INCREASED NEURONAL FIRING IN THE RAT AUDITORY-CORTEX ASSOCIATED WITH PREPARATORY SET

Extracellular single neuronal firings were recorded in the auditory co rtex of rats (n = 4) performing a visual reaction-time task with a war ning tone (10 kHz, 10 ms duration), which preceded the imperative ligh t stimulus by an interstimulus interval (ISI) of 1.4 s. Thirty-six neu ronal firings were evoked by the warning tone, with the peak latency b eing between 15 and 55 ms. Among them, nine neurons (25%) showed an in creased firing frequency following the evoked response during the ISI, which was, in average, 2.5 times as high as the firing frequency duri ng the baseline period. When the tones were presented independent of t he imperative stimulus, such sustained increase in neuronal firing was not observed. Activation of the sensory cortex during the ISI may con stitute one of the neuronal modulations related to preparatory set.