Suitability of the cingulate cortex for neural control.

Recent neuroprosthetic work has focused on the motor cortex as a source of voluntary control signals. However, the motor cortex can be damaged in upper motor neuron degenerative diseases such as primary lateral sclerosis and amyotrophic lateral sclerosis. The possibility exists that prefrontal areas may also be used in neuroprosthetic devices. Here, we report the use of the cingulate cortex in a neuroprosthetic model. Seven rats were able to significantly modulate spiking activity in the cingulate cortex in order to receive reward. Furthermore, experiments with single neurons provide evidence that the cingulate cortex neuronal modulation is highly flexible and thus useful for a neuroprosthetic device.     

Somatotopy of the motor cortex after long-term spinal cord injuryor amputation

Certain brain-computer interface (BCI) methods use intrinsic signals from the motor cortex to control neuroprosthetic devices. The organization of the motor pathways in those populations likely to use neuroprosthetic devices, therefore, needs to be determined; there is evidence that following disease or injury the representation of the body in the motor cortex may change. In this study, functional MRI measures of somatotopy following spinal cord injury (SCI) showed evidence of changes in limb representations in the motor cortex. Subjects with chronic SCI had unusual cortical patterns of activity when attempting to move limbs below their injury; amputees showed a more normal somatotopy. The functional reorganization may affect optimal implanted electrode placements for invasive BCI methods for these different populations     

Restoring lost cognitive function.

A prosthetic device that functions in a biomimetic manner to replace information transmission between cortical brain regions is considered. In such a prosthesis, damaged CNS neurons is replaced with a biomimetic system comprised of silicon neurons. The replacement silicon neurons would have functional properties specific to those of the damaged neurons and would both receive as inputs and send as outputs electrical activity to regions of the brain with which the damaged region previously communicated. Thus, the class of prosthesis proposed is one that would replace the computational function of the damaged brain and restore the transmission of that computational result to other regions of the nervous system.     

Feasibility of Neural Stimulation With Floating-Light-Activated Microelectrical Stimulators

Neural microstimulation is becoming a powerful tool for the restoration of impaired functions in the central nervous system. Microelectrode arrays with fine wire interconnects have traditionally been used in the development of these neural prosthetic devices. However, these interconnects are usually the most vulnerable part of the neuroprosthetic implant that can eventually cause the device to fail. In this paper, we investigate the feasibility of floating-light-activated microelectrical stimulators (FLAMES) for wireless neural stimulation. A computer model was developed to simulate the micro stimulators for typical requirements of neural activation in the human white and gray matters. First, the photon densities due to a circular laser beam were simulated in the neural tissue at near-infrared (NIR) wavelengths. Temperature elevation in the tissue was calculated and the laser power was retrospectively adjusted to 325 and 250 mW/cm(2) in the gray and white matters, respectively, to limit ΔT to 0.5 °C. Total device area of the FLAMES increased with all parameters considered but decreased with the output voltage. We conclude that the number of series photodiodes in the device can be used as a free parameter to minimize the device size. The results suggest that floating, optically activated stimulators are feasible at submillimeter sizes for the activation of the brain cortex or the spinal cord.     

Chronic intracortical microstimulation (ICMS) of cat sensory cortex using the Utah Intracortical Electrode Array.

In an effort to assess the safety and efficacy of focal intracortical microstimulation (ICMS) of cerebral cortex with an array of penetrating electrodes as might be applied to a neuroprosthetic device to aid the deaf or blind, we have chronically implanted three trained cats in primary auditory cortex with the 100-electrode Utah Intracortical Electrode Array (UIEA). Eleven of the 100 electrodes were hard-wired to a percutaneous connector for chronic access. Prior to implant, cats were trained to "lever-press" in response to pure tone auditory stimulation. After implant, this behavior was transferred to "lever-presses" in response to current injections via single electrodes of the implanted arrays. Psychometric function curves relating injected charge level to the probability of response were obtained for stimulation of 22 separate electrodes in the three implanted cats. The average threshold charge/phase required for electrical stimulus detection in each cat was, 8.5, 8.6, and 11.6 nC/phase respectively, with a maximum charge/phase of 26 nC/phase and a minimum of 1.5 nC/phase thresholds were tracked for varying time intervals, and seven electrodes from two cats were tracked for up to 100 days. Electrodes were stimulated for no more than a few minutes each day. Neural recordings taken from the same electrodes before and after multiple electrical stimulation sessions were very similar in signal/noise ratio and in the number of recordable units, suggesting that the range of electrical stimulation levels used did not damage neurons in the vicinity of the electrodes. Although a few early implants failed, we conclude that ICMS of cerebral cortex to evoke a behavioral response can be achieved with the penetrating UIEA. Further experiments in support of a sensory cortical prosthesis based on ICMS are warranted.     

