Showing papers on "Somatosensory system published in 1992"
TL;DR: The results indicate that the topographic reorganization within the cortex was largely due to synaptic changes intrinsic to the cortex, perhaps through the plexus of long-range horizontal connections.
Abstract: THE adult brain has a remarkable ability to adjust to changes in sensory input. Removal of afferent input to the somatosensory, auditory, motor or visual cortex results in a marked change of cortical topography1–10. Changes in sensory activity can, over a period of months, alter receptive field size and cortical topography11. Here we remove visual input by focal binocular retinal lesions and record from the same cortical sites before and within minutes after making the lesion and find immediate striking increases in receptive field size for cortical cells with receptive fields near the edge of the retinal scotoma. After a few months even the cortical areas that were initially silenced by the lesion recover visual activity, representing retinotopic loci surrounding the lesion. At the level of the lateral geniculate nucleus, which provides the visual input to the striate cortex, a large silent region remains. Furthermore, anatomical studies show that the spread of geniculocortical afferents is insufficient to account for the cortical recovery. The results indicate that the topographic reorganization within the cortex was largely due to synaptic changes intrinsic to the cortex, perhaps through the plexus of long-range horizontal connections.
830 citations
TL;DR: The adaptation of high-resolution optical imaging for use on human cortex provides a new technique for investigation of the organization of the sensory and motor cortices, language, and other cognitive processes.
Abstract: Optical imaging of animal somatosensory, olfactory and visual cortices has revealed maps of functional activity. In non-human primates, high-resolution maps of the visual cortex have been obtained using only an intrinsic reflection signal. Although the time course of the signal is slower than membrane potential changes, the maximum optical changes correspond to the maximal neuronal activity. The intrinsic optical signal may represent the flow of ionic currents, oxygen delivery, changes in blood volume, potassium accumulation or glial swelling. Here we use similar techniques to obtain maps from human cortex during stimulation-evoked epileptiform afterdischarges and cognitively evoked functional activity. Optical changes increased in magnitude as the intensity and duration of the afterdischarges increased. In areas surrounding the afterdischarge activity, optical changes were in the opposite direction and possibly represent an inhibitory surround. Large optical changes were found in the sensory cortex during tongue movement and in Broca's and Wernicke's language areas during naming exercises. The adaptation of high-resolution optical imaging for use on human cortex provides a new technique for investigation of the organization of the sensory and motor cortices, language, and other cognitive processes.
360 citations
TL;DR: Comparing the sensory responses of POm and VPM cells in urethane‐anesthetized rats is compared as a first step in determining how cortex integrates multiple sensory pathways.
Abstract: The rodent barrel field cortex integrates somatosensory information from two separate thalamic nuclei, the ventral posterior medial nucleus (VPM) and the rostral sector of the posterior complex (POm). This paper compares the sensory responses of POm and VPM cells in urethane-anesthetized rats as a first step in determining how cortex integrates multiple sensory pathways. A complete representation of the contralateral body surface was identified in POm. Trigeminal receptive fields (RFs) of POm and VPM cells were mapped by computer-controlled displacement of individual whiskers; responses were quantified by using peristimulus time histograms. Average RF size was similar in POm (5.1 whiskers) and VPM (4.4 whiskers), but evoked responses in the two nuclei differed significantly according to all other measures. VPM cells were maximally responsive to one single whisker--the "center RF." Stimulating this whisker evoked, on average, a response of 1.4 spikes/stimulus at a latency of 7 ms; surrounding whiskers evoked responses of less than 1 spike/stimulus at latencies of greater than 8 ms. In contrast, POm cells were nearly equally responsive to several whiskers. Quantitative criteria allowed us to designate a single whisker as the "center RF" and stimulating this whisker evoked, on average, a response of 0.5 spikes/stimulus at a latency of 19 ms. VPM cells, but not POm cells, were able to "follow" repeated whisker deflection at greater than 5 Hz. We conclude that, when a single whisker is deflected, VPM activates the related cortical barrel-column at short latency--before the onset of activity in POm. The timing of activation could allow POm cells to modulate the spread of activity between cortical columns.
