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PubMed1984

Depolarization-elicited accumulation of cyclic AMP in slices of rat cerebral cortex with a chronic epileptic focus.

Ferrous chloride solution was injected unilaterally into the sensorimotor cortex of rats to induce a chronic epileptic focus. Accumulation of cyclic AMP elicited by depolarizing agents was determined in slices from different cortical areas of rats 30-60 days after the injection. In anterior cortical areas which include the sensorimotor cortex, the cyclic AMP accumulation elicited by ouabain or a high concentration of potassium ion was greater in electrographic spike activity on the dominant side than on the other. In posterior cortical areas, no difference in cyclic AMP accumulation was detected. The regional difference in the depolarization-elicited accumulation of cyclic AMP is discussed with regard to the process of epileptic focus.

Animals↗
PubMed1999

Picrotoxin in the medial prefrontal cortex impairs sensorimotor gating in rats: reversal by haloperidol.

RATIONALE: Neuropathological data indicate a GABAergic dysfunction in the prefrontal cortex and hippocampus of schizophrenics. On this basis, the construct validity of an animal model of schizophrenia was tested. OBJECTIVE: This study assessed prepulse inhibition (PPI) of startle in rats after injections of the GABA antagonist picrotoxin into the prefrontal cortex and the ventral hippocampus. It was also tested if reductions in PPI are reversed by the dopamine antagonist haloperidol. PPI is a measure of sensorimotor gating and is impaired in schizophrenia patients. The hypothesis underlying this study was that blockade of prefrontocortical and hippocampal GABA receptors disrupts PPI in a dopamine-dependent way. This hypothesis was based on neuropathological data from schizophrenics indicating a loss of GABAergic neurons in the prefrontal cortex and hippocampus and on the observation that PPI is reduced in schizophrenics. METHODS: Picrotoxin (0, 5, 10 ng/0.5 microl) was infused through chronically indwelling cannulae into the medial prefrontal cortex (mPFC), into the lateral prefrontal cortex and into the ventral hippocampus. The effect on PPI was measured directly after picrotoxin infusion. The neuroleptic compound haloperidol (0.1 mg/kg) was administered intraperitoneally 30 min before testing. RESULTS: Picrotoxin in the mPFC dose-dependently reduced PPI and this effect was antagonized by systemic pretreatment with the dopamine antagonist haloperidol. No significant effects on PPI were observed after picrotoxin infusions into the lateral prefrontal cortex or into the ventral hippocampus. CONCLUSIONS: These findings indicate that acute blockade of GABA receptors in the mPFC impairs sensorimotor gating in a dopamine-dependent manner. Since PPI in rats has been shown to possess face, predictive, and construct validity as an animal model for some psychotic symptoms, we discuss the potential relevance of our findings for the pathophysiology of schizophrenia.

Animals↗
PubMedDate not supplied

[Function of the superior colliculi of the corpora quadrigemina during creation of a local focus of increased excitability in the mesencephalic reticular formation and sensomotor cortex].

In chronic experiments on waking rabbits, the foci of heightened excitability in the sensorimotor cortex and mesencephalic reticular formation affected in a similar way the background neuronal activity in the superior colliculi and that evoked by light stimuli. The effect was manifested in elimination of inhibitory pauses in the neuronal response to light stimulus and in a general increase of discharge frequency. Similarity of the cortical and reticular influences is due to their possible mediation by the same collicular interneurones participating in inhibitory pauses formation in the process of backward inhibition. Increased neuronal activity in the superior colliculi under the action of local foci in the sensorimotor cortex and mesencephalic reticular formation correlated with appearance of forelimb motor reaction to isolated light stimulus testifying to a formation of a functional connection between the visual and motor analyzers. Possible role of the superior colliculi in this process and their participation in the formation of a visually controlled reaction is discussed.

Animals↗
PubMed1996

Regional difference in cerebral blood flow and oxidative metabolism in human cortex.

