Objective. This study aimed to design and evaluate a high-speed online steady-state visually evoked potential (SSVEP)-based brain–computer interface (BCI) in an optical see-through (OST) augmented reality (AR) environment. Approach. An eight-class BCI was designed in an OST-AR headset which is wearable and allows users to see the user interface of the BCI and the device to be controlled in the same view field via the OST head-mounted display. The accuracies, information transfer rates (ITRs), and SSVEP signal characteristics of the AR-BCI were evaluated and compared with a computer screen-based BCI implemented with a laptop in offline and online cue-guided tasks. Then, the performance of the AR-BCI was evaluated in an online robotic arm control task. Main results. The offline results obtained during the cue-guided task performed with the AR-BCI showed maximum averaged ITRs of 65.50  ±  9.86 bits min−1 according to the extended canonical correlation analysis-based target identification method. The online cue-guided task achieved averaged ITRs of 65.03  ±  11.40 bits min−1. The online robotic arm control task achieved averaged ITRs of 45.57  ±  7.40 bits min−1. Compared with the screen-based BCI, some limitations of the AR environment impaired BCI performance and the quality of SSVEP signals. Significance. The results showed the potential for providing a high-performance brain–control interaction method by combining AR and BCI. This study could provide methodological guidelines for developing more wearable BCIs in OST-AR environments and will also encourage more interesting applications involving BCIs and AR techniques.

Objective. Transcranial temporally interfering stimulation (tTIS) is a noninvasive neuromodulation method, which has been reported to be able to affect the activity of small neuronal populations. To pinpoint smaller regions of the brain, a multi-channel tTIS strategy is proposed with larger numbers of electrodes and multiple sets of interfering fields. Approach. First, a computational model is adopted to prove the concept of multi-channel tTIS theoretically. Besides, animal experiments are implemented to activate motor cortex neurons in living mice and different frequencies are attempted. Finally, to better understand the envelope modulation properties of the two applied fields, tissue phantom measurement is conducted. Main results. The focality of six-channel (six electrode pairs) tTIS is increased by 46.7% and 70.2% respectively, compared with that of single-channel tTIS when maximal amplitude value drops by 3 dB and 6 dB in a numerical computation experiment. Furthermore, the focality of multi-channel tTIS is less sensitive to the electrode position. Confirmed with the myoelectricity signal, the movement frequencies of the contralateral forepaw are consistent with the corresponding difference frequencies. What is more, compared to single-channel (one electrode pair) tTIS with multi-channel (three electrode pairs) tTIS, the intensity of multi-channel tTIS stimulation is decreased by 28.5% on average in animal experiments. The c-fos-positive neurons of the target region are significantly higher than that of the non-target region. Results of the modulated envelope distribute around the whole region and its amplitude reaches a maximum at the interfering region. Significance. Both computational modeling and animal experiment validate the feasibility of the proposed multi-channel tTIS strategy and confirm that it can enhance focality and reduce scalp sensation.

Previous studies on the mechanisms of peripheral nerve injury (PNI) have mainly focused on the pathophysiological changes within a single injury site. However, recent studies have indicated that within the central nervous system, PNI can lead to changes in both injury sites and target organs at the cellular and molecular levels. Therefore, the basic mechanisms of PNI have not been comprehensively understood. Although electrical stimulation was found to promote axonal regeneration and functional rehabilitation after PNI, as well as to alleviate neuropathic pain, the specific mechanisms of successful PNI treatment are unclear. We summarize and discuss the basic mechanisms of PNI and of treatment via electrical stimulation. After PNI, activity in the central nervous system (spinal cord) is altered, which can limit regeneration of the damaged nerve. For example, cell apoptosis and synaptic stripping in the anterior horn of the spinal cord can reduce the speed of nerve regeneration. The pathological changes in the posterior horn of the spinal cord can modulate sensory abnormalities after PNI. This can be observed in cases of ectopic discharge of the dorsal root ganglion leading to increased pain signal transmission. The injured site of the peripheral nerve is also an important factor affecting post-PNI repair. After PNI, the proximal end of the injured site sends out axial buds to innervate both the skin and muscle at the injury site. A slow speed of axon regeneration leads to low nerve regeneration. Therefore, it can take a long time for the proximal nerve to reinnervate the skin and muscle at the injured site. From the perspective of target organs, long-term denervation can cause atrophy of the corresponding skeletal muscle, which leads to abnormal sensory perception and hyperalgesia, and finally, the loss of target organ function. The mechanisms underlying the use of electrical stimulation to treat PNI include the inhibition of synaptic stripping, addressing the excessive excitability of the dorsal root ganglion, alleviating neuropathic pain, improving neurological function, and accelerating nerve regeneration. Electrical stimulation of target organs can reduce the atrophy of denervated skeletal muscle and promote the recovery of sensory function. Findings from the included studies confirm that after PNI, a series of physiological and pathological changes occur in the spinal cord, injury site, and target organs, leading to dysfunction. Electrical stimulation may address the pathophysiological changes mentioned above, thus promoting nerve regeneration and ameliorating dysfunction.

