Modulation of motor excitability by cortical optogenetic theta burst stimulation

Non-Faradaic optoelectrodes for safe electrical neuromodulation

Nanoscale optoelectrodes hold the potential to stimulate optically individual neurons and intracellular organelles, a challenge that demands both a high-density of photoelectron storage and significant charge injection. Here, we report that zinc porphyrin, commonly used in dye-sensitized solar cells, can be self-assembled into nanorods and then coated by TiO2. The J-aggregated zinc porphyrin array enables long-range exciton diffusion and allows for fast electron transfer into TiO2. The formation of TiO2(e-) attracts positive charges around the neuron membrane, contributing to the induction of action potentials. Far-field cranial irradiation of the motor cortex using a 670 nm laser or an 850 nm femtosecond laser can modulate local neuronal firing and trigger motor responses in the hind limb of mice. The pulsed photoelectrical stimulation of neurons in the subthalamic nucleus alleviates parkinsonian symptoms in mice, improving abnormal stepping and enhancing the activity of dopaminergic neurons. Our results suggest injectable nanoscopic optoelectrodes for optical neuromodulation with high efficiency and negligible side effects.

External magnetic field non-invasively stimulates spinal cord regeneration in rat via a magnetic-responsive aligned fibrin hydrogel

Magnetic stimulation is becoming an attractive approach to promote neuroprotection, neurogenesis, axonal regeneration, and functional recovery in both the central nervous system and peripheral nervous system disorders owing to its painless, non-invasive, and deep penetration characteristics. Here, a magnetic-responsive aligned fibrin hydrogel (MAFG) was developed to import and amplify the extrinsic magnetic field (MF) locally to stimulate spinal cord regeneration in combination with the beneficial topographical and biochemical cues of aligned fibrin hydrogel (AFG). Magnetic nanoparticles (MNPs) were embedded uniformly in AFG during electrospinning to endow it magnetic-responsive feature, with saturation magnetization of 21.79 emu g-1. It is found that the MNPs under the MF could enhance cell proliferation and neurotrophin secretion of PC12 cellsin vitro. The MAFG that was implanted into a rat with 2 mm complete transected spinal cord injury (SCI) effectively enhanced neural regeneration and angiogenesis in the lesion area, thus leading to significant recovery of motor function under the MF (MAFG@MF). This study suggests a new multimodal tissue engineering strategy based on multifunctional biomaterials that deliver multimodal regulatory signals with the integration of aligned topography, biochemical cues, and extrinsic MF stimulation for spinal cord regeneration following severe SCI.

Assessing the mechanisms of brain plasticity by transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is a non-invasive technique for focal brain stimulation based on electromagnetic induction where a fluctuating magnetic field induces a small intracranial electric current in the brain. For more than 35 years, TMS has shown promise in the diagnosis and treatment of neurological and psychiatric disorders in adults. In this review, we provide a brief introduction to the TMS technique with a focus on repetitive TMS (rTMS) protocols, particularly theta-burst stimulation (TBS), and relevant rTMS-derived metrics of brain plasticity. We then discuss the TMS-EEG technique, the use of neuronavigation in TMS, the neural substrate of TBS measures of plasticity, the inter- and intraindividual variability of those measures, effects of age and genetic factors on TBS aftereffects, and then summarize alterations of TMS-TBS measures of plasticity in major neurological and psychiatric disorders including autism spectrum disorder, schizophrenia, depression, traumatic brain injury, Alzheimer's disease, and diabetes. Finally, we discuss the translational studies of TMS-TBS measures of plasticity and their therapeutic implications.

Consolidation of motor sequence learning eliminates susceptibility of SMAproper to TMS: a combined rTMS and cTBS study

Earlier research suggested that after 210 practice trials, the supplementary motor area (SMA) is involved in executing all responses of familiar 6-key sequences in a discrete sequence production (DSP) task (Verwey, Lammens, and van Honk, 2002). This was indicated by slowing of each response 20 and 25 min after the SMA had been stimulated for 20 min using repetitive transcranial magnetic stimulation (rTMS). The present study used a similar approach to assess the effects of TMS to the more posterior SMAproper at the end of practice and also 24 h later. As expected stimulation of SMAproper with 20 min of 1 Hz rTMS and 40 s of continuous theta burst stimulation (cTBS) immediately after practice slowed sequence execution relative to a sham TMS condition, but stimulation on the day following practice did not cause slowing. This indicates that offline consolidation makes learning robust against stimulation of SMAproper. Execution of all responses in the sequence was disrupted 0, 20, and 40 min after rTMS, but after cTBS, this occurred only after 40 min. The results suggest that it is implicit sequence knowledge that is processed by the SMAproper and that consolidates.