UNLABELLED: We sought to determine if there are regional differences in cerebral blood flow (CBF) and cerebral metabolic ratio for oxygen (CMRO2) in normal subjects during the resting state. METHODS: Regional CBF, CMRO2 and oxygen extraction fraction (OEF) in 15 normal volunteers (mean age 58.8 +/- 8.2 yr) were measured during rest using PET and a 15O-gas steady-state technique. RESULTS: CBF and CMRO2 in the visual cortex were significantly higher than those in other cortices. Additionally, OEF in the sensorimotor cortex was significantly lower than that in other cortical regions. CONCLUSION: CBF and CMRO2 in the visual cortex are always high, and low OEF in the sensorimotor cortex exists even in resting state in normal subjects. We hypothesize that these regional functional differences would result in different resistances to degeneration.

Brain↗
PubMed1981

Autoradiographic and electron microscopic degeneration evidence for axonal sprouting in the rat corticopontine system.

Newborn (2 or 3 days postnatal) rats were subjected to unilateral cerebral cortical lesions involving much of the anterior (sensorimotor) cortical surface in the right hemisphere. Three months later, the survivors were divided into two groups, one group receiving a [3H]leucine injection in the left sensorimotor cortex and the other sustaining a lesion involving the left sensorimotor cortex. Routine autoradiographic studies in the first group revealed abnormally dense axonal and terminal labeling in the pontine gray contralateral to the leucine-injected hemisphere, suggesting that much of the label was due to sprouting from intact corticopontine axons into the neonatally deafferented pontine gray. In the group with a second (adult) cortical lesion contralateral to the neonatal ablation, degenerating axons and boutons were abundant in the pontine gray contralateral to the adult lesion and at least some of these were interpreted to represent sprouted corticopontine axons and their terminals.

Animals↗
PubMed1994

Tactile exploration of shape after subcortical ischaemic infarction studied with PET.

We studied the cerebral activations related to restitution of hand function in five patients with first hemiplegic subcortical stroke due to ischaemic infarction in the area of the basal ganglia or thalamus. In two subjects, involvement of the cortico-spinal tract was demonstrated by magnetic evoked potentials. The subjects were requested to discriminate rectangular parallelepipeda of identical mass with their affected hands. Regional cerebral blood flow (rCBF) was measured with PET after intravenous bolus injection of [15O]butanol, at rest and during task execution. Evaluation of the rCBF changes was based on pixel-by-pixel t statistics of spatially standardized and averaged PET images and on a statistical distribution analysis of regions of interest in the individual subjects. For anatomical localization of the significant rCBF changes, a computerized brain atlas (Greitz et al. J Comput Assist Tomogr 1991; 15: 26-38) and a matching procedure that directly aligns individual PET and high resolution magnetic resonance images were used. The rCBF at rest and the task-induced rCBF changes varied from subject to subject, as did the residual neurological deficits at the time of PET scanning. In all subjects there were large activation areas in the motor and the sensory hand area contralateral to the affected hand. Poor performance of the task was correlated with a low rCBF in the contralateral sensorimotor cortex at rest and a bilateral activation of the primary sensorimotor cortex during task performance. The premotor cortex, ipsilateral and anterior cerebellum, contralateral to the affected hand, were also significantly activated. Further activations were observed in the contralateral premotor cortex, supplementary motor area and bilaterally in the posterior cingulate cortex, but were less consistent among the subjects. Our data suggest that recovery from hemiplegic stroke is associated with a marked reorganization of the cerebral activation patterns, including common and subject-specific activation sites. With respect to task-specific information processing a lower discrimination rate of objects compared with controls was associated with diminished activations in parietal lobe.

Adult↗
PubMed1996

Significance of the second somatosensory cortex in sensorimotor integration: enhancement of sensory responses during finger movements.