Measurement of propagation velocity driven by current microstimulation in the mouse auditory cortex in vitro

All sensory cortical areas, including the auditory cortex, are considered to be wired according to the same general laminar structure schema, commonly referred to as the canonical model of cortical circuitry. The auditory cortex in vivo , however, is functionally anisotropic; the functional organization along the tonotopic axis is qualitatively different from that orthogonal to this axis. In the current study, we examined whether the functional anisotropy of the auditory cortex observed in vivo is reflected in propagation activity driven by electric stimulation in the local microcircuitry in vitro . Using in vitro preparations of coronal and angled horizontal brain slices, we directly investigated their isotropic versus anisotropic properties using microstimulation and multi‐site recording with a multielectrode array substrate. Our results clearly demonstrated the isotropic properties of the circuits in slice preparations of the auditory cortex. Additionally, we found that driven by stimulation current in layer 4, the horizontal velocity of activity propagation in layer 2/3 was faster than the vertical velocity from layer 4 to layer 2/3 and the horizontal velocity in layer 4. On the basis of these results, we discuss the local network and its possible functions in the auditory cortex. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

The relationship between electrical stimulus and joint torque: a dynamic model.

The knowledge of the behavior of electrically activated muscles is an important requisite for the development of functional electrical stimulation (FES) systems to restore mobility to persons with paralysis. The aim of this work was to develop a model capable of relating electrical parameters to dynamic joint torque for FES applications. The knee extensor muscles, stimulated using surface electrodes, were used for the experimental preparation. Both healthy subjects and people with paraplegia were tested. The dynamics of the lower limb were represented by a nonlinear second order model, which took account of the gravitational and inertial characteristics of the anatomical segments as well as the damping and stiffness properties of the knee joint. The viscous-elastic parameters of the system were identified experimentally through free pendular movements of the leg. Leg movements induced by quadriceps stimulation were acquired too, using a motion analysis system. Results showed that, for the considered experimental conditions, a simple one-pole transfer function is able to model the relationship between stimulus pulsewidth (PW) and active muscle torque. The time constant of the pole was found to depend on the stimulus pattern (ramp or step) while gain was directly dependent on stimulation frequency.     

Statistical Long-Term Correlations in Dissociated Cortical Neuron Recordings

The study of nonlinear long-term correlations in neuronal signals is a central topic for advanced neural signal processing. In particular, the existence of long-term correlations in neural signals recorded via multielectrode array (MEA) could provide interesting information about changes in interneuron communications. In this study we propose a new method for long-term correlation analysis of neuronal burst activity based on the periodogram $alpha$ slope estimation of the MEA signal. We applied our method to recordings taken from cultured networks of dissociated rat cortical neurons. We show the effectiveness of the method in analyzing the activity changes as well as the temporal dynamics that take place during the development of such cultures. Results demonstrate that the $alpha$ parameter is able to divide the network development in three well-defined stages, showing pronounced variations in the long-term correlation among bursts.      

Role of afferent input in motor organization in health and disease.

