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At least 73 records · Page 4Linked to original sources
PubMed2001

Dynamic modulation of mossy fiber system throughput by inferior olive synchrony: a multielectrode study of cerebellar cortex activated by motor cortex.

We investigated the effects of climbing fiber synchrony on the temporal dynamics of mossy fiber system throughput in populations of cerebellar Purkinje cells (PCs). A multielectrode technique was used in ketamine-anesthetized rats that allowed both complex and simple spikes (CSs and SSs) to be recorded from multiple PCs simultaneously in lobule crus IIa. Stimulation of the tongue area of the primary motor cortex (TM1) was used to evoke cerebro-cerebellar interaction. At the single PC level, robust short-term interactions of CSs and SSs were observed after TM1 stimulation that typically consisted of an immediate depression and subsequent enhancement of SS firing after the occurrence of a CS. Such modulations of SS rate in a given PC were as robustly correlated to the CSs of simultaneously recorded PCs as they were to the CS on its own membrane-and did not require a CS on its own membrane-indicating a network basis for the interaction. Analyses of simultaneously recorded PCs using the normalized joint perievent time histogram demonstrated that CS and SS firing were dynamically correlated after TM1 stimulation in a manner that indicated strong control of mossy fiber system throughput by CS synchrony. For < or =300 ms after TM1 stimulation, most PCs showed episodic modulations in SS rate that appeared to be entrained by the population rhythm of climbing fiber synchrony. SS rhythmicity also was modulated dynamically by CSs, such that it was depressed by CSs and facilitated by their absence. Like the modulations in SS rate, a given PC's modulation in SS rhythmicity did not require it to fire a CS but was, on those instances, equally correlated to the synchronous CSs of other PCs. The data indicate that the climbing fiber system controls the temporal dynamics of SS firing in populations of PCs by using synchrony to engage intracerebellar circuitry and modulate mossy fiber system throughput.

Action Potentials↗
PubMed2000

[Treatment of central and neuropathic facial pain by chronic stimulation of the motor cortex: value of neuronavigation guidance systems for the localization of the motor cortex].

Thirty two patients with refractory central and neuropathic pain of peripheral origin were treated by chronic stimulation of the motor cortex between May 1993 and January 1997. The mean follow-up was 27. 3 months. The first 24 patients were operated according to the technique described by Tsubokawa. The last 13 cases (8 new patients and 5 reinterventions) were operated by a technique including localization by superficial CT reconstruction of the central region and neuronavigator guidance. The position of the central sulcus was confirmed by the use of intraoperative somatosensory evoked potentials. The somatotopic organisation of the motor cortex was established peroperatively by studying the motor responses at stimulation of the motor cortex through the dura. Ten of the 13 patients with central pain (77%) and nine of the 12 patients with neuropathic facial pain had experienced substantial pain relief (75%). One of the 3 patients with post-paraplegia pain was clearly improved. A satisfactory result was obtained in one patient with pain related to plexus avulsion and in one patient with pain related to intercostal herpes zoster. None of the patients developed epileptic seizures. The position of the stimulating poles effective on pain corresponded to the somatotopic representation of the motor cortex. The neuronavigator localization and guidance technique proved to be most useful identifying the appropriate portion of the motor gyrus. It also allowed the establishment of reliable correlations between electrophysiological-clinical and anatomical data which may be used to improve the clinical results and possibly to extend the indications of this technique.

Adult↗
PubMedDate not supplied

Pure motor monoparesis of a lower limb due to a small infarction in the contralateral motor cortex.

Pure motor monoparesis (PMM) is a rare condition characterized by weakness limited to one limb without sensory disturbance. We report a 42-year-old woman with PMM of the right lower limb caused by a small infarction in the contralateral motor cortex that could be detected by the magnetic resonance imaging of the brain. This case suggests that small lesions, missed by carelessly performed scans, could be a potential cause of PMM. This is especially true in the case of lower limb PMM, because the lesion may be located in the top of the frontal lobe cortex, an area that can be easily missed by routine scans. Therefore, we should pay careful attention to the opposite side of the motor cortex in examining neuroimages of PMM cases.