The functional significance of the second somatosensory cortex (SII) is poorly understood. However, lesion and cortical stimulation studies indicate that SII may be involved in sensory aspects of tactile learning and in movement control. In the present study, we explored a possible role of SII in sensorimotor integration in humans using a multichannel magnetometer. Somatosensory evoked fields (SEFs) from SII to electrical stimulation of left and right median nerves were recorded in six healthy volunteers during rest and in different test conditions. Continuous cutaneous stimulation of the right hand or face reduced the SEFs to both left and right median nerve stimulation. Right-sided finger movements increased the SEFs to right, but not left, median nerve stimulation. The responses were equally enhanced by simple finger flexion movement and by a complex finger sequence. The suppression of SEFs by competing cutaneous inputs from different areas of the body indicates that the neurones underlying the responses receive inputs from large, bilateral receptive fields. The enhancement of sensory reactions to signals from the actively moving limb but not to those from the opposite limb indicates a spatial tuning of the SII neurones to behaviourally relevant input channels, also suggesting that SII is important for the integration of sensory information to motor programmes.

Adult↗
PubMed1987

Transcallosal evoked potentials in relation to behavior in the rat: effects of atropine, p-chlorophenylalanine, reserpine, scopolamine and trifluoperazine.

Single pulse electrical stimulation of the sensorimotor cortex in waking rats produced an evoked response in the contralateral sensorimotor cortex. The slow wave response consisted of: (1) an early component that was negative at the pial surface and in layer V, and was associated with multiunit discharge; and (2) a late component that was mainly negative at the surface, positive in layer V, and was associated with multiunit suppression. Previous research suggests that the early component represents summed excitatory postsynaptic potentials; the late component summed inhibitory postsynaptic potentials. Both components could be elicited by direct stimulation of the corpus callosum and both were abolished by midline callosal section. The amplitude and duration of the late component varied with concurrent motor activity in a striking manner. It was large during waking immobility and also during face-washing, licking the paws, chewing food and drinking water, but was much reduced or absent during head movements, walking and changes in posture. Only minor changes were associated with the transition from waking immobility to slow wave sleep. A series of pharmacological experiments indicated that the behavior-related variation in the late component of the transcallosal evoked response was dependent on both cholinergic and serotonergic transmission.

Animals↗
PubMed1992

Spatial overlap of rubrospinal and corticospinal terminals with input to the inferior olive.

Somatosensory responses of cells in the dorsal accessory olive are suppressed following stimulation of the magnocellular red nucleus. Since the magnocellular red nucleus of the cat does not project directly to the dorsal accessory olive, the present experiments were designed to identify indirect pathways that might mediate suppression of olivary responsiveness. Wheat germ agglutinin-horseradish peroxidase was used to compare the location of magnocellular red nucleus terminals with the locations of cells providing input to the rostral dorsal accessory olive. Cells projecting to forelimb rostral dorsal accessory olive can be divided into two main groups: one group comprises a column of large cells located in the ventral caudal cuneate nucleus extending into lamina VI of C1 and C2, and a second group comprises smaller cells located in the ventral rostral cuneate nucleus. Terminations of fibers originating in the magnocellular red nucleus were found to target both groups of cells projecting to the dorsal accessory olive. Therefore, it is possible that the responsiveness of olivary cells is influenced via these terminations. Stimulation of sensorimotor cortex has also been shown to inhibit olivary responsiveness. Terminations from sensorimotor cortex target the same regions of cells that project to the dorsal accessory olive as those of the magnocellular red nucleus, and a similar, perhaps identical, anatomical substrate may serve to modulate olivary sensitivity by the two descending systems.

Animals↗
PubMed2001

[Clinical applications of functional magnetic resonance imaging].

Despite its immediate success as a tool for basic research, the clinical application of functional MRI(fMRI) is still limited. FMRI has proven useful for presurgical functional mapping of the eloquent cortices. Localization of the sensorimotor cortex by fMRI may be of relatively limited value because the sensorimotor cortex can often be readily localized by means of anatomical methods. In contrast, the language cortices may not be localized anatomically and the language dominant hemisphere has been determined by invasive Wada test. Previous reports have shown that fMRI can be a promising alternative to the Wada test. A recent clinical trial has suggested that fMRI can be used to diagnose Alzheimer's disease in its earliest stage, detecting subclinical deterioration of the memory function. FMRI may be useful to predict the future decline of memory in people with genetic risks. Monitoring of the functional recovery of post-stroke brains may be another promising clinical application of fMRI. FMRI has demonstrated functional reorganization of the brain that may be related to the restoration of motor and language functions.

