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PubMed1980

Amplitude of responses to perturbation in primate sensorimotor cortex as a function of task.

1. Monkeys learned to maintain hand position against a range of background forces. Short-latency responses to passive wrist extension or flexion were recorded from units in areas 4, 3, 1, and 2. Response amplitude was studied as a function of background force direction (extension or flexion). 2. For 40% of the precentral and postcentral responses, response amplitude depended on constant force direction. For these dependent responses, amplitude with background force in one direction averaged 2.8 times amplitude with background force in the opposite direction. 3. Units for which background activity varied with constant force direction were designated task related. Dependent responses from area 4 task-related units were usually larger when background activity was greater and when background force direction matched the direction of the passive movement. 4. Dependent responses from area 4 task-related units occurred significantly later than nondependent responses from the same units. 5. Since most area 4 task-related activity was explicable as a result of peripheral input via the same oligosynaptic path mediating area 4 responses to passive movements (32), the present findings imply that area 4-task-related activity may result in large part from centrally mediated change in the access of short-latency peripheral input to area 4 units. 6. The dependence of responses from non-task-related area 4 units and from non-task-related and task-related postcentral units showed no dominant correlation with background activity or with background force direction. Their dependence appeared to require no explanation other than a change in peripheral input with change in background force direction.

Animals↗
PubMed1981

Submodality distribution in sensorimotor cortex of the unanesthetized monkey.

1. Neuronal responses to cutaneous and noncutaneous stimulation were examined in the hindlimb representation of the precentral motor cortex (MI) and the first somatosensory cortex (SI) of unanesthetized monkeys. 2. MI can be divided into two distinct parts of the basis of its afferent input. The rostral part receives predominantly noncutaneous inputs, while the cutaneous input is primarily confined to the caudal part of MI. Thus, a differential distribution of submodality groups exists in the MI cortex. Caudal to MI, area 3a responds mainly to stimulation of noncutaneous receptors, in marked contrast to the caudal part of MI or area 3b. 3. The finding of a differential distribution of cutaneous inputs within MI is of significance a) to hypotheses concerning the role of somatosensory input to the MI cortex, b) to studies that attempt to characterize somatosensory inputs to MI by the proportion of neurons responsive to cutaneous and noncutaneous stimulation, and c) in that they confirm and extend similar findings recently reported for the forelimb representation of an anesthetized New World monkey (43).

Animals↗
PubMed1981

Neuronal responses in sensorimotor cortex to ramp displacements and maintained positions imposed on hindlimb of the unanesthetized monkey.

1. Neuronal responses to passively imposed displacements of the foot were examined in area 3a, the precentral motor cortex (MI), and the first somatic sensory cortex (SI) of unanesthetized monkeys. The foot displacements, in the form of "ramps" and maintained displacements, were applied at several different velocities and achieved a number of maintained positions. The response in relation to the ramp was termed a "dynamic" response, while that in association with the maintained displacement was termed a "static" response. 2. Units in the rostral part of MI (MI/r) and in area 3a usually responded in relation both the ramps and to maintained displacements. The activity of the majority of area 3a and MI/r units was strongly modulated only during ramps of one direction. Such response properties contrast with those observed in the caudal part of MI (MI/c) and areas 3b and 1 of SI, where most units responded in relation to the ramp phase of the displacement in both of two ramp directions and not to the maintained displacements. 3. Virtually all units, including those in MI, displayed a dynamic response. However, the dynamic response amplitude of area 3a neurons greatly exceeded that of MI units for equal velocities of displacement. 4. For area 3a units, peak neuronal activity was well correlated with ramp velocity over the range examined. Such units were a minority in areas 3b and 1 of SI (excluding area 3a) and MI. 5. Most area 3a units and almost half of MI/r units displayed, in addition to a dynamic response, a static response that reflected foot position. MI units were more sensitive than area 3a units to equal degrees of maintained displacement. 6. These results demonstrate that in the unanesthetized, intact animal, responses of most neurons in area 3a and MI fall into two categories: a) mixed dynamic-static responses resembling those of muscle spindle afferents, and b) purely dynamic responses. These data are consistent with the hypothesis that afferent input concerning the velocity and position of a segment of a limb may have a role in cortically mediated regulation of movement and posture, and that both areas 3a and the MI cortex may be directly involved in this regulation. 7. The cytoarchitectonic characteristics of area 3a, as defined in single-unit studies, are discussed. It is argued that the salient characteristic of area 3a in the primate is a thinned internal granular layer (layer IV) that contrasts with the heavily granular area 3b and the agranular area 4.