In the healthy brain, there is a highly organized relationship between sensory input from one part of the body and the motor cortical output to muscles acting on that same part. This work investigates whether a change in purely sensory input have an impact on the organization of the motor cortex. In a previous study transcranial magnetic stimulation (TMS) techniques were used to probe the excitability of the motor cortex hand area. A measurement of the amplitude of the motor evoked potential (MEP) to standard single-pulse stimuli given through a focal coil was done. The excitability of two types of intracortical inhibition, SICI and LICI, was also measured using a paired-pulse TMS design. SICI is thought to be sensitive to activity in GABA/sub A/-ergic systems, whereas LICI may involve activation of GABA/sub B/-ergic systems. The work of other researchers has shown that these measures could be influenced by sensory input. Yet, all of them used electrical stimulation of peripheral nerve rather than a natural input. In order to investigate a more natural input, we delivered very low-amplitude vibration to the muscle belly of individual hand muscles through a small probe. This work explores the pattern of effects on MEPs and SICI in three different intrinsic hand muscles after vibration of each muscle in turn. In addition, the study also tested LICI with a paired-pulse TMS paradigm. In conclusion, it was seen that a period of sensory input, with or without the subject's attention, produces a specific pattern of sensory-motor reorganization in human cortex which develops quickly (after only 15 minutes) and lasts for at least 30 min. Since this produces changes in the motor cortex without requiring any active motor output, it may be a promising tool for neurorehabilitation even in patients who are unable to perform the active movements conventionally employed in therapy.     

The Neurochip BCI: towards a neural prosthesis for upper limb function.

The Neurochip BCI is an autonomously operating interface between an implanted computer chip and recording and stimulating electrodes in the nervous system. By converting neural activity recorded in one brain area into electrical stimuli delivered to another site, the Neurochip BCI could form the basis for a simple, direct neural prosthetic. In tests with normal, unrestrained monkeys, the Neurochip continuously recorded activity of single neurons in primary motor cortex for several weeks at a time. Cortical activity was correlated with simultaneously-recorded electromyogram (EMG) activity from arm muscles during free behavior. In separate experiments with anesthetized monkeys, we found that microstimulation of the cervical spinal cord evoked movements of the arm and hand, often involving multiple muscles synergies. These observations suggest that spinal microstimulation controlled by cortical neurons could help compensate for damaged corticospinal projections.     

Functional near infrared spectroscopy study of age-related difference in cortical activation patterns during cycling with speed feedback

Functional decline of lower-limb affects the ability of locomotion and the age-related brain differences have been elucidated among the elderly. Cycling exercise is a common training program for restoring motor function in the deconditioned elderly or stroke patients. The provision of speed feedback has been commonly suggested to clinical therapists for facilitating learning of controlled cycling performance and maintaining motivation in training programs with elderly participants. However, the cortical control of pedaling movements and the effect of external feedback remain poorly understanding. This study investigated the regional cortical activities detected by functional near infrared spectroscopy (fNIRS) in 12 healthy young and 13 healthy elderly subjects under conditions of cycling without-(free cycling) and with feedback (target cycling). The elderly exhibited predominant activation of the sensorimotor cortex during free cycling similar to young subjects but with poorer cycling performance. The cycling performance improved in both groups, and the elderly showed increased brain activities of the supplementary motor area and premotor cortex under target cycling condition. These findings demonstrated age-related changes in the cortical control in processing external feedback and pedaling movements. Use of fNIRS to evaluate brain activation patterns after training may facilitate brain-based design of tailored therapeutic rehabilitation strategies.     

Phase-dependent effects of spinal cord stimulation on locomotor activity.

This paper examines how electrical stimulation of the spinal cord can modulate the output of the central pattern generator (CPG) for locomotion. Application of discrete current pulses to a single spinal segment was shown to affect multiple parameters of an ongoing locomotor pattern in an in vitro spinal cord. For any given stimulus, the effects on frequency, duration, and symmetry of locomotor output were strongly dependent on the phase at which stimulation was applied within the CPG cycle. Additionally, most stimuli had an immediate impact and evinced no effects on subsequent cycles. The most dramatic changes were seen when stimulation was applied during motor bursting: stimuli applied to the ipsilateral spinal hemicord increased the burst length, while stimuli applied to the contralateral spinal hemicord decreased the burst length. Smaller changes were observed when stimulating during delays between motor bursts. Thus, phasic stimulation was shown to influence the behavior of the CPG and spinal locomotion circuits on a cycle-by-cycle basis. This work represents the first step toward our ultimate goal of developing a neuroprosthetic device to restore locomotion after a severe spinal cord injury.     

