SUMMARY

At present, long-term potentiation (LTP) of synaptic transmission is the leading neurophysiologic model for learning and memory processes, despite controversial results regarding its behavioral correlates. The evidence we present in this chapter demonstrates lasting plasticity at the level of local neuronal assemblies in both hippocampus and amygdala. Local circuit plasticity (LCP) is induced by tetanic stimulation of afferent fibers and is mediated, in the hippocampus, by a reduction in GAB A release. Different interneuronal populations are suggested to be involved in the LCP and LTP and at least one type of LCP correlates with age-related spatial memory abilities while the levels of LTP that can be induced initially were found unchanged in this respect. The results suggest that GABAergic interneurons play a major role in LCP and that the involved molecular/cellular modifications do not necessarily occur at the synaptic level. Overall, these data support the conception of LCP as a candidate mnemonic device that may be involved in more than one type of memory.

Introduction

A general principle of biology is that any given behavior of an organism depends on a hierarchy of levels of organization. As applied to the brain, it means that one needs to identify the main levels of organization in order to provide a framework for understanding the principles underlying its construction and function. The study of brain and mind has led to the recognition of several important levels of analysis from large information processing blocks down to the finest details of molecular structure and subcellular biophysics.