Animals↗
PubMed1984

Cable properties of layer V neurons from cat sensorimotor cortex in vitro.

The passive cable properties of neurons from layer V of cat neocortex were studied in an in vitro slice preparation using current-clamp techniques and a single-microelectrode voltage clamp. Neurons were examined in the presence and absence of several agents that block time- and voltage-dependent conductances. The charging response to an injected current pulse was well fitted by a single exponential in 12 of 17 cells examined. By itself, this result would suggest that most of the neurons are isopotential. However, the existence of a nonisopotential region was demonstrated in all neurons examined using two alternative, independent methods: application of voltage-clamp steps and current impulses. The decay of the capacitive charging transient following a voltage-clamp step reflects charge redistribution solely in the nonisopotential region and had a mean time constant about 17% of the membrane time constant, tau m. The voltage decay following a current impulse was always fitted by (at least) two exponentials, the shorter of which was about 9% of tau m. These results suggest that a nonisopotential region exists but is electrotonically short, of relatively low-input conductance, or both, independent of a particular neuron model. Adopting Rall's (23, 24) idealized neuron model (isopotential compartment attached to a finite-length uniform cable) resulted in a mean value for the equivalent electrotonic length (L) of the nonisopotential compartment of 0.72 space constants from voltage-clamp data and 1.21 space constants from impulse-response data. A dendrite-to-soma conductance ratio (p) of 2-4 was obtained from either procedure. There were no significant differences in the cable parameters between normal cells and those where conductance-blocking agents were present. A specific membrane resistance (Rm) ranging from 2,300 to 11,700 omega X cm2 was estimated by assuming values of specific membrane capacitance reported in the literature. We conclude that large layer V neocortical neurons in vitro are electrotonically compact in the voltage range near resting potential and in the absence of significant tonic synaptic input. In this respect, their electrotonic cable properties resemble those of other mammalian neurons in vitro.

Animals↗
PubMed2000

Calcium currents in retrogradely labeled pyramidal cells from rat sensorimotor cortex.

Our previous studies of calcium (Ca(2+)) currents in cortical pyramidal cells revealed that the percentage contribution of each Ca(2+) current type to the whole cell Ca(2+) current varies from cell to cell. The extent to which these currents are modulated by neurotransmitters is also variable. This study was directed at testing the hypothesis that a major source of this variability is recording from multiple populations of pyramidal cells. We used the whole cell patch-clamp technique to record from dissociated corticocortical, corticostriatal, and corticotectal projecting pyramidal cells. There were significant differences between the three pyramidal cell types in the mean percentage of L-, P-, and N-type Ca(2+) currents. For both N- and P-type currents, the range of percentages expressed was small for corticostriatal and corticotectal cells as compared with cells which project to the corpus callosum or to the general population. The variance was significantly different between cell types for N- and P-type currents. These results suggest that an important source of the variability in the proportions of Ca(2+) current types present in neocortical pyramidal neurons is recording from multiple populations of pyramidal cells.

Animals↗
PubMed1991

Motor deficits are produced by removing some cortical transplants grafted into injured sensorimotor cortex of neonatal rats.

Fetal frontal cortex was transplanted into cavities formed in the right motor cortex of neonatal rats. As adults, the animals were trained to press two levers in rapid succession with their left forelimb to receive food rewards. Once they had reached an optimal level of performance, the effect of removing their transplants was assessed. Surgical removal of transplants significantly impaired the performance of 2 of 4 subjects. Placing a cross-strain skin graft to induce the immunological rejection of the transplants produced a behavioral deficit in 1 of 2 subjects with complete transplant removal. Skin grafts produced no behavioral effects in four subjects that had surviving transplants. Since the motor deficits produced by transplant removal resembled those observed following the removal of normal motor cortex, we propose that these three transplants functioned within the host brain. Histology showed that the procedures used to remove cortical grafts did not injure any host brains. Therefore, host brain damage is unlikely to account for the behavioral deterioration that followed transplant removals.

Animals↗
PubMed1994

Multichannel magnetoencephalographic mapping of sensorimotor cortex for epilepsy surgery.

