Functional brain changes associated with cognitive trajectories determine specific tDCS‐induced effects among older adults

Abstract

The combination of transcranial direct current stimulation (tDCS) with functional magnetic resonance imaging (fMRI) can provide original data to investigate age‐related brain changes. We examined neural activity modulations induced by two multifocal tDCS procedures based on two distinct montages fitting two N‐back task‐based fMRI patterns (“compensatory” and “maintenance”) related to high working memory (WM) in a previous publication (Fernández‐Cabello et al. Neurobiol Aging (2016);48:23–33). We included 24 participants classified as stable or decliners according to their 4‐year WM trajectories following a retrospective longitudinal approach. Then, we studied longitudinal fMRI differences between groups (stable and decliners) and across multifocal tDCS montages (“compensatory” and “maintenance”) applied using a single‐blind sham‐controlled cross‐over design. Decliners evidenced over‐activation of non‐related WM areas after 4 years of follow‐up. Focusing on tDCS effects, among the decliner group, the “compensatory”‐tDCS montage reduced the activity over the posterior regions where these subjects showed longitudinal hyperactivation. These results reinforce the notion that tDCS effects are characterized by an activity reduction and might be more noticeable in compromised systems. Importantly, the data provide novel evidence that cognitive trajectories predict tDCS effects in older adults.

Multifocal Transcranial Direct Current Stimulation in Primary Progressive Aphasia Does Not Provide a Clinical Benefit Over Speech Therapy

“…The brain fMRI evaluations showed significant changes after both interventions in a subgroup of patients: increased activity in the right frontal medial cortex and the bilateral paracingulate gyrus. These two areas do not correspond with any of the cortical areas stimulated, however distal changes induced by tDCS and capture by fMRI activity patterns have been reported in previous investigations [40]. Increased activity in the active tDCS group was observed in the anterior cingulate/paracingulate cortex, a brain region that holds a potential role in language processing, in particular for tasks that require cognitive control.…”

What Can Neural Activity Tell Us About Cognitive Resources in Aging?

“…However, some longitudinal studies ( Nyberg et al, 2010 ; Rieckmann et al, 2017 ) reported an age-related reduction in frontal activity. More specifically, older adults defined as decliners (i.e., individuals with WM performance decline across time, as opposed to so-called maintainers) showed decreased recruitment of the prefrontal cortex ( Rieckmann et al, 2017 ; Vaqué-Alcázar et al, 2020 , 2021 ). To reduce the confound of cohort effects, it might be worth contemplating the administration of routine assessment of cognitive functions throughout an individual’s life span.…”