Modulation of physiological mirror activity with transcranial direct current stimulation over dorsal premotor cortex

Long-term effects of transcranial direct current stimulation in the treatment of autism spectrum disorder: A randomized controlled trial

AIM

To compare the efficacy of 0, 5, and 20 sessions of transcranial direct current stimulation (tDCS) for reducing symptoms of autism spectrum disorder (ASD).

METHOD

Thirty-six male children with ASD (mean age 2 years 3 months, SD 4 months, age range 1 years 6 months-2 years 11 months) were balanced and stratified by age, sex, and baseline severity of ASD, to: (1) a control group that received 20 sessions of sham tDCS; (2) a 5-session tDCS group (5-tDCS) that received 5 sessions of active tDCS followed by 15 sessions of sham tDCS; and (3) a 20-session tDCS group (20-tDCS) that received 20 sessions of active tDCS. All groups participated in the special school activity of Khon Kaen Special Education Center, Thailand. The primary outcome was autism severity as measured by the Childhood Autism Severity Scale.

RESULTS

The 5-tDCS and 20-tDCS groups evidenced greater reductions in autism severity than the control group at days 5 and 14, and months 6 and 12. There were no significant differences in the outcome between the 5- and 20-tDCS groups at any time point. Within-group analysis showed clinically meaningful improvements starting at month 6 for the participants in the control group, and clinically meaningful improvements starting on day 5 in both active tDCS groups, all of which were maintained to month 12.

INTERPRETATION

The 5- and 20-session tDCS seems to reduce autism severity faster than sham tDCS. These effects maintained at least for 1 year.

Behavioural and cerebral asymmetries of mirror movements are specific to rhythmic task and related to higher attentional and executive control

Mirror movements (MM) refer to the involuntary movements or contractions occurring in homologous muscles contralateral to the unilateral voluntary movements. This behavioural manifestation increases in elderly. In right-handed adults, some studies report asymmetry in MM production, with greater MM in the right dominant hand during voluntary movements of the left non-dominant hand than the opposite. However, other studies report contradictory results, suggesting that MM asymmetry could depend on the characteristics of the task. The present study investigates the behavioural asymmetry of MM and its associated cerebral correlates during a rhythmic task and a non-rhythmic task using low-force contractions (i.e., 25 % MVC). We determined the quantity and the intensity of MM using electromyography (EMG) and cerebral correlates through electroencephalography (EEG) in right-handed healthy young and middle-aged adults during unimanual rhythmic vs. non-rhythmic tasks. Overall, results revealed (1) behavioural asymmetry of MM specific to the rhythmic task and irrespective of age, (2) cerebral asymmetry of motor activations specific to the rhythmic task and irrespective of age and (3) greater attentional and executive activations in the rhythmic task compared to the non-rhythmic task. In line with our hypotheses, behavioural and cerebral motor asymmetries of MM seem to be specific to the rhythmic task. Results are discussed in terms of cognitive-motor interactions: greater attentional and executive control required in the rhythmic tasks could contribute to the increased occurrence of involuntary movements in both young and middle-aged adults.