Spinal cord representation of motor cortex plasticity reflects corticospinal tract LTP

Although it is well known that activity-dependent motor cortex (MCX) plasticity produces long-term potentiation (LTP) of local cortical circuits, leading to enhanced muscle function, the effects on the corticospinal projection to spinal neurons has not yet been thoroughly studied. Here, we investigate a spinal locus for corticospinal tract (CST) plasticity in anesthetized rats using multichannel recording of motor-evoked, intraspinal local field potentials (LFPs) at the sixth cervical spinal cord segment. We produced LTP by intermittent theta burst electrical stimulation (iTBS) of the wrist area of MCX. Approximately 3 min of MCX iTBS potentiated the monosynaptic excitatory LFP recorded within the CST termination field in the dorsal horn and intermediate zone for at least 15 min after stimulation. Ventrolaterally, in the spinal cord gray matter, which is outside the CST termination field in rats, iTBS potentiated an oligosynaptic negative LFP that was localized to the wrist muscle motor pool. Spinal LTP remained robust, despite pharmacological blockade of iTBS-induced LTP within MCX using MK801, showing that activity-dependent spinal plasticity can be induced without concurrent MCX LTP. Pyramidal tract iTBS, which preferentially activates the CST, also produced significant spinal LTP, indicating the capacity for plasticity at the CST-spinal interneuron synapse. Our findings show CST monosynaptic LTP in spinal interneurons and demonstrate that spinal premotor circuits are capable of further modifying descending MCX control signals in an activity-dependent manner.

Designing and pilot testing a novel high-definition transcranial burst electrostimulation device for neurorehabilitation

Objective.Non-invasive brain stimulation has been promoted to facilitate neuromodulation in treating neurological diseases. Recently, high-definition (HD) transcranial electrical stimulation and a novel electrical waveform combining a direct current (DC) and theta burst stimulation (TBS)-like protocol were proposed and demonstrated high potential to enhance neuroplastic effects in a more-efficient manner. In this study, we designed a novel HD transcranial burst electrostimulation device and to preliminarily examined its therapeutic potential in neurorehabilitation.Approach.A prototype of the transcranial burst electrostimulation device was developed, which can flexibly output a waveform that combined a DC and TBS-like protocol and can equally distribute the current into 4 × 1 HD electrical stimulation by automatic impedance adjustments. The safety and accuracy of the device were then validated in a series ofin vitroexperiments. Finally, a pilot clinical trial was conducted to assess its clinical safety and therapeutic potential on upper-extremity rehabilitation in six patients with chronic stroke, where patients received either active or sham HD transcranial burst electrostimulation combined with occupational therapy three times per week for four weeks.Main results.The prototype was tested, and it was found to comply with all safety requirements. The output parameters were accurate and met the clinical study needs. The pilot clinical study demonstrated that the active HD transcranial burst electrostimulation group had greater improvement in voluntary motor function and coordination of the upper extremity than the sham control group. Additionally, no severe adverse events were noted, but slight skin redness under the stimulus electrode immediately after stimulation was seen.Conclusions.The results demonstrated the feasibility of incorporating the HD electrical DC and TBS-like protocol in our device; and the novel neuromodulatory device produced positive neurorehabilitation outcomes in a safe fashion, which could be the basis for the future clinical implementation for treating neurological diseases.Trial registration:ClinicalTrials.gov Identifier: NCT04278105. Registered on 20 February 2020.

Neurostimulation for Stroke Rehabilitation

Neurological injuries such as strokes can lead to important loss in motor function. Thanks to neuronal plasticity, some of the lost functionality may be recovered over time. However, the recovery process is often slow and incomplete, despite the most effective conventional rehabilitation therapies. As we improve our understanding of the rules governing activity-dependent plasticity, neuromodulation interventions are being developed to harness neural plasticity to achieve faster and more complete recovery. Here, we review the principles underlying stimulation-driven plasticity as well as the most commonly used stimulation techniques and approaches. We argue that increased spatiotemporal precision is an important factor to improve the efficacy of neurostimulation and drive a more useful neuronal reorganization. Consequently, closed-loop systems and optogenetic stimulation hold theoretical promise as interventions to promote brain repair after stroke.

