By Dr Ananya Mandal, MD
The thalamus is a vital structure lying deep within the brain that has several important functions. There are extensive nerve networks that send signals all around the structures of the brain including the cerebral cortex. The thalamus is involved in sensory and motor signal relay and the regulation of consciousness and sleep.
Aside from sense of smell, all other sensory processes involve a thalamic nucleus receiving a sensory signal which is then directed to the relevant cortical area.
The thalamus plays a role in controlling the motor systems of the brain which are responsible for voluntary bodily movement and coordination.
The thalamus also plays roles in the following systems.
The visual system
The thalamus receives input from the retina which is relayed to the brain via the optic nerve. Signals are sent to the lateral geniculate nucleus of the thalamus which then forwards them onto the primary visual cortex (area V1) in the occipital lobe.
The thalamus not only relays the information but also processes it, as each of the primary sensory relay areas receives information back from the cerebral cortex (called back projections).
The auditory or hearing system
The medial geniculate nucleus relays auditory information between the inferior colliculus of the midbrain and the primary auditory cortex.
The ventral posterior nucleus relays information regarding touch and perception of bodily position to the primary somatosensory cortex in the cerebral cortex.
Sleep and wakefulness
The thalamic nuclei are strongly and reciprocally linked with the cerebral cortex. This forms the thalamo-cortico-thalamic circuits which are thought to regulate consciousness and the thalamus plays a significant role in arousal, wakefulness and alertness. Damage to the thalamus is associated with risk of coma.
Reviewed by Sally Robertson, BSc