Using Deep Brain Stimulation to Treat Essential Tremor

Currently there has been a lot of effort to understand and treat essential tremor. We are fairly confident that essential tremor is caused by pathological oscillations in the cerebellar microcircuit. That being said we don't quite understand the exact cause of these oscillations, although we have a several good ideas. Despite having a solid but incomplete understanding of the disease, medications tend to be hit or miss. Generally speaking, medication tends to be successful in about 55% of those treated, the other 45% do not show any response to medication.  While many new medications and other non-invasive techniques have been developed. We have talked about external electrodes as a treatment in a previous blog, but the success rate is still limited.

Perhaps the most successful treatment (and most invasive treatment) is to use deep brain stimulation (DBS). The majority of people who get DBS show major improvement in symptoms. This is much better than medications. That being said, it is a risky surgery where a surgeon opens your brain and inserts an electrode into your brain. Not to mention it is expensive. 

So how does it work? Specifically the area targeted is an area of the thalamus called the ventral intermediate area (Vim). This is exactly the area where cerebellar outputs from areas associated with motor control pass through. Thus by injecting current into the Vim one effectively blocks the signal coming from the cerebellum. The cerebellar signal is no longer of use, as it is stuck in a pathological oscillation that no longer carries useful information, and instead induces periodic shaking. While DBS does return one to pre-disease state, it makes the essential tremor much better, and allows the patient to perform basic tasks.

One may ask, how can one block the motor cerebellar output completely, and still be able to move. This is still an open question. However one hypothesis is that cerebellum is less useful after motor learning has taken place. Another hypothesis is that the lack of full recovery could be because the cerebellum has effectively been disconnected.

Deep brain stimulation is an exciting field that is showing rapid development. There is still a lot of work to be done understanding how exactly DBS effects the neural circuits involved. Moreover, a lot of work needs to be done making DBS much more targeted to limit side effects.

Author: Alexander White