Reorganization Of Motor Cortex Research Articles

Long-term motor cortex reorganization after facial nerve severing in newborn rats.

Using the model of facial nerve injury, we have compared the effect of injury in newborn and adult rats on the adult rat motor cortex (M1). To this end, the facial nerve was severed in 10 newborn rats 2 days after birth (Newborn group) and in 10 adult rats (Adult group). In both the Control (contralateral to untouched nerve) and the Experimental (contralateral to severed nerve) hemisphere of each rat, the M1 output organization was assessed by intracortical microstimulation. Our findings demonstrated that: (i) there is no statistical difference in the percentage of movement sites and in current thresholds required to evoke movement in Control hemispheres between the Adult and Newborn groups of rats; (ii) in Adult Experimental hemispheres, neck sites expand in the medial part of the vibrissae representation more extensively than shown in Newborn Experimental hemispheres; (iii) in Newborn Experimental hemispheres eye sites expand in the medial part of the vibrissae representation more extensively than in Adult Experimental hemispheres (these sites overlap the cortical region where electrical stimulation evokes neck movement in Adult Experimental hemispheres) and (iv) in both Newborn and Adult Experimental hemispheres, forelimb sites expand similarly thereby overlapping the same cortical region, corresponding to the lateral part of the vibrissae representation. We conclude that, when the facial nerve injury is performed in the newborn rat, the pattern of movement representation differs from that obtained with the same lesion in the mature brain only in the frontal cortex corresponding to the medial part of the normal vibrissae representation.

Connections of neurons in the lumbar ventral horn of spinal cord are altered after long-standing limb loss in a macaque monkey

Explanations for the massive reorganization in primary motor cortex, M1, after limb amputation typically focus on processes that occur in cortex. Few have investigated whether changes in more peripheral parts of the pathway might also play a role in the reorganization. In the present study, we examined the integrity and connectivity of the spinal cord motoneurons in a macaque monkey (Macaca mulatta) that lost a hindlimb as a result of accidental injury more than 3.5 years earlier. To label motoneurons, multiple small injections of a neuroanatomical tracer were placed in the muscles of the hip just adjacent to the stump of the amputated leg, and in matched locations in the opposite side for control purposes. Injections of a second tracer were made in the intact foot. In the ventral horn that related to the intact hindlimb, motoneurons labeled by the hip injections were concentrated rostral and ventromedial to those labeled by the foot injections. Hip injections on the side of the amputation labeled neurons that were located well beyond the normal territory for motoneurons related to the hip and into the zone normally occupied by neurons projecting to the foot. Labeled motoneurons innervating the intact limb were significantly larger than neurons on the side of the amputation (x = 2410 and 2061 µm2, respectively). The findings suggest that many neurons survived the long-standing amputation, and made new connections with remaining intact muscles. These new patterns of connectivity likely contribute to the reorganization of motor cortex in amputees, and perhaps to abnormal behaviors like those reported by human amputees.

Handedness Shift as a Consequence of Motor Cortex Reorganization After Early Functional Impairment in Left Temporal Lobe Epilepsy—An fMRI Case Report

The impact of epileptiform activity on the functional organization of various cortical regions is currently a widely discussed topic. Our patient, suffering from left-sided temporal lobe epilepsy with typical mesiotemporal sclerosis, had a remarkable history of a clear-cut handedness shift in early childhood. In this study, we considered the possibility of the functional reorganization of the motor cortex using functional MRI. The results reflect epileptiform activity as an important formative factor for motor cortex development in our patient.

Functional magnetic resonance imaging and control over the biceps muscle after intercostal–musculocutaneous nerve transfer