300 citations
TL;DR: Comparisons with SEPs recorded from the cortical surface or from within the brain, and monkey studies of SEPs which appear to be analogs of the human potentials, should provide better answers regarding the precise generators of human long-latency SEPs.
264 citations
TL;DR: The results of this study show that the different receptive fields of multisensory neurons in the cortex of the cat anterior ectosylvian sulcus were in spatial register, and it is this register that determined the manner in which these neurons integrated multiple sensory stimuli.
Abstract: The results of this study show that the different receptive fields of multisensory neurons in the cortex of the cat anterior ectosylvian sulcus (AES) were in spatial register, and it is this register that determined the manner in which these neurons integrated multiple sensory stimuli. The functional properties of multisensory neurons in AES cortex bore fundamental similarities to those in other cortical and subcortical structures. These constancies in the principles of multisensory integration are likely to provide a basis for spatial coherence in information processing throughout the nervous system.
251 citations
TL;DR: It is suggested that brain may respond to sudden increases in energy demand in part by rapid glycolytic metabolism of glycogen, as cerebral glycogen is restricted primarily to glia, and support a close coupling of glial energy metabolism with neuronal activity.
234 citations
Book•
01 Oct 1992
TL;DR: This work focuses on the role of neurotrophic factors in functional maintenance of mature sensory neurons in adult mammals and their role in the development of vertebrate cranial sensory neurons.
Abstract: E. Perl: Function of dorsal root ganglion neurons: an overview Section I: Phenotypic diversity among sensory neurons: S.N. Lawson: Morphological and biochemical cell types of sensory neurons S.P. Hunt, P.W. Mantyh & J.V. Priestley: The organization of biochemically characterized sensory neurons H.R. Koerber & L.M. Mendell: Functional heterogeneity of dorsal root ganglion cells M.C. Nowycky: Voltage-gated ion channels in dorsal root ganglion neurons P.B. Brown & H.R. Koerber: Somatotopic organization of primary afferent projections to the spinal cord R. Fyffe: Laminar organization of primary afferent termination in the mammalian spinal cord Section II: Development of sensory neurons: N.N.M. LeDouarin, M.A. Teillet & C. Kalcheim: The cellular and molecular basis of early sensory ganglion development K.S. Vogel: Origins and early development of vertebrate cranial sensory neurons A.M. Davies: Cell death and the trophic requirements of developing sensory neurons L.F. Reichardt: Adhesive interactions that regulate neuronal behavior S.A. Scott: The development of peripheral sensory innervation patterns M. O'Donovan & M. Lee: The development of muscle afferent connections in the vertebrate spinal cord M. Fitzgerald & B. Fulton: The physiological properties of developing sensory neurons Section III: Regeneration and plasticity in mature sensory neurons: J. Diamond & A. Gloster: Regulation of the sensory innervation of skin: trophic control of collateral sprouting S.B. McMahon: Plasticity of central terminations of primary sensory neurons in the adult animal G. Grant, H. Aldskogius & J. Arvidsson: Axotomy-induced changes in primary sensory neurons R.D. Johnson & J.B. Munson: Specificity of regenerating sensory neurons in adult mammals R.M. Lindsay The role of neurotrophic factors in functional maintenance of mature sensory neurons.
224 citations
TL;DR: The cortical connections of two vestibular fields were studied in the squirrel monkey by means of retrograde tracer techniques and most neurons in area T3 responded preferentially to large‐field optokinetic stimulation and not to Vestibular stimulation.
