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At least 1,225 records · Page 68Linked to original sources
PubMed1998

Increased activation of frontal areas during arm movement in idiopathic torsion dystonia.

Most positron emission tomography (PET) studies of regional cerebral function in idiopathic torsion dystonia (ITD) have failed to show abnormalities, but there have been few studies of the changes in regional cerebral blood flow (rCBF) that occur during movement in dystonia. Using PET, we have studied six patients with familial generalized ITD both at rest and while moving a joystick with the right hand. The patterns of CBF change obtained were compared with those in six age-matched control subjects. In the dystonia group, free selection of movement was associated with relative increases in rCBF above that observed in control subjects in the left premotor area, the supplementary motor area (SMA), the anterior cingulate cortex, and the left dorsolateral prefrontal area. Subcortical increases were observed within the cerebellum and the putamen. There was a relative decrease in flow through the contralateral primary sensorimotor cortex. These findings contrast with those reported in patients with Parkinson's disease undertaking the same task in which the activity in the SMA and putamen was decreased. We suggest that arm dystonia in ITD is associated with overactivity of the premotor areas, including the SMA, and that this results from release of the thalamus from the normal inhibitory influence of the globus pallidus internal segment. Other abnormalities of basal ganglia control of brain stem centers may be involved in axial dystonia.

Adult↗
PubMed1995

Changes in neuropeptide levels after brain damage in rats.

The physiological and pathophysiological roles of neuropeptides are still not clear. The aim of our study was to detect long lasting changes of vasoactive-intestinal peptide (VIP), somatostatin (SOM) and substance P (SP) contents in the rat cerebral cortex and hippocampus after brain lesion. The experiments were performed on groups of adult male Wistar rats. The first group consisted of animals with unilateral ablation of the sensorimotor cortex performed at the age of 60 days. The second group was a control one (rats of the same age but with an intact brain). Both groups of animals were sacrificed at the age of 90-105 days and radioimmunoassay was used to determine amounts of VIP, SOM and SP. The mean values of VIP levels were decreased significantly only in contralateral cortical areas, while there was an increase of SP in lesioned animals. Our results suggest that descrete changes in neuropeptide levels occur during restorative processes after brain lesion.

Analysis of Variance↗
PubMed2001

Disinhibition of somatosensory and motor cortex in mitochondriopathy without myoclonus.

OBJECTIVE: To test electrophysiologically, if patients with mitochondriopathy but without evidence of myocloni have subclinical signs of disinhibition in motor and somatosensory cortices. METHODS: Two patients were studied and compared with age-matched control groups. RESULTS: In both patients, giant somatosensory evoked potentials after median nerve stimulation and a reduced intracortical inhibition tested by transcranial magnetic stimulation in a paired pulse paradigm indicated a dysfunction of inhibitory circuits in the motor as well as the somatosensory cortex. In addition, the somatosensory evoked 600 Hz activity recorded by magnetoencephalography was abolished. CONCLUSIONS: Patients with mitochondriopathy may suffer from a subclinical disturbance of inhibition in the sensorimotor cortex. The loss of 600 Hz activity indicates that these high-frequency oscillations could reflect the activity of inhibitory neurons in the somatosensory cortex.

Adult↗
PubMed1996

Abnormalities of the balance between inhibition and excitation in the motor cortex of patients with cortical myoclonus.

Patients with cortical myoclonus may have purely focal or multifocal jerks, or they may have additional bilateral or generalized jerks, suggesting the spread of excitatory myoclonic activity between the cerebral hemispheres and across the sensorimotor cortex. The factors contributing to this spread of activity were investigated in 10 patients with multifocal cortical myoclonus and eight patients with multifocal and bilateral or generalized cortical myoclonus. The two groups were termed 'non- spreaders' and 'spreaders' respectively. Eight of the patients were also epileptic. Motor thresholds to single transcranial magnetic shocks at rest were higher in 'non- spreaders' (median 88%, range 45-100% of stimulator output) than either 'spreaders' (50%, range 26-90%, P=0.023) or health controls (38%, range 28-53%, P<0.001). This pathological elevation in motor threshold was not simply an effect of treatment with antiepileptic drugs. Paired transcranial magnetic stimuli were used to investigate ipsilateral cortico-cortical and transcallosal inhibition, There was less (MANOVA, P<0.05) ipsilateral inhibition at interstimulus intervals (ISIs) of 1-6 ms in 'spreaders' (mean 107+/-SEM 23% of control) compared with 'non- spreaders' (75+/-15%) or healthy subjects (59+/-10%). There was also less (P<0.05) transcallosal inhibition across inhibitory timings (10, 12 and 14 ms) in the 'spreaders' (98+/-6% of control) compared with the 'non-spreaders' (64+/-8%) or healthy subjects (59+/-6%). There was no relationship between ipsilateral cortico-cortical and transcallosal inhibition and the presence or absence of epilepsy, although non-epileptic patients did have higher motor thresholds (median 85%, range 32-100% of stimulator output) than either epileptic patients (50%, range 26-90%, P<0.001) or healthy controls (38%, range 28-53%, P=0.002). Abnormalities in ipsilateral and transcallosal inhibition appear to facilitate the spread of the cortical myoclonic activity responsible for bilateral and generalized jerks. However, these abnormalities in inhibition do not play a major role in the development of generalized seizures in patients with cortical myoclonus.

