Rapid thermal waves propagated through the cerebral cortex during visual stimulation

: Fast thermowaves spreading over the brain cortex were found and investigated in acute experiments on white rats using a new method of neuroimaging: thermoencephaloscopy (TES) through the intact skull. Thermowaves (amplitude 0.005-0.1 degree C, path 2-56 mm, length 10-15 mm, duration 1.2-11.4s, speed 1-33 mm/s) were evoked by light stimulation. With a high probability (0.92) they appeared during 15s before and 26s after the rhythmical flashes (interval 1.5-3 min). In about a half of cases the wave appeared in the contralateral visual cortex (fields 17 and 18a), spread to the middle-line of the brain and to the ipsilateral hemisphere (fields 17, 18a and 7). Local circle-spreading waves in the contralateral visual cortex and other waves differing in their trajectories and spreading from the ipsilateral visual cortex were also revealed. The possible functional significance of the effect as a reflection of scanning of the cortex by the focus of selective visual attention is discussed.