应用大脑皮质体觉诱发反应地图验证循经感传的形成机制

The study is to observe the variation of functional motility in cortical somatosensory area I (SI) during propagated sensation and imitating sensation conduction along meridians with cortical somatosensory evoked potential(CSEP) topograpic map. The observation has been done on 42 volunteers and the results show that in those whose signs of propagated sensation along meiridians (PSM) were obvious when the sensation along the Gall Bladder Meiridian(GBM) passed to head and face, a red high potential signal appeared in the lower limbs representing area, which is near the middle line of cortical somatosensory evoked potential topograpic map, and a red high potential signal, jumping over the upper limbs representing area, also appeared in the face representing area, which is at the external part of cortical somatosensory evoked potential topograpic map, while in those whose PSM was not reported only a red high potential signal appeared in the lower limbs representing area. When Hegu (LI 4) was stimulated in those without PSM, usually an obvious evoked response appeared only in the upper limbs representing area. However, when Hegu was stimulted in those with PSM, the response area was larger in the upper limbs representing area and extending to face representing area. Mechanical compression can block PSM, and corresponding change will show in CSEP topographic map. This provides compelling evidence for the hypothesis Correspondence to: Professor Jin-sen Xu, Fujian Academy of TCM, Fuzhou 350003, China. Tel: (+86)591-8357-0748, Fax: (+86)591-8357-0007, Email: xujinsenjls@163.com that peripheral driver stimulation were the key element of producing PSM.     

Spatial attention modulates the cortical somatosensory representation of the digits in humans

The topographic organization of the primary somatosensory cortex adapts to alterations of afferent input. Here, electric source imaging was used to show that spatial attention modifies cortical somatosensory representations in humans. The cortical representation of the electrically stimulated digit 2 (resp. digits 2 and 3) of the right hand was more medial along the somatosensory area 3b in subjects who focused attention on digit 4 of the right hand, while it was more lateral when subjects attended digit 4 of the contralateral hand. This effect was very fast since the direction of attention was changed every 6 min. The results indicate that cortical somatosensory representations not only depend on afferent input but vary when spatial attention is directed towards different parts of the body.     

From maps to form to space: Touch and the body schema

Evidence from patients has shown that primary somatosensory representations are plastic, dynamically changing in response to central or peripheral alterations, as well as experience. Furthermore, recent research has also demonstrated that altering body posture results in changes in the perceived sensation and localization of tactile stimuli. Using evidence from behavioral studies with brain-damaged and healthy subjects, as well as functional imaging, we propose that the traditional concept of the body schema should be divided into three components. First are primary somatosensory representations, which are representations of the skin surface that are typically somatotopically organized, and have been shown to change dynamically due to peripheral (usage, amputation, deafferentation) or central (lesion) modifications. Second, we argue for a mapping from a primary somatosensory representation to a secondary representation of body size and shape (body form representation). Finally, we review evidence for a third set of representations that encodes limb position and is used to represent the location of tactile stimuli relative to the subject using external, non-somatotopic reference frames (postural representations).     

Activation of supplementary motor area during imaginary movement of phantom toes

To evaluate changes in the human cerebral cortex after lower limb amputation, we studied repetitive toe movements using functional magnetic resonance imaging. The subject did not experience any phantom pain but had a vivid sensation of the phantom limb's presence and was able to imagine the movement of her phantom toes and ankle. Actual movement of her normal limb activated the contralateral supplementary motor area (SMA), the primary motor cortex (M1), and the primary somatosensory cortex (S1). Movement of her phantom limb activated the contralateral SMA and the M1. Imaginary movement of her normal toes without actual movement activated the contralateral SMA. The slice level that was activated by the movement of the phantom limb was shifted 8 mm caudally, suggesting that cortical reorganization had occurred after the lower limb amputation.     

fMRI study of acupuncture-induced periaqueductal gray activity in humans

BOLD fMRI was used to study acupuncture-induced activation (increase in the BOLD signal from undetectable) of the periaqueductal gray (PAG) and two somatosensory cortical areas in seven healthy human subjects. Mechanical stimulation (push-pull) was given to the LI4 (Hoku) acupoint or to a non-acupoint. The stimulation paradigm consisted of 5 runs, each consisting of four 30 s On/30 s OFF periods over 30 min. The scan for each ON period was analyzed individually. The PAG and cortical areas showed different activity patterns. PAG activity was episodic and reliably demonstrated after 20-25 min of stimulation; both cortical areas, however, were active > 90% of the time. Stimulation of a non-acupoint (leg) resulted in reduced levels of PAG and cortical activity.     

