利用自举法与相干矢量虚部研究脑电信号的连通性

多导联脑电信号之间的连通性分析有助于了解脑的不同分区之间的信息交互。为了研究实验任务引起的脑区之间的连通性,提出了一种结合自举法与相干矢量虚部的统计分析方法,并用于研究左、右手运动想象任务中的信息交互。结果表明:在单侧的运动想象任务中,辅助运动皮层与对侧的运动前区及初级运动感觉皮层具有广泛的联结关系,同时提示受试是采用具有肌肉感觉的运动想象模式。该方法简洁、意义明确,可以进一步应用在脑-机接口及事件相关电位的研究中。     

Early consolidation in human primary motor cortex.

Behavioural studies indicate that a newly acquired motor skill is rapidly consolidated from an initially unstable state to a more stable state, whereas neuroimaging studies demonstrate that the brain engages new regions for performance of the task as a result of this consolidation. However, it is not known where a new skill is retained and processed before it is firmly consolidated. Some early aspects of motor skill acquisition involve the primary motor cortex (M1), but the nature of that involvement is unclear. We tested the possibility that the human M1 is essential to early motor consolidation. We monitored changes in elementary motor behaviour while subjects practised fast finger movements that rapidly improved in movement acceleration and muscle force generation. Here we show that low-frequency, repetitive transcranial magnetic stimulation of M1 but not other brain areas specifically disrupted the retention of the behavioural improvement, but did not affect basal motor behaviour, task performance, motor learning by subsequent practice, or recall of the newly acquired motor skill. These findings indicate that the human M1 is specifically engaged during the early stage of motor consolidation.     

基于图论算法的脊髓损伤后大脑皮层运动区神经元网络分析

 脊髓损伤(SCI)后大脑皮层运动区神经元的功能重组对机体功能康复的影响仍然不为人知。脊髓损伤前后,对一只在跑步机上直立行走的恒河猴的大脑皮层运动区神经元信号进行记录,利用不同神经元动作电位序列间的相关系数建立神经元网络图。为了研究神经元活动模式的变化与功能康复之间的联系,利用图论算法计算了神经元网络图的全局效能指标和神经元脆弱性指标。结果显示,不同时期神经元活动模式的显著变化意味着运动区神经元的功能重组(神经可塑性)与脊髓损伤后猴子的功能康复状态紧密相关,且这种神经功能重组对于猴子步行功能的康复起了非常重要的积极作用。     

手指按键相关脑磁图信号的功能源提取

独立分量分析(ICA)可用于分离多通道脑磁图信号(MEG)中的信号源。基于约束ICA的思想,通过在ICA模型中加入能够反映事件相关皮层神经活动特征的功能约束条件,实现了一种脑磁逆问题的解决方法,即功能源提取(FSS)方法。文中利用该方法对一例手指按键诱发MEG信号进行功能源提取,结果表明功能源位置位于对侧中央前回皮质运动区,且通过验证功能源提取所得到的分离向量与SAM法计算得到的空间滤波器系数间的相关性,验证了所提取的功能源有效。同时,功能源提取方法所提供的神经活动源的时域与频域信息,为在大量样本中探索大脑对手指运动控制的时间演化机制奠定了基础。     

Cortical ensemble activity increasingly predicts behaviour outcomes during learning of a motor task

When an animal learns to make movements in response to different stimuli, changes in activity in the motor cortex seem to accompany and underlie this learning. The precise nature of modifications in cortical motor areas during the initial stages of motor learning, however, is largely unknown. Here we address this issue by chronically recording from neuronal ensembles located in the rat motor cortex, throughout the period required for rats to learn a reaction-time task. Motor learning was demonstrated by a decrease in the variance of the rats' reaction times and an increase in the time the animals were able to wait for a trigger stimulus. These behavioural changes were correlated with a significant increase in our ability to predict the correct or incorrect outcome of single trials based on three measures of neuronal ensemble activity: average firing rate, temporal patterns of firing, and correlated firing. This increase in prediction indicates that an association between sensory cues and movement emerged in the motor cortex as the task was learned. Such modifications in cortical ensemble activity may be critical for the initial learning of motor tasks.     

