Somatosensory cortex excitability changes due to differences in instruction conditions of motor imagery

Purpose Vivid motor imagery appears to be associated with improved motor learning efficiency. However, the practical difficulties in measuring vivid motor imagery warrant new analytical approaches. The present study aimed to determine the instruction conditions for which vividness in motor imagery could be more easily seen and the excitability of the sensory cortex as it relates to the motor image. Materials and methods In total, 15 healthy, right-handed volunteers were instructed to imagine grasping a rubber ball under a verbal-only instruction condition (verbal condition), a verbal?+?visual instruction condition (visual condition), and a verbal?+?execution (physically grasping a real ball) condition (execution condition). We analyzed motor imagery-related changes in somatosensory cortical excitability by comparing somatosensory-evoked potentials in each condition with the rest (control) condition. We also used a visual analogue scale to measure subject-reported vividness of imagery. Results We found the N33 component was significantly lower in the execution condition than in the rest condition (p?Conclusions These data suggest that experiencing a movement through actual motor execution immediately prior to performing mental imagery of that movement enhances the excitability of motor-related cortical areas. It is suggested that the excitability of the motor-related region increased as a result of the motor imagery in the execution condition acting on the corresponding somatosensory cortex.     

Anatomical location of the medial lemniscus and spinothalamic tract at the pons in the human brain: A diffusion tensor tractography study

Abstract

Using diffusion tensor tractography, we investigated the anatomical location of medial lemniscus (ML) and spinothalamic tract (STT) at pons. We recruited 47 healthy volunteers. Evaluation of the anatomical location of ML and STT was performed using the highest probabilistic location at the upper, middle, and lower pons. According to findings, MLs were located around the middle to medial one-third, between midline and lateral boundary of pons in the pontine tegmentum and STTs were located posterolaterally to ML.     

Comparison of cortical activation patterns by somatosensory stimulation on the palm and dorsum of the hand

Abstract

Objectives: Little is known about differences of cortical activation according to body location. We attempted to compare brain activation patterns by somatosensory stimulation on the palm and dorsum of the hand, using functional magnetic resonance imaging (fMRI).

Method: We recruited 15 healthy right-handed volunteers for this study. fMRI was performed during touch stimulation using a rubber brush on an area of the same size on the palm or dorsum of the hand. Regions of interest (ROIs) were drawn at the primary sensory–motor cortex (SM1), posterior parietal cortex, and secondary somatosensory cortex.

Results: Group analysis of fMRI data indicated that touch stimulation on the palm resulted in production of more activated voxels in the contralateral SM1 and posterior parietal cortex than on the dorsum of the hand. The most activated ROI was found to be the contralateral SM1 by stimulation of the palm or dorsum, and the number of activated voxels (5875) of SM1 by palm stimulation was more than 2 times that (2282) of dorsum stimulation. The peak activated value in the SM1 by palm stimulation (16.43) was also higher than that of the dorsum (5.52).

Conclusion: We found that stimulation of the palm resulted in more cortical activation in the contralateral SM1 than stimulation of the dorsum. Our results suggested that the palm of the hand might have larger somatotopy of somatosensory representation for touch in the cerebral cortex than the dorsum of the hand. Our results would be useful as a rehabilitation strategy when more or less somatosensory stimulation of the hand is necessary.     

Neuronal activity controls the development of interneurons in the somatosensory cortex

BACKGROUND

Neuronal activity in cortical areas regulates neurodevelopment by interacting with defined genetic programs to shape the mature central nervous system. Electrical activity is conveyed to sensory cortical areas via intracortical and thalamocortical neurons, and includes oscillatory patterns that have been measured across cortical regions.

OBJECTIVE

In this work, we review the most recent findings about how electrical activity shapes the developmental assembly of functional circuitry in the somatosensory cortex, with an emphasis on interneuron maturation and integration. We include studies on the effect of various neurotransmitters and on the influence of thalamocortical afferent activity on circuit development. We additionally reviewed studies describing network activity patterns.

METHODS

We conducted an extensive literature search using both the PubMed and Google Scholar search engines. The following keywords were used in various iterations: “interneuron”, “somatosensory”, “development”, “activity”, “network patterns”, “thalamocortical”, “NMDA receptor”, “plasticity”. We additionally selected papers known to us from past reading, and those recommended to us by reviewers and members of our lab.

RESULTS

We reviewed a total of 132 articles that focused on the role of activity in interneuronal migration, maturation, and circuit development, as well as the source of electrical inputs and patterns of cortical activity in the somatosensory cortex. 79 of these papers included in this timely review were written between 2007 and 2016.

