Deep Brain Stimulation for Treatment Resistant Depression: Exploration of Local Field Potentials (LFP) With the Medtronic Activa Primary Cell + Sensing (PC+S) "Brain Radio" System

Major depressive disorder is a common disease. For many people, conventional treatments such as antidepressants are very helpful in relieving the symptoms of this condition. But as many as 30% of patients with depression have less than a full response or become resistant to conventional treatments. When treatment resistance develops, the depression becomes a chronic disease with a very significant burden of morbidity and mortality. The reasons that some patients develop Treatment Resistant Depression (TRD) are not known. One current theory for depression is that it results from the dysfunction of a network of regions in the brain and that in treatment resistant patients the network is permanently stuck in the dysfunctional state. We have been investigating an experimental treatment for treatment resistant depression (TRD), based on this network theory known as subcallosal deep brain stimulation (SCC DBS). This treatment involves placement of electrodes in a specific region of the brain (subcallosal cingulate cortex, area 25) and then stimulating that area with electricity, which resets the regulation of the network resulting in a significant antidepressant response. While still experimental our results suggest this may eventually be a useful treatment for some patients with TRD. The experiment described in this application is to use a new DBS device that can record the electrical activity in the brain around the site of stimulation. The electrical activity is known as Latent Field Potential (LFP) and is a reflection of the activity if the neural network. The new DBS device is an experimental device that has not been approved by the Food and Drug Administration (FDA), but allows for simultaneous recording of LFP while stimulation is being delivered. The device is manufactured by Medtronics and is known as Activa Primary Cell + Sensing(PC+S), but because it can be used to record the brain electrical activity it is also known as "the Brain Radio". The Brain Radio is based on an approved device commonly used for DBS for other conditions that has the added sensor capacity. The stimulation system is identical to that in the approved device. The goal of this investigation is to use the Brain Radio to study LFP in the brains of people with TRD before and during active stimulation. The ultimate goal is to understand the neural network that causes TRD and the changes that DBS cause in that network that results in the antidepressant effects. We will recruit 10 patients with advanced TRD and implant them with the Brain Radio system. The recording system will be to record LFP over 3 years, while patients receive stimulation. A brief discontinuation study will be conducted after 6 months of stimulation when the device will be turned off and patterns of LFP changes will be recorded. All LFP measures will be correlated with the primary clinical response outcome metric, the Hamilton Depression Rating Scale. The knowledge gained with this experiment will be invaluable to understanding the basic pathology of depression and the antidepressant response. This is a unique, first in humans test of this device and as such the results are expected to impact our understanding of depression at a fundamental basis.

Deep brain stimulation of the subcallosal cingulate white matter (SCC25 DBS) has been investigated as a new interventional strategy for treatment resistant depression (TRD). In addition to growing evidence of long-term antidepressant efficacy with chronic stimulation, immediate changes in mood, attention, and psychomotor speed during intra-operative testing have been repeatedly observed. These acute, electrode contact-specific behavioral effects have successfully guided selection of the optimal contact for chronic DBS. The presence of intraoperative behavioral effects is often predictive of long-term outcome. It is clear that sustained high frequency stimulation appears to be required to maintain the antidepressant response long-term, as discontinuation even after several years of remission is associated with deterioration and return of depression symptoms over several weeks. Imaging studies examining effects of chronic SCC25 DBS using positron emission tomography (PET) demonstrate changes in blood flow and metabolism both in the vicinity of the DBS target, and remotely in frontal cortex, ventral striatum, hypothalamus and amygdala/hippocampus. These findings, combined with more recent diffusion tensor imaging (DTI) studies, provide evidence of the anatomical and functional extent of regional changes mediating antidepressant effects of DBS over time [5-6].

Brain changes mediating the observed intra-operative behavioral changes or discontinuation-precipitated relapse are unknown. To date, none of the studies have been able to address explicit mechanisms of DBS for TRD at the neuronal level, during chronic stimulation. It is possible to make measurements of neuronal activity with available recording systems only during intraoperative testing. Given that TRD requires chronic stimulation to achieve full remission, characterization of changes in neural activity throughout the duration of stimulation and development of therapeutic response will be invaluable in further developing and refining this treatment modality. Furthermore, tracking of neural changes and their behavioral correlates with chronic stimulation and controlled discontinuation would allow characterization of physiologic markers for potential use as feedback signals for further treatment development and optimization.

This set of new experiments will build on past experience of utilizing SCC25 DBS in patients with TRD to explore potential neural correlates of antidepressant response. This will be done using the ActivaPC+S, which is a prototype DBS system developed by Medtronic that combines conventional DBS brain electrodes and pulse generator with a sensing device that can chronically read, record and download the electrical brain activity known as Local Field Potential (LFP) at the brain area surrounding the DBS electrode. These recordings can be downloaded from the implanted device with an external antenna device similar to the device used to control the pulse generator. Given the ability to record LFP locally in the brain and to transmit this information to a receiving station the ActivaPC+S device is referred to as the "Brain Radio".

The ActivaPC+S, "Brain Radio" device is an experimental system currently not approved by the FDA. This device is based on the ActivaPC system, which has FDA approval for use in Parkinson's disease, Essential Tremor and has Humanitarian Device Exemption (HDE) for Dystonia. The ActivaPC also has an HDE for use in intractable Obsessive Compulsive Disorder (OCD). The Brain Radio has sensing technology in addition to the standard stimulation capacity of the approved device that allows for real time recording of LFP in the anatomical location of the electrode both during active stimulation and when stimulation is off. As such this is a very powerful research tool that will facilitate investigation of the neuronal changes associated with antidepressant response to chronic DBS. This will be the first ever use of this unique, cutting edge system in human patients with treatment resistant depression and has the potential to provide unprecedented insight into the fundamental neuronal processes that underlie depressive illness and antidepressant response.