Fast thermal waves spreading over the cerebral cortex

Fast thermal waves spreading over the cerebral cortex were found in the white rat by infrared neuroimaging (thermoencephaloscopy) in the range of 3-5 microm. Thermal waves appeared under visual stimulation (the probability of their appearance = 0.92), and under background conditions (probability of appearance = 0.42). Typically, they moved during the period from 15 s before to 25 s after each light flash that was presented rhythmically (1.5-3 per min). The waves spread over the cerebral cortex along the limited number of typical trajectories, which are specific for the hemisphere of their origin (ipsilateral or contralateral with the side of stimulation). The waves were never recorded in a dead animal or in a thermal standard. The amplitude of the thermal waves was in the range of 0.005-0.1 degrees C, with the extent of the pathway of 2-56 mm, length of 10-15 mm, duration of 1.2-11.4 s, and velocity of 1-33 mm/s. In about half of the cases the waves appeared in the contralateral visual cortex (areas 17 and 18a), spread to the midline and crossed to the ipsilateral hemisphere (areas 17, 18a and 7). Local waves moving along a circular trajectory and rotating around the central part of the contralateral area 17 were also revealed, as well as wave rotation around the dorsal (mainly parietal) cortical fields. Possible biophysical and neurophysiological mechanisms and the functional significance of the revealed effects are discussed.