Thalamus: Definition, Anatomy, Functions, Associated Syndromes and Recovery

It is a busy place in the human brain, and a spill there can have a wide range of effects.

The thalamus, which means “internal chamber” in Greek, is in the upper part of the brainstem near the center of the brain. It has two halves, each the size of a walnut.

It is divided into different areas, which are very specifically connected to different parts of the brain. A blow to a part of the thalamus will not have the same effect as a blow elsewhere.

Anatomy:

The thalamus is a group of neuron bodies, that is, a gray matter structure, just like the cerebral cortex. But within this set, there is a series of nuclei of the thalamus:

  • Specific connection nuclei : They send sensory information to specific areas of the cerebral cortex that are specialized in working with that specific type of data coming from a specific sense.
  • Nuclei of non-specific connection : They send information to very wide areas of the cerebral cortex, without discriminating by specializations.
  • Association nuclei : They are part of an information circuit that communicates the cerebral cortex with subcortical structures.

The neurons of the thalamus

The thalamus only has reason to be if it is connected to other areas of the nervous system, and this is reflected in the type of neurons that compose it.

  • Local interneurons : Its main function is to send nerve impulses to other interneurons of the thalamus. They account for approximately 25% of the thalamus neurons.
  • Projection neurons : These nerve cells are responsible for sending information out of the thalamus, into the cerebral cortex. They make up 75% of thalamic neurons.

Functions of the Thalamus

The thalamus has many functions, including:

  • Manage our sensitivity to temperature, light and physical touch and control the flow of visual, auditory and motor information.
  • The thalamus is involved in motivation, attention and wakefulness. He is in charge of our sense of balance and awareness of our arms and legs.
  • It controls how we experience pain.
  • He is also involved in aspects of learning, memory, speech and comprehension language and even emotional experiences, expression and our personalities involve the thalamus.

It can be thought that the thalamus is a “relay station” that receives signals from the outer regions of the brain (cerebral cortex), interprets them and then sends them to other areas of the brain to complete their work.

Although relatively small, the thalamus controls a large part of how our body functions and responds to the world around us.

The thalamus has strong connections with all parts of the brain and receives information from all its parts.

Only a small part of the thalamus receives information from the outside world or sends information to the outside world. Especially the thalamus helps the cortex and other cells inside the brain to communicate with each other.

Central pain syndrome

A stroke in a certain area of ​​the thalamus can cause “thalamic pain”, also known as central pain syndrome.

The pain may be intense, usually in the affected arm and hand, and may cause an annoying feeling of burning or frostbite. Some survivors report an intense prickly sensation, such as being repeatedly pinned with needles.

A similar problem, called pseudo thalamic pain syndrome , occurs when a stroke in the white matter of the brain breaks the connections between the thalamus and the cerebral cortex, but does not damage the thalamus itself.

Central pain usually does not respond to regular painkillers and often does not occur until weeks after the stroke occurs. This can be an obstacle to the recovery of a survivor who is performing well in rehabilitation.

What makes the thalamus very special is that it is a relatively small and highly concentrated area inside the brain, and a small change in the location of the stroke can produce a substantial change in the way the attack affects the survivor. .

For example, a stroke in the thalamus can cause drowsiness, contribute to the development of epilepsy, affect a survivor’s attention span or a feeling of apathy. A spill in the front of the thalamus can affect memory, including memories of one’s life.

As a result, a patient with CVA may have what appears to be the instantaneous onset of Alzheimer’s disease.

Injury to another part of the thalamus can impede movement, balance or force. Very large blows in the thalamus can cause many problems. If both sides get hurt, destroying the connections with the rest of the brain, it can cause a coma.

Fortunately, the wiring of the brain has a degree of plasticity, and if the stroke is only in the thalamus, some people can recover and do it quite well because the rest of the brain has ways of compensating for it.

But they may not return completely to normal. Because the thalamus shares its blood supply with the brainstem, the occipital lobe, and the temporal lobe of the brain, strokes in those areas can also affect the thalamus.

Depending on which lobe is affected, the survivor may experience loss of visual field ( hemianopsia ), loss of memory or problems swallowing and breathing.

Recovery

Recovery is more challenging for these strokes because there are many more areas of the brain involved.

The way a thalamic stroke affects the survivor depends on which part of the thalamus is injured and whether the injury is on the left or right side of the thalamus.

Effects may include loss of sensation, strength and control of movement on the opposite side of the body, loss of memory, language deficits ( aphasia ) and loss of ability to remember faces. However, the prognosis for the survivors of the thalamic stroke is generally better than that of those who suffer a stroke in the cerebral cortex.