Relationship between input and output of cells in motor and somatosensory cortices of the chronic awake rat. A study using glass micropipettes.

Experiments using the same glass microelectrode (6--8 M omega) for recording and stimulating were performed on 12 rats in which 379 cortical cells were studied in 65 penetrations through the motor and somatosensory cortical zones. To avoid anaesthetic effects the rats were chronically implanted with a head system derived from the one developed by Noda et al. (1971). These animals well accepted head fixation and the peripheral receptive fields could thus be easily investigated. In a preliminary experiment the number of pyramidal cells activated by a given stimulus intensity was evaluated. The lowest threshold intensities were always observed in the Vth pyramidal layer, as well as correspondence between cell input and output. The same type of organization, with identical thresholds, existed in the so-called "Motor" and "Somatosensory" cortical zones. Movements could be obtained when stimulating near non-PT cells (600--700 micron below the cortical surface). However, thresholds were higher at this level and it is thought that the movements were due to a spread of the stimulating current to the pyramidal tract cell layer.