The thalamus acts as the principal relay station for sensory information, except smell, in the human brain.
The thalamus is a paired structure located deep within the forebrain, above the brainstem. It contains several nuclei, each with connections suited to particular types of information. Most sensory pathways send signals through thalamic nuclei before reaching the appropriate areas of the cerebral cortex.
The thalamus relays visual information through the lateral geniculate nucleus, auditory information through the medial geniculate nucleus, and somatosensory information through the ventral posterior nuclei. It also participates in motor circuits, attention, arousal, and the regulation of sleep and wakefulness.
Olfaction is the classic exception because much of the initial smell pathway reaches the olfactory cortex without first making the usual thalamic relay. However, the thalamus can still participate in later aspects of odor evaluation. Calling it a simple “switchboard” is useful as a starting metaphor, but modern neuroscience views it as an active processor that filters and shapes signals rather than merely passing them along.