Effect of the combination of high-frequency repetitive magnetic stimulation and neurotropin on injured sciatic nerve regeneration in rats

Repetitive magnetic stimulation is effective for treating posttraumatic neuropathies following spinal or axonal injury. Neurotropin is a potential treatment for nerve injuries like demyelinating diseases. This study sought to observe the effects of high-frequency repetitive magnetic stimulation, neurotropin and their combined use in the treatment of peripheral nerve injury in 32 adult male Sprague-Dawley rats. To create a sciatic nerve injury model, a 10 mm-nerve segment of the left sciatic nerve was cut and rotated through 180° and each end restored continuously with interrupted sutures. The rats were randomly divided into four groups. The control group received only a reversed autograft in the left sciatic nerve with no treatment. In the high-frequency repetitive magnetic stimulation group, peripheral high-frequency repetitive magnetic stimulation treatment (20 Hz, 20 min/d) was delivered for 10 consecutive days after auto-grafting. In the neurotropin group, neurotropin therapy (0.96 NU/kg per day) was administrated for 10 consecutive days after surgery. In the combined group, the combination of peripheral high-frequency repetitive magnetic stimulation (20 Hz, 20 min/d) and neurotropin (0.96 NU/kg per day) was given for 10 consecutive days after the operation. The Basso-Beattie-Bresnahan locomotor rating scale was used to assess the behavioral recovery of the injured nerve. The sciatic functional index was used to evaluate the recovery of motor functions. Toluidine blue staining was performed to determine the number of myelinated fibers in the distal and proximal grafts. Immunohistochemistry staining was used to detect the length of axons marked by neurofilament 200. Our results reveal that the Basso-Beattie-Bresnahan locomotor rating scale scores, sciatic functional index, the number of myelinated fibers in distal and proximal grafts were higher and axon lengths were longer in the high-frequency repetitive magnetic stimulation, neurotropin and combined groups compared with the control group. These measures were not significantly different among the high-frequency repetitive magnetic stimulation, neurotropin and combined groups. Therefore, our results suggest that peripheral high-frequency repetitive magnetic stimulation or neurotropin can promote the repair of injured sciatic nerves, but their combined use seems to offer no significant advantage. This study was approved by the Animal Ethics Committee of the Affiliated Changzhou No. 2 People’s Hospital of Nanjing Medical University, China on December 23, 2014 (approval No. 2014keyan002-01).

Neuromodulatory Effects of Transcranial Direct Current Stimulation on Motor Excitability in Rats

Transcranial direct current stimulation (tDCS) is a noninvasive technique for modulating neural plasticity and is considered to have therapeutic potential in neurological disorders. For the purpose of translational neuroscience research, a suitable animal model can be ideal for providing a stable condition for identifying mechanisms that can help to explore therapeutic strategies. Here, we developed a tDCS protocol for modulating motor excitability in anesthetized rats. To examine the responses of tDCS-elicited plasticity, the motor evoked potential (MEP) and MEP input-output (IO) curve elicited by epidural motor cortical electrical stimulus were evaluated at baseline and after 30 min of anodal tDCS or cathodal tDCS. Furthermore, a paired-pulse cortical electrical stimulus was applied to assess changes in the inhibitory network by measuring long-interval intracortical inhibition (LICI) before and after tDCS. In the results, analogous to those observed in humans, the present study demonstrates long-term potentiation- (LTP-) and long-term depression- (LTD-) like plasticity can be induced by tDCS protocol in anesthetized rats. We found that the MEPs were significantly enhanced immediately after anodal tDCS at 0.1 mA and 0.8 mA and remained enhanced for 30 min. Similarly, MEPs were suppressed immediately after cathodal tDCS at 0.8 mA and lasted for 30 min. No effect was noted on the MEP magnitude under sham tDCS stimulation. Furthermore, the IO curve slope was elevated following anodal tDCS and presented a trend toward diminished slope after cathodal tDCS. No significant differences in the LICI ratio of pre- to post-tDCS were observed. These results indicated that developed tDCS schemes can produce consistent, rapid, and controllable electrophysiological changes in corticomotor excitability in rats. This newly developed tDCS animal model could be useful to further explore mechanical insights and may serve as a translational platform bridging human and animal studies, establishing new therapeutic strategies for neurological disorders.