Thermal damage threshold of neurons during infrared stimulation

In infrared neural stimulation (INS), laser-evoked thermal transients are used to generate small depolarising currents in neurons. The laser exposure poses a moderate risk of thermal damage to the target neuron. Indeed, exogenous methods of neural stimulation often place the target neurons under stressful non-physiological conditions, which can hinder ordinary neuronal function and hasten cell death. Therefore, quantifying the exposure-dependent probability of neuronal damage is essential for identifying safe operating limits of INS and other interventions for therapeutic and prosthetic use. Using patch-clamp recordings in isolated spiral ganglion neurons, we describe a method for determining the dose-dependent damage probabilities of individual neurons in response to both acute and cumulative infrared exposure parameters based on changes in injection current. The results identify a local thermal damage threshold at approximately 60 ^°C, which is in keeping with previous literature and supports the claim that damage during INS is a purely thermal phenomenon. In principle this method can be applied to any potentially injurious stimuli, allowing for the calculation of a wide range of dose-dependent neural damage probabilities. Unlike histological analyses, the technique is well-suited to quantifying gradual neuronal damage, and critical threshold behaviour is not required.

Complementary and Alternative Treatments for Autism Spectrum Disorders: A Review for Parents and Clinicians

Complementary and alternative therapy (CAT) methods for children with autism spectrum disorders (ASD) are widespread in European countries and the Russian Federation; however, their efficacy and safety is not routinely considered by parents and clinicians when recommended or used. The current narrative review presents the most widely known CAT interventions for children with ASD synthesizing data from meta-analyses, systematic reviews, and randomized controlled trials obtained from the PubMed database based on the safety-efficacy model. We have found that, of the reviewed CATs, only the melatonin intervention can be considered safe and effective for children with ASD with comorbid sleep problems. The methods that were classified as safe but had inconclusive efficacy are recommended to be implemented only when they do not interfere with front line treatment for ASD, Applied Behavior Analysis (ABA). Methods with the lack of current evidence for the efficacy such as auditory integration therapies, bioacoustic correction, sensory integration therapy, micropolarization, animal assisted therapy, and dietary interventions should not be recommended as alternative treatments and can only be used as complimentary to ABA-based interventions. We advise against the use of chelation, hyperbaric oxygen therapy, and holding therapy due their documented harmful psychological and physical effects. When considering CAT for ASD we recommend parents and clinicians use the criteria suggested by Lofthouse and colleagues [59]: only the therapies that are safe, easy, cheap, and sensible can be recommended and used, as opposed to therapies that are risky, unrealistic, difficult, or expensive that should not be recommended or utilized.

Closed-Loop Neuromodulation in Physiological and Translational Research

Neuromodulation, the focused delivery of energy to neural tissue to affect neural or physiological processes, is a common method to study the physiology of the nervous system. It is also successfully used as treatment for disorders in which the nervous system is affected or implicated. Typically, neurostimulation is delivered in open-loop mode (i.e., according to a predetermined schedule and independently of the state of the organ or physiological system whose function is sought to be modulated). However, the physiology of the nervous system or the modulated organ can be dynamic, and the same stimulus may have different effects depending on the underlying state. As a result, open-loop stimulation may fail to restore the desired function or cause side effects. In such cases, a neuromodulation intervention may be preferable to be administered in closed-loop mode. In a closed-loop neuromodulation (CLN) system, stimulation is delivered when certain physiological states or conditions are met (responsive neurostimulation); the stimulation parameters can also be adjusted dynamically to optimize the effect of stimulation in real time (adaptive neurostimulation). In this review, the reasons and the conditions for using CLN are discussed, the basic components of a CLN system are described, and examples of CLN systems used in physiological and translational research are presented.