Brain Diseases↗
PubMed1976

[An analysis of the electrical responses of the neocortex evoked by stimulation of different hypothalamic structures].

Evoked potentials and extracellular spike activity during stimulation of the posterior, lateral, anterior, and ventro-medical hypothalamus were recorded in different areas of the neocortex in unanesthetized cats. Hypothalamo--cortical evoked potentials (HC EP) of maximal amplitude are generated in gyr. sigm. ant. with 0.5--2.5 msec latency. The responses are of positive--negative configuration and often a fast spike--like defiction appears at the positive phase. EP in gyr. suprasylv. med. are initially negative and of 2--6 msec latency. Most effective is stimulation of the posterior and lateral hypothalamus, HC EP in gyr. sigm. ant. following the frequency of stimulation up to 200/sec and being characterized not only by a high "functional lability" or reproducibility but also by the ability of posttetanic potentiation. With the aid of paired stimuli, the early fast component of the EP in the sensorimotor cortex was shown to appear at an interval of approximately 2 msec. HC EP entirely recover 50--150 msec after the conditioning stimulus. The recovery cycle is biphasic and reflect, a biphasic change of the excitability of neurons in gyr. sigm. ant. and suprasylvian associative areas of the cortex. The latency of evoked discharges of some neurons of the sensorimotor cortex during stimulation of the posterior hypothalamus, is 0.8--1.5 msec, which suggests the existence of a monosynaptic pathway for the hypothalamo--cortical discharges. The maximal amount of neurons in deep layers of gyr. sigm. ant. respond during development of the early and the main positive deflections of HC EP.

Animals↗
PubMed1998

Successful resection of arteriovenous malformations in eloquent areas diagnosed by surface anatomy scanning and motor evoked potential.

Successful resection of cerebral arteriovenous malformations (AVMs) involving the sensorimotor cortex was achieved in 17 cases. The theoretical basis for performing resection of AVMs in eloquent areas is the fact that the brain in and around the nidus about 1 mm in thickness is considered not to be functioning. It is also considered that any center of important function, when an AVM is involved, shifts to the near-by cortex from the original site. Nevertheless, it is critically important to recognize the cortex functioning as sensorimotor centers before and during operation. For this purpose, we have used surface anatomy scanning (SAS) in combination with magnetic resonance angiography. SAS is found to be very useful for the recognition of the topographical relationship between the surface anatomy and AVM. During operation, the motor cortex is identified with motor evoked potential. We have found that, in some cases, the motor center has shifted to the accessory motor cortex. With these information, it is possible to start resection of the lesion from dissection of the main feeders and dissection of the nidus from a silent cortex toward the critical area. Apparent neurological improvements were achieved in 15 of 17 patients treated surgically (88%). With this result, we think that AVMs in eloquent areas can be treated successfully when the surgery is well-designed and well-oriented with the combined use of diagnostic imaging and monitoring. As for control of intraoperative bleeding, careful attention to small but important surgical techniques avoids troublesome bleeding during AVM surgery.

Arteriovenous Malformations↗
PubMed2004

Cortical motor activation in akinetic schizophrenic patients: a pilot functional MRI study.

Akinesia is associated with supplementary motor area (SMA) dysfunction in Parkinson's disease. We looked for a similar association in patients with schizophrenia. Using functional magnetic resonance imaging (fMRI), we compared motor activation in 6 akinetic neuroleptic-treated schizophrenic patients and 6 normal subjects. Schizophrenic patients had a defective activation in the SMA, left primary sensorimotor cortex, bilateral lateral premotor and inferior parietal cortices, whereas the right primary sensorimotor cortex and a mesial frontal area were hyperactive. SMA was hypoactive in akinetic schizophrenic patients, emphasizing the role of this area in motor slowness. Other abnormal signals likely reflect schizophrenia-related abnormal intracortical connections.