Preliminary reports have shown a close correlation between the anatomic location of evoked magnetic somatosensory fields and intraoperative evoked somatosensory potentials in patients with mass lesions. We have performed magnetic source imaging (MSI) of sensory and motor (MER) evoked responses or fields on 4 patients with frontal convexity epileptic foci. The method involves (1) graphic overlaying of magnetoencephalography evoked field data and three-dimensional (3D) phase contrast magnetic resonance angiographic data on 3D MRI surface cortical renderings, and (2) correlating these data with intraoperative stimulation-mapped sensory and/or motor responses and local cortical venous anatomy. Our initial results indicate that the location of MSI evoked sensory data correlates closely with the results of intraoperative stimulation mapping. MSI MERs have tended to show a less discrete spatial topography, involving areas of cortex extending beyond the motor strip.

Brain Mapping↗
PubMed1993

Comparison of the connectional properties of the two forelimb areas of the rat sensorimotor cortex: support for the presence of a premotor or supplementary motor cortical area.

The existence of multiple motor cortical areas that differ in some of their properties is well known in primates, but is less clear in the rat. The present study addressed this question from the point of view of connectional properties by comparing the afferent and efferent projections of the caudal forelimb area (CFA), considered to be the equivalent of the forelimb area of the primary motor cortex (MI), and a second forelimb motor representation, the rostral forelimb area (RFA). As a result of various tracing experiments (including double labeling), it was observed that CFA and RFA had reciprocal corticocortical connections characterized by preferential, asymmetrical, laminar distribution, indicating that RFA may occupy a different hierarchical level than CFA, according to criteria previously discussed in the visual cortex of primates. Furthermore, it was found that RFA, but not CFA, exhibited dense reciprocal connections with the insular cortex. With respect to their efferent projection to the basal ganglia, it was observed that CFA projected very densely to the lateral portion of the ipsilateral caudate putamen, whereas the contralateral projection was sparse and more restricted. The ipsilateral projection originating from RFA was slightly less dense than that from CFA, but it covered a larger portion of the caudate putamen (in the medial direction); the contralateral projection from RFA to the caudate putamen was of the same density and extent as the ipsilateral projection. The reciprocal thalamocortical and corticothalamic connections of RFA and CFA differed from each other in the sense that CFA was mainly interconnected with the ventrolateral thalamic nucleus, while RFA was mainly connected with the ventromedial thalamic nucleus. Altogether, these connectional differences, compared with the pattern of organization of the motor cortical areas in primates, suggest that RFA in the rat may well be an equivalent of the premotor or supplementary motor area. In contrast to the corticocortical, corticostriatal, and thalamocortical connections, RFA and CFA showed similar efferent projections to the subthalamic nucleus, substantia nigra, red nucleus, tectum, pontine nuclei, inferior olive, and spinal cord.

Afferent Pathways↗
PubMed1993

Localization of the face area of human sensorimotor cortex by intracranial recording of somatosensory evoked potentials.

The authors describe a method of localizing the sensory and motor peri-rolandic cortex representing the face and intraoral structures. Somatosensory evoked potentials (SEP's) to stimulation of the chin, lips, tongue, and palate were recorded in 37 patients studied intraoperatively under general anesthesia or following chronic implantation of cortical surface electrodes. Localization by trigeminal SEP recording was validated by SEP localization of the hand area with median nerve stimulation, and by cortical stimulation of the hand and face areas. The following conclusions were drawn regarding the implementation of face area localization: 1) in general agreement with the results of cortical stimulation in humans and single-unit recordings in monkeys, there is a medial-to-lateral representation in somatosensory cortex of the hand, chin, upper lip, lower lip, tongue, and palate; 2) the chin and lip representations overlap, are adjacent to the hand area, and provide little additional localizing information if the hand area has been identified; 3) stimulation of the tongue and palate evokes reliable, large-amplitude SEP's useful for localization; 4) palatal SEP's allow localization near the sylvian sulcus; 5) for any type of trigeminal stimulation, the largest SEP's are recorded from the somatosensory cortex and provide the most consistent criterion for its identification; and 6) polarity inversion of potentials across the sulcus (a reliable localizing criterion for median nerve SEP's) is a less reliable criterion for trigeminal SEP's.

Adolescent↗
PubMed2004

Effects of hydrocephalus and ventriculoperitoneal shunt therapy on afferent and efferent connections in the feline sensorimotor cortex.

