We will be talking about deep brain stimulation (DBS) for OCD but lets take a brief diversion first. If you were ever a medical history buff you may have heard of trepanation, From the image below you can see that involves making a hole in the skull.
At first pass you would not think that making a hole in a patients skull would be the ideal remedy for medical issues such as seizures, migraines and mental disorders. It is a fairly invasive medical strategy that fortunately did not always lead to the death of the patient.
The picture above by Hieronymus Bosch shows the technique applied in the middle ages. Fortunately today’s doctors have taken this hit and miss technique and applied it in a straight forward way to address the buildup of intracranial pressure (pressure in the skull). The image below shows a modern medical device to address intracranial pressure. The is an old and brutal technique of trepanation has been updated to work relatively safely to address significant medical problems.
Let us now jump to electroconvulsive therapy, best known as ECT and made famous in the movie “One flew over the cuckoo’s nest”. The medical technique of applying a strong electrical shock to the brain seemed to help with depressive patients. Electrodes were placed at one or either side of the head and a significant electric charge was applied to the brain. When ECT was first introduced it was a hit and miss affair that sometimes left the patient with significant memory problems.
The technique has been refined and the horrible consequences of older style ECT therapy have been substantially reduced, although some memory loss is common even with modern approaches. Once again it is an old technique refined to work relatively safely to address significant medical problems.
Deep Brain Stimulation
Relatively recently a variant on the ECT technique has been developed called deep brain stimulation. ECT placed the electrodes on the outside and deep brain stimulation places tiny electrodes on the inside. Electrodes are inserted into target areas of the brain and small pulses of electrical stimulation are applied. The stimulation may increase the output of a region of neurons or activate inhibition circuits. The placement of the electrodes determines what functionality is increased or decreased. Like ECT the precise mechanisms of how deep brain stimulationworks is not fully understood but early observations using special microscopes shows the following:
- Inhibits the actions of functional elements of the brain through the release of neurotransmitters (GABA and Adenosine).
- Can excite other parts of the brain via axons and glutamate
- Changes the firing patterns of regions of the brain (much like a pacemaker in a heart)
- Grows dentate gyrus cells and make better connections to the hippocampus
With a pacemaker there is a fairly clear stimulation point that helps define the beat of the heart. Applying a regular electrical pulse at this specific point pretty much controls the whole game. For depression and OCD there is not a single point in the brain that can be fixed. Brain function is dispersed and its outcomes are achieved via complex web of controls. Some areas of the brain need to be inhibited and some need to be excited at just the right amounts.
At this point deep brain stimulation has been shown promising results for depression. If the complex neuro-mechanisms controlling OCD are worked out then in principle stimulation and inhibition to these functional areas could improve OCD symptoms. At this point deep brain stimulation is an inexact science. Regions of the brain that usually do one thing can lead to another result in another person. This makes sense when you consider the brain is not made up like a fixed road map. Each area of the brain is woven together with hundreds of thousands of unique connections – each individual connection influences the outcome of the connected region in its own special way. In years to come we will likely see the micro electrode inserted into the brain as the equivalent of electronic sledgehammers stimulating vast clumps of neurons that trigger a range of activities not unlike the scattering of billiard balls at the start of a pool game. The fact that the right balls drop into the pockets often enough is why deep brain stimulation is currently seen a future hope. In time it is hoped that it can be refined to deliver more consistent and tailored interventions.
Deep Brain Stimulation summary for OCD
The functional system for OCD treatment lies predominately in the cortico-striato-thalamocortical circuit. The two key targets are ACC (anterior cingulate cortex) and OFC (orbitofrontalcortex). The authors conclude that for treatment resistant OCD deep brain stimulation is an effective option.
Bourne, S. K., Eckhardt, C. A., Sheth, S. A., & Eskandar, E. N. (2012). Mechanisms of deep brain stimulation for obsessive compulsive disorder: effects upon cells and circuits. Frontiers in Integrative Neuroscience, 6, 29. http://doi.org/10.3389/fnint.2012.00029
By Rama, CC BY-SA 3.0 fr, https://commons.wikimedia.org/w/index.php?curid=58036467
By Rodw – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=34135969