Thermal Stimulation Neurophysiology of Pressure Phosphenes

Synesthesia of vision and somatosensory is based on physiology of interconnection of neurons in different nuclei of thalamus or areas of cerebral cortex. Work studied effect on the intensity of Pressure Phosphenes (PP) of various methods of heating eyes and hands, as well as manual influence on cervical spine. Along with subjective assessments of the PP intensity, EEG and ECG were used for chronometry of bioelectrical activity of brain and heart. From analysis of frequency and amplitude spectra of EEG, it was concluded that mechanism of PP generation is dominated by processes of redistribution and recombination of charges in retinal and LGB layers. Stimulation of PP by heating hands was associated with convergence of LGB neurons and neurons of thalamus nuclei, which are responsible for thermoreception and are adjacent to LGB. Enhancement of effect of PP stimulation by heating hands in water and in sauna was explained by resonant mechanism of heat transfer from heated water to water of physiological fluids of epidermis and water associated with proteins of ion channels of thermoreceptor membranes. It was suggested that breakdown of water clusters in physiological fluids of epidermis at temperature above 42°C promotes to transformation of thermoreceptors into pain receptors.