Responsiveness of Reorganized Primary Somatosensory (SI) Cortex after Local Inactivation of Normal SI Cortex in Chronic Spinal Cats

The cortical map of adult cats that sustained spinal cord transection at T₁₂ when they were 2 weeks old is characterized by a clear duplication of the representation of the forelimb, rostral trunk, and neck. The novel representation is located in the cortical region that is, in nonoperated animals, normally devoted to the hindlimb representation. We have investigated the possibility that the reactivation of the deprived hindlimb cortex may be mediated by corticocortical projections from normal to reorganized cortex. The primary somatosensory (SI) cortex was initially mapped to determine the boundaries of the normal and reorganized cortical representations. Somatotopically corresponding regions in both normal and reorganized cortex representing the trunk, the web space, or the shoulder were more precisely mapped. Inactivation of normal cortex was achieved by the nanoinjection of a solution of lidocaine hydrochloride stained with Chicago sky blue. Two major findings are described. First, inactivation of a circumscribed region of normal cortex representing a given receptive field (RF) failed to reduce or inhibit the responsiveness of a somatotopically corresponding RF represented in reorganized cortex. Therefore, it is unlikely that intracortical connections between normal and reorganized cortex could account for the reorganizational processes observed in cats that sustained spinal cord transection at 2 weeks of age. Second, the chemical blockade of normal cortex provoked an increase of the responsiveness and of the size of the peripheral RFs represented in reorganized cortex. This finding suggests that there are corticocortical connections (possibly topographically organized) between normal and reorganized cortex, and that these connections are inhibitory.     

Chronological Observations of Primary Somatosensory Cortical Maps in Kittens following Low Thoracic (T12) Spinal Cord Transection at 2 Weeks of Age

The present study investigated the reorganization of the somatosensory cortex in kittens following T₁₂ spinal cord transection at 2 weeks of age. Multiunit electrophysiological methods were used to map the somatosensory cortex of kittens at 3, 6, and 9 weeks after the transection. The entire reorganized cortical region was driven by substitute cutaneous inputs, primarily from the trunk, at 3 weeks after spinal cord transection. Although the level of cortical responsiveness remained the same throughout the 9 weeks studied, internal trunk representation changed, and there was an increase in shoulder girdle representation and emergence of forelimb representation. Poor somatotopic and topographic order was observed in the reorganized cortex, regardless of time posttransection. Finally, trunk receptive fields displayed a wide variety of shapes, sizes, and orientations not seen in the normal cortex.     

Responsiveness of reorganized primary somatosensory (SI) cortex after local inactivation of normal SI cortex in chronic spinal cats.

The cortical map of adult cats that sustained spinal cord transection at T12 when they were 2 weeks old is characterized by a clear duplication of the representation of the forelimb, rostral trunk, and neck. The novel representation is located in the cortical region that is, in nonoperated animals, normally devoted to the hindlimb representation. We have investigated the possibility that the reactivation of the deprived hindlimb cortex may be mediated by corticocortical projections from normal to reorganized cortex. The primary somatosensory (SI) cortex was initially mapped to determine the boundaries of the normal and reorganized cortical representations. Somatotopically corresponding regions in both normal and reorganized cortex representing the trunk, the web space, or the shoulder were more precisely mapped. Inactivation of normal cortex was achieved by the nanoinjection of a solution of lidocaine hydrochloride stained with Chicago sky blue. Two major findings are described. First, inactivation of a circumscribed region of normal cortex representing a given receptive field (RF) failed to reduce or inhibit the responsiveness of a somatotopically corresponding RF represented in reorganized cortex. Therefore, it is unlikely that intracortical connections between normal and reorganized cortex could account for the reorganizational processes observed in cats that sustained spinal cord transection at 2 weeks of age. Second, the chemical blockade of normal cortex provoked an increase of the responsiveness and of the size of the peripheral RFs represented in reorganized cortex. This finding suggests that there are corticocortical connections (possibly topographically organized) between normal and reorganized cortex, and that these connections are inhibitory.     