Abstract: The cortical connections of two vestibular fields [parieto-insular vestibular cortex (PIVC) and area 3aV] were studied in the squirrel monkey (Saimiri sciureus) by means of retrograde tracer techniques. Small iontophoretic or pressure injections of horseradish peroxidase (HRP), wheat-germ-HRP, Nuclear Yellow, and Fast Blue were administered to the cytoarchitectonic areas Ri (PIVC), 3aV, the parieto-temporal association area T3, the granular insula (Ig), and the rostral part of area 7 (7ant). The injection sites were physiologically characterized by means of microelectrode recordings and vestibular, optokinetic, or somatosensory stimulation: Area Ri is the region of the parieto-insular vestibular cortex (PIVC) as defined in macaques. The neck-trunk region of area 3a (area 3aV) also contains many neurons responding to stimulation of semicircular canal receptors. Some neurons of area T3 bordering on the PIVC also receive vestibular signals, but most neurons in area T3 responded preferentially to large-field optokinetic stimulation and not to vestibular stimulation. In none of the areas mentioned were responses to otolith stimulation found. The PIVC receives inputs from frontal and parietal cortical areas, especially areas 8a, 6, 3a, 3aV, 2, and 7ant. Area T3 receives signals from the insular and retroinsular cortex, various parts of area 7, visual areas of the parieto-occipital and parieto-temporal regions (area 19) and from a sector of the upper bank of the temporal sulcus (STS-area). The cortical afferents to area 3aV stem from areas 24, 4, 6, 7ant, from other parts of the primary somatosensory cortex, the secondary somatosensory cortex (SII), the retroinsular cortex (Ri), and the granular insula (Ig). In the border region of the areas 2 and 7ant, labelled neurons appeared after injections into both the PIVC and the area 3aV. This region is presumably the homologue to the vestibular area 2v of the macaque brain. In all regions cells within the contralateral cortex were less frequently labelled than cells in the homologous structures of the ipsilateral hemisphere. The cortical system for processing vestibular information about head-in-space movement consists mainly of the reciprocally interconnected areas PIVC and 3aV, and most likely of border regions of area 2 and 7ant. This "inner cortical vestibular circuit" also receives signals from two other cortical sensory systems, the somatosensory-proprioceptive system mediated by the primary somatosensory cortex and the visual movement system (optokinetic or visual flow signals). These visual movement signals reach PIVC via area 19 and area T3.(ABSTRACT TRUNCATED AT 400 WORDS)
223 citations
TL;DR: The preservation of functional‐metabolic coupling under a surgical dose of chloralose renders this anesthetic particularly suited for the investigation of coupling processes under conditions where the experimental requirements preclude the use of unanaesthetized animals.
Abstract: The effect of various anesthetics on the functional-metabolic coupling of cerebral cortex was studied in rats submitted to unilateral somatosensory stimulation. The regional cerebral metabolic rate of glucose (CMRglc) was measured autoradiographically using the 2-deoxyglucose method, and somatosensory activation was carried out by electrical stimulation of the left forepaw. In animals treated with 70% nitrous oxide, 0.5% halothane/70% nitrous oxide or 40 mg/kg pentobarbital, CMRglc of somatosensory cortex did not change despite generation of primary evoked cortical potentials. Anesthesia with 80 mg/kg alpha-chloralose, in contrast, led to a focal increase of CMRglc in the primary somatosensory cortex from 52.1 +/- 18.3 to 73.1 +/- 18.9 mumol/100 g/min (means +/- s.d.). Metabolic activation was strictly confined to the forelimb (FL) area of somatosensory cortex, and it exhibited a laminar pattern with maximal activation in layers I, II and IV. The preservation of functional-metabolic coupling under a surgical dose of chloralose renders this anesthetic particularly suited for the investigation of coupling processes under conditions where the experimental requirements preclude the use of unanaesthetized animals.
206 citations
TL;DR: It is reconfirmed that a significant number--at least one-third--of motor responses are distributed outside the classic narrow cortical strip, and indicates that primary motor cortex may extend beyond the gyrus immediately anterior to the Rf.
