Somatosensory cells in the parieto-occipital area V6A of the macaque

The aim of this study was to assess whether neurones of area V6A, a part of Brodmann's area 19, are modulated by passive somatosensory stimulations. Extracellular activity was recorded in four awake while passive tactile stimulations of the skin and passive rotations of the joints were performed in complete darkness and under eye movement control. Out of 240 V6A units, 78 (32%) were modulated by somatosensory stimulations. The majority of somatic receptive fields were located on both proximal and distal parts of the contralateral arm. V6A somatosensory cells may play a role in the feedback control of the actual state of the arm while reaching its target in peripersonal space.     

一种手指康复装置的机构与控制实验

背景：临床证实,在患者肢体手术后或脑神经损伤的早期康复及自发恢复期间,实施连续被动运动可以补偿患者主动运动的不足,增大其肢体活动度,同时减少相应的并发症。 目的：以正常人体手指作对指运动时手指末端轨迹(预期轨迹)参数为基础设计完成手指康复训练机械手。 方法：以连续被动运动康复理论为基础设计了一种手指康复训练机械手,该机械手主要包括四指机构和拇指机构,采用步进电机进行驱动,以实现人体拇指和四指的对指运动。 结果与结论：针对实现不同长度手指的康复要求,实施了机构对指运动实验,机构末端轨迹与预期轨迹之间的相对误差约为2%,由此表明了机构设计及控制方法的可行性,并能够较好满足患者拇指和四指对指运动的康复需求,实验结果验证了该机械手能较好的实现预期运动。下一阶段,将在现有控制实验的基础上实施真人手指康复训练实验。     

Distribution of somatic sensory and active-movement neuronal discharge properties in the MI-SI cortical border area in the rat

The rat somatosensory (SI) cortex contains a precise map of the cutaneous periphery, yet its rostromedial edge, which includes part of the fore- and hind paw representation, has been reported to functionally overlap with the electrically excitable primary motor (MI) cortex. Thus, the MI cortex in the rat contains two subregions: (i) rostrally, the "MI-agranular" cortex (i.e., "typical" MI cortex), and (ii) caudally, the "MI-SI-granular" cortex (i.e., the MI-SI overlap). The aim of this study was to assess the degree of overlap in the physiologic properties of single neurons recorded across the MI-SI boundary zone in awake, freely moving rats. Computer techniques were used to characterize both somatosensory receptive fields (cutaneous or "passive joint-manipulation") and discharge correlates of active limb movement in these MI-agranular and MI-SI-granular subregions of the MI. "Active-movement" units were defined as those which discharged strongly in correlation with specific limb movements, but in a manner which could not be predicted by their observable somatosensory properties. Of 92 completely analyzed cells in the MI-SI-granular forepaw region, 86 exhibited specific cutaneous receptive fields on the palmar surface of the forepaw. By contrast with the similarity of these neurons' responses to passive stimulation, they varied markedly in their discharge during active limb movements. For example, many did not respond when their forepaw receptive fields touched the ground during stepping. Furthermore, 31 (of 92) neurons in this region were identified as active-movement, firing in correlation with reaching movements of the forelimb. Seven of these were completely unresponsive to any sensory stimuli, but 24 exhibited an apparent convergence of cutaneous and active-movement properties. Of 86 units recorded in the MI-agranular subregion, 46 responded strongly to passive joint manipulation, but only three responded exclusively to cutaneous stimulation. Twenty-eight (of 86) cells were defined as active-movement, discharging mainly in correlation with forelimb reaching movements. Thus, the active-movement properties of neurons in these two subregions were quite similar, whereas the somatosensory properties were markedly different.     

Receptive fields of single cells in the visual cortex of the hooded rat.

