Evidence on precise time-coded symbols and memory of patterns in monkey cortical neuronal spike trains.

High-resolution examination of pulse sequences generated by single visual cortex cells of the rhesus monkey in response to precisely controlled visual stimuli has disclosed (i) that the outputs of such neurons contain highly improbable (P less than 10(-7) numbers of identical triplets of precisely repeating pulse patterns; (ii) that the precision of such matches is better than 1/6000th of a second; (iii) that there is a similarly improbable high number of precisely matching pairs of triplets and anti-triplets, about half of which are present in symmetrical quadruplets of the form A-B-A, and that precisely replicating quadruplets and quintuplets are similarly generated in improbably large numbers; (iv) that identical triplets occur highly preferentially during immediately succeeding presentation of the same stimulus to the eye; and (v) that identical triplet (and doublet) patterns occur much more frequently in the responses of the same nerve when the eye receives identical or similar stimuli in different experiments than when dissimilar stimuli are applied. From these findings it is concluded (i) that the high precision of pattern replication required for triplets of pulses in time to serve to encode specific inputs and to permit their decoding through spatial summation is met (observations i-iii); (ii) that stimulus-specific triplets symbolize components of responses to specific stimuli (observation iv); (iii) that a temporary memory store of previous responses exists (observations iv and v); and (iv) that the mammalian brain uses precise patterns of discharges in time to represent and store specific data, rather than statistical qualities associated with pulse trains to symbolize qualitative stimulus components.