Reduced transcallosal inhibition in Alzheimer’s disease compared to healthy controls

Abstract

AbstractBackgroundIn Alzheimer’s disease (AD), structural changes in the corpus callosum are known to precede clinical signs. Transcranial magnetic stimulation (TMS) can be used to study functional integrity of the corpus callosum through ipsilateral silent period (iSP). We examined iSP duration between patients with mild cognitive impairment (MCI)/AD and healthy controls.Method15 patients of AD (n = 10) and MCI (n = 5), and 15 healthy controls were recruited. All subjects completed clinical (Clinical Dementia Rating Scale, Instrumental Activities of Daily Living Scale for Elderly, Everyday Abilities scale for India, & Neuropsychiatric Inventory) and cognitive (Hindi Mental Status Examination, attention, working memory and semantic verbal memory) evaluations. Twenty single TMS pulses (suprathreshold pulse delivered to right motor cortex with the ipsilateral/right hand maintained in 20% of its maximal contraction) and twenty paired pulses (subthreshold priming pulse delivered 3ms before suprathreshold test pulse over left motor cortex) were delivered to assess inter‐cortical inhibition (iSP) and intra‐cortical inhibition (ICI) respectively.ResultiSP duration was significantly reduced (df = 27; t = ‐2.76; p‐0.01)) in the clinical group as compared to healthy controls. However, there were no significant differences in ICI. There was no significant association between iSP and clinical or cognitive performance.ConclusionThe presence of inter‐cortical rather than intra‐cortical inhibition deficits in AD supports the hypothesis of corpus callosum dysfunction in AD. A lack of association between iSP and severity indices suggest this measure may be examined as an early marker of AD.