The receptive fields of 107 single cells in area 17 of the hooded rat were examined. About half the cells responded to stationary as well as moving stimuli and about half only to movement. A variety of receptive field types were observed. Some of the cells responding to stationary stimuli had circular receptive fields, some with and some without annuli, some had elongated receptive fields, some had irregular receptive fields. Of the cells that responded only to movement, some were orientation or direction specific and some were not. Only two cells were found that responded to stimulation of the ipsilateral eye. Columnar organization of the cortex was not observed.     

Does post-movement beta synchronization reflect an idling motor cortex?

After the completion of a voluntary movement, a synchronization of cortical beta rhythms is recorded over the contralateral central region, which is assumed to reflect the termination of the motor command. In order to test this hypothesis, we compared in eight healthy subjects the synchronization of EEG beta rhythms following active and passive index extension. The passive movement was also performed after deafferentation by ischaemic nerve block in three subjects. Beta synchronization was present in all subjects after both active and passive movements, and disappeared under ischaemia in all three subjects. Post-movement beta synchronization can not solely be explained by an idling motor cortex. It may also, at least in part, reflect a movement-related somatosensory processing.     

Receptive field properties of somatosensory callosal fibres in the monkey

The corpus callosum is the principal neocortical commissure which transmits lateralized information between the hemispheres. The aim of the present experiment was to study the receptive field properties of somatosensory callosal fibres in rhesus macaque monkeys. The callosum was approached under direct visual control and axonic responses were recorded using tungsten microelectrodes. All sensory submodalities which could be examined with the available instruments were found (light touch, medium and deep pressure, joint movement and light pinches). Most fibres had receptive fields concerned with the trunk, followed by the head, with only a few responding to stimulation of the extremities. The medial borders of the unilateral receptive fields situated on the trunk and the head extended to the midline. The results are interpreted in terms of the roles of the corpus callosum in midline fusion and interhemispheric transfer.     

Somatic sensory cortex (SmI) of the prosimian primate Galago crassicaudatus: Organization of mechanoreceptive input from the hand in relation to cytoarchitecture

Mechanoreceptive input from the hand to the somatic sensory cortex (SmI) of the prosimian primate Galago crassicaudatus was examined with microelectrode mapping methods. In anesthetized animals, low threshold cutaneous input from the hand projects to SmI cortex in a single, complete, somatotopically organized pattern. Within this single pattern, cells with receptive fields on the glabrous skin of the palm, digits and digit tips are located in the rostral half, and cells with RFs on the hairy skin of the dorsal hand and digits are located in the caudal half of the hand area. The cutaneous hand area is coextensive with the densely granular architectonic region of SmI. Studies of single cells in this region of awake galagos reveal the same pattern of cutaneous input and, in addition, demonstrate the presence of cells responding to joint movement not detected in anesthetized animals. Cells responsive to joint movement are arranged in vertically oriented columns located adjacent to cutaneous columns with receptive fields on the same part of the hand. In anesthetized animals, cells rostral to the granular region, in an area typified by increasing numbers of pyramidal cells in layer V and decreasing numbers of granular cells in upper layers, respond to high threshold stimulation of large areas of the hand. The few cells isolated in this area in awake animals respond to either active or passive hand movements. In such animals, cells caudal to the granular region, in an area characterized as agranular and alaminar cortex, respond to either passive stimulation of single or multiple joints or to active hand movements. These results, together with similar findings in a related prosimian, Nycticebus coucang, emphasize the generality of a single cutaneous hand area in SmI of prosimian species. The demonstration of multiple hand areas corresponding to multiple cytoarchitectonic subdivisions in SmI of Old and New World simians illustrates the increased degree of SmI differentiation from the prosimian to the simian grade of organization. The present results further suggest that determination of the homologues of multiple areas or subdivisions within and surrounding SmI in primates will require comparisons of somatotopy, submodality, sulcal patterns, cytoarchitecture, and connectivity in representative members of prosimian and simian families.     