Mapping human visual cortex with positron emission tomography

Positron-emission tomography (PET) can localize functions of the human brain by imaging regional cerebral blood flow (CBF) during voluntary behaviour. Functional brain mapping with PET, however, has been hindered by PET's poor spatial resolution (typically greater than 1 cm). We have developed an image-analysis strategy that can map functional zones not resolved by conventional PET images. Brain areas selectively activated by a behavioural task can be isolated by subtracting a paired control-state image from the task-state image, thereby removing areas not recruited by the task. When imaged in isolation the centre of an activated area can be located very precisely. This allows subtle shifts in response locale due to changes in task to be detected readily despite poor spatial resolution. As an initial application of this strategy we mapped the retinal projection topography of human primary visual cortex. Functional zones separated by less than 3 mm (centre-to-centre) were differentiated using PET CBF images with a spatial resolution of 18 mm. This technique is not limited to a particular brain area or type of behaviour but does require that the increase in CBF produced by the task be both intense and focal.     

Restoration of grasp following paralysis through brain-controlled stimulation of muscles

Patients with spinal cord injury lack the connections between brain and spinal cord circuits that are essential for voluntary movement. Clinical systems that achieve muscle contraction through functional electrical stimulation (FES) have proven to be effective in allowing patients with tetraplegia to regain control of hand movements and to achieve a greater measure of independence in daily activities. In existing clinical systems, the patient uses residual proximal limb movements to trigger pre-programmed stimulation that causes the paralysed muscles to contract, allowing use of one or two basic grasps. Instead, we have developed an FES system in primates that is controlled by recordings made from microelectrodes permanently implanted in the brain. We simulated some of the effects of the paralysis caused by C5 or C6 spinal cord injury by injecting rhesus monkeys with a local anaesthetic to block the median and ulnar nerves at the elbow. Then, using recordings from approximately 100 neurons in the motor cortex, we predicted the intended activity of several of the paralysed muscles, and used these predictions to control the intensity of stimulation of the same muscles. This process essentially bypassed the spinal cord, restoring to the monkeys voluntary control of their paralysed muscles. This achievement is a major advance towards similar restoration of hand function in human patients through brain-controlled FES. We anticipate that in human patients, this neuroprosthesis would allow much more flexible and dexterous use of the hand than is possible with existing FES systems.     

Relation of neurons in the nonprimary motor cortex to bilateral hand movement

In the primate cerebral cortex there are at least two somatotopically organized, nonprimary motor fields rostral to the primary motor area. To understand the functions of these multiple motor representations we have compared the neuronal activity in each of these fields while monkeys performed a trained motor task, using right, left or both hands. In the nonprimary motor cortex, activity in a number of neurons was related to the movement the animal chose and performed, whereas in the primary motor cortex, changes in the firing of most neurons were simply related to activity in the contralateral muscles. This result indicates that the nonprimary motor cortex is involved in higher-order coding of the laterality of the motor response, implying that it exerts its motor control function at a higher hierarchical level than its counterpart in the primary motor cortex.     

Real-time prediction of hand trajectory by ensembles of cortical neurons in primates

Signals derived from the rat motor cortex can be used for controlling one-dimensional movements of a robot arm. It remains unknown, however, whether real-time processing of cortical signals can be employed to reproduce, in a robotic device, the kind of complex arm movements used by primates to reach objects in space. Here we recorded the simultaneous activity of large populations of neurons, distributed in the premotor, primary motor and posterior parietal cortical areas, as non-human primates performed two distinct motor tasks. Accurate real-time predictions of one- and three-dimensional arm movement trajectories were obtained by applying both linear and nonlinear algorithms to cortical neuronal ensemble activity recorded from each animal. In addition, cortically derived signals were successfully used for real-time control of robotic devices, both locally and through the Internet. These results suggest that long-term control of complex prosthetic robot arm movements can be achieved by simple real-time transformations of neuronal population signals derived from multiple cortical areas in primates.     

表象训练对动作技能向非利手迁移的影响

研究采用三组被试,一个控制组,两个实验组进行镜画试验。探讨了表象训练对动作技能向非利手迁移的影响,结果表明:正确的表象训练对动作技能向非利手的正迁移起到了显著的促进作用。     

Genetic dissection of the circuit for hand dexterity in primates

It is generally accepted that the direct connection from the motor cortex to spinal motor neurons is responsible for dexterous hand movements in primates. However, the role of the 'phylogenetically older' indirect pathways from the motor cortex to motor neurons, mediated by spinal interneurons, remains elusive. Here we used a novel double-infection technique to interrupt the transmission through the propriospinal neurons (PNs), which act as a relay of the indirect pathway in macaque monkeys (Macaca fuscata and Macaca mulatta). The PNs were double infected by injection of a highly efficient retrograde gene-transfer vector into their target area and subsequent injection of adeno-associated viral vector at the location of cell somata. This method enabled reversible expression of green fluorescent protein (GFP)-tagged tetanus neurotoxin, thereby permitting the selective and temporal blockade of the motor cortex–PN–motor neuron pathway. This treatment impaired reach and grasp movements, revealing a critical role for the PN-mediated pathway in the control of hand dexterity. Anti-GFP immunohistochemistry visualized the cell bodies and axonal trajectories of the blocked PNs, which confirmed their anatomical connection to motor neurons. This pathway-selective and reversible technique for blocking neural transmission does not depend on cell-specific promoters or transgenic techniques, and is a new and powerful tool for functional dissection in system-level neuroscience studies.     