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The total variation (TV) regularization method has been used to solve the ill-posed inverse problem of electrical resistance tomography (ERT), owing to its good ability to preserve edges. However, the quality of the reconstructed images, especially in the flat region, is often degraded by noise. To optimize the regularization term and the regularization factor according to the spatial feature and to improve the resolution of reconstructed images, a spatially adaptive total variation (SATV) regularization method is proposed. A kind of effective spatial feature indicator named difference curvature is used to identify which region is a flat or edge region. According to different spatial features, the SATV regularization method can automatically adjust both the regularization term and regularization factor. At edge regions, the regularization term is approximate to the TV functional to preserve the edges; in flat regions, it is approximate to the first-order Tikhonov (FOT) functional to make the solution stable. Meanwhile, the adaptive regularization factor determined by the spatial feature is used to constrain the regularization strength of the SATV regularization method for different regions. Besides, a numerical scheme is adopted for the implementation of the second derivatives of difference curvature to improve the numerical stability. Several reconstruction image metrics are used to quantitatively evaluate the performance of the reconstructed results. Both simulation and experimental results indicate that, compared with the TV (mean relative error 0.288, mean correlation coefficient 0.627) and FOT (mean relative error 0.295, mean correlation coefficient 0.638) regularization methods, the proposed SATV (mean relative error 0.259, mean correlation coefficient 0.738) regularization method can endure a relatively high level of noise and improve the resolution of reconstructed images.

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Object: In order to promote the functional recovery of median nerve rupture patients, this paper proposes an ultrasound-guided percutaneous nerve stimulation regimen based on finite element modeling. Method: First, according to anatomy feature, a multi-layer human forearm model is constructed. What’s more, taking current density and activate function as optimization indicators, the percutaneous nerve stimulation regimen is designed with finite element modeling, including electrical needle angel, distance and position. Finally, to test the performance of designed regimen, a total of 22 patients with median nerve rupture participate in the clinical randomized controlled trial. And the clinical treatment effect is evaluated with BMRC, grip strength, functional score of median nerve and DASH scores. Results: The designed percutaneous nerve stimulation regimen is that, parallel to each other, electrical needles are located at both ends of the injury nerve with a distance of 3 cm. Besides, clinical trial results show that, after treatment the difference in sensory function was statistically significant. In terms of motor function, the BMRC of motor and grip strength are improved in both groups after treatment and there are significant differences between groups. Besides the grip strength improvement of experimental group is 4 times higher than that of control group. On global function, the DASH scores are reduced by 29% with experimental group but only 8% with control group; functional score of median nerve improved by 24% in the experimental group and by 22% in the control group, but the difference between groups is statistically significant after treatment. Conclusion: Clinical trial results demonstrate that the designed percutaneous nerve stimulation regimen can significantly improve the sensory, motor and global function of median nerve rupture, which is a potential clinical treatment regimen. Trial registration: ChiCTR, ChiCTR2000030790. Registered14 march 2020, http://www.chictr.org.cn/ChiCTR2000030790

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