Object Recent progress in the understanding of cerebral plastic changes that occur after an intercostal nerve (ICN)–musculocutaneous nerve (MCN) transfer motivated a study with functional magnetic resonance (fMR) imaging to map reorganization in the primary motor cortex. Methods Eleven patients with traumatic root avulsions of the brachial plexus were studied. Nine patients underwent ICN–MCN transfer to restore biceps function and two patients were studied prior to surgery. The biceps muscle recovered well in seven patients who had undergone surgery and remained paralytic in the other two patients. Maps of neural activity within the motor cortex were generated for both arms in each patient by using fMR imaging, and the active pixels were counted. The motor task consisted of biceps muscle contraction. Patients with a paralytic biceps were asked to contract this muscle virtually. The location and intensity of motor activation of the seven surgically treated arms that required good biceps muscle function were compared with those of the four arms with a paralytic biceps and with activity obtained in the contralateral hemisphere regulating the control arms. Activity could be induced in the seven surgically treated patients whose biceps muscles had regained function and was localized within the primary motor area. In contrast, activity could not be induced in the four patients whose biceps muscles were paralytic. Neither the number of active pixels nor the mean value of their activations differed between the seven arms with good biceps function and control arms. The weighted center of gravity of the distribution of activity also did not appear to differ. Conclusions Reactivation of the neural input activity for volitional biceps control after ICN–MCN transfer, as reflected on fMR images, is induced by successful biceps muscle reinnervation. In addition, the restored input activity does not differ from the normal activity regulating biceps contraction and, therefore, has MCN acceptor qualities. After ICN–MCN transfer, cerebral activity cannot reach the biceps muscle following the normal nervous system pathway. The presence of a common input response between corticospinal neurons of the ICN donor and the MCN acceptor seems crucial to obtain a functional result after transfer. It may even be the case that a common input response between donor and acceptor needs to be present in all types of nerve transfer to become functionally effective.

Impairment-oriented training and training-induced adaptive motor cortex reorganisation after stroke: a fTMS study

Objective: This study investigated (1.) what type of changes in the motor cortex in stroke patients and to which degree such changes are associated with functional recovery and (2.) whether the type of motor training – rather than its intensity only – influences the success of any intervention in terms of adaptive motor cortex reorganisation and behavioural motor recovery after stroke.

Reorganization in the ipsilateral motor cortex of patients with lower limb amputation

The aim of the present study was to assess reorganization in the motor cortex of patients with lower limb amputation. We studied seven patients with traumatic lower limb amputation, and six healthy controls, using transcranial magnetic stimulation mapping, with recordings from the quadriceps femoris muscle on both sides. Motor threshold, sum of amplitudes, area and the amplitude-weighted centre of gravity (COG) of the motor output map were assessed. We found a significant lateral displacement of the COG on the hemisphere contralateral to the healthy leg, whereas other parameters did not differ significantly between sides. This finding might be indicative of cortical reorganization in the hemisphere ipsilateral to the amputation. It is discussed with respect to an altered peripheral input to this hemisphere, and to transcallosal interactions from the deafferented hemisphere.

Functional magnetic resonance imaging and control over the biceps muscle after intercostal-musculocutaneous nerve transfer.

Recent progress in the understanding of cerebral plastic changes that occur after an intercostal nerve (ICN)-musculocutaneous nerve (MCN) transfer motivated a study with functional magnetic resonance (fMR) imaging to map reorganization in the primary motor cortex. Eleven patients with traumatic root avulsions of the brachial plexus were studied. Nine patients underwent ICN-MCN transfer to restore biceps function and two patients were studied prior to surgery. The biceps muscle recovered well in seven patients who had undergone surgery and remained paralytic in the other two patients. Maps of neural activity within the motor cortex were generated for both arms in each patient by using fMR imaging, and the active pixels were counted. The motor task consisted of biceps muscle contraction. Patients with a paralytic biceps were asked to contract this muscle virtually. The location and intensity of motor activation of the seven surgically treated arms that required good biceps muscle function were compared with those of the four arms with a paralytic biceps and with activity obtained in the contralateral hemisphere regulating the control arms. Activity could be induced in the seven surgically treated patients whose biceps muscles had regained function and was localized within the primary motor area. In contrast, activity could not be induced in the four patients whose biceps muscles were paralytic. Neither the number of active pixels nor the mean value of their activations differed between the seven arms with good biceps function and control arms. The weighted center of gravity of the distribution of activity also did not appear to differ. Reactivation of the neural input activity for volitional biceps control after ICN-MCN transfer, as reflected on fMR images, is induced by successful biceps muscle reinnervation. In addition, the restored input activity does not differ from the normal activity regulating biceps contraction and, therefore, has MCN acceptor qualities. After ICN-MCN transfer, cerebral activity cannot reach the biceps muscle following the normal nervous system pathway. The presence of a common input response between corticospinal neurons of the ICN donor and the MCN acceptor seems crucial to obtain a functional result after transfer. It may even be the case that a common input response between donor and acceptor needs to be present in all types of nerve transfer to become functionally effective.