Novel magnetic stimulation methodology for low-current implantable medical devices

Recent studies highlight the ability of inductive architectures to deliver therapeutic magnetic stimuli to target tissues and to be embedded into small-scale intracorporeal medical devices. However, to date, current micro-scale biomagnetic devices require very high electric current excitations (usually exceeding 1 A) to ensure the delivery of efficient magnetic flux densities. This is a critical problem as advanced implantable devices demand self-powering, stand-alone and long-term operation. This work provides, for the first time, a novel small-scale magnetic stimulation system that requires up to 50-fold lower electric current excitations than required by relevant biomagnetic technology recently proposed. Computational models were developed to analyse the magnetic stimuli distributions and densities delivered to cellular tissues during in vitro experiments, such that the feasibility of this novel stimulator can be firstly evaluated on cell culture tests. The results demonstrate that this new stimulative technology is able to deliver osteogenic stimuli (0.1-7 mT range) by current excitations in the 0.06-4.3 mA range. Moreover, it allows coil designs with heights lower than 1 mm without significant loss of magnetic stimuli capability. Finally, suitable core diameters and stimulator-stimulator distances allow to define heterogeneity or quasi-homogeneity stimuli distributions. These results support the design of high-sophisticated biomagnetic devices for a wide range of therapeutic applications.

Transcranial Recording of Electrophysiological Neural Activity in the Rodent Brain in vivo Using Functional Photoacoustic Imaging of Near-Infrared Voltage-Sensitive Dye

Minimally-invasive monitoring of electrophysiological neural activities in real-time-that enables quantification of neural functions without a need for invasive craniotomy and the longer time constants of fMRI and PET-presents a very challenging yet significant task for neuroimaging. In this paper, we present in vivo functional PA (fPA) imaging of chemoconvulsant rat seizure model with intact scalp using a fluorescence quenching-based cyanine voltage-sensitive dye (VSD) characterized by a lipid vesicle model mimicking different levels of membrane potential variation. The framework also involves use of a near-infrared VSD delivered through the blood-brain barrier (BBB), opened by pharmacological modulation of adenosine receptor signaling. Our normalized time-frequency analysis presented in vivo VSD response in the seizure group significantly distinguishable from those of the control groups at sub-mm spatial resolution. Electroencephalogram (EEG) recording confirmed the changes of severity and frequency of brain activities, induced by chemoconvulsant seizures of the rat brain. The findings demonstrate that the near-infrared fPA VSD imaging is a promising tool for in vivo recording of brain activities through intact scalp, which would pave a way to its future translation in real time human brain imaging.

Computational model of the mechanoelectrophysiological coupling in axons with application to neuromodulation

For more than half a century, the action potential (AP) has been considered a purely electrical phenomenon. However, experimental observations of membrane deformations occurring during APs have revealed that this process also involves mechanical features. This discovery has recently fuelled a controversy on the real nature of APs: whether they are mechanical or electrical. In order to examine some of the modern hypotheses regarding APs, we propose here a coupled mechanoelectrophysiological membrane finite-element model for neuronal axons. The axon is modeled as an axisymmetric thin-wall cylindrical tube. The electrophysiology of the membrane is modeled using the classic Hodgkin-Huxley (H-H) equations for the Nodes of Ranvier or unmyelinated axons and the cable theory for the internodal regions, whereas the axonal mechanics is modeled by means of viscoelasticity theory. Membrane potential changes induce a strain gradient field via reverse flexoelectricity, whereas mechanical pulses result in an electrical self-polarization field following the direct flexoelectric effect, in turn influencing the membrane potential. Moreover, membrane deformation also alters the values of membrane capacitance and resistance in the H-H equation. These three effects serve as the fundamental coupling mechanisms between the APs and mechanical pulses in the model. A series of numerical studies was systematically conducted to investigate the consequences of interaction between the APs and mechanical waves on both myelinated and unmyelinated axons. Simulation results illustrate that the AP is always accompanied by an in-phase propagating membrane displacement of ≈1nm, whereas mechanical pulses with enough magnitude can also trigger APs. The model demonstrates that mechanical vibrations, such as the ones arising from ultrasound stimulations, can either annihilate or enhance axonal electrophysiology depending on their respective directionality and frequency. It also shows that frequency of pulse repetition can also enhance signal propagation independently of the amplitude of the signal. This result not only reconciles the mechanical and electrical natures of the APs but also provides an explanation for the experimentally observed mechanoelectrophysiological phenomena in axons, especially in the context of ultrasound neuromodulation.

