Showing papers on "Somatosensory system published in 1982"

The Parietal Cortex of Monkey and Man

Abstract: I. Introduction.- II. Anatomy and Evolution of the Parietal Lobe in Monkeys and Man.- A. Anatomy.- B. Evolution.- III. Functional Properties of Neurones in the Primary Somatosensory Cortex.- A. Comments About Methods.- B. Movement and Orientation Selective Neurones in SI.- C. Receptive Field Integration and Submodality Convergence in SI.- D. Influence of Attention on Neuronal Function in SI.- IV. Neural Connections in the Posterior Parietal Lobe of Monkeys.- A. Connections of Area 5.- B. Connections of Area 7.- C. Summary of Connections.- V. Symptoms of Posterior Parietal Lesions.- A. Humans.- 1. Visuo-Spatial Disorientation.- 2. Defects in Eye Movements.- 3. Misreaching.- 4. Constructional Apraxia.- 5. Unilateral Neglect.- 6. Gerstmann Syndrome.- B. Monkeys.- 1. Visuo-Spatial Disorientation.- 2. Defects in Eye Movements.- 3. Misreaching.- 4. Unilateral Neglect.- 5. Somatic Deficits.- C. Comparison of Monkeys and Man.- VI. Electrical Stimulation of Posterior Parietal Lobe.- A. Monkey.- B. Man.- VII. Neuronal Activity in Area 5.- A. Sensory Properties.- B. Motor Properties.- C. Sensorimotor Interaction in Area 5.- VIII.Neuronal Activity in Area 7.- A. Visual and Oculomotor Mechanisms.- 1. Visual Fixation Neurones.- 2. Visual Tracking Neurones.- 3. Saccade Neurones...- 4. Visual Sensory Neurones.- B. Somatic Mechanisms.- 1. Cutaneous Responses.- 2. Kinaesthetic Responses.- 3. Activity Related to Somatic Movements.- C. Convergence of Somatic and Visual Functions.- D. Behavioural Mechanisms.- E. Effects of Drugs.- IX. Vestibular and Auditory Responses in the Parietal Lobe.- A. Vestibular Responses.- B. Auditory Responses in Area Tpt.- X. Regional Distribution of Functions in Area 7.- A. Mapping Methods.- B. Distribution of Responses.- 1. Visual Responses.- 2. Somatic Responses.- 3. Combined Responses from Several Modalities.- C. Somatotopy in Area 7.- D. Functional Differentiation.- XI. Modification of Area 7 and Functional Blindness After Visual Deprivation.- A. Visual Deprivation.- B. Deprivation Effects on the Visual Pathways.- C. Deprivation Effects on Area 7.- XII. Functional Role of Parietal Cortex.- A. Somatosensory Cortex.- B. Parietal Association Cortex.- 1. Sensory Functions.- a) Visual Functions.- b) Somaesthetic Functions.- c) Vestibular and Auditory Functions.- 2. Motor Functions.- a) Eye Movements.- b) Somatic Movements.- c) The Command Hypothesis.- d) The Corollary Discharge Hypothesis.- 3. Behavioural Functions.- a) Sensorimotor Interaction.- b) Spatial Schema.- c) Motivation-Intention-Attention.- d) Plasticity, Learning, Memory.- 4. Cellular Machinery.- a) Functional Organization.- b) Methodological Difficulties.- c) Factors That Influence Cellular Activity.- C. Parietal Lobe as a Whole.- References.

Structural and functional definition of the motor cortex in the monkey (Macaca fascicularis)

Abstract: 1. The details of the organization of the motor cortex and its anterior and posterior border were investigated in three monkeys by a combination of techniques including intracortical microstimulation (i.c.m.s.), electrophysiological recording of cutaneous and muscle afferent inputs to single cortical neurones, and electrophysiological and anatomical identification of corticospinal neurones; in addition, data from these methods were related to cortical cytoarchitecture. 2. Almost 5000 individual cortical loci were tested with i.c.m.s. in the unanaesthetized monkeys. In this paper, we particularly consider the organization of the forelimb motor representation, and its relation to the representation of other parts of the body. I.c.m.s. thresholds of about 5 μA were common for evoking twitch movements and e.m.g. responses in distal forelimb and face, jaw and tongue muscles, but proximal forelimb, trunk and hind-limb movements also sometimes had such low thresholds. 3. The fingers were found to be represented nearest the central sulcus, with horseshoe-shaped bands of cortical tissue representing progressively more proximal muscles situated around this central `finger core'. 4. Cytoarchitectonically, the cortex having these low-threshold motor effects was characteristic of area 4. There was also a close fit between the extent of this `excitable cortex' and the extent of densely spaced corticospinal neurones identified electro-physiologically or with horseradish peroxidase labelling. In subsequent mapping of forelimb afferents to the cortex when the animal was deeply anaesthetized, low-threshold and short-latency responses to muscle nerve stimulation were rarely found in this `excitable cortex'. 5. The anterior border could be clearly established by i.c.m.s. and by the sharp boundary of corticospinal neurones. It was noted that the motor cortex extends rostrally beyond area 4 and its anterior border appears to reside in the posterior part of area 6aα (Vogt & Vogt, 1919) although it is difficult to establish the precise transition from area 4 to area 6. 6. Posteriorly, the `micro-excitable cortex' was found to be limited to regions cytoarchitectonically delineated as area 4 and did not include area 3a. On the other hand, low-threshold forelimb proprioceptive afferent inputs appeared restricted to area 3a neurones in the deeply anaesthetized animal. Corticospinal neurones were very dense in area 4, and there was a clear decrease in their occurrence in more caudal areas. However, scattered nests of corticospinal neurones were noted in areas 3a, 3b, 2, 1 and 5. It remains to be seen whether these scattered nests could be directly involved in motor control or whether they may modulate ascending somatosensory transmission, and whether they rely on sensory feed-back or inputs from other central areas for their spinal effects.