Robot assistance of motor learning: A neuro-cognitive perspective

The last several years have seen a number of approaches to robot assistance of motor learning. Experimental studies have produced a range of findings from beneficial effects through null-effects to detrimental effects of robot assistance. In this review we seek an answer to the question under which conditions which outcomes should be expected. For this purpose we derive tentative predictions based on a classification of learning tasks in terms of the products of learning, the mechanisms involved, and the modulation of these mechanisms by robot assistance. Consistent with these predictions, the learning of dynamic features of trajectories is facilitated and the learning of kinematic and dynamic transformations is impeded by robotic guidance, whereas the learning of dynamic transformations can profit from robot assistance with error-amplifying forces. Deviating from the predictions, learning of spatial features of trajectories is impeded by haptic guidance, but can be facilitated by divergent force fields. The deviations point to the existence of additional effects of robot assistance beyond the modulation of learning mechanisms, e.g., the induction of a passive role of the motor system during practice with haptic guidance.     

A three-dimensional spatiotemporal receptive field model explains responses of area MT neurons to naturalistic movies

Area MT has been an important target for studies of motion processing. However, previous neurophysiological studies of MT have used simple stimuli that do not contain many of the motion signals that occur during natural vision. In this study we sought to determine whether views of area MT neurons developed using simple stimuli can account for MT responses under more naturalistic conditions. We recorded responses from macaque area MT neurons during stimulation with naturalistic movies. We then used a quantitative modeling framework to discover which specific mechanisms best predict neuronal responses under these challenging conditions. We find that the simplest model that accurately predicts responses of MT neurons consists of a bank of V1-like filters, each followed by a compressive nonlinearity, a divisive nonlinearity, and linear pooling. Inspection of the fit models shows that the excitatory receptive fields of MT neurons tend to lie on a single plane within the three-dimensional spatiotemporal frequency domain, and suppressive receptive fields lie off this plane. However, most excitatory receptive fields form a partial ring in the plane and avoid low temporal frequencies. This receptive field organization ensures that most MT neurons are tuned for velocity but do not tend to respond to ambiguous static textures that are aligned with the direction of motion. In sum, MT responses to naturalistic movies are largely consistent with predictions based on simple stimuli. However, models fit using naturalistic stimuli reveal several novel properties of MT receptive fields that had not been shown in prior experiments.     

Daily variation and appetitive conditioning-induced plasticity of auditory cortex receptive fields

Long-term modification of cortical receptive field maps follows learning of sensory discriminations and conditioned associations. In the process of determining whether appetitive - as opposed to aversive - conditioning is effective in causing such plastic changes, it was discovered that multineuron receptive fields, when measured in rats under ketamine-sedation, vary substantially over the course of a week, even in the absence of classical conditioning and electrode movement. Specifically, a simple correlation analysis showed that iso-intensity frequency response curves of multiunit clusters and local field potentials recorded from auditory cortex are nonstationary over 7 days. Nevertheless, significant plastic changes in receptive fields, due to conditioned pairing of a pure tone and electrical stimulation of brain reward centres, are detectable above and beyond these spontaneous daily variations. This finding is based on a novel statistical plasticity criterion which compares receptive fields recorded for three days before and three days after conditioning. Based on a more traditional criterion (i.e. one day before and after conditioning), the prevalence of learning-induced changes caused by appetitive conditioning appears to be comparable to that described in previous studies involving aversive conditioning.     

Cortical neuromagnetic fields evoked by voluntary and passive hand movements in healthy adults.

Neuromagnetic fields were recorded from the left cerebral hemisphere of six healthy right-handed subjects under three different conditions: (1) externally triggered rapid voluntary extension and flexion of the right hand, (2) passive extension and flexion of the right hand, and (3) stimulation of the skin of the right index finger by means of air pressure. Location analysis using the current density analysis did not reveal any differences between motor evoked field I (MEF I) in active and passive movements, and met the maximum of cerebral activation in the contralateral precentral region. In contrast, the sensory evoked field was located clearly in the contralateral postcentral region. Additionally, a significantly shorter latency of MEF I (with respect to movement onset) was observed in flexion compared with extension in both passive and active movements. These results support the assumption that MEF I is generated by cortical activation resulting from proprioceptive, probably muscle spindle, input. The current density analysis has proved to be an appropriate method for investigating movement-related fields. Furthermore, the described method seems to be appropriate for evaluating the processes of cortical reorganization and the influence of neurorehabilitation within longitudinal studies in patients with lesions in motor centers of the brain.     

