Sensory Relay Centre
Almost all the sensory impulses (Except olfactory) reach the thalamic nuclei, which relay
them to the cerebral cortex by a series of projection fibres collectively termed as the thalamic radiations (ascending thalamocortical system). Because of this, thalamus is
usually considered the head ganglion of all the sensory system.
Centre for integration of sensory impulses.
The thalamus is not only a great relay station for all sensations, but also forms a major centre for integration and modification of peripheral sensory impulses before the impulses are projected to specific areas of cerebral cortex. This function of thalamus is called processing of sensory information. Because of this, thalamus is usually considered as a functional gateway of cerebral cortex.
Crude centre for perception of sensations.
Thalamus acts as a crude centre for sense perception. It perceives the affective nature of pain sensation, i.e., the capacity to determine whether a sensation is pleasant or unpleasant and agreeable or disagreeable.
Centre for integration of motor function.
Thalamus receives the output from the basal ganglia and the cerebellum before projecting it to the motor cortex, thereby helping in integration of motor functions by unconscious regulation of muscle tone.
Role in arousal and alertness reaction.
Majority of non-specific ascending impulses from RAS are relayed to thalamus before proceeding to the cortex. Through these fibres the thalamus is involved in controlling the level of consciousness and maintaining state of alertness and wakefulness.
Role in emotional aspect of behaviour
Because of intimate connections between thalamus and frontal cortex and hypothalamus; the thalamus is involved in subjective feeling of various emotions. Thus, it acts as a part of limbic system. It also forms a part of the Papez circuit and is concerned with the recent memory and emotions.
Role in language
Thalamus is also concerned with language (speech) function. Integration between different cortical parts by subcortical connections in the thalamus helps to achieve speech.
Role in synchronization of electroencephalogram.
Thalamus also plays an important role in the genesis of synchronization of electroencephalogram.
Centre for integration of visceral and somatic function
Thalamus receives somatic as well as autonomic sensations, and is also connected with hypothalamus. Because of this it also acts as a centre for integration of visceral and somatic functions.
Centre for sexual sensations
Thalamus also acts as a centre for perception of sexual sensations.
Centre for reflex activity
All the sensory fibres relay in thalamus, so it forms the centre for many reflex activities.