OBJECT: The authors of previous studies have suggested that connectivity within the cerebral cortex may be irreversibly altered by hydrocephalus. To examine connectivity-related changes directly, the authors conducted a study in which they used an axonal tracer in an animal model of infantile hydrocephalus. METHODS: In five hydrocephalic kittens low-pressure ventriculoperitoneal (VP) shunts were placed 10 to 14 days after induction of hydrocephalus by intracisternal kaolin injections. Wheat germ agglutinin-conjugated horseradish peroxidase was injected laterally into the motor cortex in hydrocephalic animals 9 to 15 days after kaolin injection, and 1, 2, and 4 weeks after VP shunt insertion in shunt-treated animals, and in age-matched controls. Reduction of antero- and retrograde labeling was most profound within the contralateral cortex and portions of the midbrain. Thalamic nuclei exhibited reductions in anterograde and retrograde labeling. Labeling within cell bodies of the ventral tegmental area decreased greatly in animals with untreated hydrocephalus, in which retrograde labeling was reduced in the locus coeruleus but did not affect the raphe nucleus. Shunt treatment increased both antero- and retrograde labeling of contralateral motor cortex to near-normal levels. Thalamic relay nuclei recovered antero- and retrograde labeling, although not to levels exhibited in controls. Shunt therapy restored cellular labeling within the ventral tegmental area and locus coeruleus. Recovery of labeling occurred as early as 7 days after shunt insertion. CONCLUSIONS: Collectively, analysis of these data indicates the following. 1) Cortical connectivity involving both afferent and efferent pathways was impaired in untreated hydrocephalic animals. 2) Shunt therapy improved both cortical afferent and efferent connectivity. 3) Complete reestablishment of the cortical efferent pathways, however, did not occur. Cortical pathway dysfunction, if permanent, could cause many of the motor and cognitive deficits seen clinically in children with hydrocephalus.

Afferent Pathways↗
PubMedDate not supplied

[Response of sensorimotor cortex neurons to weak disturbances of the magnetic field in Wistar rats. Cytochemical study].

The influence of weak disturbances (up to 300 microT) of natural magnetic field on the protein metabolism in neurons of sensomotor cortex (layers III and V) in Wistar rats upon learning in a complex maze was studied. It was found that sensomotor neurons were very sensitive to weak disturbances of magnetic field. The protein content increased, while the nucleus-cytoplasm ratio and osmotic state of neurons remained unchanged. The specificity of neuron's reaction manifested itself in a sharp increase of nucleus and cytoplasm dimensions. In associative neurons (layer III), both the nucleus and cytoplasm were involved in the response; in efferent neurons (layer V), only nuclear parameters changed. The variance coefficients of all parameters of protein metabolism in sensomotor neurons, independently of their functional properties, were much higher than in control, which resulted in a wide diversity of cytochemical response.

Animals↗
PubMed2002

Serotonergic modulation of supragranular neurons in rat sensorimotor cortex.

Numerous observations suggest diverse and modulatory roles for serotonin (5-HT) in cortex. Because of the diversity of cell types and multiple receptor subtypes and actions of 5-HT, it has proven difficult to determine the overall role of 5-HT in cortical function. To provide a broader perspective of cellular actions, we studied the effects of 5-HT on morphologically and physiologically identified pyramidal and nonpyramidal neurons from layers I-III of primary somatosensory and motor cortex. We found cell type-specific differences in response to 5-HT. Four cell types were observed in layer I: Cajal Retzius, pia surface, vertical axon, and horizontal axon cells. The physiology of these cells ranged from fast spiking (FS) to regular spiking (RS). In layers II-III, we observed interneurons with FS, RS, and late spiking physiology. Morphologically, these cells varied from bipolar to multipolar and included basket-like and chandelier cells. 5-HT depolarized or hyperpolarized pyramidal neurons and reduced the slow afterhyperpolarization and spike frequency. Consistent with a role in facilitating tonic inhibition, 5-HT2 receptor activation increased the frequency of spontaneous IPSCs in pyramidal neurons. In layers II-III, 70% of interneurons were depolarized by 5-HT. In layer I, 57% of cells with axonal projections to layers II-III (vertical axon) were depolarized by 5-HT, whereas 63% of cells whose axons remain in layer I (horizontal axon) were hyperpolarized by 5-HT. We propose a functional segregation of 5-HT effects on cortical information processing, based on the pattern of axonal arborization.

Action Potentials↗