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Results for “Sensorimotor Cortex”

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At least 217 records · Page 12Linked to original sources

PubMed1981

Effects of tetrodotoxin on changes in extracellular free calcium induced by repetitive electrical stimulation and iontophoretic application of excitatory amino acids in the sensorimotor cortex of cats.

Extracellular free calcium ([Ca2+]o) was measured with double barreled ion-sensitive reference electrodes in the sensorimotor cortex of cats before and after application of tetrodotoxin (TTX). Electrical stimulation of the cortical surface or of the thalamic ventrobasal complex resulted in reductions of [Ca2+]o (delta Ca) by up to 0.45 mM (baseline 1.2--1.3 mM). Iontophoretic applications of the excitatory amino acids glutamate, aspartate and DL-homocysteate evoked delta Ca by up to 1.2 mM. delta Ca were largest at a depth of 100-300 micron below cortical surface. After application of 10(-5) M TTX to the cortical surface, the delta Ca evoked by electrical stimulation disappeared and the accompanying slow negative potentials were reduced in amplitude. In contrast, delta Ca evoked by excitatory amino acids were only slightly affected. It is suggested that excitatory amino acids activate voltage-dependent postsynaptic Ca2+ conductances in neocortical neurones.

Amino Acids↗

PubMed1987

Long-latency OFF-responses from the human sensorimotor cortex to tetanizing stimulation of thenar muscles.

Neuromagnetic recordings revealed a new type of OFF-response from the human sensorimotor cortex 170-235 ms after the end of tetanization of the thenar muscles with 10-240 Hz electrical pulse trains, delivered directly to the thenar eminence or to the median nerve at the wrist. No OFF-responses were discerned when the skin of the thumb was stimulated. The role of muscle afferents in the generation of the OFF-response is discussed.

Adult↗

PubMed1992

Calcium-dependent potassium currents in neurons from cat sensorimotor cortex.

1. Ca(2+)-dependent K+ currents were studied in large pyramidal neurons (Betz cells) from layer V of cat sensorimotor cortex by use of an in vitro brain slice and single microelectrode voltage clamp. The Ca(2+)-dependent outward current was taken as the difference current obtained before and after blockade of Ca2+ influx. During step depolarizations in the presence of tetrodotoxin (TTX), this current exhibited a fast onset of variable amplitude and a prominent slowly developing component. 2. The Ca(2+)-dependent outward current first appeared when membrane potential was stepped positive to -40 mV. Downsteps from a holding potential of -40 mV revealed little or no time-, voltage-, or Ca(2+)-dependent current. When membrane potential was stepped positive to -40 mV, a prolonged Ca(2+)-dependent outward tail current followed repolarization. The decay of this tail current at -40 mV was best described by a single exponential function having a time constant of 275 +/- 75 (SD) ms. The tail current reversed at 96 +/- 5 mV in 3 mM extracellular K+ concentration ([K+]o) and at more positive potentials when [K+]o was raised, suggesting that it was carried predominantly by K+. 3. The Ca(2+)-dependent K+ current consisted of two pharmacologically separable components. The slowly developing current was insensitive to 1 mM tetraethylammonium (TEA), but a substantial portion was reduced by 100 nM apamin. Most of the remaining current was blocked by the addition of isoproterenol (20-50 microM) or muscarine (10-20 microM). 4. The time courses of the apamin- and transmitter-sensitive components were similar when activated by step depolarizations in voltage clamp, but they were quite different when activated by a train of action potentials. Applying the voltage clamp at the end of a train of 90 spikes (evoked at 100-200 Hz) resulted in an Ca(2+)-dependent K+ current with a prominent rapidly decaying portion (time constant approximately 50 ms at -64 mV) and a smaller slowly decaying portion (time constant approximately 500 ms at -64 mV). The rapidly decaying portion was blocked by apamin (50-200 nM), and the slowly decaying portion was blocked by isoproterenol (20-50 microM). 5. When recorded with microelectrodes containing 2 mM dimethyl-bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (dimethyl-BAPTA), which causes prolonged afterhyperpolarizations, the Ca(2+)-dependent K+ current evoked by step depolarizations had an extremely slow onset and decay. The current recorded after a train of evoked spikes had a similar slow decay.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMedDate not supplied

[Trace rhythm recruitment by the neurons of the rabbit sensorimotor cortex in old age].