Body image as a visuomotor transformation device revealed in adaptation to reversed vision

People adapt with remarkable flexibility to reversal of the visual field caused by prism spectacles. With sufficient time, this adaptation restores visually guided behaviour and perceptual harmony between the visible and tactile worlds. Although it has been suggested that seeing one's own body is crucial for adaptation, the underlying mechanisms are unclear. Here we show that a new representation of visuomotor mapping with respect to the hands emerges in a month during adaptation to reversed vision. The subjects become bi-perceptual, or able to use both new and old representations. In a visual task designed to assess the new hand representation, subjects identified visually presented hands as left or right by matching the picture to the representation of their own hands. Functional magnetic resonance imaging showed brain activity in the left posterior frontal cortex (Broca's area) that was unique to the new hand representations of both hands, together with activation in the intraparietal sulcus and prefrontal cortex. The emergence of the new hand representation coincided with the adaptation of perceived location of visible objects in space. These results suggest that the hand representation operates as a visuomotor transformation device that provides an arm-centred frame of reference for space perception.     

Functional dissociation of the left ventral occipito-temporal cortex in the direct and indirect retrieval of color features

Previous studies suggest that the storage/retrieval of object features is related to brain regions that are involved in the processing of these features. However, it remains unclear whether, and under what conditions, retrieving information about a feature reactivates the same region that specifically supports that feature’s perception. In this functional magnetic resonance imaging (fMRI) study, we compared brain activation in the left ventral occipito-temporal cortex during subjects performing a color perception task, and direct and indirect color retrieval tasks. After performing the color perception task to localize the regions responsible for color perception, subjects were intensively trained (outside of the scanner) to remember associations between colors and motion directions, and associations between colors and letters. Then, they were asked to perform two color retrieval tasks in the scanner, with stationary and gray scaled images as control stimuli. The results showed that the bilateral posterior occipito-temporal cortex was activated during the color perception task. When color information was retrieved by direct cues (motion direction), the same bilateral occipito-temporal region was activated. When color information was retrieved indirectly (judging whether a motion direction matched a letter by their associated colors), a region anterior to the color perception region in the left ventral occipito-temporal cortex was additionally activated. Our results provided evidence for the functional dissociation in the two subregions of the ventral occipito-temporal cortex during retrieval of color features: the posterior area might relate to perceptual features of color, while the anterior region might relate to the knowledge of associations with color.     

单次运动想象脑电的特征提取和分类

为了实现脑-计算机接口(BCI)系统,对运动想象脑电信号的特征进行了提取和分类.将大脑C3,C4处采集的二路运动想象脑电信号分成4段,分别建立六阶AR参数模型进行功率谱估计,再对每段数据的功率谱求和构造特征矢量,提供给误差反向传播算法进行左右手运动想象脑电模式分类.结果表明,该方法提取的特征向量较好地反应了运动想象脑电信号的事件相关去同步(ERD)和事件相关同步(ERS)的变化时程.另外,该方法识别率高,复杂性低,适合在线脑-计算机接口的应用.     

Dynamic coding of behaviourally relevant stimuli in parietal cortex.

A general function of cerebral cortex is to allow the flexible association of sensory stimuli with specific behaviours. Many neurons in parietal, prefrontal and motor cortical areas are activated both by particular movements and by sensory cues that trigger these movements, suggesting a role in linking sensation to action. For example, neurons in the lateral intraparietal area (LIP) encode both the location of visual stimuli and the direction of saccadic eye movements. LIP is not believed to encode non-spatial stimulus attributes such as colour. Here we investigated whether LIP would encode colour if colour was behaviourally linked to the eye movement. We trained monkeys to make an eye movement in one of two directions based alternately on the colour or location of a visual cue. When cue colour was relevant for directing eye movement, we found a substantial fraction of LIP neurons selective for cue colour. However, when cue location was relevant, colour selectivity was virtually absent in LIP. These results demonstrate that selectivity of cortical neurons can change as a function of the required behaviour.     

