Intercellular relationships in elementary neuronal ensembles.

The mechanisms of combination of cortical neurons into discrete modules or elementary ensembles, serving as functional units and forming a mosaic of activity in which incoming information is coded, have been investigated. Neurons activated primarily by terminals of specific afferents respond stably with a minimal latent period and become the centers of ensembles, whose periphery is formed by secondarily activated neurons, responding variably with a longer latent period. The stochastic participation of these neurons in the structure of the ensembles lies at the basis of plasticity of cortical mechanisms. Neurons inhibited intracortically, and possibly, via ascending inhibitory pathways, are concentrated at the periphery and near the output cells of the ensemble.