Essentials: Compulsive Behaviors & Deep Brain Stimulation | Dr. Casey Halpern

This Huberman Lab Essentials conversation opens with a question about what separates neurosurgery from neurology and psychiatry. Dr. Casey Halpern describes a broad field. Neurosurgeons remove brain tumors, clip aneurysms, treat traumatic brain injury and concussion, and operate on the spine. He notes that 90% of what neurosurgeons around the country do is herniated discs and lumbar fusions. The scope covers the entire central nervous system and the peripheral nerves, including carpal tunnel syndrome.

Halpern says the field now sub-specializes. At Penn Medicine he is chief of stereotactic functional neurosurgery, and he does only deep brain stimulation (DBS) surgery plus transcranial focused ultrasound. He describes focused ultrasound as a non-invasive way to make an ablation in the brain. It was recently FDA approved, and at the moment that approval covers tremor. In DBS, a very thin insulated wire is placed deep in a brain region involved in a condition such as Parkinson's disease. He stresses that the wire itself is not the therapy. The therapy is electrical stimulation delivered through one of several small contacts at the wire's tip.

It's a bit more like I have to implant a tool to deliver you a medication, but that medication is going to be in the form of electricity, and it's going to be delivered into a very small region of the brain.

Halpern explains that brain regions lying within a few millimeters of an electrode can, when stimulated, produce brief and temporary side effects, such as a moment of laughter or a moment of panic. The electrode can simply be shut off. He argues, though, that these side effects are often therapeutic, and that this is how DBS uses beyond movement disorders were discovered. Some Parkinson's patients have psychiatric comorbidities such as depression or obsessive-compulsive disorder, and many are highly compulsive and impulsive. During treatment aimed at tremor, some report that their gambling problem has improved or their mood has lifted.

He is careful about the explanation and says there is probably more than one reason. Removing a tremor can improve someone's mood on its own. But he also points out that the stimulated structures belong not only to motor circuits but to a limbic circuit involved in emotion. If those areas can be modulated therapeutically, step by step, therapies could be developed for other indications such as depression. Even so, he names immediate tremor relief in a patient who has trembled for 20 years as the most impressive and consistent effect. That effect is what made him want to become a neurosurgeon in college, and his goal is to build a comparable therapy for other symptoms.