Pudendal Evoked Responses

Abstract: • The dorsal nerve of the penis or clitoris, a branch of the pudendal nerve, was stimulated while averaged evoked responses over the spinal cord, sensory cortex, and bulbocavernosus muscle were recorded in a series of normal subjects. The morphologic features, peak latencies, and peripheral and central conduction times were compared with spinal and cortical evoked responses from the posterior tibial nerve. These tests are of potential clinical importance in the evaluation of sacral nerve root or plexus injuries and bowel, bladder, or sexual dysfunction.

Sensory nerve conduction in the human spinal cord: epidural recordings made during scoliosis surgery.

Abstract: This report describes the waveform and properties of somatosensory evoked potentials recorded from various levels of the human spinal cord, with electrodes inserted into the epidural space and the stimulus delivered to the posterior tibial nerve at the knee. The object was to provide a means of monitoring spinal cord function during surgery for the correction of spinal deformities. The responses could be resolved into at least three components with different activation thresholds and different conduction velocities within the spinal cord (45-80 m/s approximately). The findings are in accord with recent studies, suggesting that the fast activity may be conducted in the dorsal spinocerebellar tract and the slower waves in the posterior columns.

The Peripheral and Central Changes Resulting from Cutting or Crushing the Afferent Nerve Supply to the Whiskers

Abstract: In neonatal rats, crushing or cutting the infraorbital nerve, the sensory nerve supply to the whiskers, has been found to prevent cortical barrel formation. However, both procedures are followed by regeneration of one-third to one-half of the nerve fibres and reinnervation of the whiskers. By counting fibres in individual whisker follicle nerves, it has been shown that 29-67% (mean 45%) of the myelinated fibres regenerate to the whiskers after a crush compared to 24-56% (mean 39%) after a cut. Further differences between the crush and cut lesions were indicated by studies on the time course of regeneration. Counts of the regenerating fibres at various ages as well as recordings of cortical evoked potentials in normal, nerve-crushed and nerve-cut animals showed that recovery was 3-4 days earlier in the nerve-crushed, compared with the nerve-cut animals. In normal and nerve-crushed animals the evoked potential was first detectable 2-3 days after birth while the response after nerve cut could not be recorded until day 7. Even after 60 days the amplitude of responses on both crushed and cut pathways was only about one-third of normal, while the latency was prolonged (normal 5.8 +/- 0.25 ms, crush 6.5 +/- 0.26 ms, cut 7.7 +/- 0.67 ms). Central changes occurring as a result of nerve cut or crush have been studied by microelectrode recordings from the trigeminal nucleus (the first synaptic level) and the somatosensory cortex. These also indicate clearly the greater severity of the cut lesion. Thus, in crushed animals, all levels of the trigeminal nucleus as well as the cortex show only minor modifications. The whiskers occupy the same total area and responses from all whiskers are present at their normal sites. However, after nerve cut, the responses from both the trigeminal nucleus and cortex show clear abnormalities. The total whisker area is reduced with a concomitant expansion of responses from the nose, check, lower jaw, and whiskers by the eye and ear. In addition, only one-third to one-half of the whiskers give responses. The site of these abnormalities is localized to the trigeminal nucleus since all whiskers show innervation in the peripheral nerve. It is suggested that the longer recovery time as well as the reduced accuracy of reinnervation may contribute to the poorer central recovery after a nerve cut.

Somatotopic maps are disorganized in adult rodents treated neonatally with capsaicin.

Abstract: The somatosensory system is characterized at each stage of the projection pathways by the presence of maps formed by an orderly arrangement of cells and of the incoming fibres. Each cell responds to a definite area of skin, its receptive field (RF). If cell locations and their RFs are plotted side by side, they make up a continuous map of the body surface. Given the stability and repeatability of these maps, it was of interest to find that lesions which destroyed the input to one part of the map of the spinal cord in adults were followed by a readjustment of the RFs of cells which had lost their normal input1. It was more surprising to discover in adult cats and rats that peripheral nerve lesions which do not produce an anatomical destruction of spinal cord afferents were followed by the appearance of novel RFs in cells deprived of their normal physiological input2,3. Capsaicin given to neonatal mice or rats destroys unmyelinated afferents. We report here that this is followed by an expansion of the normal receptive fields supplied by myelinated afferents2,3. Our results suggest that unmyelinated fibres may be involved in controlling the connectivity of myelinated afferents with first central cells.