Abstract: Classic neurosurgical teaching holds that once the Rolandic fissure (Rf) has been located, there are distinct differentiated primary motor and sensory functional units confined within a narrow cortical strip: Brodmann's Areas 4 and 6 for primary motor units in front of the Rf and 3, 1, and 2 for sensory units behind the Rf. To test this assumption, we examined in detail the records of cortical mapping done by electrical stimulation of the cerebral cortex via implanted subdural electrode grids in 35 patients with seizure disorders. Of 1381 stimulations of the electrode sites, 346 (25.1%) produced primary motor or motor-arrest and sensory responses in contralateral body parts: 56.8% were primary motor responses; 16.2% were motor-arrest; 22.5% were sensory; and the remaining 4.5% were mixed motor and sensory responses. Two-thirds (65.9%) of the primary motor responses were located within 10 mm of the Rf, and the remaining one-third (34.1%) were more than 10 mm anterior to the Rf or were posterior to the Rf. Furthermore, in the patient group with brain lesions, fewer than one-third (28.1%) of the responses were within the 10-mm narrow anterior strip. Our study reconfirmed that a significant number--at least one-third--of motor responses are distributed outside the classic narrow cortical strip. In patients with brain lesions, the motor representation is further displaced outside the narrow strip. This finding indicates that primary motor cortex may extend beyond the gyrus immediately anterior to the Rf.
183 citations
TL;DR: The findings indicate that modality-specific information is relayed from postcentral cortical areas to SII along parallel channels, with cutaneous inputs transmitted via areas3b and 1, and deep inputs via areas 3a and 2.
Abstract: 1. Selective ablations of the hand representations in postcentral cortical areas 3a, 3b, 1, and 2 were made in different combinations to determine each area's contribution to the responsivity and m...
TL;DR: The results demonstrate that the responses of STT neurons to mechanical stimuli and to iontophoretically applied excitatory amino acids (EAAs) become enhanced during the development of inflammation produced by intra-articular injection of kaolin and carrageenan.
TL;DR: Evidence is provided that the responses of cortical neurons are subject to change by the introduction of locally coincident inputs into a single location, and a capacity for representational plasticity in the neocortex in the absence of peripheral stimulation is demonstrated.
Abstract: Intracortical microstimulation (ICMS) was applied to a single site in the middle cortical layers (III-IV) in the koniocortical somatosensory fields of sodium pentobarbital-anesthetized rats (Sml) and new world monkeys (area 3b). Low-threshold cutaneous receptive fields were defined in the cortical region surrounding the stimulation site prior to and following 2-6 hr of 5 microA ICMS stimulation. ICMS stimulation did not usually affect the receptive field location, size, or responsiveness to tactile stimulation of neurons at the stimulation site. However, the number of cortical neurons surrounding the stimulation site with a receptive field that overlapped with the ICMS-site receptive field increased in all studied animals, resulting in an enlarged cortical representation of a restricted skin region spanning several hundred microns. The mean size of receptive fields changed in some but not all cases. These results provide evidence that the responses of cortical neurons are subject to change by the introduction of locally coincident inputs into a single location, and demonstrate a capacity for representational plasticity in the neocortex in the absence of peripheral stimulation. These experimental observations are consistent with hypotheses that the cerebral cortex comprises radially oriented populations of neurons that share a common input, and that these inputs are shaped by coincident activity (see Edelman, 1978, 1987; Merzenich, 1987; Merzenich et al., 1990; von der Malsburg and Singer, 1988).
TL;DR: The present results demonstrate that the TRSN serves as an important link among the different sensory systems and provides a substrate through which they may gain access to the circuitry mediating orientation behavior.
Abstract: A select population of superior colliculus (SC) neurons receives and integrates information from the visual, auditory and somatosensory systems. Determining which SC neurons comprise this population and where they send their multisensory messages is important in understanding the functional impact of the SC on attentive and orientation behavior. One of the major routes by which the SC influences these behaviors is the tecto-reticulo-spinal tract, a descending pathway that plays an integral role in the orientation of the eyes, ears and head. Of the 182 tecto-reticulo-spinal neurons (TRSNs) encountered in the present study, almost all (94%) responded to sensory stimuli and the overwhelming majority (84%) were multisensory. The present results demonstrate that the TRSN serves as an important link among the different sensory systems and provides a substrate through which they may gain access to the circuitry mediating orientation behavior.
