Detection of single unit responses which are loosely time-locked to a stimulus

The way in which three-spike correlation techniques may be used to study the organization of activity among three neurons and the temporal organization of activity of a single neuron is described. This analysis was carried out for single units recorded in the auditory cortex of nitrous-oxide-anesthetized cats. It revealed the occasional presence of three-spike patterns that cannot be explained by simple synaptic relations. Such patterns may appear during the spontaneous activity of the units or may be elicited by sound stimulation. When elicited by sound, the patterns may be time-locked to the stimulus, in which case they may be revealed also by peristimulus time (PST) histograms. On some occasions the three-spike patterns were not time-locked to the stimulus and therefore could not be revealed by PST histograms. It is suggested that spatiotemporal patterns of firing which are induced by a stimulus but are not time-locked to it may reflect higher levels of processing (such as perception, or interrogation of memory) elicited by the stimulus.