CONCLUSION

Neuronal activity shapes the developmental assembly of functional circuitry in the somatosensory cortical interneurons. This activity impacts nearly every aspect of development and acquisition of mature neuronal characteristics, and may contribute to changing phenotypes, altered transmitter expression, and plasticity in the adult. Progressively changing oscillatory network patterns contribute to this activity in the early postnatal period, although a direct requirement for specific patterns and origins of activity remains to be demonstrated.

     

Specificity and Plasticity of Thalamocortical Connections in Sema6A Mutant Mice

The establishment of connectivity between specific thalamic nuclei and cortical areas involves a dynamic interplay between the guidance of thalamocortical axons and the elaboration of cortical areas in response to appropriate innervation. We show here that Sema6A mutants provide a unique model to test current ideas on the interactions between subcortical and cortical guidance mechanisms and cortical regionalization. In these mutants, axons from the dorsal lateral geniculate nucleus (dLGN) are misrouted in the ventral telencephalon. This leads to invasion of presumptive visual cortex by somatosensory thalamic axons at embryonic stages. Remarkably, the misrouted dLGN axons are able to find their way to the visual cortex via alternate routes at postnatal stages and reestablish a normal pattern of thalamocortical connectivity. These findings emphasize the importance and specificity of cortical cues in establishing thalamocortical connectivity and the spectacular capacity of the early postnatal cortex for remapping initial sensory representations.     

The Distribution of Corticocortical,Thalamocortical, and Callosal Inputs on Identified Motor Cortex Output Neurons: Mechanisms for Their Selective Recruitment

Motor cortex neurons were identified antidromically in anesthetized cats by their axonal projections to one of six targets: (1) somatosensory cortex, (2) opposite motor cortex, (3) red nucleus, (4) lateral reticular nucleus, (5) spinal cord, and (6) ventrolateral thalamus. Three inputs to motor cortex were tested for their influences on the identified cortical efferent neurons. The tested inputs originated from ipsilateral somatosensory cortex, opposite motor cortex, and ventral thalamus. Subthreshold effects of input pathways were detected by monitoring latency variations of antidromic responses.

The three afferent sources, when activated by electrical stimulation, were not equally effective on motor cortex neurons. Ipsilateral corticocortical and thalamocortical excitation were found for the majority of neurons; the influenced proportions ranged from 55% to 100%, according to the target of the output neurons. Effects from the opposite hemisphere were found for only 5% to 30% of the neurons in the same projection classes.

Many neurons (36 of 81, or 44%) were excited from more than one source, but few (5 of 37, or 14%) were influenced by all three possible sources of input, even in small regions of cortex innervated by all three of the inputs. Among 19 electrode tracks where all three inputs were present, there were only 2 tracks where all the neurons shared the same combination of inputs. Even for neurons in closest anatomical proximity (“clusters”), it was unusual (only 7 of 25 clusters) for all the neurons to have the same input pattern. Among the seven clusters where all the neurons shared the same input pattern, five of the clusters projected to the same target. These variable combinations of inputs to motor cortex neurons support the conclusion that efferent neurons could be recruited selectively from separate cortical layers or from within clusters of nearby neurons, according to the target of their axonal projection.     

Somatic and motor components of action simulation

Seminal studies in monkeys report that the viewing of actions performed by other individuals activates frontal and parietal cortical areas typically involved in action planning and execution. That mirroring actions might rely on both motor and somatosensory components is suggested by reports that action observation and execution increase neural activity in motor and in somatosensory areas. This occurs not only during observation of naturalistic movements but also during the viewing of biomechanically impossible movements that tap the afferent component of action, possibly by eliciting strong somatic feelings in the onlooker. Although somatosensory feedback is inherently linked to action execution, information on the possible causative role of frontal and parietal cortices in simulating motor and sensory action components is lacking. By combining low-frequency repetitive and single-pulse transcranial magnetic stimulation, we found that virtual lesions of ventral premotor cortex (vPMc) and primary somatosensory cortex (S1) suppressed mirror motor facilitation contingent upon observation of possible and impossible movements, respectively. In contrast, virtual lesions of primary motor cortex did not influence mirror motor facilitation. The reported double dissociation suggests that vPMc and S1 play an active, differential role in simulating efferent and afferent components of observed actions.     

Characterizing Thalamocortical Disturbances in Cervical Spondylotic Myelopathy: Revealed by Functional Connectivity under Two Slow Frequency Bands

Background and Purpose

Recent advanced MRI studies on cervical spondylotic myelopathy (CSM) revealed alterations of sensorimotor cortex, but the disturbances of large-scale thalamocortical systems remains elusive. The purpose of this study was to characterizing the CSM-related thalamocortical disturbances, which were associated with spinal cord structural injury, and clinical measures.