Passive and active lower-limb movements delay upper-limb balance reactions

This study investigated the influence of rhythmic lower-limb activity on the timing of upper-limb balance reactions. Compensatory grasping reactions were evoked in healthy subjects by rapid sagittal tilts of a chair under three conditions: (1) active leg pedaling, (2) passive (motor-driven) leg pedaling, and (3) no lower-limb movement (control task). Compared with control trials, both active and passive pedaling resulted in similar delays in the initiation (43-47 ms) and execution (12-17 ms) of grasping reactions. The similarity between effects due to active and passive movement suggests that the conditioning arose predominantly from sensory discharge associated with lower-limb movement. These results may have important implications for understanding the influence of locomotion or other ongoing movement on the control of stability.     

Neuronal activity in the basal ganglia in patients with generalized dystonia and hemiballismus.

Microelectrode recording was performed in the basal ganglia of 3 patients with generalized dystonia and 1 patient with hemiballismus secondary to a brainstem hemorrhage. Neuronal activity was recorded from the internal and external segments of the globus pallidus and assessed for mean discharge rate and pattern of spontaneous activity. The responses of neurons in the internal segment of the globus pallidus to passive and active movements were also evaluated. Mean discharge rates of neurons in both segments of the pallidum in patients with dystonia and the patient with hemiballismus were considerably lower than those reported for patients with idiopathic Parkinson's disease. In addition, the pattern of spontaneous neuronal activity was highly irregular, occurring in intermittent grouped discharges separated by periods of pauses. Although receptive fields in the dystonia patients were widened and less specific than those reported in normal monkeys, neuronal responses to movement were uncommon in the hemiballismus patient. Before surgery, patients with dystonia experienced abnormal posturing and involuntary movements. Coactivation of agonist-antagonist muscle groups was observed both at rest and during the performance of simple movements. After pallidotomy there was a significant reduction in the involuntary movement associated with these disorders and a more normal pattern of electromyographic activity during rest and movement. Given the improvement in dystonic and hemiballistic movements in these patients after ablation of the sensorimotor portion of the internal segment of the globus pallidus, we suggest that pallidotomy can be an effective treatment for patients with dystonia and also for patients with medically intractable hemiballismus. Based on the finding of decreased neuronal discharge rates in pallidal neurons, we propose that physiologically dystonia most closely resembles a hyperkinetic movement disorder. A model for dystonia is proposed that incorporates the observed changes in the rate and pattern of neuronal activity in the pallidum with data from neuroimaging with positron emission tomography and 2-deoxyglucose studies.     

Inhibitory components in responses of neurons of the lateral suprasylvian area of the cat cortex

Inhibitory components of neuronal responses to moving visual stimuli in the lateral suprasylvian area of the cat cortex have been studied. Comparison of PST histograms of responses to two opposite directions of the movement allows revealing changes in the spatial localization of discharge centres in receptive fields relative to the movement direction. In all neurons investigated which revealed monotonous stationary structure of receptive fields no subregions coincidental with the inhibitory components of the responses are found. The presented experiments have promoted a conclusion that inhibitory components of responses of observed neurons could represent aftereffects following excitation of the cell when the stimulus is crossing the discharge centre of the receptive field.     

