The effect of local cooling upon spontaneous and evoked electrical activity of cerebral cortex

The effect of local cooling of 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 stimulation of the cortical surface decreased rapidly and progressively to disappear at surface temperatures of 20–22 °C. Onset and peak latencies were prolonged with a Q10 of 1.4 and 1.7 respectively. Response duration was prolonged with decreasing amplitude, having a Q10 of about 2.6. Surface cooling to 8–12 °C was necessary to abolish all postsynaptic components of somatic and auditory evoked potentials, recruiting responses, and spontaneous barbiturate spindles. Latencies of these responses were also increased with a Q10 of 1.3–1.4 while the Q10 for amplitude was consistently higher (2.0–2.6). Allowing for a gradient of increasing temperature from surface to depth it is concluded that all synaptic processes are blocked at temperatures of 20–22 °C. Synaptic mechanisms determining latency were consistently different from those determining amplitude as judged by consistent differences in the Q10 of latency and amplitude for all postsynaptic responses studied in these experiments.