Does Repetitive Transcranial Magnetic Stimulation of Alzheimer's Patients Improve Cognition or Depression or Both?

Repetitive transcranial magnetic stimulation (rTMS) is used clinically to treat major depression and has more recently been applied as a potential treatment for Alzheimer's disease (AD). Given that the rTMS treatment protocols for AD are similar to those used for depression, we investigated whether the AD participants' cognition change after rTMS was, in part, due to a change in depressive level. Twenty-eight participants of an rTMS treatment study for AD participated in this study. We collected cognitive measures to partition them into 2 groups of subjects with marked or moderate responses (n = 13) and those with responses of small or none (n = 15). Besides, we recorded pre and post Electrovestibulography (EVestG) signals, and 2 EVestG features targeting depression were calculated from the averaged field potential curve (FPave) and low-frequency modulation of the recorded firing pattern (33-interval histogram [IH33]), respectively. We then compared these features in the above-mentioned cognitive-wise response groups. The FPave and IH33 depression-related features showed no substantial difference between pre- and post-treatment in either group in response to rTMS treatment. The change in these EVestG depression features of the AD participants was also poorly correlated with Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) change with treatment. This study's results demonstrate that cognitive improvement post rTMS is not predominantly a result of an improvement in depression.