Adolescent↗
PubMedDate not supplied

[The structure of the background EEG of the rabbit in the high-frequency portion of the spectrum].

With the purpose of studying the character and structure of high frequency bioelectric activity of rabbits cerebral cortex in the state of calm alertness, the EEG ensembles of different areas of the cortex (sensorimotor, visual, acoustic) and dorsal hippocampus were studied with FFT method. A supposition was made about the presence of systemic organization of the background EEG in rabbits cerebral cortex, reflected, in particular, in the presence of determined components both of chaotic and rhythmic character having different degrees of manifestation. Heterogeneity was revealed in distribution of energies of spectral EEG components in the studied frequency ranges from 14.7 to 100 Hz with predominance of total specific energy value in the band of 14.7-60 Hz. In coherence functions of all the studied pairs of EEG leads rhythmic component, stable in time, was absent. Functions of the mean EEG coherence in the band of 61-100 Hz had significantly greater values in comparison with the values in the band of 14.7-40 Hz.

Animals↗
PubMedDate not supplied

[Effect of noradrenaline on spatial synchronization and evoked potentials in the cerebral cortex of the rabbit].

Noradrenaline application on the cerebral cortex of rabbits leads to an increase of the level of spatial correlation of neocortical potentials. At low doses of noradrenaline, the amplitude of EPs in the visual cortex initially decreases and then increases. With increases of the noradrenaline dose, the amplitude of EPs continues to increase. Amplitude of the EPs is enhanced also in the sensorimotor cortex for which the light stimuli are not specific. Analysis of data obtained and those published by other authors, allows to suppose that in the process of conditioning, noradrenaline may act as a positive as well as a negative reinforcing factor depending on the type and the stage of conditioning.

Animals↗
PubMed2003

Cortical and cerebellar activity of the human brain during imagined and executed unimanual and bimanual action sequences: a functional MRI study.

The neural (blood oxygenation level dependent) correlates of executed and imagined finger sequences, both unimanual and bimanual, were studied in adult right-handed volunteers using functional magnetic resonance imaging (fMRI) of the entire brain. The finger to thumb opposition tasks each consisted of three conditions, two unimanual and one bimanual. Each experimental condition consisted of overt movement of the fingers in a prescribed sequence and imagery of the same task. An intricate network consisting of sensorimotor cortex, supplementary motor area (SMA), superior parietal lobule and cerebellum was identified when the tasks involved both planning and execution. During imagery alone, however, cerebellar activity was largely absent. This apparent decoupling of sensorimotor cortical and cerebellar areas during imagined movement sequences, suggests that cortico-cerebellar loops are engaged only when action sequences are both intended and realized. In line with recent models of motor control, the cerebellum may monitor cortical output and feed back corrective information to the motor cortex primarily during actual, not imagined, movements. Although parietal cortex activation occurred during both execution and imagery tasks, it was most consistently present during bimanual action sequences. The engagement of the superior parietal lobule appears to be related to the increased attention and memory resources associated, in the present instance, with coordinating difficult bimanual sequences.

Adult↗
PubMed1987

[Effect of verapamil on focal epileptic activity in the rat cerebral cortex].

Experiments were carried out on 64 nonanesthetized male Wistar rats (200-220 g). Epileptic foci were induced by the application of a filter paper saturated with a solution of benzylpenicillin sodium salt (12,000 and 20,000 U/ml) to the sensorimotor cortex. It was shown that subsequent intraperitoneal administration of verapamil (5 mg/kg and 10 mg/kg) during steady focal epileptic activity (EpA) resulted in the suppression of EpA in most animals. The antiepileptic effect of verapamil was manifested in a reduced frequency and amplitude of spike discharges, decreased power of epileptic foci and less frequent appearance of seizure (ictal) discharges. The role of Ca canals of neuronal membranes in the pathogenesis of epilepsy is discussed.