Central core control of developmental plasticity in the kitten visual cortex: I. Diencephalic lesions.

Abstract: In five, dark-reared, 4-week-old kittens the posterior two thirds of the corpus callosum were split, and a lesion comprising the intralaminar nuclei was made of the left medial thalamic complex. In addition, the right eye was closed by suture. Postoperatively, the kittens showed abnormal orienting responses, neglecting visual stimuli presented in the hemifield contralateral to the side of the lesion. Sudden changes in light, sound, or somatosensory stimulation elicited orienting responses that all tended toward the side of the lesion. These massive symptoms faded within a few weeks but the kittens continued to neglect visual stimuli in the hemifield contralateral to the lesion when a second stimulus was presented simultaneously in the other hemifield. Electrophysiologic analysis of the visual cortex, performed after the end of the critical period, revealed marked interhemispheric differences. In the visual cortex of the normal hemisphere most neurons were monocular and responded exclusively to stimulation of the open eye, but otherwise had normal receptive field properties. In the visual cortex of the hemisphere containing the thalamic lesion, the majority of the neurons remained binocular. In addition, the selectivity for stimulus orientation and the vigor of responses to optimally aligned stimuli were subnormal on this side. Thus, the same retinal signals, which in the control hemisphere suppressed the pathways from the deprived eye and supported the development of normal receptive fields, failed to do either in the hemisphere containing the thalamic lesion. Apparently, experience-dependent changes in the visual cortex require both retinal stimulation and the functioning of diencephalic structures which modulate cortical excitability and control selective attention.

Convergence of sensory inputs upon projection neurons of somatosensory cortex

Abstract: Cortico-cortical neurons and pyramidal tract neurons of the cat were tested for convergent inputs from forelimb afferents. Neurons were recorded in cortical areas 1, 2, and 3a. Consideration was given to both suprathreshold and subthreshold inputs evoked by electrical stimulation of forelimb nerves. Individual cortico-cortical neurons and also pyramidal tract neurons were characterized by convergence of multiple somatosensory inputs from different regions of skin, from several muscle groups, and between group I deep afferents and low threshold cutaneous afferents. Certain patterns of afferent input varied with cytoarchitectonic area. There was, however, no difference between area 3a and areas 1–2 in the incidence of cross-modality convergence in the form of input from cutaneous and also deep nerves. Many of the inputs were subthreshold. Arguments are presented that these inputs, though subthreshold, must be considered for a role in cortical information processing. The convergent nature of the sensory inputs is discussed in relation to the proposed specificities of cortical columns. The patterns of afferent inputs reaching cortico-cortical neurons seem to be appropriate for them to have a role in the formation of sensory fields of motor cortex neurons. PT neurons of somatosensory cortex have possible roles as modifiers of ascending sensory systems, however, the convergent input which these PT neurons receive argues against a simple relationship between the modality of peripheral stimuli influencing them and the modality of the ascending tract neurons under their descending control.

Phenytoin prolongs far‐field somatosensory and auditory evoked potential interpeak latencies

Abstract: Far-field auditory and somatosensory evoked potentials were recorded in 163 epileptic patients and 31 normal controls. Analysis of variance revealed significant effects on interpeak latencies of age, sex, and phenytoin levels in three ranges: subtherapeutic, therapeutic, and toxic. Toxic levels of phenytoin may affect peripheral and central axons, slowing conduction. Therapeutic levels of phenytoin may prolong far-field interpeak latencies by acting on synapses.

Spinal cord pathways mediating somatosensory evoked potentials

Abstract: Using a CO2 laser, discrete thoracic spinal cord lesions were made in cats anesthetized with ketamine and xylazine (Rompun). Differences in cortical somatosensory evoked potentials (SEP's) produced with high-intensity stimulation (20 times the motor threshold) of each posterior tibial nerve determined for nine different combinations of unilateral spinal cord lesions. The results of these studies show that nerve fibers in the ipsilateral dorsal column, the ipsilateral dorsal spinocerebellar tract, and the contralateral ventrolateral tracts with respect to the side of leg stimulation, contribute to cortical SEP's. A lesion of the dorsal spinocerebellar tract affected only the early waves (less than 30 msec) of the SEP from leg stimulation ipsilateral to the side of the lesion, whereas a solitary lesion of the ventrolateral tract caused changes primarily in the amplitude of later waves (greater than 30 msec) of the SEP produced by contralateral leg stimulation. Lesions involving one-half of the dorsal column caused changes in the amplitude of both the early and late waves produced by stimulation ipsilateral to the side of the lesion. The effects of various combinations of lesions on the cortical SEP's were not additive, which indicates significant interaction between afferent pathways. These findings suggest that high-intensity peripheral nerve stimulation, which activates both C and A fibers, could be used intraoperatively to assess spinal cord function with more accuracy than the current practice of using a stimulus strength of twice the motor threshold. The importance of using anesthetic agents that do not depress cortical activity (which may affect the later components of the SEP) is also emphasized.