Balanced bifrontal transcranial direct current stimulation enhances working memory in adults with high-functioning autism: a sham-controlled crossover study

Abstract

BackgroundWorking memory (WM) often is impaired in autism spectrum disorder (ASD). Such impairment may underlie core deficits in cognition and social functioning. Transcranial direct current stimulation (tDCS) has been shown to enhance WM in both healthy adults and clinical populations, but its efficacy in ASD is unknown. We predicted that bifrontal tDCS would improve WM performances of adults with high-functioning autism during active stimulation compared to sham stimulation and that such enhancement would generalize to an untrained task.MethodsTwelve adults with high-functioning ASD engaged in a battery of WM tasks that included backward spatial span, backward digit span, spatial n-back and letter n-back. While engaged, 40 min of 1.5 mA bifrontal stimulation was applied over the left and the right dorsolateral prefrontal cortices (DLPFC). Using a single-blind crossover design, each participant received left anodal/right cathodal stimulation, right anodal/left cathodal stimulation, or sham stimulation, in randomized counterbalanced order on three separate days. Following tDCS, participants again engaged in letter and spatial n-back tasks before taking the Brief Test of Attention (BTA). We used repeated-measures ANOVA to compare overall performance on the WM battery as measured by a composite of z-scores for all five measures. Post hoc ANOVAs, t tests, Friedman’s tests, and Wilcoxon signed-rank tests were used to measure the online and offline effects of tDCS and to assess performances on individual measures.ResultsCompared to sham stimulation, both left DLPFC anodal stimulation (t 11 = 5.4, p = 0.0002) and right DLPFC anodal stimulation (t 11 = 3.57, p = 0.004) improved overall WM performance. Left anodal stimulation (t 11 = 3.9, p = 0.003) and right anodal stimulation (t 11 = 2.7, p = 0.019) enhanced performances during stimulation. Enhancement transferred to an untrained task 50 min after right anodal stimulation (z 11 = 2.263, p = 0.024). The tasks that showed the largest effects of active stimulation were spatial span backward (z 11 = 2.39, p = 0.017) and BTA (z 11 = 2.263, p = 0.024).ConclusionsIn adults with high-functioning ASD, active bifrontal tDCS given during WM tasks appears to improve performance. TDCS benefits also transferred to an untrained task completed shortly after stimulation. These results suggest that tDCS can improve WM task performance and could reduce some core deficits of autism.Trial registration NCT01602263

Non-Invasive Brain Stimulation for Children with Autism Spectrum Disorders: A Short-Term Outcome Study

“…Of course, more research is needed to draw well-documented conclusions. Other authors have described improvements in particular aspects of adult ASD patients such as working memory and better syntax acquisition following single-dose anodal tDCS over the left and right dorsolateral prefrontal cortex (first case) or exclusively over the left dorsolateral prefrontal cortex [ 13 , 37 ] There were also positive changes in P300 ERP, but due to the low number of subjects in whom it was possible to carry out the passive oddball paradigm, we cannot make any comparison between the two different stimulating methods. Unfortunately, sample sizes for EEG-based connectivity analysis and ERP paradigm could not include all the patients, because, in close relationship with the complexity of the used method, when we carried out their initial electrophysiological evaluation (before intervention), not all recordings had a high enough quality for analysis.…”

Transcranial direct current stimulation in children with autism spectrum disorder: a systematic scoping review

“…The mechanisms of action consists in facilitating or inhibiting synaptic transmission, via increasing or decreasing the frequency of action potentials in endogenous neuronal firing, rather than generating action potentials per se (as in rTMS). In recent years, tDCS has been intensively investigated as a treatment for psychiatric disorders, including ASD …”

Effects of Non-invasive Neurostimulation on Autism Spectrum Disorder: A Systematic Review

“…Eight studies exclusively utilized tDCS as the therapeutic tool [ 33 - 40 ], 23 studies utilized solely rTMS as the therapeutic tool [ 41 - 63 ], and one study used both rTMS and tDCS to evaluate their therapeutic effects on ASD [ 64 ]. Six of the included articles were case-reports [ 35 , 40 , 43 , 47 , 49 , 53 ], nine were non-controlled trials [ 36 , 37 , 41 , 46 , 55 , 57 , 61 , 62 , 64 ], and the remaining 17 were controlled trials [ 33 , 34 , 38 , 39 , 42 , 44 , 45 , 48 , 50 - 52 , 54 , 56 , 58 - 60 , 63 ]. Eleven of the controlled studies used a sham group as the control [ 33 , 34 , 38 , 39 , 42 , 48 , 50 - 52 , 54 , 63 ] and the remaining six compared neuromodulated patients with waitlist controls.…”

“…Six of the included articles were case-reports [ 35 , 40 , 43 , 47 , 49 , 53 ], nine were non-controlled trials [ 36 , 37 , 41 , 46 , 55 , 57 , 61 , 62 , 64 ], and the remaining 17 were controlled trials [ 33 , 34 , 38 , 39 , 42 , 44 , 45 , 48 , 50 - 52 , 54 , 56 , 58 - 60 , 63 ]. Eleven of the controlled studies used a sham group as the control [ 33 , 34 , 38 , 39 , 42 , 48 , 50 - 52 , 54 , 63 ] and the remaining six compared neuromodulated patients with waitlist controls. Totally, 467 patients with ASD (mean age of 16.19) were treated by neuromodulation techniques in all included studies (383 patients received rTMS and 84 patients received tDCS).…”

“…Totally, 467 patients with ASD (mean age of 16.19) were treated by neuromodulation techniques in all included studies (383 patients received rTMS and 84 patients received tDCS). Nine studies recruited adult subjects with ASD [ 36 , 38 , 39 , 43 , 48 , 49 , 51 - 53 ], and the remaining studies focused on children and adolescents with ASD. Subjects covered almost the entire autistic spectrum including high function, low function and Asperger with and without verbal and cognitive impairments.…”