Thalamus

Original Editor - Lucinda hampton

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

Thalamus Structure

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

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

The thalamus is located medial to the cerebrum 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 (with the exception of olfaction) pass through this central structure.

• The thalamus transmits 98 percent of sensory information to the cortex, including vision, taste, touch and balance.
• The thalamus also conducts motor signals from the cerebral cortex to the spinal cord and ultimately to the peripheral nervous system.
• The thalamus also functions to relay information from the brain stem to the cortex, coordinating shifts in consciousness such as waking up and falling asleep.

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.

The 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.

The Epithalamus

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

The Subthalamus

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

Thalamic Function

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

The thalamus is part of the limbic system, the region of the brain largely associated with the emotions and is essential to memory and learning.

The thalamus joins a series of other machinery whose purpose is to distill sensory information into a more interpretable and manageable form before transmitting it to higher brain areas.

• The thalamus is engaged in an intimate relationship with the cerebral cortex, with numerous mutual connections. These connections make up the thalamacortical loop.
• The thalamus also modulates arousal mechanisms, maintains alertness, and directs attention to sensory events.

Functionally, the thalamus divides into five major functional components:

1. Reticular and intralaminar nuclei dealing with arousal and pain regulation.
   • The reticular formation is constantly making intelligent guesses as to what sensory object is generating these activation patterns.
   • The intralaminar circuit compares these pattern guesses with similar patterns in memory.
   • All these circuits cooperate to produce a coherent framework for the interpretation of incoming sensory data.
2. Sensory nuclei regulating all sensory domains, except olfaction
3. Effector nuclei governing motor language function
4. Associative nuclei connoting cognitive functions
5. Limbic nuclei managing mood and motivation

These specific nuclei are responsible for scanning the cerebral cortex and determining active brain regions then relaying this information to the rest of the thalamus.

Thalamus and Injury

The thalamus contributes to a broad range of critical functions therefore injury to the thalamus can present clinical signs and symptoms unique to each individual.

Some of the most common symptoms of thalamic damage or dysfunction include:

• Sensory issues such as tingling, numbness, hypersensitivity, and pain
• Vision loss or light sensitivity
• Motor impairments
• Tremors
• Attention problems
• Memory loss
• Insomnia
• Impairments to proprioception

Additional presentations unique to thalamic injury involve:

• Thalamic pain syndrome: an excruciating sensation of pain unresponsive to narcotics. Once called Dejerine-Roussy Syndrome, this condition is commonly associated with infarct affecting the ventroposterolateral thalamus .
• Pusher Syndrome (also referred to as "persons who push"): a lesion to the posterior thalamus interrupts a 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 thalamus's impacts on sleep and arousal.

Physiotherapy Treatment

Treatment for thalamic damage will revolve around restoring the abilities lost after brain injury. Treatment is symptom specific, therefore thorough and ongoing therapy assessment is required for proper management and treatment.

For more information, 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
• Desensitization treatment for thalamic pain