Biological neural networks: beyond the PDP model

The biological neural networks (BNNs) of the gravity-sensing endorgans of the inner ear, the vestibular maculas, appear to be organized in ways more complex than the parallel distributed processing (PDP) systems currently under study in the artificial neural network (ANN) field. The organization and synaptic interactions of the processing elements (PEs) have been documented by computer-assisted 3-D reconstructions of terminal and receptive fields from electron micrographs of a series of 570 sections and by the mapping of more than 300 cells. The macular BNN properties are described. Data were reduced to symbolic representations and compared with features of ANN PEs. The chief conclusions are that terminal and receptive fields of macular BNNs are not modular, since no two are identical in detail, and that the network changes in threshold properties and in organizational complexity from site to site.<>