Virtual active touch using randomly patterned intracortical microstimulation

Intracortical microstimulation (ICMS) has promise as a means for delivering somatosensory feedback in neuroprosthetic systems. Various tactile sensations could be encoded by temporal, spatial, or spatiotemporal patterns of ICMS. However, the applicability of temporal patterns of ICMS to artificial tactile sensation during active exploration is unknown, as is the minimum discriminable difference between temporally modulated ICMS patterns. We trained rhesus monkeys in an active exploration task in which they discriminated periodic pulse-trains of ICMS (200 Hz bursts at a 10 Hz secondary frequency) from pulse trains with the same average pulse rate, but distorted periodicity (200 Hz bursts at a variable instantaneous secondary frequency). The statistics of the aperiodic pulse trains were drawn from a gamma distribution with mean inter-burst intervals equal to those of the periodic pulse trains. The monkeys distinguished periodic pulse trains from aperiodic pulse trains with coefficients of variation 0.25 or greater. Reconstruction of movement kinematics, extracted from the activity of neuronal populations recorded in the sensorimotor cortex concurrent with the delivery of ICMS feedback, improved when the recording intervals affected by ICMS artifacts were removed from analysis. These results add to the growing evidence that temporally patterned ICMS can be used to simulate a tactile sense for neuroprosthetic devices.     

基于MR和PET成像的轻度阿尔茨海默病分类方法

提出了一种能准确分割与阿尔茨海默病相关的脑部区域的方法。首先,制作了最符合样本的模板;其次,在MR特征采集上,充分利用图像配准产生的形变场信息;接着,在处理PET图像时,先将其互配准到同一个体的MR图像上;最后,将提取出的各脑区特征用支持向量机分类。用全脑分类正确率为MR：0．8736,PET：0．9195,0．3MR＋0．7PET：0．8621;灰质正确率为MR：0．8736,PET：0．9195,0．3MR＋0．7PET：0．8621;双样本t检验正确率为MR：0．8391,PET：0．9195,0．3MR＋0．7PET：0．8966。在用大脑皮层分区进行分类时,MR的内嗅区皮质正确率最高（0．8391）,PET的楔前叶正确率最高（0．9195）,0．3MR＋0．7PET的内嗅区皮质正确率最高（0．9425）。试验结果表明该方法与现有方法相比,能更准确的区分轻度AD患者和正常老人,有助于AD疾病的预防及早期诊断。     

Kinetic Trajectory Decoding Using Motor Cortical Ensembles

Although most brain–machine interface (BMI) studies have focused on decoding kinematic parameters of motion such as hand position and velocity, it is known that motor cortical activity also correlates with kinetic signals, including active hand force and joint torque. Here, we attempted to reconstruct torque trajectories of the shoulder and elbow joints from the activity of simultaneously recorded units in primary motor cortex (MI) as monkeys (Macaca Mulatta) made reaching movements in the horizontal plane. Using a linear filter decoding approach that considers the history of neuronal activity up to one second in the past, we found torque reconstruction performance nearly equal to that of Cartesian hand position and velocity, despite the considerably greater bandwidth of the torque signals. Moreover, the addition of delayed position and velocity feedback to the torque decoder substantially improved the torque reconstructions, suggesting that simple limb-state feedback may be useful to optimize BMI performance. These results may be relevant for BMI applications that require controlling devices with inherent, physical dynamics or applying forces to the environment.      

Walking with WALK!

The goal of this paper is to design WALK! a cooperative, patient-driven neuroprosthetic (NP) system. In implementing sensor-supervised events to switch to subsequent medical prosthetics, NP users were able to actively control the timing of their movements. Performance and usability of WALK! was appreciated by the NP users because they were able to perceive the activities of the NP to actually support their movements. The future of NP will be based on fully implanted systems. To justify the high efforts, risks, and costs of an implantation to both NP users and health care providers, NPs have to offer true functionality that can only be achieved by a sophisticated and yet practicable control system. We believe that the WALK! control approach presented in this article can be considered a valuable contribution to the development of future neuroprosthetic systems for locomotion.     