Primary afferent units from the hairy skin of the rat hind limb

The properties of cutaneous units in the saphenous nerve of the rat have been surveyed. We studied 137 units with myelinated (A-fibre) axons conducting at 4-44 m/s. Of the A-fibre units 66% gave a rapidly adapting discharge following hair movement and could be classified into categories similar to those described previously in cat and rabbit. Two categories predominated: (1) D-hair units with slowly conducting axons and relatively large receptive fields that responded to slow movement of hairs, including down hairs when these were present and (2) G-hair units with larger axons and relatively small fields that were only excited by fast movement of guard hairs. Of the A-fibre units 20% were high threshold mechanoreceptors. As in other species, these had a wide range of conduction velocities and multi-point receptive fields. Other types of A-fibre units found were (a) sensitive, RA units not excited by hair movement, (b) relatively insensitive RA units with diffuse receptive fields and (c) slowly adapting mechanoreceptor units. We studied 149 units with unmyelinated (C-fibre) axons conducting at 0.49-0.89 m/s. Of the C-fibre units 73% were of the polymodal nociceptor type. They had small receptive fields and responded to pressure and heating. The average heat threshold was 47 degrees C (+/- 6 degrees C, S.D.). Units were often not sensitized by suprathreshold heating unlike similar units in cat and rabbit. Other C-fibre units found were sensitive mechanoreceptors (12%), cold thermoreceptors (4%) or were very insensitive or inexcitable (11%). The pattern of innervation of rat limb hairy skin resembles previously studied mammalian species. A notable feature is the large proportion of C-polymodal nociceptor units. In this respect the rat resembles the primate and differs from the cat.     

Receptive fields of motor neurons underlying local tactile reflexes in the locust

The receptive fields of motor neurons to a hind leg were mapped by recording intracellularly from their cell bodies or from the muscle fibers they innervate while stimulating mechanoreceptors on the surface of that leg. Each motor neuron is affected by a specific array of receptors that make up its receptive field. Boundaries along the anteroposterior or dorsoventral axes of the leg divide the receptive fields into excitatory and inhibitory regions. Proximodistal boundaries may correspond to the articulations between parts of the leg. Motor neurons that innervate antagonistic muscles have complementary receptive fields, so that the region that is excitatory for one is inhibitory for the other. The receptive fields of the motor neurons overlap. Tactile stimulation therefore leads to a specific local reflex that involves the coordinated movement of the segments of a leg. Five local reflexes are described, each of which moves the leg away from the site of stimulation. Afferents from the external mechanoreceptors do not synapse directly on the motor neurons, but instead on spiking local interneurons, some of which then synapse directly on motor neurons. These local interneurons have smaller receptive fields delineated by the same boundaries, so that the receptive fields of the motor neurons can be constructed from appropriate combinations of them. It is suggested that receptive fields are organized as "functional maps" that are appropriate for particular behavioral responses rather than solely to preserve or refine spatial information.     

An electrophysiological laminar analysis of single somatosensory neurons in partially deafferented rat hindlimb granular cortex subsequent to transection of the sciatic nerve

A sample of 302 neurons in rat hindlimb granular cortex was studied between 2 and 3 weeks after transection and ligation of the sciatic nerve. These neurons were compared to a control sample obtained from normal rats under similar experimental conditions. After sciatic nerve transection the proportion of neurons driven by somatic stimuli applied to the hindlimb (29.1%) was not significantly different from the proportion observed in the control sample (25.8%). The proportion of neurons with cutaneous receptive fields was also the same before and after nerve transection although the proportion of neurons responding to higher threshold taps was reduced. Spontaneously active neurons were encountered more frequently after sciatic nerve transection than in the control (45% vs 32%) and their mean discharge frequency was higher (8.6 vs 6.4 imp/s). Twice as many (10.2% vs 5.2%) spontaneously active neurons whose discharge was modulated by afferent stimuli were found after sciatic nerve transection. This and several other lines of evidence suggest that the cortical neurons were released from inhibition by the sciatic nerve transection. The number of spontaneously active neurons and the mean discharge rate were increased in each cortical lamina suggesting that the increased excitability seen after deafferentation occurred in all cortical layers. Neurons throughout the portion of the hindlimb representation studied could be driven from the remaining innervated region of the hindlimb, including one and sometimes two digits, part of the palm and most of the dorsum of the foot. More neurons were driven by receptive fields on the ankle than was the case for normal rats. Most neurons with cutaneous receptive fields were distributed in the same layers as those in the control group and had normal shapes and appearances. However, there were few of small size. Most were of moderate dimensions well within the normal range. Seven examples were found with unusually large proportions of their field extending from the foot onto the ankle and covering most of the posterior quadrant of the animal. In normal cortex the largest receptive fields were found in the middle layers. This distribution was not as clear after sciatic nerve section and a mixture of large and medium-sized receptive fields occurred at each depth. Further, some neurons with cutaneous receptive fields were found above 300 micron and below 1000 micron, depths where receptive fields were uncommon in the normal sample.     

