Brainstem input modulates globally the transmission through the lateral geniculate nucleus.

The transmission of visual information from the retina to the visual cortex through the lateral geniculate nucleus (LGN) is a complex process, which involves several neuronal mechanisms, elements, and circuits. The authors investigated this process in anesthetized, paralyzed cats by recording from LGN relay neurons, together with their retinal input, which appeared as slow (S) potentials. The major findings are: (1) The transfer ratio (LGN firing/retinal firing) fluctuated slowly and (2) these fluctuations in transfer ratio were synchronized across the nucleus, did not depend on visual stimulation, and were highly correlated with neural activity in the parabrachial nucleus of the brainstem (PBN). Electrical stimulation of the PBN increased transmission from retina to cortex through the LGN. It is concluded that the PBN, which is part of the Ascending Arousal System, can modulate globally the transmission of information through the thalamus.