QUANTITATIVE ESTIMATE OF THE INFORMATION RELAYED BY THE SCHAFFER COLLATERALS

Within the theory that describes the hippocampus as a device for the on-line storage of complex memories, the crucial autoassociative operations are ascribed mainly to the recurrent CA3 network. The CA3-to-CA1 connections may still be important, both in completing information retrieval and in re-expanding, with minimal information loss, the highly compressed representation retrieved in CA3. To quantify these effects, I have defined a suitably realistic formal model of the relevant circuitry, and evaluated its performance in the sense of information theory. Analytical estimates, calculated with mean-field, replica and saddle-point techniques, of the amount of information present in the model CA1 output, reveal how such performance depends on different parameters characterising these connections. In particular, nearly all the stored information can be preserved if the model Schaffer collaterals are endowed with an optimal degree of Hebbian plasticity, matching that of the CA3 recurrent collaterals.