Verbal Fluency in Mild Alzheimer’s Disease: Transcranial Direct Current Stimulation over the Dorsolateral Prefrontal Cortex

Abstract

Background: Recent studies showed that in healthy controls and in aphasic patients, inhibitory trains of repetitive transcranial magnetic stimulation (rTMS) over the right prefrontal cortex can improve phonemic fluency performance, while anodal transcranial direct current stimulation (tDCS) over the left prefrontal cortex can improve performance in naming and semantic fluency tasks. Objective: This study aimed at investigating the effects of cathodal tDCS over the left or the right dorsolateral prefrontal cortex (DLPFC) on verbal fluency tasks (VFT) in patients with mild Alzheimer’s disease (AD). Methods: Forty mild AD patients participated in the study (mean age 73.17±5.61 years). All participants underwent cognitive baseline tasks and a VFT twice. Twenty patients randomly received cathodal tDCS to the left or the right DLPFC, and twenty patients were assigned to a control group in which only the two measures of VFT were taken, without the administration of the tDCS. Results: A significant improvement of performance on the VFT in AD patients was present after tDCS over the right DLPFC (p = 0.001). Instead, no difference was detected between the two VFTs sessions after tDCS over the left DLPFC (p = 0.42). Furthermore, these results cannot be related to task learning effects, since no significant difference was found between the two VFT sessions in the control group (p = 0.73). Conclusion: These data suggest that tDCS over DLPFC can improve VFT performance in AD patients. A hypothesis is that tDCS enhances adaptive patterns of brain activity between functionally connected areas.

Anodal transcranial direct current stimulation (atDCS) and functional transcranial Doppler sonography (fTCD) in healthy elderly and patients with MCI: modulation of age-related changes in word fluency and language lateralization

“…These were not directly stimulated by left inferior atDCS. However, results of previous studies also show a significant effect of atDCS over the left IFG on semantic WF performance in healthy elderly participants ( Meinzer et al, 2013 ; 2015 ) and in patients with dementia-related cognitive decline ( Penolazzi et al, 2013 ; Smirni et al, 2021 ), but their experimental task procedure and the associated word retrieval of the subjects were very different and not very comparable to our tasks.…”

“…It is possible that stimulation of the temporal cortex could lead to better outcomes in MCI, as also suggested by Chen et al (2022) . Moreover, cathodal stimulation of the right DLPFC improved WF in mildly affected AD patients by supporting left hemisphere networks through short-term inhibition ( Smirni et al, 2021 ). From this, one could assume that the same stimulation conditions do not apply to MCI patients and healthy elderly and therefore do not lead to comparable results.…”

Nonmedication Devices in Development for the Treatment of Alzheimer’s Disease

“…Several studies have indicated that tDCS may improve global cognition [12,14,56,57], recognition memory [12], verbal fluency [14,16], executive function [14], and depression [15] in patients with AD. Interestingly, a single session of tDCS in the area of the left DLPFC in AD patients demonstrated enhanced recognition memory [12].…”

Transcranial Direct-Current Stimulation Improves Verbal Fluency in Children with Attention Deficit Hyperactivity Disorder (ADHD)

“…Numerous studies have explored the effects of tDCS on verbal fluency, with particular focus on the left IFG [ 50 ], right IFG [ 51 ], left dlPFC [ 52 ], and right dlPFC [ 53 ]. Among the main candidate regions, the left IFG, commonly known as Broca’s area, has been extensively investigated for its involvement in response selection, representing the verbal component of verbal fluency.…”