Functional MRI evidence for motor cortex reorganization adjacent to a lesion in a primary motor cortex.

The object of this study was to verify motor cortex reorganization in patients with primary motor cortex injury using functional magnetic resonance imaging. Ten control subjects and two patients with primary motor cortex injury, caused by a traumatic brain injury in patient 1 and meningioma in patient 2, were evaluated. Functional magnetic resonance imaging was performed using the blood oxygenation level-dependent technique at 1.5 T with hand movements. The contralateral primary sensorimotor cortex was activated by unaffected hand movements. However, only the contralateral primary sensory cortex in patient 1 and the premotor area in patient 2 were activated by affected hand movements, which were totally absent in control subjects. We believe that the hand motor function of injured primary motor cortex was shifted into the primary sensory cortex in patient 1 and premotor area in patient 2. In conclusion, this finding may reflect a functional reorganization of the motor area in patients with a primary motor cortex injury.

Time course of motor cortex reorganization following botulinum toxin injection into the vibrissal pad of the adult rat.

The present experiment studies representation patterns in the motor cortex (M1) of adult rats, 1, 3, 6, and 12 days after unilateral injection of Botulinum Toxin (BTX) into the vibrissa pad. Intracortical microstimulation (ICMS) was used to evidence changes in the representation over time and in the current thresholds required to evoke movements inside the disconnected vibrissa region. After 1 day, isolated as well as contiguous negative sites were observed within the motor cortex corresponding to the disconnected vibrissa region. Thereafter the percentage of unresponsive sites decreased so that after 6 days, the number of unresponsive sites was not significantly higher than those in the control hemispheres. Within the disconnected vibrissa region, electrical stimulation elicited forelimb, eye, ipsilateral vibrissa and neck movements. Following BTX injection, the enlargement of the forelimb representation into the disconnected vibrissa representation began during the first day and stabilized during the second week after injection. In the first days, stimulation thresholds in expanded forelimb sites were higher than those required for similar movement in normal M1 forelimb representation. These thresholds then declined so that in approximately 6 days they were similar to normal. There was no clear evidence that stimulation of sites in the medial part of disconnected vibrissa-cortex evoked eye movements during the first 6 days after BTX injection. After this time, thresholds required to evoke eye movement in expanded sites were generally similar to, and never higher than, those needed to evoke this movement in control sites. Intermingled ipsilateral vibrissa and neck movement occupies part of the medial vibrissa region. Over the 12 days, extension of the ipsilateral vibrissa representation shrank while the representation of neck movement remained unchanged. Throughout the entire time there was no change in the excitability of these sites and the thresholds remained higher than that needed to elicit the vibrissa movement normally represented in this cortical region. No significant differences in threshold were found over time for any of the other movement categories represented in M1. These results indicate that, over time, the new movements inside the disconnected vibrissa region develop differently in M1 following peripheral motor disconnection. The implications for mechanisms involved in cortical plasticity are discussed.

Use-related gene expression patterns of rat motor cortex.

Current evidence indicates reorganization of motor cortex in association with motor behavior. To investigate the molecular basis for these changes rats were fitted with limb-restricting vests which forced the use of one forelimb for 10 days. Using cDNA macroarrays, expression profiles of the corresponding motor cortices connected to the overused and immobilized limbs were analyzed. In the overused motor cortex up-regulations were observed exclusively, including genes coding for voltage-gated ion channels, trafficking and targeting proteins, and intracellular kinase network members (10 genes). In the contralateral immobilized cortex changes were restricted to down-regulation, mainly involving genes pertaining to DNA-binding, translation, neuronal signaling and metabolic pathways (9 genes). At least some of these changes are likely to represent the molecular substrate of use-dependent plasticity.

Transcranial magnetic stimulation as a tool for assessment and modulation of cortical excitability in patients with major depression

Stroke is associated with reorganization within motor areas of both hemispheres. Mapping the cortical hand motor representation using transcranial magnetic stimulation may help to understand the relationship between motor cortex reorganization and motor recovery of the affected hand after stroke.A standardized review of the pertinent literature was performed.We identified 20 trials, which analyzed the relationship between the extent and/or location of cortical hand motor representation using transcranial magnetic stimulation and motor function and recovery of the affected hand. Several correlations were found between cortical reorganization and measures of hand motor impairment and recovery.A better understanding of the relationships between the extent and location of cortical hand motor representation and the motor impairment and motor recovery of the affected hand after stroke may contribute to a targeted use of non-invasive brain stimulation protocols. In the future motor mapping may help to guide brain stimulation techniques to the most effective motor area in an affected individual.

