Relation of unit spike discharges and evoked potentials in the auditory cortex of cats

Extracellular microelectrode recordings were made from the auditory cortex of anaesthetized cats during acoustic click stimulation. The microelectrode of low resistance allowed to record evoked field potentials and unit discharges simultaneously. In distant extracellular leads the relation of unit discharges and field potentials was equivocal. Near extracellular leads revealed that the antidromic invasion of the somadendritic membrane by excitation is a frequency dependent process (just as evoked field potentials) while spike potentials can reliably be elicited from the initial segment at high frequencies. It is assumed that the excitation spreading from the initial segment to the soma-dendritic membrane represents an important component of the evoked potentials, and their frequency dependence may be traced back to inhibitions activated by afferent impulses.