Adult↗
PubMed2001

Brain areas involved in interlimb coordination: a distributed network.

Whereas behavioral studies have made significant contributions toward the identification of the principles governing the coordination of limb movements, little is known about the role of higher brain areas that are involved in interlimb coordination. Functional magnetic resonance imaging (fMRI) was used to reveal the brain areas activated during the cyclical coordination of ipsilateral wrist and foot movements. Six normal subjects performed five different tasks that were presented in a random order, i.e., isolated flexion-extension movements of the right wrist (WRIST) and right foot (FOOT), cyclical coordination of wrist and foot according to the isodirectional (ISODIR) and nonisodirectional (NON-ISODIR) mode, and rest (REST). All movements were auditory paced at 66 beats/min. During the coordination of both limb segments, a distributed network was identified showing activation levels in the supplementary motor area (SMA), cingulate motor cortex (CMC), premotor cortex (PMC), primary sensorimotor cortex (M1/S1), and cerebellum that exceeded the sum of the activations observed during the isolated limb movements. In addition, coordination of the limb movements in different directions was associated with extra activation of the SMA as compared to movements in the same direction. It is therefore concluded that the SMA is substantially involved in the coordination of the nonhomologous limbs as part of a distributed motor network. Accordingly, the long-standing exclusive association that has been made between this medial frontal area and bimanual (homologous) coordination needs to be abandoned and extended towards other forms of interlimb coordination (nonhomologous).

Adult↗
PubMed1990

Chronic effects of the selective serotoninergic neurotoxin, methylenedioxyamphetamine, upon cerebral function.

The amphetamine derivative methylenedioxyamphetamine selectively destroys serotoninergic terminals in the brain. We have studied the effects of this toxin upon resting cerebral function, as reflected in rates of glucose utilization. Rats were injected subcutaneously with either 1 ml/kg saline (n = 5) or 20 mg/kg methylenedioxyamphetamine (n = 5) twice daily for four days. Local cerebral glucose utilization was measured between six and nine weeks after treatment using [14C]2-deoxyglucose quantitative autoradiography. Samples of frontal cortex taken from these animals for in vitro [3H]paroxetine binding showed a 64% reduction in 5-hydroxytryptamine uptake sites. In the majority of the 31 functionally diverse brain areas analysed, no significant changes were measured, but significant (P less than 0.05) increases in glucose use were found in neocortical regions e.g. anterior cingulate cortex (+16%) and sensorimotor cortex (+21%). However, the most profound increases were found in globus pallidus (+30%) and hippocampus molecular layer (+34%). It would appear, therefore, that treatment with methylenedioxyamphetamine results in long-lasting alterations in cerebral functional activity.

3,4-Methylenedioxyamphetamine↗
PubMed2005

Glucose transporter plasticity during memory processing.

Various types of learning, including operant conditioning, induce an increase in cellular activation concomitant with an increase in local cerebral glucose utilization (LCGU). This increase is mediated by increased cerebral blood flow or changes in brain capillary density and diameter. Because glucose transporters are ultimately responsible for glucose uptake, we examined their plastic expression in response to cellular activation. In vitro and in vivo studies have demonstrated that cerebral glucose transporter 1 (GLUT1) expression consistently parallels changes in LCGU. The present study is the first to investigate the effect of memory processing on glucose transporters expression. Changes in GLUT expression produced by training in an operant conditioning task were measured in the brain of CD1 mice. Using semi-quantitative immunohistochemistry, Western blot and real time RT-PCR the cerebral GLUT1 and GLUT3 expression was quantified immediately, 220 min and 24 h following training. Relative to sham-trained and naive controls, operant conditioning training induced an immediate increase in GLUT1 immunoreactivity level in the hippocampus CA1 pyramidal cells as well as in the sensorimotor cortex. At longer post-learning delays, GLUT1 immunoreactivity decreased in the sensorimotor cortex and putamen. Parallel to the changes in protein levels, hippocampus GLUT1 mRNA level also increased immediately following learning. No effect of learning was found on hippocampal GLUT3 protein or mRNA expression. Measures of changes in glucose transporters expression present a link between cellular activation and glucose metabolism. The learning-induced localized increases in GLUT1 protein as well as mRNA levels observed in the present study confirm the previous findings that GLUT1 expression is plastic and respond to changes in cellular metabolic demands.