Areal Distributions of Cortical Neurons Projecting to Different Levels of the Caudal Brain Stem and Spinal Cord in Rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Ag_m), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb.

The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI. Injections in lateral SI representing the face produced dense terminal label in the contralateral trigeminal complex. Injections in cortex devoted to the forelimb and forepaw labeled the contralateral cuneate nucleus and parts of the dorsal horn of the spinal cord. The cortical injections also demonstrated interconnections of parts of SI with some of the other regions of cortex with projections to the spinal cord, and provided further evidence for the existence of PV in rats.     

Chronological observations of primary somatosensory cortical maps in kittens following low thoracic (T12) spinal cord transection at 2 weeks of age.

The present study investigated the reorganization of the somatosensory cortex in kittens following T12 spinal cord transection at 2 weeks of age. Multiunit electrophysiological methods were used to map the somatosensory cortex of kittens at 3, 6, and 9 weeks after the transection. The entire reorganized cortical region was driven by substitute cutaneous inputs, primarily from the trunk, at 3 weeks after spinal cord transection. Although the level of cortical responsiveness remained the same throughout the 9 weeks studied, internal trunk representation changed, and there was an increase in shoulder girdle representation and emergence of forelimb representation. Poor somatotopic and topographic order was observed in the reorganized cortex, regardless of time posttransection. Finally, trunk receptive fields displayed a wide variety of shapes, sizes, and orientations not seen in the normal cortex.     

Areal distributions of cortical neurons projecting to different levels of the caudal brain stem and spinal cord in rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Agm), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb. The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neurons of the thalamic ventrobasal complex,labeled with horseradish peroxidase,projecting to the primary somatosensory cortex in cats

The morphology and localization of neurons of the thalamic ventrobasal complex projecting to the primary somatosensory cortex were studied in cats by the retrograde axonal transport of exogenous horseradish peroxidase method. Different types of neurons were detected: triangular, round with symmetrical processes, oval with processes diverging asymmetrically, and fusiform. Tagged neurons were distributed as two large populations in the central region of the complex adjoining the boundaries of the two nuclei. Comparison with the somatotopic map showed that the tagged neurons were concentrated mainly in the projection area of the forelimb and head. Since microinjections of peroxidase into the somatosensory cortex also were given in the projection areas for the forelimb and head, the results confirm the neurophysiological concept of strict somatotopic organization of thalamocortical input.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. A. A. Ukhtomskii Physiological Institute, Leningrad. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 125–129, March–April, 1979.     

A Brain-Machine-Muscle Interface for Restoring Hindlimb Locomotion after Complete Spinal Transection in Rats

A brain-machine interface (BMI) is a neuroprosthetic device that can restore motor function of individuals with paralysis. Although the feasibility of BMI control of upper-limb neuroprostheses has been demonstrated, a BMI for the restoration of lower-limb motor functions has not yet been developed. The objective of this study was to determine if gait-related information can be captured from neural activity recorded from the primary motor cortex of rats, and if this neural information can be used to stimulate paralysed hindlimb muscles after complete spinal cord transection. Neural activity was recorded from the hindlimb area of the primary motor cortex of six female Sprague Dawley rats during treadmill locomotion before and after mid-thoracic transection. Before spinal transection there was a strong association between neural activity and the step cycle. This association decreased after spinal transection. However, the locomotive state (standing vs. walking) could still be successfully decoded from neural recordings made after spinal transection. A novel BMI device was developed that processed this neural information in real-time and used it to control electrical stimulation of paralysed hindlimb muscles. This system was able to elicit hindlimb muscle contractions that mimicked forelimb stepping. We propose this lower-limb BMI as a future neuroprosthesis for human paraplegics.     

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.     