Animals↗
PubMed2003

Task-dependent modulations of cortical oscillatory activity in human subjects during a bimanual precision grip task.

Oscillations are a widespread feature of normal brain activity and have been reported at a variety of different frequencies in different neuronal systems. The demonstration that oscillatory activity is present in motor command signals has prompted renewed interest in the possible functions of synchronous oscillatory activity within the primate sensorimotor system. In the current study, we investigated task-dependent modulations in coupling between sensorimotor cortical oscillators during a bimanual precision grip task. The task required a hold-ramp-hold pattern of grip force to be exerted on a compliant object with the dominant right hand, while maintaining a steady grip with the nondominant hand. We found significant task-related modulation of 15- to 30-Hz coherence between magnetoencephalographic (MEG) activity recorded from the left sensorimotor cortex and electromyographic (EMG) activity in hand muscles on the right side. This coherence was maximal during steady hold, but disappeared during the ramp movements. Interestingly coherence between the right sensorimotor MEG and left-hand EMG showed a similar, although less deeply modulated, task-related pattern, even though this hand was maintaining a simple steady grip. No significant ipsilateral MEG-EMG coherence was observed in the 15- to 30-Hz passband for either hand. These results suggest that the cortical oscillators in the two sensorimotor cortices are independent to some degree but that they may share a common mechanism that attenuates the cortical power in both hemispheres in the 15- to 30-Hz range during movements of one hand. The results are consistent with the hypothesis that oscillatory activity in the motor system is important in resetting the descending motor commands needed for changes in motor state, such as those that occur in the transition from movement to steady grip.

Adult↗
PubMed1999

Tetrodotoxin prevents posttraumatic epileptogenesis in rats.

Severe cortical trauma frequently causes epilepsy that develops after a long latency. We hypothesized that plastic changes in excitability during this latent period might be initiated or sustained by the level of neuronal activity in the injured cortex. We therefore studied effects of action potential blockade by application of tetrodotoxin (TTX) to areas of cortical injury in a model of chronic epileptogenesis. Partially isolated islands of sensorimotor cortex were made in 28- to 30-day-old male Sprague-Dawley rats and thin sheets of Elvax polymer containing TTX or control vehicle were implanted over lesions. Ten to 15 days later neocortical slices were obtained through isolates for electrophysiological studies. Slices from all animals (n = 12) with lesions contacted by control-Elvax (58% of 36 slices) exhibited evoked epileptiform field potentials, and those from 4 rats had spontaneous epileptiform events. Only 2 of 11 lesioned animals and 6% of slices from cortex exposed to TTX in vivo exhibited evoked epileptiform potentials, and no spontaneous epileptiform events were observed. There was no evidence of residual TTX during recordings. TTX-Elvax was ineffective in reversing epileptogenesis when implanted 11 days after cortical injury. These data suggest that development of antiepileptogenic drugs for humans may be possible.

Action Potentials↗
PubMed2002

Mind's ear in a musician: where and when in the brain.

The temporospatial pattern of brain activity during auditory imagery was studied using magnetoencephalography. Trained musicians were presented with visual notes and instructed to imagine the corresponding sounds. Brain activity specific to the auditory imagery task was observed, first as enhanced activity of left and right occipital areas (average onset 120-150 ms after the onset of the visual stimulus) and then spreading to the midline parietal cortex (precuneus) and to such extraoccipital areas that were not activated during the visual control condition (e.g., the left temporal auditory association cortex and the left and right premotor cortices). The latest activations, with average onset latencies of 270-400 ms clearly separate from the earliest ones, occurred in the left sensorimotor cortex and the right inferotemporal visual association cortex. These data imply a complex temporospatial activation sequence of multiple cortical areas when musicians recall firmly established audiovisual associations.

Adult↗
PubMed2006

Changes in neuropeptide Y protein expression following photothrombotic brain infarction and epileptogenesis.