Driving Plasticity in Human Adult Motor Cortex Is Associated with Improved Motor Function after Brain Injury

Changes in somatosensory input can remodel human cortical motor organization, yet the input characteristics that promote reorganization and their functional significance have not been explored. Here we show with transcranial magnetic stimulation that sensory-driven reorganization of human motor cortex is highly dependent upon the frequency, intensity, and duration of stimulus applied. Those patterns of input associated with enhanced excitability (5 Hz, 75% maximal tolerated intensity for 10 min) induce stronger cortical activation to fMRI. When applied to acutely dysphagic stroke patients, swallowing corticobulbar excitability is increased mainly in the undamaged hemisphere, being strongly correlated with an improvement in swallowing function. Thus, input to the human adult brain can be programmed to promote beneficial changes in neuroplasticity and function after cerebral injury.

Sensory motor organization and re-organization in normals and patients using a combined MEG and fMRI approach

A review of the research activity on the organization and re-organization of the sensory motor cortex carried out at the Institute of Advanced Biomedical Technology of the University of Chieti, Italy, is presented. These studies were performed by means of magnetoencephalography (MEG) and functional magnetic resonance (fMRI), that were used either independently or, when possible, in combination, to take maximum advantage of the high temporal resolution of the former technique and of the high spatial resolution of the latter. The most interesting results obtained both in basic research and in the clinical field will be illustrated. In particular, we will deal with: (i) the organization of the primary and secondary sensory areas with respect to different stimulus intensities and different district stimulations, (ii) the area activated during execution of complex motor tasks, such as handwriting, versus simple movements, (iii) the possibility of identifying the epileptogenic area with respect to functional landmarks from the interictal activity of patients with or without a lesion, as well as the localization of functional reference points in pre-surgical mapping and, finally, (iv) monitoring of plasticity phenomena in patients affected by vascular lesions during the recovery phase.

Reorganization of human motor cortex after hand replantation.

In 10 patients, reorganizational changes of the motor cortex contralateral to a replanted hand (MCreplant) were studied one to 14 years after complete traumatic amputation and consecutive successful replantation of the hand. The organizational state of MCreplant was assessed for the deafferentated and peripherally deefferentated hand-associated motor cortex and the adjacent motor representation of the proximal arm. For this, response maps were established for the first dorsal interosseus and biceps brachii muscle using focal transcranial magnetic stimulation (TMS) on a skull surface grid. Characteristics of the maps were center of gravity (COG), number of effective stimulation sites, amplitude sum, and amplitudes and response threshold at the optimal stimulation point. The COG is defined by the spatial distribution of response amplitudes on the map and lies over the cortex region with the most excitable corticospinal neurones supplying the recorded muscle. The COG of the biceps map in MCreplant was shifted laterally by 9.8 +/- 3.6 mm (range 5.0-15.7 mm). The extension of the biceps map in MCreplant was increased and the responses were enlarged and had lowered thresholds. For the muscles of the replanted hand, the pattern of reorganization was different: Response amplitudes were enlarged but thresholds, COG, and area of the cortical response map were normal. The different reorganizational phenomena observed for the motor cortical areas supplying the replanted hand and the biceps brachii of the same arm may be influenced by a different extent of deafferentation and by their different role in hand motor control.

Cortical reorganization in motor cortex after graft of both hands

Cortical organization shifts after sensory deprivation, but the reversibility of this reorganization has not been studied. Here, using functional magnetic resonance imaging (fMRI), we investigated the dynamics of cortical reorganization in a patient's motor cortex before and after bilateral hand transplantation. We found that amputation-induced cortical reorganization was reversed following hand transplantation.