Analysis of the Factors Related to the Effectiveness of Transcranial Current Stimulation in Upper Limb Motor Function Recovery after Stroke: a Systematic Review

Transcranial direct current stimulation is one of the non-invasive techniques whose main mechanism of action is based on its modulation of cortical excitability. The objective of this study is to analyze the variables (i.e, demographics, clinicals, stimulation parameters) that could influence into the responses during rehabilitation of the upper extremity in patients with stroke. Our systematic review has been performed by searching full-text articles published from January 2008 to December 2018 in Embase, Medline, PubMed and Cochrane Library databases. Studies with adult patients with ischemic or hemorrhagic stroke at any stage of evolution were included. We compared interventions with any type of transcranial direct current stimulation (anodal, cathodal or bihemispheric, also known as dual) regarding improvement of upper extremity motor function. We included 14 studies with 368 patients, of whom almost 89% have ischemic etiology and more than half are males. Most patients were considered subacute or chronic, while only two studies were selected with patients in the acute phase. Different methods of using transcranial direct current stimulation with several complementary therapies were identified, such as virtual reality, robot therapy, Occupational Therapy, Physiotherapy, Constraint Induced Movement Therapy or Peripheral Nerve Stimulation. In conclusion, there is not significant evidence due to heterogeneity of clinical data and therapies. Clinical studies with greater number of participants and protocols standardized could outline this assessment in future studies.

Biological and anatomical factors influencing interindividual variability to noninvasive brain stimulation of the primary motor cortex: a systematic review and meta-analysis

Noninvasive brain stimulation (NIBS) modifies corticospinal excitability (CSE) historically in a predictable manner dependent on stimulation parameters. Researchers, however, discuss high degrees of variability between individuals, either responding as expected or not responding as expected. The explanation for this interindividual variability remains unknown with suggested interplay between stimulation parameters and variations in biological, anatomical, and physiological factors. This systematic review and meta-analysis aimed to investigate the effect of variation in inherent factors within an individual (biological and anatomical factors) on CSE in response to NIBS of the primary motor cortex. Twenty-two studies were included investigating genetic variation (n=7), age variation (n=4), gender variation (n=7), and anatomical variation (n=5). The results indicate that variation in brain-derived neurotrophic factor genotypes may have an effect on CSE after NIBS. Variation between younger and older adults also affects CSE after NIBS. Variation between age-matched males and females does not affect CSE after NIBS, but variation across the menstrual cycle does. Variation between skull thickness and brain tissue morphology influences the electric field magnitude that ultimately reaches the primary motor cortex. These findings indicate that biological and anatomical variations may in part account for interindividual variability in CSE in response to NIBS of the primary motor cortex, categorizing individuals as responding as expected (responders) or not responding as expected (nonresponders).

Treatment of post-traumatic joint contracture in a rabbit model using pulsed, high intensity laser and ultrasound

Post-traumatic joint contracture induced by scar tissues following a surgery or injury can leave patients in a permanent state of pain and disability, which is difficult to resolve by current treatments. This randomized controlled trial examines the therapeutic effect of pulsed high-intensity laser (PHIL) and pulsed high-intensity focused ultrasound (PHIFU) for post-traumatic joint contracture due to arthrofibrosis. The peak power levels of both PHIL and PHIFU are much higher than that of laser or ultrasound currently used in physical therapy, while short pulses are utilized to prevent damage. To test the effectiveness of these treatments, a rabbit knee model for joint contracture was established. Twenty-one rabbits were split into four groups: untreated control (n  =  5), PHIL (n  =  5), PHIFU (n  =  5), and a PHIL  +  PHIFU group (n  =  6). Maximum extension of the surgically modified rabbit knee was compared to that of the contralateral control knee over the course of 16 weeks. The rabbits in the untreated control group maintained a relatively consistent level of joint contracture, while every rabbit in each of the treatment groups had improved range of motion, eventually leading to a restoration of normal joint extension. Average recovery time was 7.6  ±  1.5 weeks for the PHIL treatment group, 9.8  ±  3.7 weeks for the PHIFU group, and 8.0  ±  2.2 weeks for the combined treatment group. Histopathology demonstrated reduced density and accelerated resorption of scar tissues in the treated knee joints. This study provides evidence that both PHIL and PHIFU are effective in treating post-traumatic joint contracture in rabbits and warrant further investigation into the underlying mechanisms to optimize PHIL and PHIFU based treatments in a larger number of animals.