TL;DR: The laminar distribution of each group of cells shows prominent differences, indicating that the cellular composition was different from layer to layer, and the density of GABA-LIR neurons was highest in layer IV, whereas that of PV-negative GABA-lir neurons was almost constant throughout the layers.
Abstract: The number of neuronal and glial cells in the rat somatosensory cortex (barrel area) has been estimated by a stereological method, the disector, using pairs of toluidine blue-stained, plastic-embedded 0.5-μm-thick sections, 1.5 μm distant from each other. Chemical properties of those disector-counted cells were further analyzed by postembedding immunocytochemical methods on adjacent semithin sections. Thus we were able to analyze quantitatively number, distribution, and proportion of five cell types: (1) gamma-aminobutyric acid-(GABA)-negative neurons; (2) GABA-like immunoreactive (GABA-LIR) neurons; (3) a specific calcium-binding protein parvalbumin-immunoreactive (PV-IR) neurons, a subpopulation of GABA-LIR neurons; (4) S-100β-LIR glial cells (astrocytes); and (5) S-100β-negative glial cells (oligodendrocytes and microglia). The densities of total cells, glial cells, and neurons in the rat somatosensory cortex were 85.4 × 103/mm3, 30.5 × 103/mm3, and 54.9 × 103/mm3, respectively. Of all neurons 25% and 14% were GABA-LIR and PV-IR, respectively; all PV-IR neurons are GABA-LIR, and thus about 54% of GABA-LIR neurons are PV-positive. The number of total cells under a unit surface area of 1 mm2 through the thickness of the somatosensory cortex was 171.6 × 103; the number of neurons and glial cells were 110.2 × 103 and 61.4 × 103, respectively. There were 27.7 × 103 GABA-LIR neurons and 15.0 × 103 and 12.7 × 103 PV-IR neurons and PV-negative GABA-LIR neurons, respectively. The laminar distribution of each group of cells shows prominent differences, indicating that the cellular composition was different from layer to layer. The density of GABA-LIR neurons was highest in layer IV. The numerical density of PV-IR neurons was 2–4 times higher in layer IV than in layers II/III, V, and VI, whereas that of PV-negative GABA-LIR neurons was almost constant throughout the layers.
TL;DR: Cortical maturation was associated with the increased tendency of monoaminergic receptors to concentrate preferentially in the superficial cortical layers and an impressive coordination in the expression and regulation of these functionally relevant proteins in the cerebral cortex during infancy and adolescence.
Abstract: Quantitative in vitro autoradiography was used to study the postnatal development of monoaminergic receptors (D1 and D2 dopaminergic, 5-HT1 and 5-HT2 serotonergic, and alpha 1, alpha 2, and beta noradrenergic sites) in the prefrontal, primary motor, somatosensory, and visual cortex of rhesus monkeys at birth and 1, 2, 4, 8, 12, 36, and 60 months of age. The density of all receptors studied increased rapidly within the first 2 postnatal months to levels as high as two times that recorded in the adults. After the fourth month, receptor density began a decline that subsided around the time of puberty. This course of developmental change was similar in all cortical layers and in all regions examined. However, the magnitude of the transient overproduction and eventual reduction in receptor density varied across the cortical layers and cytoarchitectonic areas in a manner specific to the individual receptor sites. Overall, cortical maturation was associated with the increased tendency of monoaminergic receptors to concentrate preferentially in the superficial cortical layers. The common developmental course of monoaminergic receptors in diverse cytoarchitectonic areas reveals an impressive coordination in the expression and regulation of these functionally relevant proteins in the cerebral cortex during infancy and adolescence.
