Aim:
Several studies have found an increase in hippocampal volume following a series of electroconvulsive therapy (ECT), but the effect on cortical thickness has been less investigated. We aimed to examine the short- and long-term effect of ECT on changes in cortical thickness and their associations with clinical outcome.

Methods:
Using 3 Tesla MRI-scanner, we obtained T1-weighted brain images of 18 severely depressed patients at three time points: befor, right after, and six months after a series of ECT. The thickness of 68 cortical regions was extracted using Free Surfer, and Linear Mixed Model was used to analyse the longitudinal changes.

Results:
We found significant increases in cortical thickness of 26 regions right after the series of ECT, mainly within the frontal, temporal and insular cortex. The thickness returned to the baseline-values at six-month follow-up. No significant decreases in cortical thickness were detected. The increase in thickness of the right lateral orbitofrontal cortex was correlated to at greater antidepressant effect, r-0.75, p-0.0005. None of the regions showed any associations with cognitive side effects.

Conclusion:
The findings support the neurotrophic hypothesis of ECT's mechanism of action and do not support the notion that ECT has a harmful effect on the cortex.