Neural correlates of mental rehearsal in dorsal premotor cortex

Behavioural and imaging studies suggest that when humans mentally rehearse a familiar action they execute some of the same neural operations used during overt motor performance. Similarly, neural activation is present during action observation in many of the same brain regions normally used for performance, including premotor cortex. Here we present behavioural evidence that monkeys also engage in mental rehearsal during the observation of sensory events associated with a well-learned motor task. Furthermore, most task-related neurons in dorsal premotor cortex exhibit the same activity patterns during observation as during performance, even during an instructed-delay period before any actual observed motion. This activity might be a single-neuron correlate of covert mental rehearsal.     

基于小波方差的运动想象脑电信号特征提取

针对区分两种不同运动想象(想象左手运动和想象右手运动)的脑-机接口任务,提出了以小波方差作为分类特征的方法.首先深入研究了小波变换以及小波方差的计算方法,结合验证脑电图(EEG)存在的ERD/ERS现象,然后利用小波分解系数方差对C3,C4导联脑电信号进行特征提取,最后采用最简线性分类器进行分类,采用分类正确率作为主要评价标准.结果表明,最大分类正确率为85%,最佳分类时间段为4~6.5 s.与BCI竞赛和其他方法相比,在保证分类正确率的前提下,所使用的特征提取和分类方法更加简单,具有较高的参考价值.     

低复杂度的多符号差分空时分组编码在快速瑞利衰落信道中的研究

为了降低多符号差分检测(MSDD)算法的高计算复杂度,提出了2个低复杂度的算法,分别是简单化的M算法(SMA)和改进的多符号反馈检测(IMDFD)算法.SMA是在M算法的基础上,通过删除对后续搜索过程不起作用的路径数,来达到和M算法性能相同,但复杂度降低的目的;而IMDFD算法结合了SMA和MDFD算法的思想,通过联合估计最大化值和设置序列长度值的方法,不仅达到低复杂度,而且还克服了MDFD算法的错误传播和低信噪比下低性能的问题.仿真结果显示,这2种算法通过增加观察间隔,都能很好的填补差分检测和相关检测之间的间距,并且随着星座点数的增加,SMA算法和IMDFD算法之间的性能间距在逐渐拉大,相对来说SMA算法具有稍高的复杂度但却有更好的性能.     

Performance monitoring by the supplementary eye field

Intelligent behaviour requires self-control based on the consequences of actions. The countermanding task is designed to study self-control; it requires subjects to withhold planned movements in response to an imperative stop signal, which they can do with varying success. In humans, the medial frontal cortex has been implicated in the supervisory control of action. In monkeys, the supplementary eye field in the dorsomedial frontal cortex is involved in producing eye movements, but its precise function has not been clarified. To investigate the role of the supplementary eye field in the control of eye movements, we recorded neural activity in macaque monkeys trained to perform an eye movement countermanding task. Distinct groups of neurons were active after errors, after successful withholding of a partially prepared movement, or in association with reinforcement. These three forms of activation could not be explained by sensory or motor factors. Our results lead us to put forward the hypothesis that the supplementary eye field contributes to monitoring the context and consequences of eye movements.     

Cortical control of a prosthetic arm for self-feeding

Arm movement is well represented in populations of neurons recorded from the motor cortex. Cortical activity patterns have been used in the new field of brain-machine interfaces to show how cursors on computer displays can be moved in two- and three-dimensional space. Although the ability to move a cursor can be useful in its own right, this technology could be applied to restore arm and hand function for amputees and paralysed persons. However, the use of cortical signals to control a multi-jointed prosthetic device for direct real-time interaction with the physical environment ('embodiment') has not been demonstrated. Here we describe a system that permits embodied prosthetic control; we show how monkeys (Macaca mulatta) use their motor cortical activity to control a mechanized arm replica in a self-feeding task. In addition to the three dimensions of movement, the subjects' cortical signals also proportionally controlled a gripper on the end of the arm. Owing to the physical interaction between the monkey, the robotic arm and objects in the workspace, this new task presented a higher level of difficulty than previous virtual (cursor-control) experiments. Apart from an example of simple one-dimensional control, previous experiments have lacked physical interaction even in cases where a robotic arm or hand was included in the control loop, because the subjects did not use it to interact with physical objects-an interaction that cannot be fully simulated. This demonstration of multi-degree-of-freedom embodied prosthetic control paves the way towards the development of dexterous prosthetic devices that could ultimately achieve arm and hand function at a near-natural level.