Peter Putnam (1927-1987) was not widely known in his lifetime, but he laid the groundwork for a revolution in cognitive science. His influence is likely to spread in decades to come as the world catches up with his pioneering studies on the operation of the nervous system. With this insight of how the nervous system works, Putnam worked out its implications for virtually every branch of human knowledge, from the foundations of mathematics and physics, to psychology, the arts, social science, and the diversity of human cultures, history, religion, and philosophy.
Putnam was the first person to see (1964 paper) that the human brain functions on Darwinian principles.
The differentiation and emergence of new neural pathways in the brain manifests itself, in the world, as new human behaviors and new social institutions. The neuroelectric activity in the brain takes place on the order of milliseconds. Contrast this to the differentiation and emergence of whole new species in the natural environment, over decades, millenia, and millions of years.
Though the time constants are different, the essential Darwinian principles of random variation and natural selection, identified by Putnam in his model as random search and relative dominance within the nervous system, are fundamentally the same. This is clearly shown in: ON THE ORIGIN OF ORDER IN BEHAVIOR, Peter Putnam, Robert Fuller, "GENERAL SYSTEMS", 1966. That short article (36 pages) is reproduced in full on this website.
In his book "The Organization of Behavior, A Neuropsychological Theory", published in 1949, Donald O. Hebb enunciated what is now known as the "Hebb Postulate", which states that "When an axon of cell A excites a cell B and repeatedly and persistently takes part in firing it, some growth process or chemical change occurs in one or both cells such that A's efficiency in firing B is increased." (p. 62)
Putnam's "Neural Conditioned Reflex Principle" (NCRP) is an alternative statement of Hebb's Postulate, generalizing it to include the establishment and strengthening of inhibitory or negative facilitations, as well as the excitatory or positive correlations.
Putnam's NCRP reflects the critical importance of the inhibitory activity of the nervous system in the the shaping of the pathways' relative dominance whose excitation leads to the emission of behavior. No stable neural pathways or circuits of relative dominance with associated learned behavior could ever emerge without the fundamental activity of inhibition within the nervous system as the source of self-regulation of neural circuitry.
Putnam's nervous system model provides an elaborate and detailed explanation of the interaction between both positive and negative facilitations within the nervous system that result in the differentiation of the patterns on neuronal activity that lead to learning of new behaviors and the ever-increasing complexity of the organization of the nervous system and of its effective behavioral emissions in the widest variety of environmental contexts.
What is perhaps most original in Putnam's work is that he tried to place our subjective experience of consciousness Ė everything we tell ourselves about our "selves" Ė in the context of a mechanistic view of mind which sees it arising out of electrical interactions governed by the laws of physics, chemistry, etc.
The dichotomy of mind and brain is one of the most tantalizing problems in cognitive science. On the one hand there is the view that all brain function is a Darwinian machine in action. On the other hand there is the interior view we have of ourselves as being "Barry" who likes X and hates Y and feels this and that and reacts this way and that way and it is all so very important to Barry whether he lives or dies, etc., etc. The challenge is to make this subjective experience of ourselves consistent with the idea that we are embodied in a very special type of self-organizing neurobiochemical machine operating in accordance with the laws of physics.
In a phrase, how does consciousness relate to mechanism? How can we reconcile our knowledge of brains with our experience as brains? Putnam explored this question and probably did more to square these two perspectives than any other physicist, theoretical neuroscientist, or philosopher to date.
Putnam's model of the nervous system had antecedents, especially in Hebb, and also the whole class of experimental findings of the neuroscience of his time (late 50ís early 60ís). However, he was the first to see that the time was ripe and enough experimental evidence was available to begin the construction of an overall functional model of the operation of the nervous system. The accumulating evidence from the neurosciences continues to confirm the broad outlines of his model.
Hebbian plasticity; distributed neural networks; computational and connectionist modeling; the idea of conflict and conflict resolution Ė these are ideas in Putnamís model that date to the late 50ís and early 60ís. The model of the brain that is currently emerging within neuroscience gets closer and closer to Putnamís ideas, set down so many years ago. (Also the more recent concept of 'Enactment')
The best expositions of Peter Putnamís model are in:
A drive (a pin stuck in the leg) will initiate a random search - a search over all the past actions associated with this drive, actions encoded in neural networks. So, the pin causes pain and the brain calls up every previous action that has ever helped deal with similar pain in the past. How does it decide among all of those actions? It lets them play out in parallel - multiple neural networks firing simultaneously. Some of the networks will inhibit or undercut others. The one that doesn't get undercut and manages to repeat and reinforce itself will garner up enough strength to excite a motor neuron and emit its associated act. That's the sort of "survival of the fittest" idea in the context of a neural Darwinism. So random search brings past history into parallel, lets them compete, and then the winner (which wins by virtue of invariance) emits. The emitted behaviors form a linear chain, which is constantly broken up and brought into parallel inside the nervous system in order to decide on the next act in the linear chain. It's quite an elegant idea! Putnam emphasizes that only that which makes a difference in determining the order of that chain can be perceived, or subjectively experienced.