SUMMARY

If the hippocampus is a site for spatial learning, then it should be possible to see changes occurring in its representation of space following learning. How would we recognize such changes? It is argued in this chapter that if the synaptic plasticity hypothesis of learning is true, then to attribute changes in neuronal activity to memory formation, we need (1) to know what the neurons' inputs were before and after learning, and (2) to show that these changed in a meaningful way. By “meaningful” is meant that they altered the cognitive representation in a manner congruent with the actual experience of the animal. Although it is not yet feasible to record single inputs onto hippocampal cells in awake, behaving animals, it is possible to infer the strengths of these inputs by recording the responses of the neurons to environmental stimuli. By showing that the inputs change in an appropriate way following experience, it is possible to derive a simplified model of memory formation that looks at the cognitive representation directly, independent of the animal's behavior. This approach may circumvent some of the difficulties involved in trying to relate very low-level processes, such as synaptic plasticity, with very high-level processes, such as behavior.

Introduction

The hypothesis that a long-term potentiation (LTP)-like process underlies memory formation has the drawback that it is difficult to think of an experimental result that could definitively refute it. For every piece of evidence that appears to falsify the hypothesis, there is either another piece of evidence or a hand-waving argument that explains it away.