Adult↗
PubMed1992

Functional properties of single neurons in the face primary motor cortex of the primate. I. Input and output features of tongue motor cortex.

1. We have recently demonstrated that reversible, cooling-induced inactivation of the face motor cortex results in a severe impairment in the ability of monkeys (Macaca fascicularis) to perform a tongue-protrusion task but produces only relatively minor effects on the performance of a biting task by the same monkeys. To establish a neuronal correlate for these different behavioral relations, the present study has detailed the afferent input and intracortical microstimulation (ICMS)-defined output features of a population of face motor cortical neurons, and in a subsequent study we have documented the activities of the same population of neurons during the performance of the tongue-protrusion and biting tasks. 2. Of the 231 single neurons recorded within the face motor cortex, 163 were located at sites from which ICMS (less than or equal to 20 microA) could evoke tongue movements (i.e., "tongue-MI" sites) at the lowest threshold for eliciting orofacial movements. The remainder were located at sites from which ICMS evoked jaw movements ("jaw-MI" sites), face movements ("face-MI" sites), or at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 3. We confirmed the general organizational features of the face motor cortex that have been defined in previous studies, but we documented in detail the organizational features for tongue-MI. Thus we found that tongue movements were well represented, whereas jaw-closing movements were poorly represented; the representations for face, jaw, and tongue movements were overlapped; the same ICMS-evoked tongue movement could be multiply represented within tongue-MI; tongue-MI was characterized by a prominent input from superficial mechanosensory afferents, whereas there was little evidence for deep input; a close spatial match was found between ICMS-defined motor output and somatosensory afferent input for tongue-MI. 4. A variety of tongue movements could be evoked by ICMS at tongue-MI sites and were categorized into protrusion, retrusion, laterally directed, and other types of tongue movement. Low-threshold (i.e., less than or equal to 5 microA) ICMS-defined tongue-MI sites, which were considered to represent "efferent zones" projecting relatively directly to motoneurons, were reconstructed three dimensionally to provide insights into the spatial organization of tongue-MI. Examples of each of the four low-threshold efferent-zone categories were usually found throughout the ICMS-defined tongue-MI without any apparent preferential distribution. Furthermore, different low-threshold efferent-zone categories had close spatial relationships to each other in cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Serotonergic neurotransmission in the spinal cord and motor cortex of patients with motor neuron disease and controls: quantitative autoradiography for 5-HT1a and 5-HT2 receptors.

Serotonin 5-HT is a potent modulator of motor neuron excitability in the spinal cord. Serotonergic neurotransmission, because of its effects on glutamatergic excitation, may be relevant to the pathogenesis and therapy of motor neuron disease (MND). The human motor system was studied at two levels, spinal cord and motor cortex, by autoradiography for the 5-HT1A and 5-HT2 receptor subclasses. In addition, biochemical estimations of indole metabolites were performed in the spinal cord. Post mortem tissue from control cases and MND patients showed a reduction in 5-HT1A receptor binding in the cervical (p < 0.01) but not lumbar ventral horn in MND. 5-HT2 receptors were preserved in the ventral horn at both levels and were focally abundant around motor neuron somata. Tissue levels of 5-HT were unchanged in the spinal cord in MND. The metabolite 5-HIAA was increased in the cervical spinal cord in MND as was the molar ratio of 5HIAA:5-HT, implying that there may be an increased turnover of 5HT. In the motor cortex and premotor cortex the 5-HT1A receptor remained unchanged in MND. There was a 20% reduction in 5-HT2 receptor binding sites (p < 0.05) across all the cortical laminae with preservation of the normal pattern of laminar binding. These changes in two levels of the motor system in MND most likely represent physiological adaptations in the spinal cord and motor cortex rather than primary involvement of the serotonergic system in the pathogenesis of the disease.