Methods

A total of 17 patients with degenerative CSM and well-matched control subjects participated. Thalamocortical disturbances were quantified using thalamus seed-based functional connectivity in two distinct low frequencies bands (slow-5 and slow-4), with different neural manifestations. The clinical measures were evaluated by Japanese Orthopaedic Association (JOA) score system and Neck Disability Index (NDI) questionnaires.

Results

Decreased functional connectivity was found in the thalamo-motor, -somatosensory, and -temporal circuits in the slow-5 band, indicating impairment of thalamo-cortical circuit degeneration or axon/synaptic impairment. By contrast, increased functional connectivity between thalami and the bilateral primary motor (M1), primary and secondary somatosensory (S1/S2), premotor cortex (PMC), and right temporal cortex was detected in the slow-4 band, and were associated with higher fractional anisotropy values in the cervical cord, corresponding to mild spinal cord structural injury.

Conclusions

These thalamocortical disturbances revealed by two slow frequency bands inform basic understanding and vital clues about the sensorimotor dysfunction in CSM. Further work is needed to evaluate its contribution in central functional reorganization during spinal cord degeneration.     

Screening for genes that wire the cerebral cortex

Thalamocortical projections convey visual, somatosensory and auditory information to the cerebral cortex. A recent report in Neural Development shows how a forward genetic screen has enabled the identification of novel mutations affecting specific decision points of thalamocortical axon pathfinding.     

Estimation of conduction velocity of the spino-thalamic tract in man

This is the first report of estimating conduction velocity (CV) of the slowly conducting somatosensory spinal tracts or the spino-thalamic tract (STT) in man. The CV of the STT was measured by recording somatosensory evoked potentials (SEPs) following CO₂ laser stimulation of the hand and foot, which was previously shown to cause pain or heat sensation by activating cutaneous nociceptors and by its ascending signals through Aδ fibers and probably STT. When the CV of Aδ fibers was assumed to be 10–15 m/sec, the CV of STT was found to be approximately 8–10 m/sec in normal young subjects. It was slightly slower in subjects over 60 years of age. In contrast, the CV of the posterior column, which was calculated based on SEPs following electrical stimulation of the median and posterior tibial nerves, was approximately 50–60 m/sec.     

Nonoverlapping Thalamocortical Connections to Normal and Deprived Primary Somatosensory Cortex for Similar Forelimb Receptive Fields in Chronic Spinal Cats

The fluorescent dye retrograde tracing technique, using fast blue in combination with fluorogold, was used to examine thalamocortical projections from the ventrobasal complex to primary somatosensory cortex in chronic spinal cats that sustained T12 cord transection at 2 weeks of age. Following cord transection at this age, it has been shown that forelimb afferents can excite the deprived hindlimb projection zone, in addition to the region of somatosensory cortex that they normally occupy (McKinley et al, 1987). These two regions of cortex are separated by over 10 mm, thus facilitating the determination of whether the forelimb representation in “hindlimb cortex” is derived from the sector of the ventrobasal complex of the thalamus representing the forelimb, hindlimb, or both. Injections of the two dyes into separate regions of the cortex that were excited by the same peripheral forelimb receptive fields produced single labeling of two nonoverlapping clusters of thalamic neurons. This finding suggests that the projections for these two areas are independent and distinct, and indicates that altered thalamocortical projections do not contribute the critical component underlying reorganizational changes observed at the cortical level after spinal cord transection. It is hypothesized that the degree of reorganization required to achieve the magnitude of change observed in the cortex must occur below the level of the thalamocortical relay.     

Decoding visual roughness perception: an fMRI study

Abstract

The neural substrates of tactile roughness perception have been investigated by many neuroimaging studies, while relatively little effort has been devoted to the investigation of neural representations of visually perceived roughness. In this human fMRI study, we looked for neural activity patterns that could be attributed to five different roughness intensity levels when the stimuli were perceived visually, i.e., in absence of any tactile sensation. During functional image acquisition, participants viewed video clips displaying a right index fingertip actively exploring the sandpapers that had been used for the behavioural experiment. A whole brain multivariate pattern analysis found four brain regions in which visual roughness intensities could be decoded: the bilateral posterior parietal cortex (PPC), the primary somatosensory cortex (S1) extending to the primary motor cortex (M1) in the right hemisphere, and the inferior occipital gyrus (IOG). In a follow-up analysis, we tested for correlations between the decoding accuracies and the tactile roughness discriminability obtained from a preceding behavioural experiment. We could not find any correlation between both although, during scanning, participants were asked to recall the tactilely perceived roughness of the sandpapers. We presume that a better paradigm is needed to reveal any potential visuo-tactile convergence. However, the present study identified brain regions that may subserve the discrimination of different intensities of visual roughness. This finding may contribute to elucidate the neural mechanisms related to the visual roughness perception in the human brain.     