Reorganization of Motor and Somatosensory Cortex in Upper Extremity Amputees with Phantom Limb Pain

Phantom limb pain (PLP) in amputees is associated with reorganizational changes in the somatosensory system. To investigate the relationship between somatosensory and motor reorganization and phantom limb pain, we used focal transcranial magnetic stimulation (TMS) of the motor cortex and neuroelectric source imaging of the somatosensory cortex (SI) in patients with and without phantom limb pain. For transcranial magnetic stimulation, recordings were made bilaterally from the biceps brachii, zygomaticus, and depressor labii inferioris muscles. Neuroelectric source imaging of the EEG was obtained after somatosensory stimulation of the skin overlying face and hand. Patients with phantom limb pain had larger motor-evoked potentials from the biceps brachii, and the map of outputs was larger for muscles on the amputated side compared with the intact side. The optimal scalp positions for stimulation of the zygomaticus and depressor labii inferioris muscles were displaced significantly more medially (toward the missing hand representation) in patients with phantom limb pain only. Neuroelectric source imaging revealed a similar medial displacement of the dipole center for face stimulation in patients with phantom limb pain. There was a high correlation between the magnitude of the shift of the cortical representation of the mouth into the hand area in motor and somatosensory cortex and phantom limb pain. These results show enhanced plasticity in both the motor and somatosensory domains in amputees with phantom limb pain.

Spinal Cord Atrophy and Reorganization of Motoneuron Connections Following Long-Standing Limb Loss in Primates

Primates with long-standing therapeutic amputations of a limb at a young age were used to investigate the possibility that deefferented motor nerves sprout to new muscle targets. Injections of anatomical tracers into the muscles proximal to the amputated stump labeled a larger extent of motoneurons than matched injections on the intact side or in normal animals, including motoneurons that would normally supply only the missing limb muscles. Although the total numbers of distal limb motoneurons remained normal, some distal limb motoneurons on the amputated side were smaller in size and simpler in form. These results suggest that deprived motoneurons survive and retain function by reinnervating new muscle targets. The sprouted motor efferents may account for some of the reorganization of primary motor cortex that follows long-standing amputation.

Reorganization of primary motor cortex in adult macaque monkeys with long-standing amputations.

The organization of primary motor cortex (M1) of adult macaque monkeys was examined years after therapeutic amputation of part of a limb or digits. For each case, a large number of sites in M1 were electrically stimulated with a penetrating microelectrode, and the evoked movements and levels of current needed to evoke the movements were recorded. Results from four monkeys with the loss of a forelimb near or above the elbow show that extensive regions of cortex formerly devoted to the missing hand evoked movements of the stump and the adjoining shoulder. Threshold current levels for stump movements were comparable to those for normal arm movements. Few or no sites in the estimated former territory of the hand evoked face movements. Similar patterns of reorganization were observed in all four cases, which included two monkeys injured as adults, one as a juvenile, and one as an infant. In a single monkey with a hindlimb amputation at the knee as an infant, stimulation of cortex in the region normally devoted to the foot moved the leg stump, again at thresholds in the range for normal movements. Finally, in a monkey that had lost digit 5 and the distal phalanges of digits 2-4 at 2 yr of age, much of the hand portion of M1 was devoted to movements of the digit stumps.

The reorganization of somatosensory and motor cortex after peripheral nerve or spinal cord injury in primates

The reorganization of somatosensory and motor cortex after peripheral nerve or spinal cord injury in primates

Reorganization in Primary Motor Cortex of Primates with Long-Standing Therapeutic Amputations

Intracortical microstimulation was used to investigate the organization of primate primary motor cortex (M1) in three squirrel monkeys and two galagos years after the therapeutic amputation of an injured forelimb or hindlimb. In two squirrel monkeys with forelimb amputation, physiological results were correlated with the distribution of corticospinal neurons after injections of tracers into the lower cervical segments of the spinal cord. Distributions of labeled corticospinal neurons helped identify the locations of the former forelimb cortex in M1. Evoked movements from M1 ipsilateral to the missing limb were not obviously different from M1 of normal controls. Stimulation in the deefferented part of M1 contralateral to the missing limb elicited movements of the remaining proximal muscles as well as movements from adjacent body representations in all cases. Stimulation in the deefferented forelimb cortex evoked shoulder stump, trunk, and orofacial movements, whereas stimulation in the deefferented hindlimb cortex evoked hip stump, trunk, and tail movements. Movements were evoked from all sites in the deprived cortex, so that there were no unresponsive zones. Minimal levels of current necessary to evoke these movements varied from those in the normal range to those of much higher levels, with the average threshold higher than normal. Finally, multiunit recording from the two galagos revealed that the deprived portions of S1 were responsive to touch or taps on the stump and neighboring body parts.