SYNAPTIC PLASTICITY AS BASIS OF BRAIN ORGANIZATION

Synaptic plasticity may be regarded as the basis of brain organization. We have two sources of knowledge: physiological experiments on simple model systems and considerations owing from functional requirements. This investigation tries to exploit the second source. The vital task of the nervous system is appropriate response to external situations. This requires a mapping of external situations into inner states which preserves the relevant metric of the environment. This in turn requires an appropriate con guration space of inner states of \symbols". According to classical theories the state of the brain is aptly described by noting the set of cells|the \assembly"|active within a psychological moment. This view is criticised here. States which have the same global distribution of features would be confused with each other. Attempts to repair the situation, with the help of an unnatural representation by cardinal units and restrictions on nervous connectivity, lead to an unrealistically narrow con guration space. The di culties can, however, be solved with the help of a more di erentiated interpretation of physiology, in which temporal correlations between cellular signals play the role of relational variables, and with a new hypothetical physiological function, synaptic modulation, according to which synaptic weights undergo temporary changes under the control of the temporal ne-structure in cellular signals. According to this new