Switching, relaying, and regulation The diencephalon is known as the in-between brain, between higher- and lower-level structures. It contains the thalamus, routing sensory signals (except for olfactory signals) to the cortical regions and routing motor signals to the spinal cord. Optic nerve signals are routed through the lateral geniculate nucleus of the thalamus to the primary visual cortex. Being more than a switchboard, the thalamus directs attention by modulating sensory signals and is critical for sustaining normal consciousness; if its intralaminar nuclei are damaged, a permanent coma typically follows.
Below the thalamus lies the hypothalamus, with nuclei maintaining homeostasis by regulating temperature, blood pressure, salt levels, appetite, thirst, and sexual behavior, as well as sleep-wake cycles. Much hypothalamic regulation occurs via the pituitary gland, which secretes hormones into the bloodstream. The hypothalamus is also connected to the reticular formation (involved in alertness and sleep- wake states) of the brainstem and receives hormonal signals from many places in the body through the cardiovascular system.
Thalamic syndrome Damage to the thalamus, such as from an infarct, can lead to heightened pain sensitivity because the thalamus relays and modulates sensory signals.
Hypothalamic disorders As the hypothalamus controls the pituitary gland, hypothalamic disorders can have many hormonal effects.
The diencephalon routes and modulates neural signals and controls hormonal signals. It’s a highly interconnected structure involved in most, if not all, aspects of mental life. Damage to this structure is often life threatening.