(Copyright © 2009)

 

Memory is situational because consciousness is situational. Everything that happens takes place in the particular circumstances that frame our life worlds at the time. Consciousness is a matter of being alive to our current life situation as the mind configures it.

 

Exhibit A. I am at scout camp the second week in August, 1945. It is Sunday, so there’s nothing to do. The sun is shining. I go for a walk with a friend down a dirt road lined with tall trees. Everything is different somehow. Looking into the sky, I picture a bomb falling, falling, falling. Earlier, at breakfast, I’d seen a story in the camp director’s newspaper about an American plane dropping an A-bomb on Hiroshima, a city in Japan. I don’t know what an A-bomb is, but I know it is bad. I am scared.

 

Exhibit B. I am in eighth grade. The war is over. My father is renting a cinderblock house in Sarasota for a year. My mission is to help dismantle Sarasota Army Air Base, soon to close. On Saturdays, wrench and screwdrivers in my pocket, I ride with bus driver Russ Shin (from his name tag), north to the airfield, but get off where he turns west and the railroad tracks continue north through the swamp. I walk along the tracks, cross a trestle, to the dump in the southeast corner of the airfield. Crawling under the fence, I am among the remains of planes, trucks, and all sorts of military gear. My personal stock pile. I pick up smoke grenades and dye packets. Radio equipment. Skipping the tubes of prophylactic ointment, I climb in the cockpit of a wingless plane and unscrew gauges of all kinds. Gyroscopes! Checking the time, I gather my haul—by now including pilot’s seat and dummy bomb—and head back, loaded much heavier than when I came, along the elevated rail bed through the swamp. What’s that noise? Looking ahead—a locomotive heading my way. No sir, I’m not going to ditch any of this stuff. I can’t go back, I’d miss the bus. And I’m not going into that swamp! Which leaves the bank under the trestle. I figure I can just make it. Flapping and rattling, I plod towards it as fast as I can. The train keeps coming. I keep plodding. Just as the train reaches the trestle, so do I. I taste the heat and smell of the steam as I dive under the tracks onto the bank below, my feet in the water. I feel how fast my heart is beating. No time to sit around. I keep going and meet Russ at the corner. Saying nothing, he just looks at me. When I get home, I put the stuff under my bed. Next day, I use a can opener to take the bottom off one of the smoke grenades. I show it to Jack Tisdale who lives across the street. In his living room, we use a lens to focus sunlight streaming in the window onto the cake of white. Wisps of smoke, then billows. We drop the grenade on the rug and run out the door. Jack tells me later everything in the house is coated with white powder. I am surprised how angry some grownups can get.

 

Exhibit C. For reasons unknown, in 2001, 90% of the eelgrass in Taunton Bay died back. Which is an ecological tragedy because eelgrass beds provide habitat for all manner of sea creatures including cod, flounder, crabs, periwinkles, and amphipods. I’ve been worrying that bone for seven years. What I know through personal experience is that no sea lavender appeared that year, periwinkles died by tens of thousands, the water was cloudy, ledges were extremely slippery as if coated with slime, and Maine had the lowest rainfall in 111 years. Looking at photographs from earlier years, I saw that eelgrass reached maximum extent and density in 1973, year of the heaviest snowmelt since records have been kept. Since 1992, I’ve flown aerial overflights to check on eelgrass in the bay. It was down in the 1980s, as it was in the drought years of the 1930s, but making a nice recovery throughout the 1990s. Boaters noticed how thick it was getting because it clogged their propellers. Then in 2001 it crashed. And only now in 2008 and 2009 is slowly coming back in some places but not others.

I’ve been trying to make myself conscious of the circumstances which prevailed in 2001 so I could accurately characterize the situation and figure out what the significant variables might have been that led to the dieback. What I notice from aerial photographs is that eelgrass is recovering in areas fed by both salt- and freshwater. That is, where the bay is brackish, as in stream channels and where melt- and rainwater flow off the land. The dieback, I think now, has something to do with the amount of salt in the water flowing over the eelgrass beds. Salinity is highly variable in Taunton Bay, ranging from pure fresh water on the flats at low tide (when it rains) to the salty flows coming over the reversing falls from Frenchman Bay and the Gulf of Maine beyond.

I now believe the eelgrass dieback was triggered by the drought that reached its peak in 2001, causing slight dilution and unusually high salinities, allowing eelgrass dieback disease to flourish whereas runoff and rainfall usually moderate the salinity, and thus keep the ever-present disease organisms in check. This makes sense because Taunton Bay is a closed bay largely surrounded by land (unlike open bays which are subject to greater flushing by marine waters), so periods of low runoff and rainfall produce pronounced changes in salinity. Too, global warming may have given the disease organism a significant boost in 2001.