This study characterized morphological changes in the cortex and hippocampus of Sprague-Dawley rats following photothrombotic infarction and epileptogenesis with emphasis on the distribution of neuropeptide Y (NPY) expression. Animals were lesioned in the left sensorimotor cortex and compared with age-matched naive and sham-operated controls by immunohistochemical techniques at 1, 3, 7, and 180 days post-lesioning (DPL). NPY immunostaining was assessed by light microscopy and quantified by the optical fractionator technique using unbiased stereological methods. At 1, 3, and 7 DPL, the number of NPY-positive somata in the lesioned cortex was increased significantly compared to controls and the contralateral cortex. At 180 DPL, lesioned epileptic animals with frequent seizure activity demonstrated significant increases of NPY expression in the cortex, CA1, CA3, hilar interneurons, and granule cells of the dentate gyrus. In addition to NPY immunostaining, neuronal degeneration, cell death/cell loss, and astroglial response were assessed with cell-specific markers. Nissl and NeuN staining showed reproducible infarctions at each investigated time point. FJB-positive somata were most abundant in the infarct core at 1 DPL, decreased markedly at 3 DPL, and virtually absent by 7 DPL. Activated astroglia were detected in the cortex and hippocampus following lesioning and the development of seizure activity. In summary, NPY protein expression and morphological changes following cortical photothrombosis were time-, region-, and pathologic state-dependent. Alterations in NPY expression may reflect reactive or compensatory responses of the rat brain to acute infarction and to the development and expression of epileptic seizures.

Animals↗
PubMed2006

Contralesional neural plasticity and functional changes in the less-affected forelimb after large and small cortical infarcts in rats.

Some studies have found that unilateral cerebral damage produces significant deficits in the ipsilesional, "less-affected", body side. Other studies have found that such damage results in a paradoxical hyperfunctionality of the ipsilesional body side and a facilitation of learning-induced neuroplastic changes in the contralesional motor cortex. The purpose of this study was to determine whether these effects co-exist and/or vary with lesion severity. After small or large unilateral ischemic lesions of the sensorimotor cortex (SMC) or sham operations, adult male rats were trained for 20 days to acquire a motor task, skilled reaching for food, for the first time with the ipsilesional forelimb. Analyses of movement patterns indicated lesion-size-dependent ipsilesional abnormalities in grasping, retrieving and releasing food pellets. Despite these impairments, success rates were significantly increased and aiming errors reduced in lesion groups compared with sham operates. Performance was best in rats with small lesions that had more minor ipsilesional impairments. In the motor cortex contralateral to the lesion and trained limb, there were significant increases in the density of dendrites immunoreactive for microtubule-associated protein-2 (MAP2) and of N-methyl-D-aspartate receptor subunit 1 (NMDAR1) immunoreactivity compared with sham operates. These effects were correlated with reaching performance. Therefore, enhanced motor skill learning in the "less-affected" forelimb and contralesional neuroplastic changes are muted after larger lesions and co-exist with ipsilesional impairments. These effects may be related to a denervation-induced neural restructuring of the contralesional cortex that both disrupts pre-existing motor engrams and facilitates the establishment of new ones.

Animals↗
PubMed1996

Alignment of coexisting cortical maps in a motor control model.

How do multiple feature maps that coexist in the same region of cerebral cortex align with each other? We hypothesize that such alignment is governed by temporal correlations: features in one map that are temporally correlated with those in another come to occupy the same spatial locations in cortex over time. To examine the feasibility of this hypothesis and to establish some of its detailed implications, we studied a multilayered, closed-loop computational model of primary sensorimotor cortex. A simulated arm moving in three dimensions formed the external environment for the model cortical regions. Coexisting proprioceptive and motor maps formed and generally aligned in a fashion consistent with the temporal correlation hypothesis. For example, in simulated proprioceptive sensory cortex the map of elements responding strongly to stretch of a particular muscle matched the map of tension sensitivity in antagonist muscles. In simulated primary motor cortex the map of elements responding strongly to increased tension in specific muscles matched the map of output elements for the same muscles. These computational results suggest specific experimental measurements that can support or refute the temporal correlation hypothesis for map alignments.

Brain Mapping↗
PubMed1983

Synaptic inputs of feline rubrospinal neurons from the parietal association cortex, pretectum and medial lemniscus, and their lesion-induced sprouting.