Motor cortical reorganization is present after a single attack of multiple sclerosis devoid of cortico-spinal dysfunction

Object

While occurrence of motor cortical reorganization has been clearly demonstrated in patients with multiple sclerosis (MS), it is not yet clear whether this cortical reorganization constitutes a response to cortico-spinal lesions or to more diffuse damage affecting the neuronal network involved in motor act preparation, or both. We proposed to investigate the changes in the activation pattern during a simple motor task devoid of cortico-spinal dysfunction occurring in patients with clinically isolated syndrome (CIS) suggestive of MS.

Materials and methods

Among 15 right-handed CIS patients, we selected eight patients with a preserved central motor pathway established by motor evoked potentials. Ten healthy right-handed gender- and age-matched volunteers were also included. After morphological MRI, subjects performed calibrated conjugated finger flexion and extension movements during fMRI acquision.

Results

In CIS patients, simple movements of the non-dominant hand induced recruitment of the anterior cingulate cortex (BA32) usually involved in complex motor movements. This reorganization was correlated with the diffuse brain tissue damage (brain T ₂ lesion load).

Conclusion

These results suggest that at least part of the cortical reorganization observed during very simple tasks in the earliest stage of MS occurs whether or not the efferent pathways are intact.     

Work toward real-time control of a cortical neural prothesis.

Implantable devices that interact directly with the human nervous system have been gaining acceptance in the field of medicine since the 1960's. More recently, as is noted by the FDA approval of a deep brain stimulator for movement disorders, interest has shifted toward direct communication with the central nervous system (CNS). Deep brain stimulation (DBS) can have a remarkable effect on the lives of those with certain types of disabilities such as Parkinson's disease, Essential Tremor, and dystonia. To correct for many of the motor impairments not treatable by DBS (e.g. quadriplegia), it would be desirable to extract from the CNS a control signal for movement. A direct interface with motor cortical neurons could provide an optimal signal for restoring movement. In order to accomplish this, a real-time conversion of simultaneously recorded neural activity to an online command for movement is required. A system has been established to isolate the cellular activity of a group of motor neurons and interpret their movement-related information with a minimal delay. The real-time interpretation of cortical activity on a millisecond time scale provides an integral first step in the development of a direct brain-computer interface (BCI).     

Neural Decoding of Hand Motion Using a Linear State-Space Model With Hidden States

The Kalman filter has been proposed as a model to decode neural activity measured from the motor cortex in order to obtain real-time estimates of hand motion in behavioral neurophysiological experiments. However, currently used linear state-space models underlying the Kalman filter do not take into account other behavioral states such as muscular activity or the subject's level of attention, which are often unobservable during experiments but may play important roles in characterizing neural controlled hand movement. To address this issue, we depict these unknown states as one multidimensional hidden state in the linear state-space framework. This new model assumes that the observed neural firing rate is directly related to this hidden state. The dynamics of the hand state are also allowed to impact the dynamics of the hidden state, and vice versa. The parameters in the model can be identified by a conventional expectation-maximization algorithm. Since this model still uses the linear Gaussian framework, hand-state decoding can be performed by the efficient Kalman filter algorithm. Experimental results show that this new model provides a more appropriate representation of the neural data and generates more accurate decoding. Furthermore, we have used recently developed computationally efficient methods by incorporating a priori information of the targets of the reaching movement. Our results show that the hidden-state model with target-conditioning further improves decoding accuracy.      

Stereoscopic imaging: a real-time, in depth look

There is a general push for biometric-based solutions to replace keys, ID cards, passwords and PINs. Facial recognition, as one of the computational biometrics technologies, has received renewed attention and publicity lately, but for its inaccurate results. One major reason for the inaccuracy is the fact that, generally, facial recognition tools are rooted in 2D imaging methods which are limited to front-profile 2D photographs with a maximum divergence of 20 degrees. 3D facial imaging technology eliminates much of the nagging problems, but the benefits come with the added cost of processing time, especially in the case of stereoscopic imaging. The requirement of timely processing is particularly important in access control applications. The distributed algorithm we propose represents a novel step in solving the 3D imaging problem using power processing. The algorithm enables cameras, fitted with special boards, to generate 3D images in less time than with existing methods. The algorithm exploits the well-known properties/constraints from the stereovision field. Thus, it is very reliable. The obvious impact areas for this work are the capture, display and transmission of stereoscopic images. However, other areas, such as stereoscopic HDTV, can benefit from a faster technique.