Thermoimaging of the brain.

A new method of neuroimaging is proposed that is based on the recording of weak changes in infra-red radiation from the brain. Thermoencephaloscopy (TES) uses a combination of thermovision and digital image processing techniques and allows one to make a dynamic investigation of the thermal fields of the cerebral cortex through an unopened skull. Today the method is characterized by: (i) differential thermosensitivity of up to 0.002 degrees C; (ii) instrumental temporal resolution 40 ms (25 thermomaps/s); (iii) time of the temperature measurement in the part of an object that correspondes to one pixel on digital thermomap is equal to 2.4 microseconds; (iv) instrumental spatial resolution of up to 70 microns/pixel; and (v) the thermomap size is 10880 pixels (128 x 85). TES allows detection of an appearance and study of topography and dynamics of the small (from 140 to 300 microns) and precisely localized zones of activation or deactivation of the cerebral cortex that are modally and regionally specific with respect to stimuli modality and parameters and to the state of an animal. Up to now such studies were performed with white rats, rabbits, cats, monkeys and humans under different kinds of sensory stimulation, motor tasks, conditioning (associative learning). Fast thermowaves spreading over the brain cortex along specific trajectories were revealed under sensory stimulation. The mechanisms of the recorded phenomena are discussed: (i) joule heating produced by ion currents through membranes of activated neurones; (ii) metabolic thermoproduction; (iii) thermal convection by the local cerebral blood flow; and (iv) thermodipole formation in the cortical foci with changed lCBF.