TL;DR: The results indicate that pain perception in man is associated with somatosensory cortical inhibition, and regional cerebral blood flow studies were done in humans using single photon emission computed tomography with the radiotracer Tc99m-HMPAO and magnetic resonance imaging localization.
TL;DR: Results indicate that neither peripherally evoked nor spontaneous activity are required for qualitatively normal pattern formation in the rat's primary somatosensory cortex.
TL;DR: This study shows that in normal monkeys the nonnociceptive, lemniscal component of the somatosensory pathways at spinal, brainstem, and thalamic levels is distinguished by cells and fibers immunoreactive for the calcium-binding protein parvalbumin, whereas cells of the nocICEptive component at these levels are distinguished by immunoreactivity for 28-kDa calbindin.
Abstract: Chronic deafferentation of skin and peripheral tissues is associated with plasticity of representational maps in cerebral cortex and with perturbations of sensory experience that include severe "central" pain. This study shows that in normal monkeys the nonnociceptive, lemniscal component of the somatosensory pathways at spinal, brainstem, and thalamic levels is distinguished by cells and fibers immunoreactive for the calcium-binding protein parvalbumin, whereas cells of the nociceptive component at these levels are distinguished by immunoreactivity for 28-kDa calbindin. Long-term dorsal rhizotomies in monkeys lead to transneuronal degeneration of parvalbumin cells at brainstem and thalamic sites accompanied in the thalamus by a down-regulation of gamma-aminobutyric acid type A receptors and an apparent increase in activity of calbindin cells preferentially innervated by central pain pathways. Release from inhibition and imbalance in patterns of somatosensory inputs from thalamus to cerebral cortex may constitute subcortical mechanisms for inducing changes in representational maps and perturbations of sensory perception, including central pain.
Journal Article•
TL;DR: It is concluded that GAL may have an important role in the control of nervous impulses that underlie pain states that can occur after peripheral nerve injury.
TL;DR: Reaction time to Suprathreshold transcranial stimulation to the motor cortex seems to transiently inhibit the neurons responsible for initiation of motor programs involving muscles in which motor evoked potentials have been induced, thereby prolonging the reaction time.
Abstract: We studied the effect of different go-signals on the reaction time in nine normal human subjects trained to respond by rapidly flexing one arm. Reaction times to auditory stimuli were shorter than those to visual or somatosensory stimuli, and were inversely correlated with the stimulus intensity. The reaction time was longest to a transcranial (magnetic or electric) stimulus delivered over the contralateral motor cortex that was sufficiently strong to induce a motor evoked potential in the responding biceps. Conversely, reaction time was shortest to either subthreshold transcranial stimulation over the same scalp position or to transcranial stimulation over the ipsilateral motor cortex regardless of intensity. Suprathreshold transcranial stimulation to the motor cortex seems to transiently inhibit the neurons responsible for initiation of motor programs involving muscles in which motor evoked potentials have been induced, thereby prolonging the reaction time. On the other hand, a subthreshold stimulus either disinhibits or directly activates such neurons leading to a shorter reaction time. Transcallosal connections between the motor cortices may account for the short reaction time to ipsilateral transcranial stimulation.
TL;DR: It is demonstrated that physiologic stimulation can induce immediate early response genes in cortical cells, and that multiple immediateEarly response genes react to a stimulus.
TL;DR: In this article, an image analysis detection technique revealed regions of maximal activity, or features, that formed a patchy pattern of activation reminiscent of the known anatomic patterns of cortico-striate terminals.