Reduced somatosensory hand representation in thalidomide-induced dysmelia as revealed by fMRI

The concept of cerebral plasticity suggests that the hand representation in somatosensory cortex is abnormal in congenital malformation disorders. To investigate this issue we studied 11 subjects with different degrees of upper extremity dysmelia due to thalidomide embryopathy in comparison to 10 control subjects. In the affected subjects fingers are typically missing in radio-ulnar order beginning with the thumb. Haemodynamic responses to electrical stimulation of the radial-most and ulnar-most fingers were measured in each subject using functional magnetic resonance tomography. The size of the hand area in the primary somatosensory cortex was estimated by calculating the Euclidian distance between corresponding activation peaks on the lateral postcentral gyrus. The cortical somatosensory hand representation was found to be significantly smaller in dysmelic subjects as compared with the control subjects (P <0.001). The shrinkage of the hand area was not proportional to the number of missing fingers. Furthermore, the cortical representation of the ulnar fingers in the dysmelic subjects was shifted towards the cortical thumb representation of the control group. We suggest that the unproportional reduction of the hand area together with the observed shift may reflect use-dependent rather than malformation-induced reorganization of the somatosensory hand area.     

Bilateral alterations in somatosensory cortical processing in hemiplegic cerebral palsy

Aim In individuals with cerebral palsy (CP), cerebral insults during early development may induce profound reorganization of the motor representation. This study determined the extent of alterations in cortical somatosensory functions in adolescents with hemiplegic CP with subcortical brain lesions. Method We recorded somatosensory evoked magnetic fields in response to hand area stimulation from eight adolescents with hemiplegic CP (five females and three males; mean age 14y 6mo, SD 2y 3mo) and eight age‐ and sex‐matched healthy comparison adolescents (mean age 15y 4mo, SD 2y 4mo). All participants in the CP group had purely subcortical brain lesions in magnetic resonance images. Results The somatosensory representation of the affected limb was contralateral (i.e. ipsilesional), but detailed inspection of the evoked responses showed alterations bilaterally. In the primary somatosensory cortex, the representation areas of digits II and V were in both hemispheres closer to each other in participants with CP than in comparison participants [ANOVA main effect group F_1,14=5.58; p=0.03]. In addition, the morphology of median nerve evoked fields was altered in the participants with CP. Interpretation In hemiplegic CP, modification of the somatosensory cortical network extends beyond what would be expected based on the unilateral symptoms and the anatomical lesion. Further understanding of the functional alterations in the sensorimotor networks may aid in developing more precisely designed rehabilitation strategies.     

Preserved somatosensory conduction in complete spinal cord injury: Discomplete SCI

ObjectiveSpinal cord injury (SCI) disrupts the communication between brain and body parts innervated from below-injury spinal segments, but rarely results in complete anatomical transection of the spinal cord. The aim of this study was to investigate residual somatosensory conduction in clinically complete SCI, to corroborate the concept of sensory discomplete SCI.MethodsWe used fMRI with a somatosensory protocol in which blinded and randomized tactile and nociceptive stimulation was applied on both legs (below-injury level) and one arm (above-injury level) in eleven participants with chronic complete SCI. The experimental design accounts for possible confounding mechanical (e.g. vibration) and cortico-cortical top-down mechanisms (e.g. attention/expectation).ResultsSomatosensory stimulation on below-level insensate body regions activated the somatotopically corresponding part of the contralateral primary somatosensory cortex in six out of eleven participants.ConclusionsOur results represent afferent-driven cortical activation through preserved somatosensory connections to the brain in a subgroup of participants with clinically complete SCI, i.e. sensory discomplete SCI.SignificanceIdentifying patients with residual somatosensory connections might open the door for new rehabilitative and restorative strategies as well as inform research on SCI-related conditions such as neuropathic pain and spasticity.     