Spectral analysis (ACG and gSP) of the impulse activity of the neurones of the old rabbits sensorimotor cortex allowed to reveal a trace recruitment of the rhythm--CR analogue to time--in after-action f rhythmic stimulation. Connection was established between the number of presented series of periodic electrocutaneous stimulation and expressiveness of the trace rhythm recruitment depending on the animals age. Trace rhythm recruitment took place slower in old animals (54-56 months) than in young ones (up to 1 year), chiefly in 2-3 experimental days after 2-4 series of rhythmic stimulation and was preserved in a small percent of cases the next day after stimulation. In the background activity of a number of neurones an initial periodicity was discovered, which was intensified under the influence of stimulation by another frequency, or the initial rhythm was extinguished, and stimulation rhythm was reproduced. Periodical stimulation in very old animals (66-85 months) practically did not evoke plastic reconstructions of the cortical neurones. Under the influence of the stimulation a non-specific trace increase of the frequency of neurones background activity of the old animals was observed. The revealed characteristics of plastic neurones properties may testify to projected disturbances of mnestic processes at definite age stages of normal aging.

Action Potentials↗

PubMedDate not supplied

[Effect of dominant motivation on the functional organization of the auditory input into the sensorimotor cortex of the cat brain].

To consider the role of dominant motivation in functional organization of acoustic input to the sensorimotor cortex (SMC), a comparison was made of frequency reflection of tonal bursts in the rostral neocortex summary reactions, and for comparison, in the parietal association cortical area (PC), in the normal state, during pregnancy and after the kittens birth. During pregnancy an increase of the amplitude of averaged evoked potentials (AEP) of SMC and PC was observed practically in the whole studied frequency range. After kittens birth the range of changes narrowed and reactions with maximum amplitude were recorded in females to presentation of tonal bursts with frequencies which corresponded to spectral characteristics of their own kittens vocalizations. However, absolute value of changes of AEPs amplitude, observed in PC were less expressed. As a role the obtained data testify that reorganization of frequency selectivity of SMC acoustic input observed under the influence of dominant motivation, conforms to a change of kittens acoustic signals biological meaning for females in lactation period.

Acoustic Stimulation↗

PubMed1999

Bilateral neuromagnetic activation of human primary sensorimotor cortex in preparation and execution of unilateral voluntary finger movements.

Extracranial magnetoencephalographic activity was separately recorded (25 channels) from bilateral primary sensorimotor cortex (M1-S1) of normal right-handers during unilateral finger movements. Standard dipole analysis indicated only a contralateral M1-S1 source for first movement-evoked field (MEF1) peaking at about 115 ms after electromyographic onset. However, the subtraction of the magnetic field generated by this source from the recorded magnetic field disclosed a low-amplitude ipsilateral central-parietal MEF1 that was explained by an ipsilateral M1-S1 source.

Adult↗

PubMed1998

Changes in field potentials and membrane currents in rat sensorimotor cortex following repeated tetanization of the corpus callosum in vivo.