The second somatosensory region of the cat thalamus

Recording focal evoked potentials showed that the second somatosensory region of the cat thalamus is located in the posterolateral part of the ventral posteromedial nucleus. The zone of representation of the hindlimb lies somewhat laterally, posteriorly, and superiorly to the zone of the forelimb. The zone of representation of the mouth lies more medially still. Latent periods of responses arising in both regions of the thalamus to cutaneous stimulation of the contralateral limbs are about equal. Neurons of the second somatosensory region of the thalamus send projections to cortical area S2. It can be concluded from the results that formation of the structure of double representation of the somatosensory systems in the cat is completed at the thalamic level.     

Decoding Hindlimb Movement for a Brain Machine Interface after a Complete Spinal Transection

Stereotypical locomotor movements can be made without input from the brain after a complete spinal transection. However, the restoration of functional gait requires descending modulation of spinal circuits to independently control the movement of each limb. To evaluate whether a brain-machine interface (BMI) could be used to regain conscious control over the hindlimb, rats were trained to press a pedal and the encoding of hindlimb movement was assessed using a BMI paradigm. Off-line, information encoded by neurons in the hindlimb sensorimotor cortex was assessed. Next neural population functions, or weighted representations of the neuronal activity, were used to replace the hindlimb movement as a trigger for reward in real-time (on-line decoding) in three conditions: while the animal could still press the pedal, after the pedal was removed and after a complete spinal transection. A novel representation of the motor program was learned when the animals used neural control to achieve water reward (e.g. more information was conveyed faster). After complete spinal transection, the ability of these neurons to convey information was reduced by more than 40%. However, this BMI representation was relearned over time despite a persistent reduction in the neuronal firing rate during the task. Therefore, neural control is a general feature of the motor cortex, not restricted to forelimb movements, and can be regained after spinal injury.     

Muscarinic cholinergic receptor binding in rat hindlimb somatosensory cortex following partial deafferentation by sciatic nerve transection.

Peripheral nerve injury or amputation leads to extensive changes within the central representations of the mammalian body surface. The mechanisms responsible for post-traumatic reorganization of these maps in adults may also, at least partly, underlie a more general feature of the somatosensory system--the capacity for stimulus-dependent plasticity. Acetylcholine has been implicated in both of these processes. We studied the binding of the ligands [3H]QNB and [3H]pirenzepine in rat hindlimb somatosensory cortex from 1 to 14 days following sciatic nerve transection. Although the [3H]QNB binding was not different from normal levels in tissue homogenates of the affected somatosensory cortex, differences were demonstrated when binding was measured on a layer-by-layer basis. [3H]QNB binding was changed only in certain layers, at certain times. The predominant effects appeared to be a decrease in binding in the middle layers from 4 to 14 days after the transection. Combining the [3H]QNB data with data obtained from the more M1-selective ligand [3H]pirenzepine suggested that complex changes occur among several muscarinic receptors, including receptors with non-M1 subtype characteristics. Moreover, unilateral nerve transection affects the hindlimb somatosensory regions in both hemispheres.     

Reorganization of the Intact Somatosensory Cortex Immediately after Spinal Cord Injury

Sensory deafferentation produces extensive reorganization of the corresponding deafferented cortex. Little is known, however, about the role of the adjacent intact cortex in this reorganization. Here we show that a complete thoracic transection of the spinal cord immediately increases the responses of the intact forepaw cortex to forepaw stimuli (above the level of the lesion) in anesthetized rats. These increased forepaw responses were independent of the global changes in cortical state induced by the spinal cord transection described in our previous work (Aguilar et al., J Neurosci 2010), as the responses increased both when the cortex was in a silent state (down-state) or in an active state (up-state). The increased responses in the intact forepaw cortex correlated with increased responses in the deafferented hindpaw cortex, suggesting that they could represent different points of view of the same immediate state-independent functional reorganization of the primary somatosensory cortex after spinal cord injury. Collectively, the results of the present study and of our previous study suggest that both state-dependent and state-independent mechanisms can jointly contribute to cortical reorganization immediately after spinal cord injury.     