Animals↗
PubMed2005

[Pathophysiological mechanisms implicated by high-frequency stimulation in Parkinson's disease: the restoration of high and low frequency oscillatory systems].

INTRODUCTION: Increased neuronal activity in the internal pallidum (GPi) and the subthalamic nucleus (STN) has been clearly demonstrated in Parkinsonian models, and the two structures have thus been selected as therapeutic targets for functional neurosurgery. High-frequency electrical stimulation of the GPi or the STN improves the parkinsonian symptoms but also dyskinesias directly by GPi stimulation or indirectly by reduction of L-Dopa associated with STN stimulation. According to Alexander's model of the organisation of the basal ganglia, electrical stimulation of GPi or STN should have led to uncontrolled hyperkinesia. This apparent paradox could be explained on one hand by the involvement of different anatomo-functional areas within these structures and on the other by spatial and temporal changes in neuronal discharge patterns in the basal ganglia which in turn produce variations in synchronisation. RESULTS: Event-related (de)synchronisation (ERD) has enabled us to study variations in subcortico-cortical oscillatory activity: it has been shown that high-frequency electrical stimulation of the GPi/STN increases desynchronisation of low frequency rhythms (mu and beta,<30 Hz) during movement preparation and execution and augments post-movement synchronisation. Stimulation also decreases the abnormal frontocentral spreading of desynchronisation during movement preparation. CONCLUSIONS: In accordance with previous coherence analyses, electrical stimulation of STN is likely to restore the activity of high-frequency and low-frequency systems, as evidenced by a decrease in the hypersynchronisation of low-frequency rhythms at rest and restoral of a high-frequency rhythm during movement. Stimulation may improve spatial selectivity by activating the selected programs in conjunction with the primary sensorimotor cortex, whilst inhibiting competitive programs represented by abnormal spreading outside the primary sensorimotor cortex.

Basal Ganglia↗
PubMed1998

Temporary interference in human lateral premotor cortex suggests dominance for the selection of movements. A study using transcranial magnetic stimulation.

It is known that damage to the left hemisphere can lead to movement deficits, and that patients with apraxia have difficulty in selecting movements. Neurophysiological recording studies and lesion studies have shown that the premotor cortex is important for the selection of movements in monkeys. In this study we used transcranial magnetic stimulation (TMS) to disrupt the processing in human premotor cortex. We applied TMS to normal healthy volunteers over the premotor and primary motor areas while they carried out choice reaction time and simple reaction-time tasks. We measured response times of either hand as subjects were stimulated over the left and right hemisphere separately. We found that we were able to delay responses by stimulating at short cue-stimulus intervals (100-140 ms) over premotor cortex and at longer cue-stimulus intervals (300-340 ms) over primary motor cortex while subjects performed the choice reaction-time task with the contralateral hand. We were also able to delay responses with the ipsilateral hand while stimulating over the left premotor cortex, but not while stimulating over the right premotor cortex or either sensorimotor cortex. Premotor cortex stimulation alone disrupts an early stage of movement selection; motor cortex stimulation disrupts the movements at a later stage of execution. There was no distinguishing short cue-stimulus interval effect when premotor cortex was stimulated in the simple reaction time paradigm, where the movement selection demands of the task are kept to a minimum. We conclude that the premotor cortex is important for selecting movements after a visual cue and that the left hemisphere is dominant for the rapid selection of action.

Analysis of Variance↗