In a recent poster presented at the 2015 Society of Biological Psychiatry meeting Martin Lan and colleagues presented data from the first study of structural changes in the brain following TMS.
In the study, 27 patients in an episode of major depression underwent MRIs before and after receiving TMS treatment.
Several cortical regions related to cognitive appraisal, the subjective experience of emotion, and self-referential thought increased in volume following TMS treatment: the anterior cingulate, the cingulate body, the precuneous, right insula, and gray matter in the medial frontal gyrus.
The increases ranged from 5.3% to 15.7%, and no regions decreased in volume. More than 92% of the participants showed increased gray matter in all of these regions.
It is interesting to note that these are not the areas of the brain that are stimulated by TMS. TMS stimulates the dorsolateral prefrontal cortex, which is involved in mindfulness meditation and other non-emotion-based reflection and awareness, whereas these areas of the brain are medial and involved in emotion regulation and emotional decision-making.
How exactly this change relates to the mechanism of action of TMS in treating depression is unclear. As the authors noted, the brain changes were not correlated with antidepressant response to TMS.
Lan and colleagues concluded that TMS likely had neuroplastic effects in areas of the brain that are important for emotion regulation.
It is reassuring to note that there were no negative changes in brain volumes.