Reproducibility of tDCS Results in a Randomized Trial: Failure to Replicate Findings of tDCS-Induced Enhancement of Verbal Fluency.

BACKGROUND: Transcranial direct current stimulation (tDCS) has been shown to enhance verbal productivity, but the finding and extent of enhancement vary across studies. Few attempts to replicate positive tDCS findings have been reported, suggesting the possibility of publication bias. OBJECTIVE: We aimed to replicate the tDCS methodology and findings of Cattaneo, Pisoni, and Papagno (2011, Neuroscience 183:64-70) in a new population sample. We hypothesized that our study of anodal tDCS would improve verbal fluency production similarly to the original study. METHODS: In our single-blind, sham-controlled crossover experiment, 14 healthy young adults were randomly assigned to receive 2 mA of anodal and sham stimulation to the Broca area in counterbalanced order before completing verbal fluency tasks. RESULTS: Participants tolerated the stimulation well. Despite closely mirroring the original study methods, we saw no main effect of stimulation condition: F1,13=0.002, P=0.97, letter fluency sham mean (standard deviation)=16.8 (2.3), letter fluency anodal=17.5 (3.8), category fluency sham=25.3 (5.4), or category fluency anodal=24.7 (5.2), η≤0.01. CONCLUSIONS: While tDCS may enhance cerebral functions in general, the lack of consistency between studies suggests either that this tDCS protocol does not affect verbal fluency or, at minimum, that tDCS may be more sensitive to experimental conditions than has been thought. Our findings also highlight the need for replication studies in brain stimulation research. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (Identifier NCT01602263).

Asymmetric prefrontal cortex activation in relation to markers of overeating in obese humans.

Dietary restraint is heavily influenced by affect, which has been independently related to asymmetrical activation in the prefrontal cortex (prefrontal asymmetry) in electroencephalograph (EEG) studies. In normal weight individuals, dietary restraint has been related to prefrontal asymmetry; however, this relationship was not mediated by affect. This study was designed to test the hypotheses that, in an overweight and obese sample, dietary restraint as well as binge eating, disinhibition, hunger, and appetitive responsivity would be related to prefrontal asymmetry independent of affect at the time of assessment. Resting EEG recordings and self-report measures of overeating and affect were collected in 28 overweight and obese adults. Linear regression analyses were used to predict prefrontal asymmetry from appetitive measures while controlling for affect. Cognitive restraint and binge eating were not associated with prefrontal asymmetry. However, disinhibition, hunger, and appetitive responsivity predicted left-, greater than right-, sided prefrontal cortex activation independent of affect. Findings in this study add to a growing literature implicating the prefrontal cortex in the cognitive control of dietary intake. Further research to specify the precise role of prefrontal asymmetry in the motivation toward, and cessation of, feeding in obese individuals is encouraged.

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

BACKGROUND: Working 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. METHODS: Twelve 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. RESULTS: Compared to sham stimulation, both left DLPFC anodal stimulation (t11 = 5.4, p = 0.0002) and right DLPFC anodal stimulation (t11 = 3.57, p = 0.004) improved overall WM performance. Left anodal stimulation (t11 = 3.9, p = 0.003) and right anodal stimulation (t11 = 2.7, p = 0.019) enhanced performances during stimulation. Enhancement transferred to an untrained task 50 min after right anodal stimulation (z11 = 2.263, p = 0.024). The tasks that showed the largest effects of active stimulation were spatial span backward (z11 = 2.39, p = 0.017) and BTA (z11 = 2.263, p = 0.024). CONCLUSIONS: In 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.

Brain activation in restrained and unrestrained eaters: an fMRI study.

Restraint theory has been used to model the process that produces binge eating. However, there is no satisfactory explanation for the tendency of restrained eaters (REs) to engage in counterregulatory eating, an ostensible analogue of binge eating. Using functional magnetic resonance imaging (fMRI), the authors investigated brain activation of normal weight REs (N = 9) and unrestrained eaters (UREs; N = 10) when fasted and fed and viewing pictures of highly and moderately palatable foods and neutral objects. When fasted and viewing highly palatable foods, UREs showed widespread bilateral activation in areas associated with hunger and motivation, whereas REs showed activation only in the cerebellum, an area previously implicated in low-level processing of appetitive stimuli. When fed and viewing high palatability foods, UREs showed activation in areas related to satiation and memory, whereas REs showed activation in areas implicated in desire, expectation of reward, and goal-defined behavior. These findings parallel those from behavioral research. The authors propose that the counterintuitive findings from preload studies and the present study are due to the fact that REs are less hungry than UREs when fasted and find palatable food more appealing than UREs when fed.