The Effect of TDCS on Inhibitory Control and Its Transfer Effect on Sustained Attention in Children with Autism Spectrum Disorder: An fNIRS Study

Background

Autism Spectrum Disorder (ASD) is a type of neurodevelopmental disorder characterized by social communication impairments, narrow interests, and repetitive behaviors. Many studies have found that individuals with ASD exhibit significant deficits in inhibitory control. This deficiency is particularly evident during childhood and adolescence and may stem from developmental disturbances in specific brain regions of these individuals. Therefore, addressing inhibitory control deficits in ASD children during their formative years is crucial for their future development in other capabilities.

Currently, interventions targeting the inhibitory control abilities of individuals with ASD primarily include behavioral training. However, the effectiveness of such single-method training is not ideal, often requiring longer intervention periods. Transcranial Direct Current Stimulation (TDCS), an emerging neuromodulation technique, has gained considerable attention in cognitive neuroscience and clinical fields in recent years due to its good safety and tolerability. The mechanism of TDCS involves applying a weak direct current to target neurons, thereby modulating neuronal membrane potentials and altering cortical excitability. Generally, anodal TDCS increases neuronal excitability, while cathodal TDCS decreases it. Studies have shown that TDCS can enhance the effectiveness of behavioral therapies.

Research Source

The study titled “The effect of tdcs on inhibitory control and its transfer effect on sustained attention in children with autism spectrum disorder: an fnirs study” was jointly completed by Liu Chen, Bang Du, Ke Li (co-first authors), Kaiyun Li (corresponding author), Tingting Hou, Fanlu Jia from the School of Education and Psychology, University of Jinan, China, and Li Li from the Special Education Center School of Boshan, Zibo, China. The article was published on April 30, 2024, in the journal Brain Stimulation.

Research Methods

Procedure

This study aimed to explore the effects of multiple TDCS sessions combined with inhibitory control training on the inhibitory control, near transfer effects (interference control), and far transfer effects (sustained attention, attention stability) in children with ASD. The study also employed functional Near-Infrared Spectroscopy (fNIRS) to measure changes in brain activity corresponding to these effects.

The experiment included 28 children with ASD, who were randomly assigned to either the real TDCS group or the sham TDCS group. The experimental group received 15 minutes of double-frontopolar TDCS at 1.5mA intensity daily for eight consecutive days, along with computerized go/no-go inhibitory control training tasks. Behavioral performance was assessed using various tasks, including the Dog/Monkey and Day/Night Stroop tasks (inhibitory control), Continuous Performance Test (CPT), and cancellation tests (sustained attention). Additionally, inhibitory control and sustained attention were evaluated in classroom and home settings.

fNIRS and TDCS Parameters

fNIRS recorded the changes in oxygenated hemoglobin (HbO) in participants’ brains during the computerized Day/Night Stroop task and Continuous Performance Test. TDCS parameters were set with an anode electrode placed at the left prefrontal region (F3) and a cathode electrode at the right prefrontal region (F4), with each stimulation session lasting 15 minutes at a 1.5mA intensity. The sham TDCS received the same duration as the real TDCS but only delivered brief current stimulation at the beginning and end, with no current during the experiment.

Data Processing

fNIRS data were analyzed using NIRSpark software, employing a General Linear Model (GLM) to process the hemoglobin concentration time-series data. Behavioral data were statistically analyzed using SPSS 25.0 software, conducting F-tests on the performance of different groups at various time points.

Research Results

Near Transfer Effect

Results from the near transfer tasks (Dog/Monkey and Day/Night Stroop tasks) showed that children with ASD who received simultaneous TDCS and go/no-go training exhibited significant improvement in inhibitory control (scores on the Dog/Monkey task, reaction time difference, and accuracy rate in the Day/Night Stroop task). This suggests that applying TDCS in the bilateral frontal regions effectively enhances inhibitory control abilities in children with ASD and transfers these effects to similar tasks.

Far Transfer Effect

In the far transfer tasks (Continuous Performance Test and cancellation test), children with ASD showed significant improvements in reaction time (RT) and attention stability (LISAS scores) after receiving simultaneous TDCS and inhibitory control training. This indicates that TDCS enhances sustained attention in children with ASD and that this effect can be observed across different types of tasks.

Physiological Response

fNIRS results demonstrated that children with ASD who received TDCS exhibited significant increases in oxygenated hemoglobin (HbO) in the right frontal pole area (FPA) and bilateral dorsolateral prefrontal cortex (DLPFC) during task completion. This signifies that TDCS not only improved behavioral performance but also enhanced the activity of relevant brain regions in children with ASD.

Classroom and Daily Life Performance

In classroom settings, children with ASD showed significant improvements in the frequency and total duration of sustained attention, with a significant reduction in the total duration of problem behaviors. However, no significant improvements in inhibitory control and sustained attention scores were observed in daily life settings.

Conclusion

This study found that multiple TDCS sessions combined with inhibitory control training significantly improved inhibitory control abilities and their transfer effects in children with ASD, with effects observable in classroom settings. However, significant improvements were not found in daily life settings.

Research Significance

This study suggests that TDCS combined with inhibitory control training is a promising, safe, and effective method for enhancing inhibitory control abilities and sustained attention in children with ASD. This method not only helps improve behavioral performance but also significantly enhances the activity of relevant brain regions. Future research can explore the long-term effects of TDCS with different parameters and training intensities and its applicability to a broader population. Furthermore, investigating changes in brain functional connectivity and networks can provide more evidence for understanding the neural mechanisms of ASD patients.

Future Research Directions

Although this study made significant contributions to the understanding of TDCS effects on ASD, it has some limitations. For instance, this study only included ASD children with an IQ above 60. Expanding the age and IQ range in future studies could improve the generalizability of the findings. Additionally, combining research on neural functional connectivity and changes within different brain regions can further elucidate the neural mechanisms of inhibitory control in ASD patients.