Repeated, daily tetanization of the corpus callosum induces lasting changes in sensorimotor cortex field potential responses, but the synaptic populations that mediate these responses and support long-term potentiation (LTP) have not been characterized. Current source density analyses of field responses were compared between control animals and those in which LTP was induced by 10 daily series of tetanizations. Tetanization and paired-pulse stimulation (100 ms interval) enhanced the duration of initial (approximately 3 ms onset) deep-negative population spike activity generated by a current sink in layer V that peaked repeatedly at a frequency of approximately 400 Hz. The early (approximately 10 ms to peak) surface-negative component of field responses was generated by a current sink in upper layer V and a source in layer VI. This monosynaptic component followed high stimulation frequencies, recovered quickly from the effects of anaesthesia, and was enhanced by both tetanization and paired-pulse stimulation. The late (approximately 20 ms to peak) surface-negative component was generated by a sink in upper layer V and a source deep in layer V, and was greatly enhanced by tetanization and paired-pulse stimulation. The late component did not follow high-frequency stimulation and recovered slowly from anaesthesia, suggesting that it is driven polysynaptically. Potentiation of monosynaptic thalamic and cortico-cortical afferents probably mediates enhancements of the early component and population spikes, while potentiation of polysynaptic afferents to layer V may contribute to growth in the late component.

Animals↗

PubMed1988

Multiple potassium conductances and their functions in neurons from cat sensorimotor cortex in vitro.

1. Potassium conductances were studied in large layer V neurons using an in vitro slice preparation of cat sensorimotor cortex. The kinetics and pharmacological sensitivity of K+ currents were studied directly using single microelectrode voltage clamp and indirectly by evoking single or multiple spikes and recording the spike repolarization and subsequent afterhyperpolarizations (AHPs). 2. A fast-decaying afterhyperpolarization (fAHP) and a subsequent medium-duration afterhyperpolarization (mAHP) followed a single spike. The amplitude and duration of the mAHP increased when multiple spikes were evoked at a fast rate (e.g., 100 Hz), and a slower afterhyperpolarization (sAHP) appeared only after sustained repetitive firing. 3. All AHPs were reduced by membrane potential hyperpolarization and raised extracellular K+ concentration, suggesting they were caused by an increased K+ conductance. Only the mAHP and sAHP reversed at the estimated value of potassium equilibrium potential (-100 mV), whereas the mean reversal potential of the fAHP was nearly identical to the mean value of resting potential (-71 mV). 4. Mechanisms underlying spike repolarization, the fAHP, and the mAHP were investigated. Two rapidly activating outward currents, a fast-inactivating current and a slowly inactivating delayed rectifier, were detected by voltage clamp. Both currents were reduced rapidly by tetraethylammonium (TEA). The fast transient current was reduced slowly after divalent cations were substituted for Ca2+ (through a mechanism unrelated to blockade of Ca2+ channels), whereas the delayed rectifier was unaffected. 5. Spike duration was increased and the fAHP was abolished only by blocking agents that reduced the fast outward currents. Effects of extracellular and intracellular TEA were similar. Effects of TEA and Ca2+-free perfusate were additive and resembled the effects of intracellular Cs+. The addition of apamin, d-tubocurare, or Cd2+ was ineffective. We conclude that the two fast outward currents reflect pharmacologically and kinetically separate K+ conductances that are primarily responsible for spike repolarization and the fAHP. 6. Voltage-clamp studies revealed two additional outward currents, which were persistent and Ca2+-mediated. Each current activated and deactivated slowly, but the kinetics of one component were approximately 10 times slower than the other. The decay of these currents gave rise to AHPs resembling the mAHP and the early sAHP. 7. Neither the mAHP nor the sAHP was reduced by TEA. The mAHP was reduced when divalent cations were substituted for Ca2+ or when Cd2+, apamin, or d-tubocurare were added.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMedDate not supplied

Ultrastructure of neurons of the sensorimotor cortex in progeny of rats receiving alcohol during pregnancy.

We have studied the dynamics of ultrastructural changes in the neurons of the sensorimotor cortex on days 21, 30, and 60 of life in offspring of rats given 20% alcohol (2 g/kg) during pregnancy. Moderate antenatal alcoholization leads to certain disturbances in the ultrastructure of the cortical neurons and their dendrites. This is manifested as the presence of signs of retardation in the maturation of nervous cell populations as dystrophic changes in the neurons and their dendrites, and as display of the repair character with their own dynamics in the postnatal period of ontogenesis. The first two categories of the ultrastructural changes in the cortical neurons become more manifest at early stages of postnatal development of the offspring, and the repair processes at the age of two months. Despite the presence of the repair shifts, the dystrophic changes in the neurons of a hypoxic nature are present up to the period of sexual maturation. This shows that the antenatal alcoholic intoxication in the offspring is manifested in postnatal ontogenesis for a long period.

