This is a work in progress and is Copyright 2004 by Ralph E. Kenyon, Jr. Do not copy or quote without permission.
To develop this rudimentary structure, we need to add intermediate levels of processing. A simple nerve impulse that contracts a fiber to cause a cilia to twitch might be all that is needed for a simple microorganism. But an entire group of neurons, all interconnected, would be needed to manage the contraction of hundreds of muscle cells in a coordinated way to manage a pushing motion of a simple leg. Moreover, that clump of cells would need to be working in direct contact with another clump of cells that received sensory data from the muscles, joints, tendons, etc., and translated that data into position information that the first clump could use to determine when to stop its pushing motion. Since the dominant motion for organisms would be preferentially in one direction, namely the forward direction, it makes sense that the contralateral connections for this control system (and sensory system) would dominate in evolution.
With increasing complexity and tissue specialization, the formation of specialized organs pushed the organism in the evolutionary direction of a central nervous system dominated by contralateral connections. We can see residual ipsilateral connections in such things as defensive or protective reflexes. Prick the left side of the body and the left side withdraws. These reflex arcs don't work by going all the way to the brain on the contralateral side of the body; the reflex is echoed back immediately from the same side of the body through ipsilateral connections.
It is well known that our brains are wired with massive contralateral connections, with the exception of half the visual field. However, a detailed look shows that the visual field is contralaterally connected to the brain, so that the right visual field is represented in the left half of the brain and the left visual field is represented in the right half of the brain.
The fact that the sensory processing and the motor processing needs to be in close communication dictates why we see these areas immediately adjacent to each other in the brain. In the human brain these areas face each other across the central fissure. (*)
The next thing that is needed is memory, memory of the sensory experiences and the associated motor actions in association with the overall value to the organism of the experience. Without some form of memory, learning is not possible. The organism needs to be able to learn to recognize and approach beneficial situations as well as to recognize and flee hazardous situations. Some of this recognition will get "built in" by evolution, such as an appetite for good foods, and a revulsion of some toxic substances, as well as some of the basic reflexes. But, initially, memory must associate and record sensory information, motor responses, and the resulting benefit or detriment.
In order for memory to be useful, there needs to be a mechanism that associates the sensory part of current conditions with the sensory part of memory. Moreover, there needs to be a mechanism that can activate the remembered motor response associated with the remembered sensory situation. And, the "remembering" process must be capable of modifying the associated value to the organism such that repeated good results strengthen the association and inconsistent results weaken the association. ("Good results" can, of course, include escaping from noxious stimuli.) Studies have shown that this can be accomplished by increasing and decreasing dendritic connections within the nervous system and strengthening excitory and inhibitory synapses. Simulations of neural networks have shown that the appropriate outputs can be generated from matching inputs with as few as three layers of neurons.
As the remembering function evolves more and more capability of remembering more and more detail, the necessity for associative functions to abstract similarities from the memories also grows - necessitating differentiation of sorts that distinguishes neuronal tissue that specializes in association from the sensory and motor neuronal tissue that evolved previously. Recent research has shown that the simple process of reading a verb activates neurons in the motor control areas of the brain associated with the body parts that the verb in question requires. [Reading the word 'lick' activates the motor area associated with the tongue. (*)] Researchers concluded that understanding the action word involves the parts of the brain that are used to implement the behavior implied by the word. (It would be interesting to see this research extended to test whether words that are primarily associated with sensing activate appropriate portions of the sensory homunculus representation in the brain. I can't think of any words that are both sensory in nature and fundamentally associated with a particular part of the body. Would "smelly feet" stimulate the foot area of the sensory homunculus? I suspect it might, but it involves composing the meanings of two different words, and the effect might be more diffuse.)
We can generalize that imagining ourselves performing some action involves activating the appropriate motor areas of the brain in a way the closely resembles the activation of those areas during the actual performance of the action. A similar effect should be observable when thinking about particular imagined or remembered sensory experiences - to the degree that these experiences are localizable to a particular part or parts of the body.
For self-awareness, the system must contain a model or map of itself with self-monitoring for conditions or states and responses for various monitored conditions.
A mobile organism must develop the ability to map or model the environment. For self-awareness the map must include an analog or representation of the organism itself within the environment. A secondary map of the combined map of the organism in its environment must be capable of "identifying" the self portion of the secondary map with the direct experiences. For example, seeing one's own hand two close to the fire must be identified with the sensation of heat pain from the fire. Reflex actions can cause jerking back the hand, and sensory experiences of pain can identify the action required in response to the environmental conditions abtstractable at the level of the primary mapping, but, in order to communicate about the event, a secondary or higher mapping is required in order to identify the proximity of a part of the self to the fire and to identify that the part of the self is a part of the self as distinct from any hand. Of course, communication requires a yet higher level association of the internal (non-verbal) mappings to the representations for the verbal motor processes.
In many lower level species specific-to-each-species calls have been identified that are associated with near reflex response reactions. A human mimicking the call can induce the associated behavior in the hearer. Duck hunters mimic various duck calls to entice the ducks closer. Prairie dog danger calls spook all dogs within earshot to scamper for safety. Low level "understanding" of these calls must, in light of the recent research, must involve a fairly direct connection with the areas of the brain that control the appropriate motor responses. We can envision that, as evolution produced higher level species with more complex brains, additional level of abstraction via additional neuronal structures became possible within these more advanced brains. The species-specific nature of the calls indicate that the brain's processing need not be connected to or associated with methods for recognizing one's own species. Co-evolution itself can guide stimulus-response patterns to provide compartmentalization of species and associated sounds. It seems to me that an additional level of association is required to "connect" species recognition (necessary for reproduction) to instinctive stimulus-response patterns.
Two guiding principles mitigate the evolutionary process, fitness and economy. The "fitness" of a response is determined by its survival value for the individual and the species on a statistical basis. The "economy" of a response is determined by how much it costs the organism as compared to the benefit it reaps. The evolution of any behavior, behavior change, tissue development, etc., depends on these two factors - its contribution to the survivability of the species (gene pool) and its cost-benefit ratio.
Notes for continuing this development:
The two halves of the brain each contain a circulating limbic system, and the corpus callosum conveys a monitoring of one system into the opposite system. Imagine standing between two parallel mirrors, each reflecting the other. One can see for hundreds of levels of reflection and as many copies of oneself. Imagine the bicameral brain functioning similarly.
|This page was updated by Ralph Kenyon on
2009/11/16 at 11:00
and has been accessed
hits per month.