Neural Basis of Limb Ownership in Individuals with Body Integrity Identity Disorder

Our body feels like it is ours. However, individuals with body integrity identity disorder (BIID) lack this feeling of ownership for distinct limbs and desire amputation of perfectly healthy body parts. This extremely rare condition provides us with an opportunity to study the neural basis underlying the feeling of limb ownership, since these individuals have a feeling of disownership for a limb in the absence of apparent brain damage. Here we directly compared brain activation between limbs that do and do not feel as part of the body using functional MRI during separate tactile stimulation and motor execution experiments. In comparison to matched controls, individuals with BIID showed heightened responsivity of a large somatosensory network including the parietal cortex and right insula during tactile stimulation, regardless of whether the stimulated leg felt owned or alienated. Importantly, activity in the ventral premotor cortex depended on the feeling of ownership and was reduced during stimulation of the alienated compared to the owned leg. In contrast, no significant differences between groups were observed during the performance of motor actions. These results suggest that altered somatosensory processing in the premotor cortex is associated with the feeling of disownership in BIID, which may be related to altered integration of somatosensory and proprioceptive information.     

Convergence between projections from different thalamic nuclei to columns of the rat somatosensory cortex

Primuline fluorochrome retrograde transport technique was used to investigate sources of thalamocortical projections to a single rat somatosensory cortex column connected with the projection of the C₃ vibrissa. Labeled cells were identified in eight different thalamic nuclei: two specific, five nonspecific, and one association nucleus. Labeled neurons differed in the degree of stain accumulated as well as cell numbers and density of distribution from one nucleus to another, indicative of the different arborization patterns of their axons within the cortex. Highest numbers of heavily stained cells as well as highest density of distribution were observed in the ventral thalamic nucleus. The convergence seen between different thalamocortical inputs on to a single somatosensory cortex column explains the functional differences observed between neurons belonging to the same column and makes the formation of functionally distinct neuronal groupings appear possible on this structural basis.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 168–174, March–April, 1989.     

Sources of thalamic projections in the region of vibrissal representation in the rat somatosensory cortex studied by horseradish peroxide labeling

The retrograde horseradish peroxidase (HRP) transport method was used to study the location and morphology of neuron groups in the ventrobasal complex of the thalamus projecting to the region of vibrissal representation in the somatosensory cortex in rats. Injection of HRP into a circumscribed region of the somatosensory cortex revealed the following pattern of organization of the thalamocortical relay groups of neurons. Labeled neurons were located in the ventroposterolateral nucleus of the ventrobasal complex and were associated in groups 100–120 µ in diameter. Staining of several groups, even after minimal injections of HRP, and an increase in the number of labeled cells in each group with an increase in the zone of injection of HRP in the cortex suggest the presence of both convergence and divergence of specific thalamocortical pathways. The different shapes of the relay neurons and differences in the degree of HRP accumulation by them may indicate differences in their functional role in thalamocortical integration.Research Institute of Neurocybernetics, Rostov State University. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 631–635, November–December, 1982.     

Relationship between somatosensory function and the spinothalamocortical pathway in chronic stroke patients

Abstract

Diffusion tensor tractography (DTT) allows for identification and evaluation of the spinothalamic tract and its thalamocortical pathway (STP). We attempted to investigate the relationship between tactile sensation and the STP in chronic stroke patients. We measured fractional anisotropy, mean diffusivity, and tract volume of the STP. The tactile sensation score of the affected side in patients with preserved STP integrity was higher compared with that of patients with an interrupted STP. The remaining volume and integrity of the STP in the affected hemisphere were important factors for tactile sensation of the affected side in chronic patients with intracerebral hemorrhage (ICH).     

Depression at thalamocortical synapses: the key for cortical neuronal adaptation?

Neuronal adaptation to repetitive sensory stimuli is ubiquitous in the mammalian cortex. Despite its prevalence, the cellular mechanisms underlying this basic physiological property remain a matter of dispute. In this issue of Neuron, Chung et al. provide conclusive evidence that depression of thalamocortical synapses may play a significant role in the expression of neuronal adaptation in the rat somatosensory cortex.     