Long-term effects of concussion on relevancy-based modulation of somatosensory-evoked potentials

ObjectiveThe purpose of this investigation was to better understand the effects of concussions on the ability to selectively up or down-regulate incoming somatosensory information based on relevance.MethodsMedian nerve somatosensory-evoked potentials (SEPs) were elicited from electrical stimulation and recorded from scalp electrodes while participants completed tasks that altered the relevance of specific somatosensory information being conveyed along the stimulated nerve.ResultsWithin the control group, SEP amplitudes for task-relevant somatosensory information were significantly greater than for non-relevant somatosensory information at the earliest cortical processing potentials (N20-P27). Alternatively, the concussion history group showed similar SEP amplitudes for all conditions at early processing potentials, however a pattern similar to controls emerged later in the processing stream (P100) where both movement-related gating and facilitation of task-relevant information were present.ConclusionsPreviously concussed participants demonstrated impairments in the ability to up-regulate relevant somatosensory information at early processing stages. These effects appear to be chronic, as this pattern was observed on average several years after participants’ most recent concussion.SignificanceGiven the role of the prefrontal cortex in relevancy-based facilitation during movement-related gating, these findings lend support to the notion that this brain area may be particularly vulnerable to concussive forces.     

Functional MRI finding by proprioceptive input in patients with thalamic hemorrhage

Little is known about the recovery mechanism of somatosensory function in thalamic hemorrhage. We investigated the recovery mechanism of somatosensory function, using functional MRI (fMRI) findings by proprioceptive input in chronic patients with thalamic hemorrhage. Eleven consecutive chronic patients with thalamic hemorrhage who showed severe proprioceptive dysfunction were recruited. The subscale for kinesthetic sensation of the Nottingham Sensory Assessment (NSA) was used for determination of proprioceptive function. fMRI was performed during passive movements of the metacarpophalangeal joint. From fMRI, the laterality index (LI) was calculated for assessment of the relative activity in the ipsilateral versus the contralateral primary sensori-motor cortex (SM1). The average LI for affected and unaffected hand stimulation was 0.89 and 0.90, respectively, and there was no significant difference between LIs (p> 0.05). In addition, LI of the affected hand stimulation was positively related to NSA scores (r=0.790, p< 0.05). Our results for LI suggest that the cortical activation pattern of SM1 was similar in the affected and unaffected hemispheres. Therefore, it appears that the proprioceptive function of the affected hand likely recovered by the normally existing medial lemniscus and its thalamocortical pathway in our patients.     

Functional deactivations: multiple ipsilateral brain areas engaged in the processing of somatosensory information

Somatosensory signals modulate activity throughout a widespread network in both of the brain hemispheres: the contralateral as well as the ipsilateral side of the brain relative to the stimulated limb. To analyze the ipsilateral somatosensory brain areas that are engaged during limb stimulation, we performed functional magnetic resonance imaging (fMRI) in 12 healthy subjects during electrical median nerve stimulation using both a block- and an event-related fMRI design. Data were analyzed through the use of model-dependent (SPM) and model-independent (ICA) approaches. Beyond the well-known positive blood oxygenation level-dependent (BOLD) responses, negative deflections of the BOLD response were found consistently in several ipsilateral brain areas, including the primary somatosensory cortex, the supplementary motor area, the insula, the dorsal part of the posterior cingulate cortex, and the contralateral cerebellum. Compared to their positive counterparts, the negative hemodynamic responses showed a different time course, with an onset time delay of 2.4 s and a peak delay of 0.7 s. This characteristic delay was observed in all investigated areas and verified by a second (purely tactile) event-related paradigm, suggesting a systematic difference for brain areas involved in the processing of somatosensory information. These findings may indicate that the physiological basis of these deactivations differs from that of the positive BOLD responses. Therefore, an altered model for the negative BOLD response may be beneficial to further model-dependent fMRI analyses.     

