1970. The effect of local cooling upon spontaneous and evoked electrical activity of cerebral cortex. Can. J. Physiol. Pharrnacol. 48, 640-652.The effect of local cooling sf the surface of the cerebral cortex by means of a metal chamber implanted in the skull was studied while recording evoked and spontaneous electrical activity from the center of a cooled area of 1 cm2. Direct cortical responses to local stirnulatioir of the cortical surface decreased rapidly and progressively to dissppear at starface ternpcratures of 20-22 "C. Onset and peak latencies were prolonged with a Qlo of 1.4 and 1.7 respectively.Response duration was prolonged with decreasing an-nplitude, having a Q,, of about 2.6. Surface cooling to 8-12 "C was necessary to abolish all postsynaptic components of sorn;ltic and auditory evoked potentials, recruiting responses, and spontaneous barbiturate spindles. Latencies of these responses were also increased with a el,, of 1 .?-1.4 while the Qlo for arnplitude was consistently higher (2.8-2.4). Allowing for a gradient of increasing temperature from stirface to depth it is concluded that all synaptic processes are blockcd at tennperatrares of 20-22 "C. Synaptic mechanisms determining latency were csnsistenaly different from those afetern-mining amplitude as judged by consistent diflerences in the Qlo sf latency and amplitude for all postsynaptic responses studied in these experiments.