Response variations of neurons in the lateral geniculate body of the freely moving rat

Abstract

The influence of the motivational state on the discharge rate and flash evoked activity of 57 single units of the dorsal lateral geniculate body (LGB) was investigated using extracellular microelectrodes. Flashes were presented either alone (control group) or followed by water reinforcement (trained group). With decreasing thirst motivation the background activity of most of the cells of both groups changed. This change consisted mainly in a decrease of the discharge rate. After satiation two thirds of the cells exhibited response variations to light stimuli. In trained thirsty animals in 10 out of 19 cells these changes were of very high degree, as the usual response pattern consisting in a sequence of excitatory and inhibitory phases was lost. Under such conditions the light acted as a conditioned stimulus in the thirsty animal. Nonvisual stimuli preceding the flashes and evoking inhibiton of the reflex behavior in trained rats produced small response modulations in about two thirds of the cells of either animal group. The assumption is made that the motivational state of the animal or environmental stimuli not belonging to the original conditioned stimulus - unconditioned stimulus (CS-US) paradigm are less effective in producing response changes of cells to physically equal stimuli than the biological relevance of the stimulus.