Thalamus

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton, Jess Bell, Stacy Schiurring, Kirenga Bamurange Liliane, Uchechukwu Chukwuemeka, Vidya Acharya, Rucha Gadgil and Mason Trauger  

Thalamus Structure

The thalamus is located centrally in the brain, just above the brainstem.

The thalamus is located medial to the cerebral hemispheres and consists of two oval-shaped masses connected by the intermediate mass. Each mass consists of several groups of nuclei that serve different functions. Motor and sensory pathways (except olfaction) pass through this central structure.

The thalamus can be divided into approximately 60 regions known as thalamic nuclei. Each nucleus has unique pathways as inputs and various projections as outputs, most of which send information to the cerebral cortex.

Hypothalamus

• Located inferior to the thalamus
• Two rounded eminences protrude from the back, called mammillary bodies
• Anteriorly, the hypothalamus is connected to the pituitary gland by a long stalk called the infundibulum, also known as the pituitary stalk

The hypothalamus plays a major role in maintaining homeostasis via the autonomic nervous system, the neuroendocrine system, and the limbic system. It regulates emotions, hormone production from the pituitary gland, and body functions such as appetite, body temperature, reproduction, and circadian rhythms.

Epithalamus

• Located behind the thalamus
• Includes the pineal gland, which secretes the hormone melatonin in response to darkness, regulating our circadian rhythms and sleep-wake cycles

Subthalamus

• Located beneath the thalamus
• Includes the subthalamic nucleus, which is functionally considered part of the basal ganglia

Thalamic Function

The thalamus functions as a relay station between the brain and the body, filtering through various types of sensory and motor information.

Note the central location of the thalamus in relation to other subcortical structures and the cerebral cortex.

• The thalamus has many connections with the cerebral cortex, which are known as thalamacortical loops
• It transmits nearly all sensory information to the cortex, including vision, taste, touch and balance, but excludes olfactory information
• It conducts motor signals from the cerebral cortex to the spinal cord and ultimately to the peripheral nervous system
• The thalamus also modulates arousal mechanisms, maintains alertness, and directs attention to sensory events
• The thalamus has connections with a number of structures of the limbic system, including the hippocampus, mammillary bodies, and fornix, so it has a role in learning and episodic memory

The thalamus can be divided into five major functional components.

1. Reticular and intralaminar nuclei: involved in arousal and pain regulation
2. Sensory nuclei: regulate sensory domains, apart from olfaction
3. Effector nuclei: govern motor and language functions
4. Associative nuclei: involved in cognitive functions
5. Limbic nuclei: manage mood and motivation

These specific nuclei help to scan the cerebral cortex and determine active brain regions, relaying this information to the rest of the thalamus.

Thalamus and Injury

The thalamus is involved in many critical functions, and injury to the thalamus can cause a range of issues, including:

• sensory issues (e.g. pain, paraesthesia, numbness, hypersensitivity)
• vision impairment
• motor impairment
• tremor
• issues with attention
• memory impairment
• sleep difficulties
• proprioception impairment

The following presentations are unique to thalamic injury:

• thalamic pain syndrome: an excruciating sensation of pain that does not respond to narcotics. Once called Dejerine-Roussy Syndrome, this condition is commonly associated with infarction of the ventroposterolateral thalamus.
• Pusher syndrome (also referred to as "persons who push"): a lesion to the posterior thalamus interrupts the connection to the vestibular nuclei, leading to lateropulsion in the direction of the impaired side.
• vegetative state and coma: a lesion to the non-specific (intralaminar and reticular) nuclei. Coma may occur due to the role of the thalamus in sleep and arousal.

Additional Resources

For more information on treatment options, please read the following articles:

• Traumatic Brain Injury
• Traumatic Brain Injury Clinical Guidelines
• Physiotherapy Management of Traumatic Brain Injury
• Physical Activity Guidelines for Traumatic Brain Injury
• Stroke: The Role of Physical Activity
• Stroke: Clinical Guidelines
• Post-Stroke Pain
• Mirror Therapy
• Management of pushing tendencies
• Desensitisation for thalamic pain