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

Neurosurgery is a broad field: brain tumors, aneurysms, traumatic injury, spine surgery, and peripheral nerve disorders like carpal tunnel. But Dr. Halpern specializes in stereotactic functional neurosurgery — placing thin, insulated wires deep into the brain to deliver electrical stimulation. The wire itself isn't the therapy; the electricity is. For Parkinson's patients, stimulation can stop a tremor instantly, an effect so consistent it inspired Halpern to become a neurosurgeon.

But the most striking discoveries came from side effects. When electrodes drifted a few millimeters off target, patients experienced brief moments of laughter, panic, or relief from depression. Parkinson's patients with comorbid OCD reported that their gambling urges or compulsions melted away. These observations suggested that the motor circuits being targeted overlapped with limbic circuits involved in emotion and impulse control. If stimulation could modulate mood and compulsion as reliably as it stopped tremor, it could become a therapy for psychiatric disease.

Halpern's lab is now focused on understanding where obsessions and cravings originate in the brain — and how to interrupt them. The goal is not just to treat symptoms, but to decode the circuits that drive compulsion at its source, using the same precision that makes tremor treatment so effective.

Halpern views OCD, addiction, and binge eating disorder as sharing a core dysfunction: the «urge despite the risk.» A heroin addict pursues a fix despite lethal consequences. An OCD patient checks the stove despite knowing it's off. A binge eater consumes thousands of calories despite health risks. All involve a reward-seeking behavior that has hijacked normal judgment.

The nucleus accumbens, part of the ventral striatum, is central to this circuit. It gates reward-seeking behavior, and when perturbed — by repeated drug exposure, chronic stress, or other factors — it seems to gate compulsive behavior instead. In animal models, rats with dysfunctional nucleus accumbens will pursue rewards despite foot shocks. The cortical areas that project to the nucleus accumbens, including the prefrontal and orbitofrontal cortex, are also hyperactive in OCD patients, failing to inhibit the compulsive urge.

Halpern's hypothesis is that if this circuit can be modulated — either by stimulation, ablation, or eventually non-invasive methods — it could restore the ability to control behavior. The challenge is finding the precise target and the right parameters to deliver therapy that is symptom-specific, not just symptom-adjacent.

Transcranial magnetic stimulation (TMS) is FDA-approved for depression, OCD, and nicotine addiction. Focused ultrasound is approved for tremor and can deliver ablations without an incision. Both are scalable in ways that surgery is not — Halpern notes that only 200,000 deep brain stimulation surgeries have ever been performed, far too few to address the 50 million Americans with severe psychiatric or eating disorders.

But non-invasive tools lack the precision of surgery. TMS effects are temporary and not always reproducible. Ultrasound ablations are permanent but require knowing exactly where to aim. Halpern argues that invasive studies — placing electrodes in awake patients, recording during symptom provocation, mapping circuits at millimeter resolution — are essential to identify the targets that non-invasive tools will one day hit. His team is seeking FDA approval to implant stereoelectroencephalography (sEEG) electrodes in OCD patients, the same technique used in epilepsy surgery, to map obsession circuits in humans.

Once targets are validated, non-invasive modulation could follow. Halpern envisions a future where TMS or ultrasound can be delivered with surgical precision, guided by invasive data, to treat compulsion, craving, and impulsivity at scale. But first, we must get into the brain to understand what signals to disrupt.