Effects of visual information regarding tactile stimulation on the somatosensory cortical activation:a functional MRI study

Many studies have investigated the evidence for tactile and visual interactive responses to activation of various brain regions. However, few studies have reported on the effects of visuo-tactile multisensory inte-gration on the amount of brain activation on the somatosensory cortical regions. The aim of this study was to examine whether coincidental information obtained by tactile stimulation can affect the somatosensory cortical activation using functional MRI. Ten right-handed healthy subjects were recruited for this study. Two tasks (tactile stimulation and visuotactile stimulation) were performed using a block paradigm during fMRI scanning. In the tactile stimulation task, in subjects with eyes closed, tactile stimulation was applied on the dorsum of the right hand, corresponding to the proximal to distal directions, using a rubber brush. In the visuotactile stimulation task, tactile stimulation was applied to observe the attached mirror in the MRI chamber reflecting their hands being touched with the brush. In the result of SPM group analysis, we found brain activation on the somatosensory cortical area. Tactile stimulation task induced brain acti-vations in the left primary sensory-motor cortex (SM1) and secondary somatosensory cortex (S2). In the visuo-tactile stimulation task, brain activations were observed in the both SM1, both S2, and right posterior parietal cortex. In all tasks, the peak activation was detected in the contralateral SM1. We examined the ef-fects of visuo-tactile multisensory integration on the SM1 and found that visual information during tactile stimulation could enhance activations on SM1 compared to the tactile unisensory stimulation.     

Age-related changes across the primary and secondary somatosensory areas: An analysis of neuromagnetic oscillatory activities

ObjectiveAge-related changes are well documented in the primary somatosensory cortex (SI). Based on previous somatosensory evoked potential studies, the amplitude of N20 typically increases with age probably due to cortical disinhibition. However, less is known about age-related change in the secondary somatosensory cortex (SII). The current study quantified age-related changes across SI and SII mainly based on oscillatory activity indices measured with magnetoencephalography.MethodsWe recorded somatosensory evoked magnetic fields (SEFs) to right median nerve stimulation in healthy young and old subjects and assessed major SEF components. Then, we evaluated the phase-locking factor (PLF) for local field synchrony on neural oscillations and the weighted phase-lag index (wPLI) for cortico-cortical synchrony between SI and SII.ResultsPLF was significantly increased in SI along with the increased amplitude of N20m in the old subjects. PLF was also increased in SII associated with a shortened peak latency of SEFs. wPLI analysis revealed the increased coherent activity between SI and SII.ConclusionsOur results suggest that the functional coupling between SI and SII is influenced by the cortical disinhibition due to normal aging.SignificanceWe provide the first electrophysiological evidence for age-related changes in oscillatory neural activities across the somatosensory areas.     

The early negative potential evoked by stimulation of the tibial nerve in man

The scalp response to stimulation of the tibial nerve at the level of the medial malleolus was systematically analysed. It was recorded 2 cm posterior to the vertex and at the sites corresponding to cortical representation of the hand. The existence of an early negative wave with a peak latency of 37.2 ± 2.29 ms and amplitude of ?0.69 ± 0.40 μV was established (being half the amplitude of the first positive wave (P40) over the vertex). This wave was named N37 in respect of the peak latency and polarity. N37 was the first event recorded after stimulation of the tibial nerve at this level as the onset latency was 32.2 ± 1.75 ms and that of P40 over the vertex 33.8 ± 2.28 ms. It was recorded with the highest amplitude over the hand primary somatosensory area after stimulation of the opposite foot.N37 evoked by stimulation of the tibial nerve at the ankle and N20 evoked by stimulation of the arm nerve are both the primary negativities of the evoked potential. However, N37 is not recorded with maximum amplitude over the leg primary somatosensory area and it is rounded and longer lasting than N20. In spite of these differences the two initial negative electrical phenomena are not necessarily generated by different functional structures. The possible generators of N37 are discussed.     

Neural generators of tibial nerve P30 somatosensory evoked potential studied in patients with a focal lesion of the cervicomedullary junction

The tibial nerve P30 potential was studied in 6 patients with focal lesions located in the vicinity of the cervicomedullary junction. P30 potential was unaffected while cortical P39 was abnormal in the patients with a supramedullary lesion affecting the somatosensory pathway just above its decussation. Conversely, P30 was abnormal in the presence of a lesion situated caudally to the cervicomedullary junction affecting the lower limb sensory fibers just below their decussation. Median nerve P14 behaved similarly to the P30 potential in these cases. These clinical observations suggest that P30 potential, as P14 of median nerve somatosensory evoked potentials, is generated in the lower brain stern probably before the decussation of the sensory fibers; nucleus gracilis and medial lemniscus fibers in the lower brain stem are probably the anatomical structures generating P30 potential. This suggests that P30 potential may be used to study intraspinal and intracranial conduction times separately in the afferent somatosensory pathways. © 1996 John Wiley & Sons, Inc.     

