TEMPORAL AND SPATIAL PROPERTIES OF LOCAL CIRCUITS IN NEOCORTEX

A large body of anatomical data has detailed many complexities of neoc ortical circuity, and physiological studies have indicated some roles for this circuity, in the complex functions of the cortex. Until recen tly, however we had little precise information about the spatiotempora l properties of synaptic connections between individual neocortical ne urones. Studies of synaptic responses elicited in one neocortical neur one by action potentials in another, and parallel morphological studie s that have identified these neurones and the synaptic connections bet ween them, have now described these parameters for certain types of lo cal circuit connection in the neocortex. Same of these studies confirm ed previous observations and inferences, but others provided major sur prises. Evidence indicates that the class of bath the presynaptic and postsynaptic neurone together determine a wide range of synaptic prope rties, such as the type of postsynaptic receptors involved and the tem poral pattern of transmitter release, so that each type of synapse dis plays unique properties. A role far retrograde diffusible messages in determining the temporal properties of these circuits is postulated.