Adult↗
PubMed2002

Motor cortex stimulation in the treatment of deafferentation pain. I. Localization of the motor cortex.

MRI and electrophysiological techniques to localize the primary motor cortex (MC) were performed on patients considered for MC stimulation for the treatment of deafferentation pain. The representation and trajectory of the rolandic fissure (RF) were accurately localized by external cranial landmarks and radiopaque fiducials superimposed on oblique MRI sections. In addition, the scalp distribution of the corticocortical responses elicited by acute epidural stimulation [motor cortex (MC) in frontal and sensory cortex (SC) in parietal scalp regions], and analgesic responses at the topographical representation of the painful periphery elicited by subacute epidural stimulation were found to be simple and reliable procedures to localize MC, SC and RF.

Causalgia↗
PubMed1985

Responses of cat motor cortex neurons to cortico-cortical and somatosensory inputs.

Intracellular techniques were used to investigate a cortico-cortical path from sensory cortex to motor cortex of cats. Cortico-cortical epsps were evoked in motor cortex neurons by microstimulation of area 3a. Epsps with latencies between 1.2 and 2.4 ms were identified as monosynaptic. These short latency cortico-cortical effects were recorded in layers II through VI of the motor cortex. Neurons with monosynaptic cortico-cortical epsps also received excitatory inputs from forelimb nerves, usually from both muscle and cutaneous afferent fibers. The epsps evoked from forelimb nerves in motor cortex neurons were preceded by neural activity in somatosensory cortex. Time delays between arrival of inputs in sensory cortex and in motor cortex were compared to the latencies of cortico-cortical epsps in the same motor cortex neurons. It was apparent that the timing was appropriate for the identified cortico-cortical path to have relayed some sensory inputs to motor cortex.

Animals↗
PubMed2000

Is there an optimal age for recovery from motor cortex lesions? I. Behavioral and anatomical sequelae of bilateral motor cortex lesions in rats on postnatal days 1, 10, and in adulthood.

Rats were given bilateral lesions of the motor cortex on the day of birth (P1), tenth day of life (P10), or in adulthood. They were trained on several motor tasks (skilled forelimb reaching, beam traversing, tongue extension), general motor activity, and a test of spatial learning (Morris water task). Although all lesion groups were impaired at skilled reaching, the P10 group was less impaired than either of the other two lesion groups. Furthermore, on the other motor tests the P10 group did not differ from controls whereas both P1 and adult groups were impaired. Only the P1 lesion group was impaired at the acquisition of the Morris water task. Anatomical analyses revealed that the P1 and P10 rats had smaller brains than the other two groups as well as having a generalized decrease in cortical thickness. Dendritic analysis of layer III pyramidal cells in the parietal cortex revealed a decrease in apical arbor in the lesion groups and an increase in the basilar arbor of the P1 and adult lesion animals. The P1 and adult operated groups showed an increase in spine density in the basilar dendrites of layer V pyramidal cells. Finally, analysis of the pattern of corticospinal projections revealed that the P1 animals had a markedly wider field of corticospinal projection neurons than any of the other groups. The widespread anatomical changes in all lesion groups versus the relatively better behavioral recovery after P10 lesions suggests that day 10 represents an optimal period for adapting to brain damage and subsequent brain reorganization.

Age Factors↗
PubMed1997

Neural correlates of a spatial sensory-to-motor transformation in primary motor cortex.

