POSSIBLE STRATEGIES FOR FINDING THE SUBSTRATE FOR LEARNING-INDUCED CHANGES IN THE HIPPOCAMPAL CORTEX

For long-lasting memory traces, structural synaptic changes remain a p robable mechanism. However, in higher animals it has proved difficult to provide positive evidence for this notion. The main reason may be t hat the changes are subtle and are to be found in a relatively small s ubset of synapses and in a distributed manner in the cellular network in question. Here, we discuss possible strategies for finding structur al changes in the hippocampus associated with spatial learning, an act ivity for which this structure is important, Spatial learning may indu ce new excitatory synapses in a small subset of hippocampal CA1 neuron s because we observe a higher spine density without alteration in dend ritic length or branching. The dendritic synapses are regularly spaced , irrespective of spine density, suggesting the operation of an inters ynaptic dispersing force. (C) 1995 John Wiley and Sons, Inc.