Bidirectional completion of cell assemblies in the cortex

Reciprocal pathways are presumedly the dominant wiring organization for cortico-cortical long range projections5. This paper examines the hypothesis that synaptic modification and activation flow in a reciprocal cortico-cortical pathway correspond to learning and retrieval in a bidirectional associative memory (BAM): Unidirectional activation flow may provide the fast estimation of stored information, whereas bidirectional activation flow might establish an improved recall mode. The idea is tested in a network of binary neurons where pairs of sparse memory patterns have been stored in bidirectional synapses by fast Hebbian learning (Willshaw model). We assume that cortical long-range connections shall be efficiently used, i.e., in many different hetero- associative projections corresponding in technical terms to a high memory load. While the straight-forward BAM extension of the Willshaw model does not improve the performance at high memory load, a new bidirectional recall method (CB-retrieval) is proposed accessing patterns with highly improved fault tolerance and also allowing segmentation of ambiguous input. The improved performance is demonstrated in simulations. The consequences and predictions of such a cortico-cortical pathway model are discussed. A brief outline of the relations between a theory of modular BAM operation and common ideas about cell assemblies is given.

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