Differential Grey Matter Changes in Sensorimotor Cortex Related to Exceptional Fine Motor Skills

Functional changes in sensorimotor representation occur in response to use and lesion throughout life. Emerging evidence suggests that functional changes are paralleled by respective macroscopic structural changes. In the present study we used voxel-based morphometry to investigate sensorimotor cortex in subjects with congenitally malformed upper extremities. We expected increased or decreased grey matter to parallel the enlarged or reduced functional representations we reported previously. More specifically, we expected decreased grey matter values in lateral sensorimotor cortex related to compromised hand function and increased grey matter values in medial sensorimotor cortex due to compensatory foot use. We found a medial cluster of grey matter increase in subjects with frequent, hand-like compensatory foot use. This increase was predominantly seen for lateral premotor, supplementary motor, and motor areas and only marginally involved somatosensory cortex. Contrary to our expectation, subjects with a reduced number of fingers, who had shown shrinkage of the functional hand representation previously, did not show decreased grey matter values within lateral sensorimotor cortex. Our data suggest that functional plastic changes in sensorimotor cortex can be associated with increases in grey matter but may also occur in otherwise macroscopically normal appearing grey matter volumes. Furthermore, macroscopic structural changes in motor and premotor areas may be observed without respective changes in somatosensory cortex.     

The interaction of the somatosensory evoked potentials to simultaneous finger stimuli in the human central nervous system. A study using direct recordings

In order to investigate the interaction of sensory electrophysiologic fields arising from the adjacent second (II) and third (III) fingers and the distant second and fifth (V) fingers, direct recordings of somatosensory evoked potentials (SEPs) were performed from the sensory and motor cortices, the sensory thalamic nucleus (nucleus ventralis caudalis, VC) and the cuneate nucleus in humans during neurosurgical operations. Electrical stimulation was given to the II, III or V fingers individually, and also to pairs of either the II and III fingers or the II and V fingers simultaneously. The interaction ratio OR) was devised as the ratio of amplitude attenuation caused by the simultaneous stimulation to two fingers compared with the amplitude of the arithmetically summed SEPs to the individual stimulation of two fingers. The IRs were calculated on N20 and P25 from the sensory cortex, P22 from the motor cortex, P17_thal from the VC, and N16_cune and P35_cune from the cuneate nucleus.With both stimulations to the II and III fingers and the II and V fingers, P25 showed the greatest IR, followed by P22, then by P17_thal while N16_cune exhibited the smallest IR. N20 and P35_cune showed similar IRs and significantly greater IRs with II and III finger stimulation compared with II and V finger stimulation.These results thus indicate that the interaction of somatosensory impulses occurs in several structures along the sensory pathway in CNS, including the cuneate nucleus, the sensory thalamic nucleus, as well as sensory and motor cortices, with the greatest IRs in the cerebral cortices and the weakest ones in the brain-stem. They also suggest that the receptive fields of the fingers in the cortical area generating N20 are arranged according to the order of the fingers while those in the generating sites for cortical P25 and P22, thalamic P17_thal and cuneate N16_cune tend to be arranged in clusters, while P35_cune is possibly modulated by the somatosensory cortex through a long-loop feedback pathway.     

Organisation of the motor cortex differs between people with and without knee osteoarthritis

IntroductionThe aim of this study was to investigate possible differences in the organisation of the motor cortex in people with knee osteoarthritis (OA) and whether there is an association between cortical organisation and accuracy of a motor task.MethodsfMRI data were collected while 11 participants with moderate/severe right knee OA (6 male, 69 ± 6 (mean ± SD) years) and seven asymptomatic controls (5 male, 64 ± 6 years) performed three visually guided, variable force, force matching motor tasks involving isolated isometric muscle contractions of: 1) quadriceps (knee), 2) tibialis anterior (ankle) and, 3) finger/thumb flexor (hand) muscles. fMRI data were used to map the loci of peak activation in the motor cortex during the three tasks and to assess whether there were differences in the organisation of the motor cortex between the groups for the three motor tasks. Root mean square of the difference between target and generated forces during muscle contraction quantified task accuracy.ResultsA 4.1 mm anterior shift in the representation of the knee (p = 0.03) and swap of the relative position of the knee and ankle representations in the motor cortex (p = 0.003) were found in people with knee OA. Poorer performance of the knee task was associated with more anterior placement of motor cortex loci in people with (p = 0.05) and without (p = 0.02) knee OA.ConclusionsDifferences in the organisation of the motor cortex in knee OA was demonstrated in relation to performance of knee and ankle motor tasks and was related to quality of performance of the knee motor task. These results highlight the possible mechanistic link between cortical changes and modified motor behavior in people with knee OA.