Primary motor cortex (MC) has been strongly implicated in motor processing, but there have been relatively few attempts to determine whether MC may also play a role in either sensory or context-dependent processing. In the present study, neuronal activity in MC was characterized in relation to the planning and execution of visually instructed limb movements whose trajectories were dissociated from their spatial targets. This design permitted the dissociation of neuronal activity related to motor processing from activity related to sensory or context-dependent processing. Two macaque monkeys were trained to perform a visually instructed, delayed reaching paradigm with indirect visual feedback. Subjects used the right forelimb to capture targets presented on a video display by moving a two-dimensional joystick whose position was reflected by a cursor. The target to be capture on each trial was indicated by a visual instruction stimulus (IS), which was separated from a movement-triggering stimulus (TS) by a variable delay. The direction of forelimb movement was dissociated from the location of the target by varying the spatial mappings between joystick and cursor across two conditions, unrotated (0 degrees offset between cursor and limb direction) and rotated (90 degrees offset). Task-related activity was recorded from a total of 180 MC neurons. The focus of this study was on directionally tuned neuronal activity that included phasic, stimulus-related activity following the IS; tonic, set-related activity between IS and TS; and phasic, movement-related activity following the TS. Of the entire sample of MC neurons with directionally tuned activity, 119 cells were tested both under rotation conditions, permitting dissociation of directional responses that depended on target locations from those that depended on limb trajectory. Task-related neuronal activity was classified as target dependent if it covaried exclusively with target location across both conditions, and as limb dependent if it covaried exclusively with limb trajectory. Directional activity that did not fulfill criteria for either target or limb dependence, because of changes across rotation conditions, was classified as complex. Approximately one quarter of MC neurons showed weak, but consistent, stimulus-related activity that was directionally tuned (24%, 29 of 119). Nearly all of the directionally classifiable stimulus-related activity was target dependent (94%, 15 of 16 responses), with the exception of a single limb-dependent response (6%, 1 of 16). A majority of MC neurons showed set-related activity that was directionally tuned (61%, 72 of 119). Of the directionally classifiable set-related activity, there were comparable numbers of target-dependent (37%, 16 of 43) and limb-dependent responses (35%, 15 of 43), with the remainder being complex (27%, 12 of 43). Movement-related activity following the TS was considered to be early or late, depending on whether it preceded or followed the onset of movement. The large majority of MC neurons showed early movement-related activity that was directionally tuned (86%, 102 of 119): among those whose neurons early activity was directionally classifiable, there were only one third as many target-dependent responses (14%, 11 of 79) as limb-dependent responses (43%, 34 of 79), with the remainder being complex (43%, 34 of 79). There was also a large majority of MC neurons that showed late movement-related activity that was directionally tuned (84%, 100 of 119): among those whose late activity was directionally classifiable, there were only one ninth as many target-dependent responses (5%, 4 of 88) as there were limb-dependent responses (41%, 36 of 88), with the remainder being complex (55%, 48 of 88). The instructed delay task employed in this study required a sensory-to-motor transformation through which the instructed target location was associated with a limb movement of the appropriate direction. (ABSTRACT TRUNCATED)

Action Potentials↗
PubMed2004

Interactions between cognitive and sensorimotor functions in the motor cortex: evidence from the preparatory motor sets anticipating a perturbation.

The many signs of cognitive processes in the activation pattern of the primary motor cortex or in corticospinal (CS) excitability gave rise to the idea that the motor cortex is a crucial node in the processing of cognitive information related to sensorimotor functions. Moreover, it became clear that the preparatory motor sets offer a privileged window to investigate the interaction between cognitive and sensorimotor function in the motor cortex. In the present review, we examine how the study of the preparatory motor sets anticipating a mechanical movement perturbation contributes to enlightening this question. Following the initial observation made by Hammond that some components of the stretch reflex can be modulated by a prior intention either to resist or to relax in response to a subsequent perturbation, first evidence of the phenomenon was obtained in behaving monkeys. Moreover, this study related this peripheral fact to the observed anticipatory activity of motor cortex neurons after a prior instruction telling the animal how to respond to the subsequent perturbation, which triggered the instructed movement. Indeed, this anticipatory activity was found to be different according to the instruction. In the 1980s, this work inspired a lot of studies in human beings that brought support to the idea of a cognitive tuning of the long latency stretch response (LLSR). Specifically, the MI component of the response was shown to be modulated by a prior intent to resist versus to let go when faced with the perturbation. Recently, new approaches have been developed to obtain evidence of a cognitive tuning of CS excitability, thanks to transcranial magnetic stimulation (TMS). TMS has been used both as a reliable tool for quantifying the CS excitability via the motor evoked potentials (MEPs), and to centrally perturb the organization of movement. Such central perturbations offer the unique opportunity to activate the descending motor tracts while shunting, for a short time period, the ascending tracts assisting the movement. Thus, CS excitability was measured before the movement was perturbed. These studies demonstrated the readiness of the CS tract to be involved in anticipatory compensatory responses to central movement perturbations induced by TMS in relation to the subject's cognitive attitudes. The question of the cerebral regions upstream of the motor cortex that could be responsible for this modulation in CS excitability remains largely open.

