Participation of the lateral geniculate body in mechanisms of brain activation.

The significance of the lateral geniculate body for nonspecific activation of the brain was elucidated in experiments on cats. It was established that when the connections of the lateral geniculate body remain intact, its stimulation elicits the usual activation of the EEG, but at higher threshold values of the current (120-190 microA) than when the mesencephalic reticular formation of the medial center of the thalamus is stimulated (50-80 microA). If only direct connections with the cortex remain, however, and the others are disrupted, the threshold for activation increases to 220-400 microA. When the lateral geniculate body is coagulated, cortical activity occurs only in response to very bright light flashes (250-1000 1x). All of this indicates that, in addition to carrying out its principal function of processing and sending the basic flow of visual impulsation to higher optical centers, the lateral geniculate body may be the source of activating transmissions sent to the cortex. Nonspecific stimulation that develops in the cortex is subsequently regulated by the cortex itself; the cortex plays a leading role in these processes.