Broadly, five neural circuits are involved in symptom generation in OCD:
- Ventral Cognitive: IFG, vlPFC, ventral caudate, and thalamus: Impaired response inhibition, difficulties in preventing inappropriate thoughts or behaviours
- Ventral Affective: OFC, NAcc and thalamus: Reward system dysfunction , reflecting a reduced sensitivity to rewards coupled with exaggerated anticipation of punishments in some patients which leads to feelings of relief/reward obtained by completing compulsive and/or avoidance behaviours
- Dorsal Cognitive: pre-SMA, dlPFC, dmPFC, dorsal caudate, and thalamus: Executive dysfunction (cognitive control)
- Frontolimbic,: vmPFC and amygdala: Intolerance of ambiguity ( reflecting an inability to cope with uncertainty, pathological doubts, e.g., in checking)
- Sensorimotor: the SMA, posterior putamen, and thalamus: Sensory phenomena (aversive or uncomfortable sensations that accompany and/or drive repetitive behaviours, feeling that things are “not just right”; the sensation of feeling dirty)
What Neural Networks to target?
- Dysregulated fear” and “intolerance of uncertainty” profiles may be best treated using therapies that aim to reduce hyperactivity in the fronto-limbic circuit and increase hypoactive dorsal cognitive circuit top-down control of the fronto-limbic circuit.
- Sensory phenomena” and “excessive habit-formation” profiles could be addressed by treatments aiming to reduce excessive sensorimotor circuit activity (habit-reversal training, SMA rTMS) and for sensory phenomena only, regulate insula activity (H-coil insula TMS)
- For the “impaired response inhibition” profile, treatments aiming to increase ventral cognitive circuit hypoactivity.
- Altered reward responsiveness” profile, suggested therapies targeting reward mechanisms of the ventral affective circuit
- Executive dysfunction” profile would involve increasing hypoactivity in the dorsal cognitive circuit (dlPFC, and pre-SMA rTMS
See Shepard et al ( 2022: https://doi.org/10.1590/1516-4446-2020-1709 )
Findings from a recent meta-analysis by Dehghani-Arani et al (2024) (https://www.mdpi.com/2077-0383/13/18/5358#app1-jcm-13-05358) suggest:
- ** Overall rTMS treatments are significantly better compared to sham treatment (medium effect size)
- Obsessions respond better than compulsions to rTMS treatment.
- **The bilateral DLPFC has a large effect size ( Best, but bit a pinch of salt, not good when outlier studies were removed from the meta-analysis).
- **The SMA stimulation also had a large effect size. The pre-SMA rTMS appears to induce electrical fields in more circuits relevant to OCD pathophysiology.
- **Stimulation of the OFC, lDLPC and other cortical regions did not show significant effect.
- **Optimal number of pulses seem to be between 800-1200 per session.
- Treatment duration of upto 4 weeks seems optimal (though 1-2 weeks treatment showed the best results).