The projection of the opossum's visual field on the cerebral cortex

The visual cortex of the opossum was studied by means of evoked potential and multi-unit recordings, and a map of the visual field in V_I was constructed: Evoked responses were observed in regions extending beyond the boundaries of striate cortex. Different patterns of response were obtained depending on the cortical region undergoing exploration: in a posteromedial region, coincident with striate area, complex waveforms were obtained, contrasting with the simpler forms observed in a region localized anterolaterally. V_I, which corresponds to cytoarchitectonic area 17, has a topography of projections similar to that found in other mammals: the upper visual field represented posteriorly, the temporal field represented medially, the lower field represented anteriorly and the nasal part laterally. A large proportion of V_I is devoted to the region of binocular representation, which covers approximately100° at the level of the horizontal meridian. The cortical representation of the vertical meridian extends to approximately 60°above and below the center of gaze, suggesting that the cortical representation of the visual field is more restricted than the visual field available to the contralateral hemiretina. Our results suggest that the extreme periphery of the field is not represented in V_I. In its lateral border the projection does not end at the vertical meridian, it extends 5° into the ipsilateral hemififield of vision, so that approximately 10° of visual field is represented in both hemispheres. There is a reversal of representation along the lateral border of V_I, in a region which coincides with the cytoarchitectonic boundaries of striate and peristriate areas, suggesting the existence of at least a second representation of the visual field in the neocortex of the opossum, corresponding to V_II of other animals. The magnification factor in V_I varied from 7°/mm observed at the cortical representation of the center of gaze, to 30°/mm at the extreme periphery of the field, along the horizontal meridian. A comparable decrease was also observed along the vertical meridian, towards the upper and lower limits of the visual field.     

Electrical somatosensory stimulation modulates hand motor function in healthy humans

In healthy people, electrical somatosensory stimulation modulates excitability in contralateral cortical motor areas. The question whether this is associated with a change in motor performance is still under debate. The effect of electrical somatosensory stimulation on motor performance of the hand was investigated in 14 healthy right-handed subjects. Subjects performed index finger and hand tapping movements as well as reach-to-grasp movements towards small and large cubes with each hand prior to (baseline condition) and following 2-hour electrical somatosensory stimulation (trains of 5 pulses at 10 Hz with 1 ms duration delivered at 1 Hz with an intensity on average 60 % above the individual somatosensory threshold) of the (i) right median nerve, (ii) left median nerve, (iii) right tibial nerve (control stimulation) and (iv) left tibial nerve (control stimulation) on separate occasions at least one week apart. The order of sessions was counterbalanced across subjects. Somatosensory stimulation of the median nerves, but not of the tibial nerves, reduced the frequency and velocity of index finger and hand tapping movements performed with the stimulated hand, compared to baseline. In contrast, the kinematics of reach-to-grasp movements remained unaffected by somatosensory stimulation. The data suggest that somatosensory stimulation interferes with the processing of highly automated open-loop motor output at the stimulated limb, as reflected by tapping movements, but not with the processing of closed-loop motor performance, as reflected by reach-to-grasp movements.     

Motor cortex stimulation in patients with post-stroke pain: conscious somatosensory response and pain control

