Exploratory Study of the Neurophysiological Monitoring of the Efficacy of Transcranial Alternating Current Stimulation as a Treatment for Alzheimer’s Disease

Abstract

Neurophysiological changes due to either real or sham transcranial alternating current stimulation (tACS) when paired with cognitive exercises were assessed in 35 patients with Alzheimer’s disease (AD) or AD mixed with cerebrovascular disease utilizing Electrovestibulography (EVestG) in comparison with ADAS-Cog, as the primary outcome measure of cognitive function. Both measures were made at baseline (Week 0, W0), post (W5) and follow-up (W12). For EVestG a comparative analysis of the interval histogram (IH33) of the neuronal firing pattern was made. The results were further analysed based on the patients’ modified Hachinski Ischaemic Score (HIS) to determine the impact of cerebrovascular disease (cvd) on EVestG responses. Important findings include: (i) For real tACS stimulation the differences observed between right and left side responses were primarily a consequence of the tACS electrodes’ positioning. (ii) Based on EVestG responses, those with HIS ≥ 2 benefit more than those with HIS < 2 from real tACS stimulation by W12 (p = 0.014). (iii) The EVestG-detected frequency shifts in neural activity for real tACS show significant differences for subgroups HIS < 2 and HIS ≥ 2 (p = 0.012, W5), supporting a different time course and possible mechanisms. (iv) For the real tACS stimulation an improved cognitive score generally manifested at W12 as an increase in firing rate. (v) Cognitive exercises alone (sham tACS) appear to slow or prevent further overall decline. We conclude cognitive exercises plus real tACS appears to be effective but depending on cvd levels have different time constants and perhaps different overall modes of action. Further, the IH33 measure is shown to be effective at monitoring the effect of cognitive exercises alone (sham tACS) or with real tACS.