By this exercise I have approximated the consciousness I might have had in 2001 if I had kept track of all that was going on in the world of local eelgrass beds at the time. By doing my best to recreate those conditions, I have tried to make myself aware of the prevailing situation that led to the decline. At least I can make an educated guess with more certainty than I could have when I didn’t know how much I didn’t know.

 

The larger question remaining is where in the brain does situational consciousness come together as a gateway to both situational memory and informed behavior which is more-or-less appropriate to the circumstances within which it arises? The anterior cingulate cortex (see Reflection 60: Discovery) receives all the appropriate inputs (motivational, emotional, sensory, cognitive, remembered, anticipatory) as well as direct input from peripheral eye fields (what we see out of the corner of our eye), feeding forward to motor planning and execution areas of the frontal lobe. The locus where these various strands of consciousness come together could well serve as the seat of both situational consciousness and—when arousal is sufficient—situational memory (by a perhaps less direct route).

 

This is conjecture on my part. Maybe it has some heuristic value. My contribution is the details I glean through introspection, which animal and clinical studies generally do not provide. I offer it in this blog to give the world a chance to judge what it is worth. For me the reward is in the pursuit of understanding while I still have a mind to keep me entertained.

 

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Reflection 60: Discovery

February 6, 2009

(Copyright © 2009)

 

From ninth grade, I still remember the shock I got when teachers in two different classes talked about the same thing. In social studies we were studying map projections. One day, the difference between Mercator and conic projections came up. It was a great class because I suddenly realized there was no way to map the surface of a sphere onto a flat plane without distorting or doing violence to the image. Several periods later, in geometry, the teacher showed on the blackboard how lines projected from the center of a circle onto a straight line would represent equal sectors of the circle by different lengths on the line. She gave Mercator projection as an example. So that’s why Greenland always looks so big. Eureka! Classes in school didn’t exist in a vacuum. They could be about the same world as seen from different points of view. I always assumed they were separated by some universal law. I don’t think I have ever been more excited by classroom learning. It wasn’t something I was taught, it was something I discovered on my own, as if by accident.

 

Three cheers for serendipity. Accidental or coincidental learning is powerful stuff. There’s no mad scientist deliberately trying to pair the sound from the loudspeaker with an electric shock soon to come. Since nobody arranged for it to happen, it has to be true. At least that’s how it seems.

 

I spend hours trying to dope out my own consciousness. Reading about lateral and orbital prefrontal connections with the anterior cingulate cortex, how the amygdala fits in, the hippocampus, the senses, bodily feedback—all connected to motor areas that will implement decisions with the precision they deserve.

 

I consult results from animal research, clinical studies of brain damage in humans, functional neuroimaging, and my particular method—introspection of my own conscious life, trying to keep up with what my mind has to show me.

 

Finally, I come to the conclusion that consciousness is shaped by the situations in which it emerges so resultant actions will be more-or-less appropriate to the specific conditions that apply. I carry the idea around in the back of my mind that consciousness has got to be situationally relevant. Whatever areas of the brain are involved, they have to work together in representing current situations, detailing the factors involved, the locales, how I feel about things, my relevant experience, options, motivation, what I hope to achieve—all in direct contact with motor planning areas so that once I decide what to do, I can make my move with some confidence that it will suit the occasion. I am on the outlook for confirmation that I am on the right track. Then I read this:

 

Our results suggest that the [anterior cingulate cortex] integrates inputs from other emotion-related areas and frontal cortex, and sends the information to motor executive centers to behave appropriately in a variety of specific motivational or emotional contexts.[A]

 

Reading those words, I say, “Yes, that’s got to be right. Prefrontal cortex, emotion, motivation, leading to action suitable to the situation—I couldn’t have said it better myself. It’s got to be right.” For monkeys, at least. Actually, I don’t even know if it’s right for monkeys, but for human’s it’s got to be true. At least that’s how I feel. I always come down from such surety after a while and get on with my work. Then, further along in Gazzaniga, I come across this:

 

Thus, posterior cingulate and adjacent precuneus cortex can be hypothesized as a region of the brain associated with the continuous gathering of information about the world around us.[B]

 

This is not dealing with the sensory world of rats or monkeys, this is a study done with humans. Not the anterior cingulate this time, but close to it. Tying sensory input into the mix. Making the situation (world around us) more explicit. Another piece of the puzzle fits into place. Does the posterior cingulate in the parietal lobe feed sensory information to the anterior cingulate in the frontal lobe next door? I assume it does, and probably vice versa, but I haven’t found out for sure.

