The thalamus (from the Greek word meaning “chamber”) is centrally located between the cerebral cortex and the midbrain and is known for its role in relaying sensory and motor signals to the cerebral cortex, and the regulation of sleep, consciousness, and alertness—rather like a hub of information flow from the senses to the cortex. It is believed the thalamus processes sensory information in addition to relaying it to the primary sensory areas and receiving feedback from the cerebral cortex. It plays major roles in the support of motor and language systems and (in connection with the hippocampus) spatial memory critical for episodic memory.
Interestingly, a common genetic variation in humans is that of the serotonin transporter 5-HTTLPR; as well, people who inherit two short alleles (SERT-ss) also have more neurons and larger volume in parts of the thalamus. The SERT-ss inheritance is linked to a greater vulnerability to depression, PTSD, and suicide. The dorsal thalamus also plays a role in the inhibition of compulsive behaviour—we will look at this more closely later on when we consider the so-called OCD loop that involves the orbitofrontal cortex, striatum, and thalamus.
The thalamus is important for sleep regulation, in particular slow-wave sleep cycles, and it also coordinates parts of the cortex as sleep changes from state to state—an orchestration that works hand-in-hand with the activity of the hippocampus during sleep.
In sum, the thalamus seems to be more than just a relay of sensory information and is integral to brain function in a cortico–thalamo–cortical pathway of processing.