Synaptic inputs of rubrospinal (RN) neurons from the cerebral cortex, pretectal area (PRT), and medial lemniscus (ML) were investigated electrophysiologically in the cat. Stimulation of the ipsilateral parietal association cortex (PASC) and secondary sensory area (SII) produced slow-rising about 3 msec rise time monosynaptic EPSPs which were, in some cases, followed by hyperpolarizations, similar to the sensorimotor cortex (SM)-induced PSPs previously observed. Stimulation of the contralateral cerebral cortex never produced detectable PSPs. Topographical arrangement of PASC-rubral projection was found. Stimulation of the lateral part of PASC induced EPSPs predominantly in RN cells innervating the cervicothoracic spinal segments, while stimulation of the medial part of PASC produced EPSPs predominantly in RN cells innervating the lumbosacral cord. Furthermore, PASC-induced EPSPs were more frequently recorded at the rostral half of RN than at the caudal half. Monosynaptic EPSPs and multisynaptic IPSPs were induced by stimulation of the ipsilateral PRT and ML. PRT- and ML-induced EPSPs had times-to-peak of 1.0 +/- 0.4 msec (mean +/- S.D.) and 1.6 +/- 0.5 msec, respectively, which were intermediate to those of the cerebral peduncle (CP)- and nucleus interpositus of the cerebellum (IP)-induced EPSPs. Furthermore, sensitivity of amplitudes of PRT-induced EPSPs to membrane hyperpolarization was intermediate to those of CP- and IP-EPSPs, and that of ML-induced EPSPs was lower than that of IP-EPSPs. Therefore, it is likely that synapses of PRT and ML fibers are formed between the distal dendrites where CP-rubral synapses terminate and soma where IP-rubral synapses terminate. PASC-induced EPSPs after chronic IP and SM lesions had a new fast-rising component and the effectiveness of ML stimulation to induce the unit spike of RN cells was clearly increased in IP and SM lesioned cats. It was suggested that PASC-rubral fibers sprouted and formed new synapses at the proximal portions of soma-dendritic membranes of RN cells after IP and SM destructions. Collateral fibers to RN cells of the pyramidal tract were also shown to sprout new synapses following IP and ML lesions.

Animals↗
PubMed1985

The postural reaction to the drop of a hindlimb support in the standing cat remains following sensorimotor cortical ablation.

The postural response to an unexpected drop of either hindlimb platform was studied in the freely standing cat. The vertical forces, the forelimb electromyographic (EMG) activities and the movement of the trunk were analysed. A stereotyped diagonal pattern of support was observed. The imposed unloading of one hindlimb was followed by unloading of the diagonally opposite forelimb and loading of the two other limbs. In the ipsilateral loaded forelimb, the force increase is preceded by an activation of the biceps and is concomitant with a triceps coactivation. In the contralateral unloaded forelimb, reciprocal changes of biceps (activation) and triceps (inhibition) were observed and preceded the force decrease. Lateral or vertical displacement or rotation of the vertebral column at the high thoracic level, as evidenced by movie recording, began no earlier than 100 ms after the hindlimb drop and thus followed the EMG changes. Unilateral sensorimotor cortex ablation had no effect on this pattern or on the latencies of forelimb myographic responses. These results suggest that the hindlimb drop triggers stereotyped forelimb EMG responses which are organized centrally and that these responses are not mediated via a sensorimotor cortical loop.

Animals↗
PubMed1988

Lateral difference in responsiveness of norepinephrine-sensitive cyclic AMP-generating systems of rat cerebral cortex with iron-induced epileptic activity.

Responsiveness of norepinephrine-sensitive cyclic AMP-generating systems was examined in slices of different cortical areas of rats showing electrographic spike and wave complexes after unilateral injection of ferrous chloride solution into the sensorimotor cortex. Accumulation of cyclic AMP elicited by norepinephrine was greater on the injection side of the cortex than on the other. Similar lateral differences were detected in cyclic AMP levels antagonized by phentolamine or propranolol, in which 8-phenyltheophylline almost completely inhibited the elicitation of cyclic AMP accumulation by a norepinephrine-propranolol combination but not by a norepinephrine-phentolamine combination. These results suggest that alterations in cyclic AMP generation through the beta-adrenoceptor-coupled adenylate cyclase system and through alpha-adrenergic activation of the adenosine receptor-coupled adenylate cyclase system are closely related to the electrographic activity of iron-induced epilepsy.

Animals↗
PubMed1986

Cyclic AMP levels in slices of epileptic cortex of the rat: effects of glutamate and 3-isobutyl-1-methylxanthine.

Accumulation of cyclic AMP elicited by glutamate was examined in slices from different cortical areas of rats 30 to 60 days after ferrous chloride solution was injected into the left sensorimotor cortex to induce an epileptic focus. In the anterior cortex of rats showing dominant electrographic spike activity on either side of the cortex, the glutamate-elicited accumulation of cyclic AMP was greater on the dominant side than on the other. In the anterior cortex of rats showing nearly equal spike activity on either side, the accumulation was greater on the side ipsilateral to the injection site than on the other. Different inhibitory effects of 3-isobutyl-1-methylxanthine on the elicitation of cyclic AMP accumulation by glutamate was observed in relation to the patterns of spike activity.

1-Methyl-3-isobutylxanthine↗