 

That’s how it goes—using every resource available, you just have to keep pressing into the mystery ahead. The trick is not leaping to conclusions but staying open. One day your social studies and math teachers will strike a chord in your brain, and you’ll be on your way. No one can do it for you. Discovering the ins and outs of your own consciousness is the adventure of a lifetime.

 


[A] Ono, Taketoshi, and Hisao Nishijo. Neurophysiological Basis of Emotion in Primates: Neuronal Responses in the Monkey Amygdala and Anterior Cingulate Cortex. Pages 1099-1114 in Gazzaniga, Michael S., Editor-in-Chief, The New Cognitive Neurosciences, Second Edition. The MIT Press, 2000, page 1111.

[B] Raichle, Marcus E. The Neural Correlates of Consciousness: An Analysis of Cognitive Skill Learning. Pages 1305-1318. Same source as above, page 1315.

 

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(Copyright © 2009)

 

In the movie Donovan’s Brain, poor Donovan is reduced to a brain hooked up to wires in a jar, sharing his thoughts through a loudspeaker in the lab. We often entertain the careless thought that, like Donovan, the brain represents the consciousness of a whole person. But the brain is only part of a body which keeps it active and alive. A brain abstracted from its body is a dead brain. In discussing activities in different parts of the brain, it is essential to remember that no mental activity would be happening apart from the context the body provides. The brain is not the motor under the hood (“bonnet” in England) that makes us work. Heart, liver, kidneys, fingers, toes, and all the other parts of a functioning organism are implicit in pictures of the brain by itself.

 

Having said that, right now I want to consider the human brain as a complex organ which itself is composed of parts. My focus is on parts of the brain which may contribute to consciousness in particular. If you read books or articles about the brain, you very quickly encounter terms used by neuroscientists, terms which have limited currency outside the lab. Since I myself have uses such terms in earlier posts (amygdala, hippocampus, cerebral cortex, cerebellum), I want to lay the groundwork for future posts so that such terms will be helpful in developing further insights into consciousness. To do that, I will refer to two illustrations. 

 

 

illustration-1-72

Illustration 1. Here, the left side of the cerebral hemisphere is divided into four lobes, each represented by a different color. The frontal lobe is shown in blue, parietal lobe in yellow, temporal lobe in green, and occipital lobe in pink. The cerebellum (not part of the cerebral cortex) is also shown, looking like a ball of yarn in black in white tucked under the temporal lobe.

 

cut-away-view-72

Illustration 2. Here outer layers of the left cerebral hemisphere are cut away to suggest the locations of several parts which lie deeper in the brain near the midline between the two hemispheres. (Clockwise from the top) The corpus callosum consists of nerve fibers connecting the two hemispheres. The cerebral cortex is made up of six layers of nerve cells and the fibers connecting them one to another. The thalamus is a complex relay station between the cerebral cortex and other parts of the central nervous system. The cerebellum contains over half the cells in the brain, and is largely devoted to eye and muscle coordination. The brain stem is the seat of cognitive and emotional arousal systems. The hippocampus facilitates long-term memory storage and retrieval. Not shown, but near the hippocampus is the amygdala which plays an essential role in emotional responses including fear and anxiety. The hypothalamus regulates the autonomic nervous system which maintains life-sustaining processes at appropriate levels; it is a key link between the body’s nervous and hormonal systems.

 

The human brain contains an estimated 100 billion nerve cells, each of which may form 1-10 thousand connections with other cells, producing well over 100 trillion opportunities for activation and feedback. When a given neuron (brain cell) fires, it receives feedback from other cells as a kind of consensus concerning whether it should continue to fire or not. Feedback shapes every activity in the brain and, ultimately, the conscious and unconscious processes governing bodily functions and behavior.

 

 

BBC Brain Map

 

For this post I will give a brief run-through of the functions of the various areas of the brain I have listed above, more or less according to the order in which they have been introduced.

 

Cerebellum. A fixture of the vertebrate brain, the cerebellum is particularly developed in primates and humans. It controls balance, spatial orientation, eye movements, muscle movements (as in reaching and locomotion), and planning of such movements. When there is a discrepancy between movements as planned and executed, the cerebellum facilitates correction.

 

Cerebral Cortex. Cell bodies in the cerebral cortex are arranged in thin layers near the outer surface of the cerebral hemispheres. This arrangement facilitates orderly routing of inputs and outputs between related areas of the brain. The surface of the cortex is larger than that of the inside of the skull because of its folding into valleys (sulci) and hills (gyri), which greatly expands the number of neurons that can fit into a small space. The bulk of the cortex consists of interconnecting fibers. Among vertebrates, humans have the most finely elaborated cortex, allowing detailed planning and execution of a wide diversity of behaviors. The cortex is divided into lobes (named after neighboring bones of the skull) based on prominent anatomical features. These designations are somewhat arbitrary, but the cellular architecture exhibited in different areas lends support to the integrity of different functions within separate lobes (see separate listings below).

