The projection of individual axons from the parabrachial region of the brain stem to the dorsal lateral geniculate nucleus in the cat

In mammals, the retinogeniculocortical pathway is the pri-mary afferent route to visual cortex. The flow of information along this pathway can be modulated at the thalamic level (i.e., at the lateral geniculate nucleus) as a function of arousal, attention, and phenomena such as eye movements. Phys-iological studies indicate that an important source of this state-dependent influence on geniculate neuronal respon-siveness is the parabrachial region of the brain stem. We used the anterograde tracer Phaseolus vulgaris leucoagglu-tinin to study the anatomical connections between the parabrachial region and the lateral geniculate nucleus. La-beled parabrachial axons are found throughout the thala-mus, including all laminae of the lateral geniculate nucleus, the lateral posterior-pulvinar complex, the ventral lateral ge-niculate nucleus, the perigeniculate nucleus, and the retic