DYNAMICS OF ONGOING ACTIVITY - EXPLANATION OF THE LARGE VARIABILITY IN EVOKED CORTICAL RESPONSES

Evoked activity in the mammalian cortex and the resulting behavioral r esponses exhibit a large variability to repeated presentations of the same stimulus. This study examined whether the variability can be attr ibuted to ongoing activity, Ongoing and evoked spatiotemporal activity patterns in the cat visual cortex were measured with real-time optica l imaging; local field potentials and discharges of single neurons wer e recorded simultaneously, by electrophysiological techniques. The evo ked activity appeared deterministic, and the variability resulted from the dynamics of ongoing activity, presumably reflecting the instantan eous state of cortical networks, In spite of the large variability, ev oked responses in single trials could be predicted by linear summation of the deterministic response and the preceding ongoing activity, Ong oing activity must play an important role in cortical function and can not be ignored in exploration of cognitive processes.