Small systems of neurons.

M any neurobiologists believe that the unique character of indi­ vidual human beings, their dis­ position to feel, think, learn and remem­ ber, will ultimately be shown to reside in the precise patterns of synaptic inter­ connections between the neurons of the brain. Since it is difficult to examine pat­ terns of interconnections in the human brain, a major concern of neurobiology has been to develop animal models that are useful for studying how interacting systems of neurons give rise to behavior. Networks of neurons that mediate com­ plete behavioral acts allow one to ex­ plore a hierarchy of interrelated ques­ tions: To what degree do the properties of different neurons vary? What deter­ mines the patterns of interconnections between neurons? How do different pat­ terns of interconnections generate dif­ ferent forms of behavior? Can the inter­ connected neurons that control a certain kind of behavior be modified by learn­ ing? If they can, what are the mecha­ nisms whereby memory is stored? Among the many functions that emerge from the interactions of m:u­ rons, the most interesting are the func­ tions concerned with learning (the abili­ ty to modify behavior in response to ex­ perience) and with memory (the ability to store that modification over a period of time). Learning and memory are per­ haps the most distinctive features of the mental processes of advanced animals, and these features reach their highest form in man. In fact, human beings are what they are in good measure because of what thcy have learned. It is therefore of theoretical importance, for the under­ standing of learning and for the study of behavioral evolution, to determine at what phylogenetic level of neuronal and behavioral organization one can begin to recognize aspects of the learning and Such systems are the elementary units of mental function. Studies ofsimple animals such as the large snail Aplysia show that small systems a/neurons are capable of memory processes that characterize hu­ man behavior. This determination is also of practical importance. The dif­ ficulty in studying the ceJlular mecha­ nisms of memory in the brain of man or other mammals arises because such brains are immensely complex. For the human brain ethical issues also preclude this kind of study. It would therefore be congenial scientifically to be able to ex­ amine these processes effectively in sim­ ple systems. It could be argued that the study of memory and …