A possible principle of kinesthetic compensation

The movement of the cat forelimb was studied under the conditions of complete transection of the classical somatosensory pathways from the limb to the cortex of the contralateral hemisphere. It was demonstrated that in animals with the intact system of the somatosensory (kinesthetic) feedback, the parameters of the same memorized movement varied widely from response to response whereas the exclusion of lemniscus projections from the control system led to the poor movement pattern and to the appearance of motor stereotypy. The hypothesis is advanced that deficit of kinesthetic information in this case is compensated for not only by the other intact connections of the kinesthetic analyzer but also due to the conversion of the nervous system to the central-programmed level control which itself demands less participation of the somatosensory feedback. The non-crossed projections of the kinesthetic analyzer are capable of forming and correcting this program and of ensuring the effect afferentation as well. The same principle of the functioning may take place in any compensatory reconstructions in the CNS.     

Comparison of the Connectional Properties of the Two Forelimb Areas of the Rat Sensorimotor Cortex: Support for the Presence of a Premotor or Supplementary Motor Cortical Area

The existence of multiple motor cortical areas that differ in some of their properties is well known in primates, but is less clear in the rat. The present study addressed this question from the point of view of connectional properties by comparing the afferent and efferent projections of the caudal forelimb area (CFA), considered to be the equivalent of the forelimb area of the primary motor cortex (MI), and a second forelimb motor representation, the rostral forelimb area (RFA). As a result of various tracing experiments (including double labeling), it was observed that CFA and RFA had reciprocal corticocortical connections characterized by preferential, asymmetrical, laminar distribution, indicating that RFA may occupy a different hierarchical level than CFA, according to criteria previously discussed in the visual cortex of primates. Furthermore, it was found that RFA, but not CFA, exhibited dense reciprocal connections with the insular cortex. With respect to their efferent projection to the basal ganglia, it was observed that CFA projected very densely to the lateral portion of the ipsilateral caudate putamen, whereas the contralateral projection was sparse and more restricted. The ipsilateral projection originating from RFA was slightly less dense than that from CFA, but it covered a larger portion of the caudate putamen (in the medial direction); the contralateral projection from RFA to the caudate putamen was of the same density and extent as the ipsilateral projection. The reciprocal thalamocortical and corticothalamic connections of RFA and CFA differed from each other in the sense that CFA was mainly interconnected with the ventrolateral thalamic nucleus, while RFA was mainly connected with the ventromedial thalamic nucleus. Altogether, these connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area. In contrast to the corticocortical, corticostriatal, and thalamocortical connections, RFA and CFA showed similar efferent projections to the subthalamic nucleus, substantia nigra, red nucleus, tectum, pontine nuclei, inferior olive, and spinal cord.     

Multiple Representations of the Body and Input-Output Relationships in the Agranular and Granular Cortex of the Chronic Awake Guinea Pig

The organization of somatosensory input and the input-output relationships in regions of the agranular frontal cortex (AGr) and granular parietal cortex (Gr) were examined in the chronic awake guinea pig, using the combined technique of single-unit recording and intracortical microstimulation (ICMS). AGr, which was cytoarchitectonically subdivided into medial (AGrm) and lateral (AGrl) parts, also can be characterized on a functional basis. AGrl contains the head, forelimb, and most hindlimb representations; only a small number of hindlimb neurons are confined in AGrm. Different distributions of submodalities exist in AGr and Gr: AGr receives predominantly deep input (with the exception of the vibrissa region, which receives cutaneous input), whereas neurons of Gr respond almost exclusively to cutaneous input. The cutaneous or deep receptive field (RF) of each neuron was determined by natural peripheral stimulation. All studied neurons were activated by small RFs, with the exception of lip, nose, pinna, and limb units of lateral Gr (Grl), for which the RFs were larger.

