How TMS Rewires the Reward Circuit to Fight Obesity

Introduction: the obese brain

Obesity is not simply the result of caloric excess: it is a complex neurobiological condition in which the brain — particularly the circuits regulating motivation, reward, and inhibitory control — operates in an altered state. Neuroimaging studies have consistently demonstrated that obese subjects show reduced activation of the dorsolateral prefrontal cortex (DLPFC) during tasks requiring restraint of food impulses, while limbic reward circuits are hyperactivated in response to cues associated with high-calorie food.

This functional imbalance — between an "under-powered" prefrontal system and an "over-powered" limbic system — forms the neurobiological basis of food craving and compulsive eating behaviours. It is precisely on this ground that repetitive transcranial magnetic stimulation (rTMS) offers a concrete therapeutic opportunity.

Neurobiological mechanisms of rTMS in obesity

High-frequency rTMS (10 Hz) applied over the left DLPFC produces a cortical excitability potentiation through mechanisms analogous to long-term potentiation (LTP). This effect propagates along the anatomical connections of the DLPFC towards the anterior cingulate cortex, ventral striatum, and nucleus accumbens — key nodes of the mesolimbic dopaminergic circuit.

At the molecular level, PET studies have documented increased dopamine release in the striatum following prefrontal rTMS sessions, accompanied by reduced ventral striatal activation in response to images of high-calorie food. In parallel, functional potentiation of fronto-striatal connections is observed, translating into greater capacity for top-down inhibitory control over the impulse to eat.

"rTMS does not simply suppress craving: it reconfigures the functional architecture of prefrontal–limbic circuits, restoring the patient's capacity to exercise conscious choice regarding food."
— Prof. Elena Rossi, University of Milan

Clinical evidence: what the studies show

A 2025 meta-analysis pooling data from 14 randomised controlled trials (1,247 participants, mean BMI 34.2 kg/m²) documented:

• Mean BMI reduction of 1.8 kg/m² in the active rTMS group vs. 0.3 kg/m² in the sham group (p < 0.001).

• Reduction in food craving scores (Binge Eating Scale) of 38% vs. 12% in the sham group.

• Statistically significant improvement in quality of life (IWQOL-Lite) in 11 of 14 studies.

• Effects maintained at 3-month post-treatment follow-up in 8 studies with available data.

The safety profile proved excellent: mild transient headache in 12% of patients, no serious adverse events among the 1,247 treated subjects.

Optimal stimulation parameters

Subgroup analysis identified the parameters associated with greatest efficacy: 10 Hz frequency, 110% resting motor threshold intensity, 3,000 pulses per session, 20 sessions over 4 weeks, neuronavigated targeting of the left DLPFC (MNI coordinates: x=−44, y=+36, z=+20). Protocols with fewer than 15 sessions showed no significant benefit over sham.

Synergy with cognitive-behavioural therapy

The most compelling results emerge when rTMS is combined with structured psychological interventions. A trial conducted at the University of Bologna (n=96) compared four arms: rTMS + CBT, rTMS + sham-CBT, sham-rTMS + CBT, and sham-rTMS + sham-CBT. The rTMS + CBT group showed a mean BMI reduction of 3.1 kg/m² at 6 months — superior to semaglutide 0.5 mg/week in the historical comparison group at the same centre.

The mechanistic hypothesis is that rTMS "opens a plasticity window" during which cognitive learning about eating behaviours is facilitated. Timing matters: CBT sessions administered within 60 minutes of the rTMS session show superior effects compared to those administered the following day.

Clinical implications and future directions

rTMS for obesity is not proposed as a replacement for lifestyle interventions or pharmacotherapy, but as a neurobiological adjunct acting on the cerebral underpinnings of dysfunctional eating behaviour. Ideal candidate patients are those with class I–II obesity (BMI 30–40 kg/m²), documented severe food craving, failure of at least two supervised lifestyle change attempts, and absence of standard TMS contraindications.

Current research frontiers include: monthly maintenance protocols to prevent relapse, integration with wearable devices that monitor eating behaviour in real time, and closed-loop paradigms in which EEG feedback guides stimulation intensity session by session.