Animals↗
PubMed1997

Increased activity of the ipsilateral motor cortex during a hand motor task in patients with brain tumor and paresis.

PURPOSE: To look for changes in the motor cortex in patients with brain tumors. METHODS: Both cerebral hemispheres in seven patients with brain tumors were examined with functional MR imaging during a motor task performed by the hand opposite the site of tumor. The ratio of the activated area in the motor cortex ipsilateral/contralateral to the tested hand was calculated for each subject. Twenty healthy subjects were also examined in the same manner for comparison. RESULTS: The ratio of the ipsilateral/contralateral activated area was abnormally high in three patients with tumor-related paresis of the tested hand. The ratio was significantly greater in patients with paresis than in healthy subjects. CONCLUSION: This study demonstrated increased activity in the ipsilateral (unaffected) motor area during a hand motor task in patients with brain tumor and paresis, which was thought to reflect compensatory reorganization induced by the functional damage.

Adult↗
PubMed1987

Transcranial stimulation of the motor cortex to produce motor-evoked potentials.

Monitoring of the nervous system using evoked potentials is a developing tool. A new evoked potential, the motor-evoked potential (MEP), based on a traditional test, uses brain stimulation to monitor the motor system. The MEP complements the existing modalities, which are wholly sensory. The MEP can be prompted by direct stimulation of the motor cortex, but, in a more general way, by transcranial stimulation. Electric or magnetic means can be used. One electric system involves placement of an electrode on the scalp over the motor cortex, paired with a cathodal plate on the roof of the hard palate. Recording electrodes are placed over the spinal cord, peripheral nerves, and muscles. Signals are recorded with a standard, evoked-potential, signal-averaging computer. Animal studies indicate that the electric stimulus activates primarily the pyramidal system to produce a descending evoked potential in the ventral and dorsolateral spinal cord. It is more sensitive than the sensory-evoked potential to spinal cord injury produced by the weight-drop method in cats. The peripheral nerve responses, much more sensitive to injury than the cord responses, can be altered by metabolic abnormalities. To date, the MEP has been an accurate indicator of ambulation in chronic spinal cord injury in animals. Parallel clinical development in the operating room has shown that the test is valuable; and it monitors brainstem or cortex manipulation, as well as cord manipulation. Safety studies are encouraging. The MEP is developmentally and technically demanding, but it has produced high quality signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Mapping motor cortex projections to single motor units in humans with transcranial magnetic stimulation.

We devised a method to investigate the cortical organization of corticomotoneurons (CMs) to upper limb muscles. A spike-triggering technique was used, in which a tonically discharging single motor unit (SMU) triggered transcranial magnetic stimulation (TMS) of motor cortex, and the probability of producing short-latency discharges (primary excitatory responses [PERs]) was measured. PER probabilities were mapped in 34 SMUs, using a 16 cm(2) scalp grid with the central reference point having a probability of 0.5. Maps showed a single optimum point of scalp stimulation and significant decreases in PER probability with shifts of 2 cm from this point, for all subjects. These findings suggest that the colony of CMs projecting to an individual SMN is contained within a small volume of motor cortex. Changes in PER probability with shifts in stimulation site may reflect the organization of other intracortical neurons mediating TMS activation of these CMs.