Animals↗

PubMed1999

Inverted pyramidal neurons in chimpanzee sensorimotor cortex are revealed by immunostaining with monoclonal antibody SMI-32.

We used the monoclonal antibody SMI-32 to label pyramidal cells of sensorimotor cortex in two chimpanzees. The majority of the pyramidal cells had typical vertically oriented apical dendrites that extended towards the pial surface. A small population of pyramidal cells varied from this orientation, so that the apical dendrites were 20 degrees or more from radial, and were often inverted, extending away from the pial surface. When numbers of non-inverted and inverted pyramidal cells were compared, less than 1% were found to be inverted.

Animals↗

PubMed1983

The long-term effects of removal of sensorimotor cortex in infant and adult rhesus monkeys.

A comparison is made between the long-term effects of the unilateral removal of sensorimotor cortex in infant and adult rhesus monkeys. Both infants and adults recovered to a remarkable extent. They walked, climbed and jumped with ease. However, neither infant nor adult monkeys could grip food by using thumb and forefinger independently of the other fingers. It was demonstrated in the adults that there was a permanent impairment in the use not only of the fingers but also the wrist and forearm. The results do not support the claim made by Kennard (1942) that infants recover more completely than adults from the effects of brain lesions. An analysis of the relevant evidence suggests that compensation occurs only when the animal is very immature at the time of operation. The brain is much more mature in a neonatal monkey than a rat or hamster. True compensation can probably only occur in monkeys if the lesion is made well before birth.

Animals↗

PubMed1992

[Interactions of the superior colliculus and the sensorimotor cortex in the alert rabbit].

The tonic increased influence of the superior colliculus (SC) on the formation of visual responses of the sensorimotor cortex (SMC) was shown on the alert rabbits. It was shown that SC influence was realized through tectothalamocortical (nucleus lateralis posterior) canal relation. It was established that SMC of the alert rabbits in its turn exerts the inhibitory phasic influence on SC function. The obtained data are discussed in the light of participation of the colliculo-cortical and cortico-collicular interactions in the organization of the visual-motor coordination necessary for realization of the visual controlled behaviour.

Animals↗

PubMed1983

Changes in [Ca2+]0, [K+]0 and neuronal activity during oenanthotoxin-induced epilepsy in cat sensorimotor cortex.

Effects of the convulsant drug oenanthotoxin on field potentials, neuronal discharges and extracellular free Ca2+ and K+ concentrations were studied in the sensorimotor cortex of cats. Fifteen to 20 min after topical OETX application spike activity developed (surface negative, deeper layers positive) with a frequency of 0.5-1/sec. With the maturation of the focus spikes became multipeaked and the reversal point of field potential polarity shifted deeper into the cortex. Spontaneous seizures developed when the spike activity had become negative in polarity in recording depths of 1300 micron below the cortical surface. Spontaneous seizures were associated with large rises in [K+]0 and reductions in [Ca2+]0 (delta [K+]0, delta [Ca]0). The latter were often larger than maximum changes in normal cortex. The decay in [Ca2+]0 associated with spontaneous seizures tended to precede the onset of ictal activity. The findings suggest that OETX, like other epileptogenic drugs, uses Ca2+-dependent mechanisms for the initiation of epileptiform activity.

Alkynes↗

PubMed1983

Epileptiform activity induced in single cells of the sensorimotor cortex of the cat by intracellularly applied scorpion venom.

Oscillations of 5 to 15 mV in the membrane potentials of neurons of the sensorimotor cortex of normal, awake cats were produced within 15 to 45 s after intracellular injection of Centruroides sculpturatus (c.s.) venom, but not after control injections of KCl. In every cell injected with c.s. venom, the oscillations eventually gave way to paroxysmal depolarizing shifts of appearance similar to that seen in epileptic cells. The results suggest that cortical epileptiform activity can be produced by the local action of c.s. venom, an agent known to alter the gating mechanism of sodium channels. Disruption of sodium gating may represent an intrinsic cellular mechanism involved in epileptogenesis.