Effect of pulsed transcranial ultrasound stimulation at different number of tone-burst on cortico-muscular coupling

Background

Pulsed transcranial ultrasound stimulation (pTUS) can modulate the neuronal activity of motor cortex and elicit muscle contractions. Cortico-muscular coupling (CMC) can serve as a tool to identify interaction between the oscillatory activity of the motor cortex and effector muscle. This research aims to explore the neuromodulatory effect of low-intensity, pTUS with different number of tone burst to neural circuit of motor-control system by analyzing the coupling relationship between motor cortex and tail muscle in mouse. The motor cortex of mice was stimulated by pulsed transcranial ultrasound with different number of tone bursts (NTB = 100 150 200 250 300). The local field potentials (LFPs) in tail motor cortex and electromyography (EMG) in tail muscles were recorded simultaneously during pTUS. The change of integral coupling strength between cortex and muscle was evaluated by mutual information (MI). The directional information interaction between them were analyzed by transfer entropy (TE).

Results

Almost all of the MI and TE values were significantly increased by pTUS. The results of MI showed that the CMC was significantly enhanced with the increase of NTB. The TE results showed the coupling strength of CMC in descending direction (from LFPs to EMG) was significantly higher than that in ascending direction (from EMG to LFPs) after stimulation. Furthermore, compared to NTB = 100, the CMC in ascending direction were significantly enhanced when NTB = 250, 300, and CMC in descending direction were significantly enhanced when NTB = 200, 250, 300.

Conclusion

These results confirm that the CMC between motor cortex and the tail muscles in mouse could be altered by pTUS. And by increasing the NTB (i.e. sonication duration), the coupling strength within the cortico-muscular circuit could be increased, which might further influence the motor function of mice. It demonstrates that, using MI and TE method, the CMC could be used for quantitatively evaluating the effect of pTUS with different NTBs, which might provide a new insight into the effect of pTUS neuromodulation in motor cortex.

Imaging-Guided Dual-Target Neuromodulation of the Mouse Brain Using Array Ultrasound

Neuromodulation is an important method for investigating neural circuits and treating neurological and psychiatric disorders. Multiple-target neuromodulation is considered an advanced technology for the flexible optimization of modulation effects. However, traditional methods such as electrical and magnetic stimulations are not convenient for multiple-target applications due to their disadvantages of invasiveness or poor spatial resolution. Ultrasonic neuromodulation is a new noninvasive method that has gained wide attention in the field of neuroscience, and it is potentially able to support multiple-target stimulation by allocating multiple focal points in the brain using an array transducer. However, there are no reports in the literature of the efficacy of this technical concept, and an imaging tool for localizing the stimulation area for evaluating the neural effects in vivo has been lacking. In this study, we designed and fabricated a new system specifically for imaging-guided dual-target neuromodulation. The design of the array transducer and overall system is described in detail. The stimulation points were selectable on a B-mode image. In vivo experiments were carried out in mice, in which forelimbs shaking responses and electromyography outcomes were induced by changing the stimulation targets. The system could be a valuable tool for imaging-guided multiple-target stimulation in various neuroscience applications.