Microelectrode mapping experiments revealed the existence of three spatially separate, incomplete body maps in which somatosensory and motor representations overlap. One body map, with limbs medially and head rostrolaterally, is contained in AGr. A second map, comparable to the first somatosensory cortex (SI) of other mammals, is found in Gr, with hindlimb, trunk, forelimb, and head representations in an orderly mediolateral sequence. An unresponsive zone separates the head area from the forelimb region. A third map, with the forelimb rostrally and the hindlimb caudally, lies adjacent and lateral to the SI head area. This limb representation, which is characterized by an upright and small size compared to that found in SI, can be considered to be part of the second somatosensory cortex (SII). A distinct head representation was not recognized as properly belonging to SII, but the evidence that neurons of the SI head region respond to stimulation of large RFs located in lips, nose, and pinna leads us to hypothesize that the SII face area overlaps that of SI to some extent, or, alternatively, that the two areas are strictly contiguous and the limits are ambiguous, making them difficult to distinguish.

The input-output relationships were based on the results of RF mapping and ICMS in the same electrode penetration. The intrinsic specific interconnections of cortical neurons whose afferent input and motor output is related to identical body regions show a considerable degree of refinement. The input-output correspondence is especially pronounced for neurons with small RFs. This study confirms and extends similar data recently reported for other rodents.     

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.     

Changes in Glial Cell Line-derived Neurotrophic Factor Expression in the Rostral and Caudal Stumps of the Transected Adult Rat Spinal Cord

Limited information is available regarding the role of endogenous Glial cell line-derived neurotrophic factor (GDNF) in the spinal cord following transection injury. The present study investigated the possible role of GDNF in injured spinal cords following transection injury (T₉–T₁₀) in adult rats. The locomotor function recovery of animals by the BBB (Basso, Beattie, Bresnahan) scale score showed that hindlimb support and stepping function increased gradually from 7 days post operation (dpo) to 21 dpo. However, the locomotion function in the hindlimbs decreased effectively in GDNF-antibody treated rats. GDNF immunoreactivty in neurons in the ventral horn of the rostral stump was stained strongly at 3 and 7 dpo, and in the caudal stump at 14 dpo, while immunostaining in astrocytes was also seen at all time-points after transection injury. Western blot showed that the level of GDNF protein underwent a rapid decrease at 7 dpo in both stumps, and was followed by a partial recovery at a later time-point, when compared with the sham-operated group. GDNF mRNA-positive signals were detected in neurons of the ventral horn, especially in lamina IX. No regenerative fibers from corticospinal tract can be seen in the caudal segment near the injury site using BDA tracing technique. No somatosensory evoked potentials (SEP) could be recorded throughout the experimental period as well. These findings suggested that intrinsic GDNF in the spinal cord could play an essential role in neuroplasticity. The mechanism may be that GDNF is involved in the regulation of local circuitry in transected spinal cords of adult rats.     

Striatal input from the ventrobasal complex of the rat thalamus

We have analyzed whether caudal regions of the caudate putamen receive direct projections from thalamic sensory relay nuclei such as the ventrobasal complex. To this aim, the delivery of the retrograde neuroanatomical tracer Fluoro-Gold into the caudal caudate putamen resulted in the appearance of retrogradely labeled neurons in the ventral posteromedial and ventral posterolateral thalamic nuclei. These projections were further confirmed with injections of the anterograde tracers biotinylated dextran amine or Phaseolus vulgaris leucoagglutinin into these thalamic nuclei, by showing the existence of axonal terminal fields located in the caudal striatum. These results support the existence of direct projections linking the thalamic ventrobasal complex and the caudal striatum in the rat, probably via collateralization of thalamocortical axons when passing through the caudate putamen, and therefore supporting the putative involvement of the caudal striatum in sensory-related functions.     

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.