Contra-lateral desynchronized alpha oscillations linearly correlate with discrimination performance of tactile acuity

Objective. We used EEG to investigate cortical oscillatory activities during the tactile discrimination task and characterize the correlation between the EEG features and subjects' discrimination performance. Approach. Transcutaneous electrical nerve stimulation (TENS) was applied on two finger areas (thumb and index for healthy hands, thumb and index-projected areas for disabled hands) to evoke two kinds of tactile sensations (vibration and pressure) with three levels of intensities (low, medium and high). Four forearm amputees and thirteen able-bodied subjects were recruited to discriminate the specific intensity and area of the applied stimulation. We assessed the discrimination performance [discrimination accuracy rate (AR) and response time (RT)] to quantify the tactile acuity. During the stimulation, EEG signals were recorded and the evoked cortical oscillatory activities were analyzed. Linear regression analyses were performed between EEG features and tactile discrimination performance. Main results. Spectral analysis revealed that alpha ERD over somatosensory regions persisted the whole task period and was related to the sensory information processing. Alpha ERD over prefrontal regions was only found during the stimulation judgement period and might reflect advanced cognitive process. There was no linear correlation between prefrontal alpha ERD and tactile discrimination performance. While contralateral somatosensory alpha ERDs exhibited significantly negative correlations with ARs (r < -0.7, p < 0.05) and positive correlations with RTs (r > 0.65, p < 0.05). Specifically, the fitting results of higher alpha band (10-13 Hz) were superior to lower alpha band (8-10 Hz). Significance. Alpha ERD over contralateral somatosensory cortex could be used as an objective index for the evaluation of tactile acuity and might have the potential to be applied in sensory rehabilitation for amputees.