Engineered Axonal Tracts as "Living Electrodes" for Synaptic-Based Modulation of Neural Circuitry

Brain-computer interface and neuromodulation strategies relying on penetrating non-organic electrodes/optrodes are limited by an inflammatory foreign body response that ultimately diminishes performance. A novel "biohybrid" strategy is advanced, whereby living neurons, biomaterials, and microelectrode/optical technology are used together to provide a biologically-based vehicle to probe and modulate nervous-system activity. Microtissue engineering techniques are employed to create axon-based "living electrodes", which are columnar microstructures comprised of neuronal population(s) projecting long axonal tracts within the lumen of a hydrogel designed to chaperone delivery into the brain. Upon microinjection, the axonal segment penetrates to prescribed depth for synaptic integration with local host neurons, with the perikaryal segment remaining externalized below conforming electrical-optical arrays. In this paradigm, only the biological component ultimately remains in the brain, potentially attenuating a chronic foreign-body response. Axon-based living electrodes are constructed using multiple neuronal subtypes, each with differential capacity to stimulate, inhibit, and/or modulate neural circuitry based on specificity uniquely afforded by synaptic integration, yet ultimately computer controlled by optical/electrical components on the brain surface. Current efforts are assessing the efficacy of this biohybrid interface for targeted, synaptic-based neuromodulation, and the specificity, spatial density and long-term fidelity versus conventional microelectronic or optical substrates alone.

Three Research Strategies of Neuroscience and the Future of Legal Imaging Evidence

Neuroscientific imaging evidence (NIE) has become an integral part of the criminal justice system in the United States. However, in most legal cases, NIE is submitted and used only to mitigate penalties because the court does not recognize it as substantial evidence, considering its lack of reliability. Nevertheless, we here discuss how neuroscience is expected to improve the use of NIE in the legal system. For this purpose, we classified the efforts of neuroscientists into three research strategies: cognitive subtraction, the data-driven approach, and the brain-manipulation approach. Cognitive subtraction is outdated and problematic; consequently, the court deemed it to be an inadequate approach in terms of legal evidence in 2012. In contrast, the data-driven and brain manipulation approaches, which are state-of-the-art approaches, have overcome the limitations of cognitive subtraction. The data-driven approach brings data science into the field and is benefiting immensely from the development of research platforms that allow automatized collection, analysis, and sharing of data. This broadens the scale of imaging evidence. The brain-manipulation approach uses high-functioning tools that facilitate non-invasive and precise human brain manipulation. These two approaches are expected to have synergistic effects. Neuroscience has strived to improve the evidential reliability of NIE, with considerable success. With the support of cutting-edge technologies, and the progress of these approaches, the evidential status of NIE will be improved and NIE will become an increasingly important part of legal practice.

Development of Electrical Neural Stimulator Generating Periodic and Non-periodic Signals and Supporting Closed-loop Experimental System

It is essential to build a system to generate proper neural stimulus signals with adjusting parameters. We developed a stimulator with up to four channels for separate settings in periodic and non-periodic modes. The device can support a closed-loop experimental system which utilizes neural information in real time as a feedback for controlling stimuli. To confirm whether stimulating signals are properly produced and delivered inside the brain, two experiments with rats were conducted. We observed that the change of firing rates and the cross-power spectral density increased after stimulation which meant that electric signals were transferred well and that they affected the neurons' activities. Thus, it is expected that the stimulator can be utilized to produce appropriate stimulation signals in accordance with various objectives.

Neurobionics and the brain-computer interface: current applications and future horizons

The brain-computer interface (BCI) is an exciting advance in neuroscience and engineering. In a motor BCI, electrical recordings from the motor cortex of paralysed humans are decoded by a computer and used to drive robotic arms or to restore movement in a paralysed hand by stimulating the muscles in the forearm. Simultaneously integrating a BCI with the sensory cortex will further enhance dexterity and fine control. BCIs are also being developed to: provide ambulation for paraplegic patients through controlling robotic exoskeletons; restore vision in people with acquired blindness; detect and control epileptic seizures; and improve control of movement disorders and memory enhancement. High-fidelity connectivity with small groups of neurons requires microelectrode placement in the cerebral cortex. Electrodes placed on the cortical surface are less invasive but produce inferior fidelity. Scalp surface recording using electroencephalography is much less precise. BCI technology is still in an early phase of development and awaits further technical improvements and larger multicentre clinical trials before wider clinical application and impact on the care of people with disabilities. There are also many ethical challenges to explore as this technology evolves.

