SYMMETRICAL TEMPORAL PATTERNS IN CORTICAL SPIKE TRAINS DURING PERFORMANCE OF A SHORT-TERM-MEMORY TASK

The trion model is a highly structured representation of cortical orga nization, which predicts families of symmetric spatial-temporal firing patterns inherent in cortical activity. The symmetries of these inher ent firing patterns are used by the brain in short-term memory to perf orm higher level computations. In the present study, symmetric tempora l patterns were searched for in spike trains recorded from cells in pa rietal cortex of a monkey performing a short-term memory task. A new m ethod of analysis was used to map neuronal firing into sequences of in tegers representing relative levels of firing rate about the mean (i.e . -1, 0 and 1). The results of this analysis show families of patterns related by symmetry operations. These operations are: i. the intercha nging of all the +1's and -1's in a given pattern sequence (C symmetry ), ii. the inverting of the temporal sequence of the mapping (T symmet ry), and iii. the combination of the two previous operations (CT symme try). Patterns of a given family are found across cells, especially in the memory periods of the task; in most cases they reoccur within a g iven spike train. The pattern families predicted by the model and repo rted here should be further investigated in multiple microelectrode an d EEG recordings.