An area that includes the subthalamic nucleus (STN), a structure of the basal ganglia, specialized nerve clusters in the brain that direct voluntary movement. it is located between the thalamus, the substantia nigra, and the hypothalamus, and as are other structures in the brain it is a paired, or bilateral, structure. The subthala-mus has a number of distinctive cell clusters that have different but integrated roles in voluntary movement. The functions of some of these areas and their roles in motor function are poorly understood.
Subthalamic Nucleus (STN)
The area of significance in Parkinson’s disease is the subthalamic nucleus (STN), a dense cluster of neurons in the center of the subthalamus. The STN receives nerve signals from the globus pallidus externus (external pallidus, or GPe) and sends nerve signals to the globus pallidus internus (internal pallidus, or GPi). These signals integrate with neuron communication from other structures of the basal ganglia. The GPi then sends on the mix of nerve signals to the thalamus, which in turn filters and organizes them before passing them through to the cerebral cortex (the part of the cerebrum that initiates the “call to action” setting into motion the sequence of events necessary for voluntary movement).
The dopamine depletion characteristic of Parkinson’s disease allows the STN to become over-active in generating nerve signals to inhibit muscle activity. These signals flood the thalamus, which in turn decreases excitation of the cerebral cortex. Scientists believe this action is what causes motor symptoms such as bradykinesia and rigidity.
Subthalamotomy
Creating lesions in the STN, in surgical techniques similar to pallidotomy and thalamotomy, is an INVESTIGATIONAL TREATMENT used to provide long-term relief of these symptoms by interrupting or blocking some of the sTN’s cells from functioning. Neurosurgeons have performed this surgery, called subthalamotomy, on about two dozen people who had late stage Parkinson’s disease in open-label studies. The majority experienced significant improvements in their Parkinson’s symptoms and were able to reduce the levels of anti-parkinson’s medications they had been taking before the experimental surgery. However, as with almost all other surgical procedures for Parkinson’s, the damage of Parkinson’s continues to progress.
The STN is a much smaller structure within the brain than either the thalamus or the pallidus. Targeting it requires great precision, and the margin of error is very narrow. As with other ablative procedures, deep brain stimulation (DBS) offers many safety advantages over subthalamotomy. it remains unclear whether subthalamotomy offers any advantages over the more established ablative procedures of pallidotomy and thalamotomy, which also entail significant risk but target larger and better understood structures of the brain’s movement system and therefore have a somewhat more comfortable margin of error.