A Neurophysiological Perspective on a Preventive Treatment against Schizophrenia Using Transcranial Electric Stimulation of the Corticothalamic Pathway

Schizophrenia patients are waiting for a treatment free of detrimental effects. Psychotic disorders are devastating mental illnesses associated with dysfunctional brain networks. Ongoing brain network gamma frequency (30–80 Hz) oscillations, naturally implicated in integrative function, are excessively amplified during hallucinations, in at-risk mental states for psychosis and first-episode psychosis. So, gamma oscillations represent a bioelectrical marker for cerebral network disorders with prognostic and therapeutic potential. They accompany sensorimotor and cognitive deficits already present in prodromal schizophrenia. Abnormally amplified gamma oscillations are reproduced in the corticothalamic systems of healthy humans and rodents after a single systemic administration, at a psychotomimetic dose, of the glutamate N-methyl-d-aspartate receptor antagonist ketamine. These translational ketamine models of prodromal schizophrenia are thus promising to work out a preventive noninvasive treatment against first-episode psychosis and chronic schizophrenia. In the present essay, transcranial electric stimulation (TES) is considered an appropriate preventive therapeutic modality because it can influence cognitive performance and neural oscillations. Here, I highlight clinical and experimental findings showing that, together, the corticothalamic pathway, the thalamus, and the glutamatergic synaptic transmission form an etiopathophysiological backbone for schizophrenia and represent a potential therapeutic target for preventive TES of dysfunctional brain networks in at-risk mental state patients against psychotic disorders.

Network neuroscience

Despite substantial recent progress, our understanding of the principles and mechanisms underlying complex brain function and cognition remains incomplete. Network neuroscience proposes to tackle these enduring challenges. Approaching brain structure and function from an explicitly integrative perspective, network neuroscience pursues new ways to map, record, analyze and model the elements and interactions of neurobiological systems. Two parallel trends drive the approach: the availability of new empirical tools to create comprehensive maps and record dynamic patterns among molecules, neurons, brain areas and social systems; and the theoretical framework and computational tools of modern network science. The convergence of empirical and computational advances opens new frontiers of scientific inquiry, including network dynamics, manipulation and control of brain networks, and integration of network processes across spatiotemporal domains. We review emerging trends in network neuroscience and attempt to chart a path toward a better understanding of the brain as a multiscale networked system.

Non-invasive brain stimulation as a tool to study cerebellar-M1 interactions in humans

The recent development of non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS) has allowed the non-invasive assessment of cerebellar function in humans. Early studies showed that cerebellar activity, as reflected in the excitability of the dentate-thalamo-cortical pathway, can be assessed with paired stimulation of the cerebellum and the primary motor cortex (M1) (cerebellar inhibition of motor cortex, CBI). Following this, many attempts have been made, using techniques such as repetitive TMS and transcranial electrical stimulation (TES), to modulate the activity of the cerebellum and the dentate-thalamo-cortical output, and measure their impact on M1 activity. The present article reviews literature concerned with the impact of non-invasive stimulation of cerebellum on M1 measures of excitability and "plasticity" in both healthy and clinical populations. The main conclusion from the 27 reviewed articles is that the effects of cerebellar "plasticity" protocols on M1 activity are generally inconsistent. Nevertheless, two measurements showed relatively reproducible effects in healthy individuals: reduced response of M1 to sensorimotor "plasticity" (paired-associative stimulation, PAS) and reduced CBI following repetitive TMS and TES. We discuss current challenges, such as the low power of reviewed studies, variability in stimulation parameters employed and lack of understanding of physiological mechanisms underlying CBI.

Synapse engineering: A new level of brain modulation

Brain modulation is a powerful approach to study brain function in vivo. Tremendous progress had been made by controlling brain activity with different brain modulation tools. Synapse is the more fundamental functional unit of brain. In theory, synapse engineering could modulate brain function more precisely. However this had not been possible until recently. Our review provides a brief introduction of various brain modulation methods, and elaborates on a recently developed synapse-engineering tool. This technique allows modulation of specific synapses in vivo for the first time and has been used to clarify the causal role of synaptic plasticity in learning and memory. We also discuss its potentials for further development.