A structure in the brain that filters and organizes nerve signals passing between the cerebral cortex and other brain structures that control movement, primarily the basal ganglia, brain-stem, and cerebellum. It is a paired structure made of gray matter (dense neuron bodies) that straddles the upper portion of the brainstem; each side is about the size and shape of a walnut. The thalamus also processes sensory signals and is the site within the brain where pain recognition begins.
A small area within the center of the thalamus, called the ventral intermediate nucleus (VIM), becomes overactive in Parkinson’s disease and many other tremor disorders. It is theorized that the imbalance of neurotransmitters in the brain that results from the dopamine depletion that characterizes Parkinson’s creates chaotic neuron communications that barrage the thalamus, overwhelming its ability to inhibit them. This causes Dysfunctional movements that manifest as tremors and rigidity (muscles in continual contraction).
Dopaminergic anti-parkinson’s medications that replace or extend the presence of dopamine, such as levodopa and the dopamine agonists, help to restore the brain’s neurotransmitter balance, putting neuron communication under control and reducing the numbers and chaos of nerve signals to the thalamus. This effect calms the signals that travel to the muscles in the body, relieving the tremors and rigidity for the duration of the medication’s effectiveness. As Parkinson’s disease progresses, these medications are less effective and symptoms persist or worsen. Some people with Parkinson’s have what doctors call tremor-predominant Parkinson’s, in which their primary symptoms are tremors; these can be severe enough to be debilitating. thalamotomy (surgery to interrupt the flow of nerve signals from the thalamus) often can relieve symptoms in these cases, although not all those with Parkinson’s who reach such a stage are good candidates for surgery. Other health problems such as heart disease or diabetes, and other symptoms of Parkinson’s disease such as bradykinesia and akinesia, which do not improve after thalamotomy can tip the balance on surgery’s overall effectiveness in providing relief.