Abstract
The current study aims to determine the brain areas critical for response to anodal transcranial direct current stimulation (tDCS) in PPA. Anodal tDCS and sham were administered over the left inferior frontal gyrus (IFG), combined with written naming/spelling therapy. Thirty people with PPA were included in this study, and assessed immediately, 2 weeks, and 2 months post-therapy. We identified anatomical areas whose volumes significantly predicted the additional tDCS effects. For trained words, the volumes of the left Angular Gyrus and left Posterior Cingulate Cortex predicted the additional tDCS gain. For untrained words, the volumes of the left Middle Frontal Gyrus, left Supramarginal Gyrus, and right Posterior Cingulate Cortex predicted the additional tDCS gain. These findings show that areas involved in language, attention and working memory contribute to the maintenance and generalization of stimulation effects. The findings highlight that tDCS possibly affects areas anatomically or functionally connected to stimulation targets.
Highlights
Primary Progressive Aphasia (PPA) is a progressive loss of language abilities due to neurodegeneration (Mesulam, 1982, 2001, 2008)
After controlling for left AG volumes, the left Posterior Cingulate Cortex (l-posterior Cingulate Cortex (PCC)) volumes were associated with stimulation effects (ΔR2 = 14.3%, β = 0.40, p < 0.05)
Therapy response under transcranial Direct Current Stimulation (tDCS) becomes relatively greater than for individuals receiving Sham as the left PCC volume increases, while the pattern is in the opposite direction for Sham (Fig. 4, panel C; results are summarized on Table 2)
Summary
Primary Progressive Aphasia (PPA) is a progressive loss of language abilities due to neurodegeneration (Mesulam, 1982, 2001, 2008). Individuals with lvPPA have atrophy in the left inferior parietal lobe and the left posterior superior temporal gyrus (Gorno-Tempini et al, 2004; Josephs et al, 2013; Rohrer et al, 2010) These individuals tend to present with impaired word retrieval and sentence repetition with production of phonological paraphasias. Those with nfvPPA present with predominantly left frontal atrophy, including the left inferior frontal gyrus (IFG), pre-motor and supplementary motor areas, and the left insula (Grossman, Mickanin, Onishi, Hughes, D’Esposito, Ding, & Reivich, 1996; Josephs et al, 2006; Nestor et al, 2003). Individuals with nfvPPA present with non-fluent speech with agrammatic language production (possibly with apraxia of speech) and impaired syntactic comprehension of complex sentences
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