 

Corpus Callosum. Nerve fibers connecting corresponding areas of the left and right cerebral hemispheres cross the midline of the brain in a large bundle known as the corpus callosum. These fibers appear white because of the myelin sheaths wrapping individual fibers, greatly increasing the speed of transmission. Each fiber is the axon connecting the body of a particular cell on one side of the cortex to related cells on the opposite side. In general, nerve cells (neurons) on one side of the brain control functions performed on the other.

 

Frontal Lobe. The frontal lobe of cerebral cortex extends forward of the central sulcus at the top of the brain which separates it from the parietal lobe to the rear. Cells in the primary motor area are arranged along the central sulcus as a topographical map of the muscles in areas of the body which they control, extending from feet represented in the fissure between hemispheres, through legs, trunk, arms, hands, fingers, head, face, and mouth arrayed across the surface of the primary motor area of the cortex. Forward of that is the premotor area where planning of motor behaviors takes place. Speech muscles in tongue and lips are controlled in Wernicke’s area within the frontal lobe. Working memory (or focused attention) integrate three different areas—lateral, orbital, and cingulate—within prefrontal cortex to provide what some researchers believe to be the neurological basis of consciousness.

 

Parietal Lobe. Similar to the motor map in the frontal lobe, a sensory map of the body spreads across neurons at the leading edge of the parietal lobe. Touch, pain, and temperature signals are processed in the parietal lobe, which also processes the interplay between visual and bodily sensations.

 

Occipital Lobe. At the back of the brain, the occipital lobe is devoted entirely to primary and subsequent visual processing. There are some 40 visual processing areas in the brain, but they all depend on signals received from the occipital lobe.

 

Temporal Lobe. Primary auditory processing takes place in the temporal lobe, as well as later stages of visual processing, including image recognition. The amygdala and hippocampus exist in pairs (one on each side of the brain) and are located deep within the temporal lobes near the midline between the two hemispheres.

 

Thalamus. As a relay station, the thalamus receives signals from sensory receptors and sends output to cortical sensory processing areas. Thalamic activity coordinates electrical activity in cortical neurons, giving rise to synchronized waves (basis of the electroencephalogram—the EEG). Consciousness, it is thought, represents synchronized activity throughout the cerebral cortex. Ascending pathways from the brain stem and hypothalamus pass through the thalamus en route to the cerebral cortices, conveying vital signals that maintain arousal, vigilance, and responsiveness to sensory stimuli. Injury to the thalamus can bring about loss of consciousness.

 

Brain Stem. The difference between sleep and wakefulness is largely told by neurons in the brain stem where both autonomic and emotional stimuli come into play with profound implications for arousal, attention, and consciousness. Though this region of the brain is primitive in some senses, its involvement in such basic processes suggests that consciousness is not necessarily a latecomer on the evolutionary totem pole.

 

Hippocampus. A specialized region of cortical cells near the midline of the brain, the hippocampus is essential to laying down and retrieving long-term memories. It is involved in learning and establishing spatial relations. Alzheimer’s disease involves failure of hippocampal function.

 

Amygdala. The amygdala comes into play in threatening situations. Sensory input reaches the amygdala from the thalamus by two different routes, one slow but made clear by the cerebral cortex, the other fast but relatively unprocessed and therefore crude. In emergencies, the fast route may spur immediate, life-saving action. The amygdala generates outputs affecting blood pressure, stress hormones, and both startle and immobilizing reflexes. It also kicks into the hippocampus, enabling long-term memory of emotional situations. Feelings of fear, anxiety, anger, and loathing are conscious signs of activity in the amygdala, location of a sophisticated early warning network.

 

Hypothalamus. The hypothalamus maintains homeostasis across a wide range of circumstances by providing inputs to the autonomic nervous system (which silently regulates bodily functions, including sexual arousal), the hormonal system, and the motivational system. It maintains a feedback loop by which neuronal activity can stimulate hormone production, and hormones in turn can affect brain activation. By such means, the hypothalamus integrates autonomic and hormonal functions with behavior.

 

Anterior Cingulate Cortex. On the medial surface of the cerebral hemispheres, the cingulate cortex arcs above the fibers of the corpus callosum crossing beneath it. Much like the brain stem, anterior cingulate cortex participates in homeostasis, emotions, attention, sleep and wakefulness, learning, and consciousness itself. Cingulate cortex also receives musculoskeletal inputs, and sends a large variety of output signals to motor areas related to speech, movement, and other bodily responses. Lesion studies suggest that patients with damage to this area are deprived of an active inner (conscious) life.

 

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