzymes are chemical catalysts that speed up metabolic reactions by lowering energy barriers and orient molecules for collisions. Enzymes truly empower the cell to harness the momentum of the atoms inside of it by influencing the type of collisions that occur.
When we measure the metabolism or energy expenditure in organisms, we measure the chemical bonds made possible through photosynthesis. We don’t measure the ambient heat, which is really the energetic substrate for life on a molecular level. It would be really interesting to me to find out what really powers us more, food or all of the energy available to us in the form of molecular kinetic energy. Clearly there would potentially be many different but valid ways to measure both and clearly they interact such as when metabolism increases temperature.