The role of the parietal lobe in task-irrelevant suppression during learning

Boosting proactive motor control via statistical learning with brain stimulation

Visual statistical regularities are nested patterns of information extracted to build a predictive internal model that guides attentional and motor decisions. Here, we sought to understand the contributions of the left and right frontoparietal areas in modulating the effect of this expectancy implementation on premotor preparation. Healthy subjects were asked to detect a high-contrast stimulus target presented simultaneously with a distractor, with preceding color cues indicating, trial by trial, the pairing between the response hand and the upcoming stimuli locations. Performance was measured at baseline, and immediately after a one-session training on the task. During the training target locations appeared 75% of the time to the right of the distractor, a regularity unnoticed by participants. The training session was paired with unilateral transcranial random noise stimulation (tRNS) or sham stimulation over the left or right frontoparietal cortex in a counterbalanced design. Results showed a significant response bias in reaction times after training, with faster responses for targets to the right of the distractor. This bias was enhanced by right, but not left, frontoparietal stimulation, highlighting a hemispheric asymmetry in proactive motor control. The implicit nature of learning, as evidenced by subjects' unawareness of probability distributions, underscores how proactive motor control quickly adapts to statistical regularities. Results suggest a dominant role for the right hemisphere in mediating attentional learning effects, with implications for understanding lateralized functions in adaptation of the motor control.

The effect of transcranial random noise stimulation (tRNS) over bilateral parietal cortex in visual cross-modal conflicts

In complex sensory environments, visual cross-modal conflicts often affect auditory performance. The inferior parietal cortex (IPC) is involved in processing visual conflicts, namely when cognitive control processes such as inhibitory control and working memory are required. This study investigated the effect of bilateral IPC tRNS on reducing visual cross-modal conflicts and explored whether its efficacy is dependent on the conflict type. Forty-four young adults were randomly allocated to receive either active tRNS (100-640 Hz, 2-mA for 20 min) or sham stimulation. Participants repeatedly performed tasks in three phases: before, during, and after stimulation. Results showed that tRNS significantly enhanced task accuracy across both semantic and non-semantic conflicts compared to sham, as well as a greater benefit in semantic conflict after stimulation. Correlation analyses indicated that individuals with lower baseline performance benefited more from active tRNS during stimulation in the non-semantic conflict task. There were no significant differences between groups in reaction time for each conflict type task. These findings provide important evidence for the use of tRNS in reducing visual cross-modal conflicts, particularly in suppressing semantic distractors, and highlight the critical role of bilateral IPC in modulating visual cross-modal conflicts.

Enhancing visual perceptual learning using transcranial electrical stimulation: Transcranial alternating current stimulation outperforms both transcranial direct current and random noise stimulation

Diverse strategies can be employed to enhance visual skills, including visual perceptual learning (VPL) and transcranial electrical stimulation (tES). Combining VPL and tES is a popular method that holds promise for producing significant improvements in visual acuity within a short time frame. However, there is still a lack of comprehensive evaluation regarding the effects of combining different types of tES and VPL on enhancing visual function, especially with a larger sample size. In the present study, we recruited four groups of subjects (26 subjects each) to learn an orientation discrimination task with five daily training sessions. During training, the occipital region of each subject was stimulated by one type of tES-anodal transcranial direct current stimulation (tDCS), alternating current stimulation (tACS) at 10 Hz, high-frequency random noise stimulation (tRNS), and sham tACS-while the subject performed the training task. We found that, compared with the sham stimulation, both the high-frequency tRNS and the 10-Hz tACS facilitated VPL efficiently in terms of learning rate and performance improvement, but there was little modulatory effect in the anodal tDCS condition. Remarkably, the 10-Hz tACS condition exhibited superior modulatory effects compared with the tRNS condition, demonstrating the strongest modulation among the most commonly used tES types for further enhancing vision when combined with VPL. Our results suggest that alpha oscillations play a vital role in VPL. Our study provides a practical guide for vision rehabilitation.