We analyzed the conscious sensory responses to cortical stimulation of 31 patients with post-stroke pain who underwent motor cortex stimulation (MCS) therapy. During surgery for electrode placement, a sensory response (tingle projected to a localized peripheral area) was elicited by high-frequency stimulation (50 Hz) in 23 (84%) from the somatosensory cortex, and in 16 (52%) from the motor cortex without muscle contraction. Unpleasant painful sensation was induced or their original pain was exacerbated in 12 patients (39%) when the somatosensory cortex was stimulated and in two (6%) when the motor cortex was stimulated. Somatosensory responses were induced in eight (25%) even by low-frequency stimulation (1-2 Hz) of the motor cortex at an intensity below the threshold for muscle contraction. In contrast, among 20 nonpain patients who underwent a similar procedure for cortical mapping in epilepsy or brain tumor surgery, a sensory response was produced by high-frequency stimulation in only eight (40%; p < 0.02) from the somatosensory cortex and four (20%; p < 0.03) from the motor cortex. Pain sensation was not induced by stimulation of the somatosensory cortex (p < 0.002) or motor cortex in any of these patients. In addition, none of these patients reported a sensory response to low-frequency stimulation. In both of the two post-stroke pain patients who reported abnormal pain sensation in response to stimulation of the motor cortex, MCS failed to control their post-stroke pain. These findings imply that the sensitivity of the perceptual system even to activity of the motor cortex is heightened in post-stroke pain patients, which can sometimes hinder pain control by MCS.     

Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

BackgroundParalysis and neuropathy, affecting millions of people worldwide, can be accompanied by significant loss of somatosensation. With tactile sensation being central to achieving dexterous movement, brain-computer interface (BCI) researchers have used intracortical and cortical surface electrical stimulation to restore somatotopically-relevant sensation to the hand. However, these approaches are restricted to stimulating the gyral areas of the brain. Since representation of distal regions of the hand extends into the sulcal regions of human primary somatosensory cortex (S1), it has been challenging to evoke sensory percepts localized to the fingertips.Objective/hypothesisTargeted stimulation of sulcal regions of S1, using stereoelectroencephalography (SEEG) depth electrodes, can evoke focal sensory percepts in the fingertips.MethodsTwo participants with intractable epilepsy received cortical stimulation both at the gyri via high-density electrocorticography (HD-ECoG) grids and in the sulci via SEEG depth electrode leads. We characterized the evoked sensory percepts localized to the hand.ResultsWe show that highly focal percepts can be evoked in the fingertips of the hand through sulcal stimulation. fMRI, myelin content, and cortical thickness maps from the Human Connectome Project elucidated specific cortical areas and sub-regions within S1 that evoked these focal percepts. Within-participant comparisons showed that percepts evoked by sulcal stimulation via SEEG electrodes were significantly more focal (80% less area; p = 0.02) and localized to the fingertips more often, than by gyral stimulation via HD-ECoG electrodes. Finally, sulcal locations with consistent modulation of high-frequency neural activity during mechanical tactile stimulation of the fingertips showed the same somatotopic correspondence as cortical stimulation.ConclusionsOur findings indicate minimally invasive sulcal stimulation via SEEG electrodes could be a clinically viable approach to restoring sensation.     

Primary somatosensory cortex modulation of tactile responses in nucleus gracilis cells of rats

Corticofugal influences from the primary somatosensory cortex to the gracilis nuclei were studied with single unit recordings performed in urethane-anaesthetized rats. Two types of neurons were identified: low firing rate (LF) neurons, which could be activated antidromically by medial lemniscus stimulation; and high firing rate (HF) neurons. The effects of electrically stimulating the contralateral primary somatosensory cortex were studied in two situations: when the stimulated cortical area and specific gracilis cells had overlapping receptive fields and when the receptive fields of the cells and primary somatosensory cortex did not overlap. Cortical stimulation facilitated cortical and tactile responses in most gracilis neurons (68% and 58% for LF and HF neurons, respectively) with overlapping receptive fields. When receptive fields were different, cortical stimulation inhibited tactile response in most LF neurons (58%) and some HF neurons (20%). Trains of cortical shocks during sensory stimulation demonstrated that the facilitatory and inhibitory effects outlasted the stimulation period by 5 min. The facilitatory effect was decreased by iontophoretic application of the N-methyl-D-aspartate (NMDA) receptor antagonist APV (50 mm). However, APV did not modify the intensity of the tactile response inhibition in cells with nonoverlapping receptive fields, although, its duration was decreased (<5 min). Iontophoretic application of the gamma-aminobutyric acid (GABA)(A) antagonist bicuculline (20 mm) blocked the cortically evoked inhibition in cells with nonoverlapping receptive fields. The results indicate that the somatosensory cortex precisely controls somatosensory transmission throughout the gracilis nucleus by means of NMDA and GABA(A) receptor activation.