Light- and dopamine-regulated receptive field plasticity in primate horizontal cells

Center-surround antagonistic receptive fields (CSARFs) are building blocks for spatial vision and contrast perception. Retinal horizontal cells (HCs) are the first lateral elements along the visual pathway, and are thought to contribute to receptive field surrounds of higher order neurons. Primate HC receptive fields have not been found to change with light, and dopaminergic modulation has not been investigated. Recording intracellularly from HCs in dark-adapted macaque retina, we found that H1-HCs had large receptive fields (λ = 1,158 ± 137 μm) that were reduced by background light (-45%), gap junction closure (-53%), and D1 dopamine receptor activation (-48%). Tracer coupling was modulated in a correlative manner, suggesting that coupling resistance plays a dominant role in receptive field formation under low light conditions. The D1 antagonist SCH23390 increased the size of receptive fields (+13%), suggesting tonic dopamine release in the dark. Because light elevates dopamine release in primate retina, our results support a dopaminergic role in post-receptoral light adaptation by decreasing HC receptive field diameters, which influences the center-surround receptive field organization of higher-order neurons and thereby spatial contrast sensitivity.     

Discharge of inferior olive cells during reaching errors and perturbations

It is widely believed that inferior olive (IO) neurons signal the occurrence of movement errors. The IO compares descending motor commands with information about movement and detects mismatches. Presumably, this error signal is used by the cerebellum to improve motor performance. To test this theory, we trained cats to reach out, grasp and retrieve a handle on cue. After training, the handle was displaced on selected trials so the cats would reach but miss the handle. Fifty-five IO cells with receptive fields on the forelimb were tested with the displaced handle condition. No cell fired at or near the time of "expected" contact, but some cells fired when the cats struck objects while attempting to grasp. A mismatch between a motor command and expected result is not sufficient to activate IO neurons; appropriate stimulation must occur. To define conditions for appropriate stimulation, the limb was stimulated at various times during the task. Sixty-six cells (including the 55 tested under the displaced handle condition) were tested with mechanical stimulation during quiet stance, and 98% responded to stimulation. A smaller percentage (68%) fired when stimulation was introduced during the reaching task, and the probability of these responses varied with the subdivision of the olive as well as the phase of the task. We conclude that it is unlikely that IO discharge provides information about movement or movement error. Olivary cells respond reliably to appropriate somatosensory stimulation but not to active movement or movement error.     

Tay-Sachs disease and normal cerebellar cells in culture: elevated levels of lysosomal enzymes in Tay-Sachs disease cells

The receptive fields of the sensorimotor cortex neurons identified by electrocutaneous stimulation were modified by microelectrophoretically applied picrotoxin which is known to reduce inhibition. a relatively short application of picrotoxin (90 nA during 3-6 min) markedly increased the size of the neuronal receptive fields in the sensorimotor cortex. Control application of glutamate showed that additional depolarization did not affect receptive fields of the spontaneously active units. Our results together with other work in this field further support the hypothesis that inhibitory processes play a major role in forming functional properties of the cerebral cortex neurons.