Objective. Transcranial magnetic stimulation (TMS) as a safe, noninvasive brain regulation technology has been gradually applied to clinical treatment. Traditional TMS devices do not adjust output based on real-time brain activity information when regulating the cerebral cortex, but the current activity information from the brain, especially the EEG phase, may affect the stimulation effect. It is necessary to calculate the synchronous EEG phase during TMS. Approach. In this study, a set of closed-loop TMS device a fast EEG phase prediction algorithm based on the AR model was designed to meet the demand. EEG data for twenty-seven healthy college students were collected to verify the accuracy of the algorithm. Main results. The calculation results showed that the prediction accuracy of the AR model algorithm is better than that of the conventional algorithm when the model order is lower, and the prediction accuracy will increase with improvements in the signal quality. Significance. When the experimental environment is good, the EEG data with a high SNR can be recorded, and when the order of the AR model is properly set, the prediction algorithm can make correct judgments most of the time and the stimulation pulse can be output when the EEG phase reaches a set value.
Objective: Mental workload is the result of the interactions between the demands of an operation task and the skills, behavior and perception of the performer. Working under a high mental workload can significantly affect an operator’s ability to choose optimal decisions. However, the effect of mental schema, which reflects the level of expertise of an operator, on mental workload remains unclear. Here, we propose a theoretical framework for describing how the evolution of mental schema affects mental workload from the perspective of cognitive processing. Approach: we recruited 51 students to participate in a 10-day simulated UAV flight training. The EEG PSD metrics were used to investigate the changes in neural responses caused by variations in the mental workload at different stages of mental schema evolution. Main results: It was found that mental schema evolution influenced the direction and change trends of the frontal theta PSD, parietal alpha PSD, and central beta PSD. Initially, before the mental schema was formed, only the frontal theta PSD increased with increasing task difficulty; when the mental schema was initially being developed, the frontal theta PSD and the parietal alpha PSD decreased with increasing task difficulty, while the central beta PSD increased with increasing task difficulty. Finally, as the mental schema gradually matured, the trend of the three indicators did not change with increasing task difficulty. However, differences in the frontal PSD became more pronounced across task difficulty levels, while differences in the parietal PSD narrowed. Significance: Our results describe the relationship between the EEG power spectrum and the mental workload of UAV operators as the mental schema evolved. This suggests that EEG indicators can not only provide more accurate measurements of mental workload but also provide insights into the development of an operator's skill level.
Objective: TMS-EEG technology has played an increasingly important role in the field of neuroscience, and closed loop TMS has also been gradually concerned. However, the characteristics of closed-loop TMS-EEG were few discussed. To study the dependence of EEG reactivity on cortical oscillation phase under TMS stimulation, we explored in detail the TMS-EEG characteristics induced by closed-loop TMS contingent on occipital alpha phase Approach: By collecting thirty healthy volunteers’ closed-loop TMS-EEG data, we verified the real-time accuracy of our closed-loop system and analyzed the inter-trial phase coherence (ITPC) value, the TMS-induced natural frequency, the N100 TMS-evoked potential (TEP) and the spatial characteristics of TMS-EEG data. Main results: The ITPC value of closed-loop TMS-EEG was higher than that of open loop TMS-EEG, suggesting that our research improves the repeatability of TMS-EEG experiments; the alpha power induced by 0-degree TMS was higher than that induced by 180-degree stimulation in the central region and parietal/occipital lobe; the N100 amplitude of 90-degree (3.85μV) stimulation was significantly higher than that of 270-degree (1.87μV) stimulation, and the latency of the N100 of the 90-degree stimulation (mean 95.01ms) was significantly less than that of the 270-degree stimulation (mean 113.94ms); the topographical distributions of the N45-P70-N100 potential were significantly affected by the O1 alpha phase at the moment of TMS. Significance: Our experimental results provided support for the dependence of EEG reactivity on cortical oscillation phase under TMS stimulation.
In the emerging field of neuroergonomics, mental workload assessment is one of the most important problems. Previous studies have made some progress on the relationship between task difficulties and mental workload, but how the mental schema, a reflection of the understanding and mastery degree of a task, affects mental workload has not been clearly discussed. There is emerging appreciation for the role of theta-gamma coupling (TGC) in high-level cognitive functions. Here, we attempt to further our understanding of how mental schema development and task difficulty had an impact on mental workload from the perspective of TGC. Specifically, the variation of TGC coupling strength and coupling pattern was estimated with different test orders and task difficulties performed by 51 students in a 10-day simulated quadrotor UAV flight training and test tasks. During the training, TGC increased with mental schema development. For the test tasks, TGC did not change with increasing task difficulty before the operator formed a mental schema but decreased with the increasing mental workload after the formation of the mental schema. Our results suggest that TGC was a robust indicator of mental schema development and could be biased by task difficulty. In conclusion, TGC can be a promising measure of mental workload, but only for experienced operators.
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