Fractional anisotropy changes after several weeks of daily left high-frequency repetitive transcranial magnetic stimulation of the prefrontal cortex to treat major depression.

OBJECTIVES

As part of a sham controlled treatment trial using daily left repetitive transcranial magnetic stimulation (rTMS), brain changes associated with 4 to 6 weeks of treatment were examined using diffusion tensor imaging to noninvasively evaluate prefrontal white matter (WM) microstructure. A decrease in fractional anisotropy values of the left prefrontal WM could indicate damage to the region.

METHODS

Diffusion tensor imaging was performed before and after 4 to 6 weeks of daily rTMS treatments. Mean fractional anisotropy levels associated with active rTMS and sham rTMS for the right and left prefrontal WM were assessed.

RESULTS

Adequate images were acquired for 8 participants (active n = 4, sham n = 4) before and after rTMS. A mean increase was found for the left prefrontal WM. The mixed model revealed a trend toward a significant treatment group × region interaction effect (P = 0.11). Furthermore, simple region effects (left prefrontal WM vs right prefrontal WM) were at a trend toward significance for difference after treatment within the active rTMS group (P = 0.07), but not within the sham rTMS group (P = 0.88).

CONCLUSIONS

Repetitive transcranial magnetic stimulation resulted in no evidence of damage to WM on the side of stimulation. Diffusion tensor imaging may offer a unique modality to increase our understanding of mechanisms of action for rTMS.