Adult↗
PubMedDate not supplied

Changes in dry weight of pyramidal cell nuclei in the motor cortex during local motor-food conditioning.

The formation of a local motor-food conditioned reflex in rats, consisting of pressing on a level with the unpreferred paw, in one session led to a decrease in dry weight of the large pyramidal cell nuclei in the area of representation of that paw in the motor cortex. Frequent repetition of the local motor-food conditioned reflex consisting of pressing on the level with the preferred paw was not accompanied by any such changes. It is suggested that changes in dry weight of the large pyramidal cell nuclei in the area of representation of the unpreferred paw are due to involvement of these neurons in the formation of the new motor coordination (the local conditioned reflex).

Animals↗
PubMed1988

Noninvasive mapping of human motor cortex.

Human motor cortex was stimulated using brief, high-voltage electrical stimulation. Constant-voltage stimuli were delivered through a bipolar surface stimulator with the anode placed at multiple positions on the scalp and the cathode situated 2.5 cm anterior to the anode. Recordings were bilateral from the abductor pollicis brevis, tibialis anterior, and risorius. We averaged the amplitudes of three muscle responses obtained from stimulation of each scalp position and assigned the resultant value to that position. The findings in eight normal volunteers were similar and reproducible. The maximal responses of the right hand were obtained when stimulating over C3, of the left hand when stimulating over C4, of the right and left legs when stimulating over Cz, and of the right side of the mouth when stimulating over T3.

Adult↗
PubMed1997

Patterns of inputs to the parietal cortex efferent neurons from the motor cortex and cerebellum in the cat.

Responses of parietal association cortex efferent neurons to motor cortex and cerebellar nuclei stimulation were studied intracellularly in anaesthetized cats. Efferent neurons of the parietal cortex were identified according to their antidromic activation on stimulation of the motor cortex, pontine nuclei proper and red nucleus. Monosynaptic excitatory postsynaptic potentials of ipsilateral anterior suprasylvian and lateral gyri neurons to motor cortex stimulation have been established. Oligo- and polysynaptic excitatory responses of parietal cortex efferent neurons to cerebellar nuclei stimulation have been recorded. Correlation between the latencies of cerebellar-induced excitatory postsynaptic potentials and antidromic invasion of neurons on stimulation of different parietal cortex efferent projections (corticocortical, corticopontine, corticorubral) has been obtained. A similar correlation has been found between the latencies of excitatory postsynaptic potentials evoked on stimulation of one of the cerebellar nuclei and latencies of antidromic invasion induced on stimulation of all studied parietal cortex efferent systems. Feedforward and feedback mechanisms in the input-output organization of parietal association cortex have been discussed.

Animals↗
PubMed2003

Specific functions of the motor cortex in reorganizing coordinations during motor training in animals and humans.

The involvement of the motor cortex in learning movements has recently attracted much attention. One aspect of motor learning is the inhibition of innate synergies which interfere with performance of the acquired movement. Various models of operant responses in dogs have demonstrated the critical role of the motor cortex in the reorganization and inhibition of interfering synergies during learning. The role of the motor cortex and corticospinal influences in the formation of new coordinations in humans was studied here in patients with organic lesions of the cerebral circulation involving the internal capsule, using postural coordination and movements in a bimanual unloading response as an example. Formation of the forearm stabilization response was deeply lesioned on the afflicted side. Some degree of impairment was also seen on the ipsilateral side, but it was no different from the level of learning impairment in patients with lesions not involving the internal capsule or in patients with parkinsonism. The existence of specific contralateral influences of the motor cortex and non-specific descending influences on the process of motor learning is proposed.

Aged↗