When Stroke Affects the Thalamus
The thalamus is a busy place in the human brain, and a stroke there can have a wide range of effects.
The thalamus is a busy place in the human brain, and a stroke there can have a wide range of effects. Jeremy Schmahmann, professor of neurology at Harvard Medical School, director of the ataxia unit and member of the cognitive behavioral neurology unit at Massachusetts General Hospital, shared more about this type of stroke.
The thalamus, which means "inner chamber" in Greek, is on top of the brainstem near the center of the brain. It has two halves, each about the size of a walnut. "The thalamus is divided into many different areas, which are connected very specifically to different parts of the brain," Dr. Schmahmann said. "A stroke in one part of the thalamus will not have the same effect as a stroke in another part."
The thalamus has many functions, including:
- It manages our sensitivity to temperature, light and physical touch and controlling the flow of visual, auditory and motor information;
- The thalamus is involved in motivation, attention and wakefulness;
- It’s in charge of our sense of balance and awareness of our arms and legs;
- It controls how we experience pain;
- It’s also involved in aspects of learning, memory, speech and understanding language; and
- Even emotional experiences, expression and our personalities involve the thalamus.
The thalamus can be thought of as a "relay station," receiving signals from the brain’s outer regions (cerebral cortex), interpreting them, then sending them to other areas of the brain to complete their job.
Though relatively small, the thalamus controls a big part of how our bodies function and respond to the world around us. "The thalamus has dense connections to all the parts of the brain and receives information from all parts of the brain," Dr. Schmahmann said. Only a small part of the thalamus receives input from the outside world or sends information to the outside world. Mostly the thalamus helps the cortex and other cells deep within the brain to communicate with each other.
"The thing that makes the thalamus quite special is that it’s a relatively small, very concentrated area deep inside the brain, and a small change in the location of the stroke can produce a substantial change in how the stroke affects the survivor," Dr. Schmahmann said.
For example, a stroke in the thalamus may cause drowsiness, contribute to the development of epilepsy, impact a survivor’s attention span, or a sense of apathy.
A stroke in the front part of the thalamus can affect memory, including memories about one’s own life. "As a result, a stroke patient can have what looks like instant onset of Alzheimer’s disease," Dr. Schmahmann said.
Injury to another part of the thalamus may impede movement, balance or strength.
Very large strokes in the thalamus can cause many problems. If both sides are injured, destroying connections to the rest of the brain, it may result in coma. "Fortunately, the brain’s wiring has a degree of plasticity, and if the stroke is only in the thalamus, some people can recover and do quite nicely because the rest of the brain has ways of making up for it," Dr. Schmahmann said. "But they may not completely return to normal."
Because the thalamus shares its blood supply with the brainstem, occipital lobe and temporal lobe of the brain, strokes in those areas can also affect the thalamus. Depending on which lobe is affected, the survivor may experience visual field loss (hemianopsia), memory loss or problems with swallowing and breathing.
Recovery is more challenging for these strokes because there are many more areas of the brain involved.
How 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 it. Effects can include loss of sensation, strength and control of movement of the opposite side of the body, memory loss, language deficits (aphasia), and a loss of the ability to remember faces. However, according to Dr. Schmahmann, the prognosis for survivors of thalamic stroke is generally better than those who experience stroke in the cerebral cortex.