Cortical Anatomical Variations and Efficacy of rTMS in the Treatment of Auditory Hallucinations

Repetitive transcranial magnetic stimulation (rTMS) shows high inter-subject variability in its efficacy for treating resistant auditory verbal hallucinations in schizophrenia. Currently, the response of an individual patient to rTMS treatment cannot be predicted. It is possible that cortical anatomical characteristics could affect the therapeutic response.

We hypothesized that rTMS efficacy is related to anatomical variations underlying the stimulation target in the left temporal cortex. We investigated two regions of interest (ROIs) that have been implicated in rTMS: the left temporal cortex, where the stimulation is delivered, and the primary hand motor cortex, where the stimulation strength is determined by the resting motor threshold (rMT).

Fifteen patients with schizophrenia (DSM IV) underwent rTMS and magnetic resonance imaging. The scalp-to-cortex distance (SCD) and the grey matter density (GMD) were measured in both ROIs. Linear regression models were used to investigate the relationships between these measures and the clinical efficacy of rTMS.

Treatment efficacy was highly predicted by the temporal SCD and the GMD in the temporal and primary hand motor cortex regions. In contrast, the rMT was not predicted by the primary hand motor cortex SCD or GMD.

These results suggest that rTMS treatment efficacy could be related to the depth of the temporal target. The data raise the question of whether rMT is the best measure for assessing the stimulation intensity in treating patients with schizophrenia.