A brain–computer interface (BCI) establishes a direct communication pathway between the human brain and a computer. It has been widely used in medical diagnosis, rehabilitation, education, entertainment, and so on. Most research so far focuses on making BCIs more accurate and reliable, but much less attention has been paid to their privacy. Developing a commercial BCI system usually requires close collaborations among multiple organizations, e.g., hospitals, universities, and/or companies. Input data in BCIs, e.g., electroencephalogram (EEG), contain rich privacy information, and the developed machine learning model is usually proprietary. Data and model transmission among different parties may incur significant privacy threats, and hence, privacy protection in BCIs must be considered. Unfortunately, there does not exist any contemporary and comprehensive review on privacy-preserving BCIs. This article fills this gap, by describing potential privacy threats and protection strategies in BCIs. It also points out several challenges and future research directions in developing privacy-preserving BCIs.

Brain-machine interfaces (BMIs) provide a promising information channel between the biological brain and external devices and are applied in building brain-to-device control. Prior studies have explored the feasibility of establishing a brain-brain interface (BBI) across various brains via the combination of BMIs. However, using BBI to realize the efficient multidegree control of a living creature, such as a rat, to complete a navigation task in a complex environment has yet to be shown. In this study, we developed a BBI from the human brain to a rat implanted with microelectrodes (i.e., rat cyborg), which integrated electroencephalogram-based motor imagery and brain stimulation to realize human mind control of the rat’s continuous locomotion. Control instructions were transferred from continuous motor imagery decoding results with the proposed control models and were wirelessly sent to the rat cyborg through brain micro-electrical stimulation. The results showed that rat cyborgs could be smoothly and successfully navigated by the human mind to complete a navigation task in a complex maze. Our experiments indicated that the cooperation through transmitting multidimensional information between two brains by computer-assisted BBI is promising.

Closed-loop electrical stimulation is emerging as a promising neural modulation therapy for refractory epilepsy. However, the efficacy of electrical stimulation is less than optimal and the mechanism of seizure control is still unclear. In this work, we evaluated the acute seizure control efficacy of multi-site closed-loop stimulation (MSCLS) in a rodent model with a custom designed closed-loop neurostimulator. A total of 18 rats were injected with kainic-acid (KA) in CA3 of the left hippocampus to induce acute temporal lobe seizures. Instead of single target stimulation, four target sites in left hemisphere including CA1 and CA3 of the hippocampus, sub-thalamic nucleus (STN) and M1 region of motor cortex were selected for both recording and stimulation. A low-cost efficient multi-site seizure detection algorithm was implemented in the neurostimulator for MSCLS. With MSCLS treatment, the rats without status-epilepsy (SE) significantly reduced the seizure duration and the number of generalized seizures in each site. When considering the rats developed SE, MSCLS could also alleviate the seizure severity, but had little effect on seizure duration and seizure number. In conclusion, although the efficacy of MSCLS was still limited by stimulation sites, stimulation parameters, and seizure model chosen in this study, MSCLS itself would be a promising direction for refractory seizure treatment.

A thorough understanding of the spatiotemporal dynamics of blood supply and tissue viability is of great importance in stroke researches. In the current study, vascular and cellular responses to focal ischemia were monitored with optical coherence tomography on chronic rat photothrombotic stroke model. The 3D mapping of blood perfusion and cellular scattering were achieved by analyzing the temporal dynamics and depth attenuation of intrinsic backscattered light respectively. Optical coherence tomography revealed that vessels of different types presented various spatial and temporal dynamics during the photothrombotic occlusion and the later recovery period. The large distal middle cerebral arteries presented a spontaneous recanalization and the small pial microvessels presented a reperfusion along with newly appeared vessels from the peripheral into the core area. The cortical capillary perfusion presented a weak recovery. Compared to the male group, the female rats showed a faster vascular recovery after photothrombotic. Moreover, the dynamic changes of the cellular scattering signal showed a high spatial and temporal correlation with the cortical capillary perfusion. Combined with well-designed photothrombotic stroke model and chronic optical window, optical coherence tomography imaging offers a unique approach to improve the understanding of stroke procedure and evaluate the treatment outcomes.

Modulation of brain circuits by electrical stimulation has led to exciting and powerful therapies for diseases such as Parkinson's. Because human brain organization is based in mesoscale (millimeter-scale) functional nodes, having a method that can selectively target such nodes could enable more precise, functionally specific stimulation therapies. Infrared Neural Stimulation (INS) is an emerging stimulation technology that stimulates neural tissue via delivery of tiny heat pulses. In nonhuman primates, this optical method provides focal intensity-dependent stimulation of the brain without tissue damage. However, whether INS application to the human central nervous system (CNS) is similarly effective is unknown. To examine the effectiveness of INS on human cerebral cortex in intraoperative setting and to evaluate INS damage threshholds. Five epileptic subjects undergoing standard lobectomy for epilepsy consented to this study. Cortical response to INS was assessed by intrinsic signal optical imaging (OI, a method that detects changes in tissue reflectance due to neuronal activity). A custom integrated INS and OI system was developed specifically for short-duration INS and OI acquisition during surgical procedures. Single pulse trains of INS with intensities from 0.2 to 0.8 J/cm² were delivered to the somatosensory cortex and responses were recorded via optical imaging. Following tissue resection, histological analysis was conducted to evaluate damage threshholds. As assessed by OI, and similar to results in monkeys, INS induced responses in human cortex were highly focal (millimeter sized) and led to relative suppression of nearby cortical sites. Intensity dependence was observed at both stimulated and functionally connected sites. Histological analysis of INS-stimulated human cortical tissue provided damage threshold estimates. This is the first study demonstrating application of INS to human CNS and shows feasibility for stimulating single cortical nodes and associated sites and provided INS damage threshold estimates for cortical tissue. Our results suggest that INS is a promising tool for stimulation of functionally selective mesoscale circuits in the human brain, and may lead to advances in the future of precision medicine.