Sleep as a predictor of tDCS and language therapy outcomes

Abstract

Study objectives: To determine whether sleep at baseline (before therapy) predicted improvements in language following either language therapy alone or coupled with transcranial direct current stimulation (tDCS) in individuals with primary progressive aphasia (PPA).

Methods: Twenty-three participants with PPA (mean age 68.13 ± 6.21) received written naming/spelling therapy coupled with either anodal tDCS over the left inferior frontal gyrus (IFG) or sham condition in a crossover, sham-controlled, double-blind design (ClinicalTrials.gov identifier: NCT02606422). The outcome measure was percent of letters spelled correctly for trained and untrained words retrieved in a naming/spelling task. Given its particular importance as a sleep parameter in older adults, we calculated sleep efficiency (total sleep time/time in bed x100) based on subjective responses on the Pittsburgh Sleep Quality Index (PSQI). We grouped individuals based on a median split: high versus low sleep efficiency.

Results: Participants with high sleep efficiency benefited more from written naming/spelling therapy than participants with low sleep efficiency in learning therapy materials (trained words). There was no effect of sleep efficiency in generalization of therapy materials to untrained words. Among participants with high sleep efficiency, those who received tDCS benefitted more from therapy than those who received sham condition. There was no additional benefit from tDCS in participants with low sleep efficiency.

Conclusion: Sleep efficiency modified the effects of language therapy and tDCS on language in participants with PPA. These results suggest sleep is a determinant of neuromodulation effects.Clinical Trial: tDCS Intervention in Primary Progressive Aphasia https://clinicaltrials.gov/ct2/show/NCT02606422.

Keywords: PPA; language therapy; predictor; sleep; tDCS.

Figure 1.

CONSORT diagram.

Figure 2.

Study design model.

Figure 3.

Effects of sleep efficiency on language therapy outcomes. Blue represents high sleep efficiency. Red represents low sleep efficiency. The numbers in blue and red represent the number of participants with high versus low sleep efficiency. * p ≤0.05, ** p ≤0.01, *** p ≤0.005.

Figure 4.

Effects of sleep efficiency and tDCS on language therapy outcomes. Pink represents tDCS condition. Orange represents sham condition. The numbers in blue and red represent the number of participants in each condition. * p ≤0.05, ** p ≤0.01, *** p ≤0.005.