Animals↗

PubMed1987

On the action of intravenous picrotoxin in the sensorimotor cortex of the cat.

The action of topical convulsants, such as strychnine, is not exerted equally on all sets of neurons in the sensorimotor cortex of cats. Small-field neurons near the surface are influenced whereas deeper, wide-field neurons are affected only indirectly. The agent, picrotoxin, was used to test whether or not the deeper neurons are spared the effects of topical convulsants simply because of their location. Picrotoxin, injected intravenously, produced enhancement of the corticofugal reflex discharge evoked by stimulation of any of the four paws and by auditory stimulation. The surface-recorded primary evoked response was also enhanced but only slightly, far less than with topical application. The evoked response in the medial lemniscus was not altered by picrotoxin, but that in the thalamic radiations was enhanced. The drug diazepam, injected intravenously, diminished the enhancements of both the corticofugal reflex discharge and the evoked potential, in some cases reducing the responses to amplitudes smaller than control values. Single-cell recordings in other laboratories have shown that intravenous picrotoxin converts small-field cells to wide-field cells, and that diazepam reverses this effect. The increase in the surface-recorded primary response and the size of the increase in the corticofugal reflex suggest that there is also a direct effect on wide-field neurons or on the pathway leading to them.

Animals↗

PubMedDate not supplied

[Plastic reorganization of the activity of sensorimotor cortex neurons during elaboration of a cellular analog of a temporary connection].

A study of plastic reorganizations of neuronal responses in the rabbit sensorimotor cortex was made on a cellular analogue of conditioned connection where stimulation of the ventrobasal thalamic complex (VBC) was used as a conditioned stimulus, while polarization of the cell through a recording microelectrode, as an unconditioned one. The responses of 60% of the studied neurones to the stimulation of the VBC showed significant plastic changes after the pairing of thalamic stimulation with polarization. The changes obtained met the criteria of identification of conditioned reactions. One of the possible mechanisms of the recorded plastic reorganizations of neuronal reactions consists in a selective increase in the effectiveness of excitatory synapses, whose subthreshold activation coincided with the cell activation. These data may be regarded as manifestation of a hypothetic reverse influence of neuronal discharges on the effectiveness of the synaptic transmission.

Animals↗

PubMed1987

[Early changes in the ultrastructure of axodendritic synapses in the rat sensorimotor cortex following whole-body irradiation with high-dose fast neutrons].

Changes in morphometric parameters have been established in axodendritic synapses of sensorimotor cortex of adult mature rats exposed to neutron irradiation. Neutron irradiation dose and summarized dose rate were 10 Gy and 0.35 Gy, respectively. The changes were observed 0.25, 1, 3, 6 and 24 hours after irradiation. The observations suggest an increase in synaptic activity, with the range of irradiation action and functional characteristics decreasing in subsequent time periods.

Animals↗

PubMed1984

[Asymmetry of the interaction of transcallosal and thalamocortical flows in the sensorimotor cortex].

The interaction between transcallosal potentials and responses to stimulation of the contralateral sciatic nerve was studied in symmetrical areas of the cat sensorimotor cortex. The interacting responses and the resulting EPs were characterized by a functional interhemisphere asymmetry of an individual form. In transcallosal conditioning with 10-ms interstimuli intervals, the positive components of the EPs prevailed in the left hemisphere. The characteristics of the interhemisphere asymmetry were determined by the animal sex: the spatial--temporal interaction of the flows had different features in different hemispheres, was characterized by unequal markedness of asymmetry of the EP components as well as by opposite character of the asymmetry in animals of different sex. The characteristics of the EP interhemisphere asymmetry seem to be determined by an interaction of dominant foci occurring under these conditions in each of the hemispheres.

Animals↗