Hramov, A. | Search bioRxiv

bioRxiv2021

A BCI-based vibrotactile neurofeedback training improves motor cortical excitability during motor imagery

In this study, we address the issue of whether vibrotactile feedback can enhance the motor cortex excitability translated into the plastic changes in local cortical areas during motor imagery (MI) BCI-based training. For this purpose, we focused on two of the most notable neurophysiological effects of MI - the event-related-desynchronization (ERD) level and the increase in cortical excitability assessed with navigated transcranial magnetic stimulation (nTMS). For TMS navigation, we used individual high-resolution 3D brain MRIs. Ten BCI-naive and healthy adults participated in this study. The MI (rest or left/right hand imagery using Graz-BCI paradigm) tasks were performed separately in the presence and absence of feedback. To investigate how much the presence/absence of vibrotactile feedback in MI BCI-based training could contribute to the sensorimotor cortical activations, we compared the MEPs amplitude during MI after training with and without feedback. In addition, the ERD levels during MI BCI-based training were investigated. Our findings provide evidence that applying vibrotactile feedback during MI training leads to (i) an enhancement of the desynchronization level of mu-rhythm EEG patterns over the contralateral motor cortex area corresponding to the MI of the non-dominant hand; (ii) an increase in motor cortical excitability in hand muscle representation corresponding to a muscle engaged by the MI.

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bioRxiv2020

High-level stimulus template modulates neuronal response at the earlier processing stages

There is ample evidence that the brain matches sensory information with internal templates, but the details of this mechanism remain unknown. Here we consider the processing of repeatedly presented ambiguous stimuli with high ambiguity (HA) and low ambiguity (LA) and analyze how the processing depends on the ambiguity of the previous stimulus. On the behavioral level, we report a faster response to the HA stimulus after HA stimuli and a faster response to the LA stimulus after LA stimuli. The EEG analysis reveals that when HA stimulus follows LA stimuli, the neuronal activity in the sensory areas attenuates at the early processing stage but enhances during the latter stages. It evidences the hierarchical processing organization where low levels process the stimulus details, and high levels represent its interpretation. It also confirms that on low levels, HA and LA stimuli processing is similar due to their similar morphology. Therefore, the brain uses the LA stimulus template on the low levels to reduce the demands when processing the HA stimulus details. When LA stimulus follows HA stimuli, the attenuated response in the sensory regions accompanies high response in the frontal cortex. Namely, we observe high{theta} power in the medial frontal cortex and high {beta} power in the right inferior frontal cortex. It shows activation of the top-down cognitive control functions detecting the mismatch between the LA stimulus and the HA stimulus template and transfer this template to the low processing levels. Significance statementThe brain attenuates its response to repeatedly presented similar stimuli. When an ambiguous visual stimulus follows unambiguous stimuli with the same morphology, the neuronal response in sensory areas decreases at the early processing stage but enhances during the latter stages. It evidences hierarchical processing organization where low levels process the details, and high levels represent the interpretation. It also confirms that the brain uses templates on different levels to reduce the processing demands. When an unambiguous stimulus follows ambiguous stimuli, a low response in the sensory regions accompanies high response in the frontal cortex. It manifests activation of the top-down mechanisms to detect the mismatch between an unambiguous stimulus and an ambiguous template and transfer this template to low levels.

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