Intracortical horizontal connections of neurons in cat and monkey motor cortex

The present paper deals with the study of the structure of horizontal neuron chains, one of the aspects of intracortical intraneuronal relationships. The motor cortex (field 4) of cats and lower monkeys (Papio hamadryas and Macacus rhesus s. M. mullata) was treated by the impregnating method of Golgi--Kopsh. The drawings of neurons from 90-micrometer sections were made by means of a camera lucida. Three possible pathways of impulse transmission along neuron chains in a horizontal direction were revealed. These were: a pyramido-pyramidal system of connections which may possibly spread excitatory influence among several columns; a basket-pyramidal connection system; and connections which arise from successive switchings between neighboring neurons of one layer.