Abstract: 2-Deoxy-D-[14C]glucose autoradiography was used in awake rats to map neural activity in the sensorimotor sector of striatum. Stimulation of hindlimb, trunk, or forelimb activated primary sensory cortex in a localized columnar pattern, indicating activation of somatosensory receptors and a discrete cortical functional unit. In sensorimotor striatum, an image analysis detection technique revealed regions of maximal activity, or features, that formed a patchy pattern of activation reminiscent of the known anatomic patterns of cortico-striate terminals. Ipsilateral as well as contralateral activation was observed. The activated areas revealed a body map in striatum that was organized in a manner consistent with cortical topography (dorsoventrally: hindlimb, trunk, forelimb) at most anteroposterior levels, similar to that found in other species. However, at other levels, a different organization (e.g., trunk, hindlimb, forelimb) was observed. Furthermore, the arrangements of body region and side were also unique at different anteroposterior levels. Thus, functional activity showed multiple, different juxtapositions of body elements--i.e., a combinational map. The data suggest that striatum may provide an anatomic substrate for different combinations of inputs necessary to select and integrate movement.
TL;DR: The somatosensory P3 was reduced to ipsilateral stimuli at electrodes over the lesioned hemisphere with partial P3 preservation observed at electrode sites over the non-lesioned hemisphere and support the critical role of temporal-parietal cortex in P3 generation.
TL;DR: The study demonstrates that the C-T paradigm has potential for use in the assessment of spinal and cortical sensorimotor integration by providing quantitative information which cannot be obtained through isolated assessment of sensory and/or motor pathways.
TL;DR: The dramatic changes in the responses of “nociceptive” neurones to stimuli applied to the paw with the ligated sciatic nerve and the clear decrease in their activation threshold to mechanical and thermal stimuli could account for some of the abnormal pain-related behaviours that were exhibited.
Abstract: Single-unit recordings were made under moderate gaseous anaesthesia in the hindpaw representation area of the two primary somatosensory motor cortices (SmI) of rats (n = 58) rendered mononeuropathic by four loose ligatures placed around one common sciatic nerve 2–3 weeks beforehand. The rats exhibited clear hyperalgesia and allodynia from the paw with the ligated sciatic nerve, to both mechanical and thermal stimuli. From the tested neuronal population (n = 640), about the same proportion could be activated by somatic stimuli in each cortex: 165/362 (45%) in the cortex contralateral to the ligated sciatic nerve (Cc), 105/278 (37%) in the cortex ipsilateral to the ligated sciatic nerve (Ci). Neurones driven by light touch, exhibited RFs strictly contralateral to the recording sites. Their proportion and response characteristics were similar regardless of recording side. However, the number of neurones with RFs in the sciatic nerve territory was above 95% in the Ci, and was dramatically reduced to 43 % in the Cc. By contrast, the number of neurones with RFs supplied by the saphenous nerve reached 57% on this side. Although the RF size of all the neurones appeared roughly normal, there were fewer Cc than Ci neurones with RFs located on the paw itself and with RFs of extremely small size in the sciatic nerve territory. The proportion of neurones responding to a joint stimulus was significantly higher in the Cc than in the Ci. The neuronal responses to joint stimuli of the paw with the ligated sciatic nerve were significantly more sustained than those recorded in the Ci and elicited from the normal paw. The proportion of neurones driven by mechanical stimulation which gave rise to nociceptive reactions in freely moving animals, i.e. “nociceptive” neurones, was comparable in each cortex. However, half of the Cc neurones exhibited paroxysmal discharges occuring without intentional stimulation and of long duration (l min to several minutes). Only 66% of Cc but 93% of Ci “nociceptive” neurones were exclusively activated by pinch. The remaining Cc neurones were also activated by applying moderate pressure to the paw with the ligated nerve. Pinch responses from the paw with the ligated nerve were often more intense and of longer duration than responses elicited from the intact paw. The “nociceptive” Cc neurones were especially sensitive to thermal stimuli of 39–44° C when the stimuli were applied to the paw with the ligated nerve. They also responded vigorously to a 10° C stimulus applied to this paw. They were therefore, sensitive to thermal stimuli usually considered to be in the non-noxious range. In the SmI cortex opposite to the ligated sciatic nerve, there was no change in the proportion of somatosensory neurones, but a rearrangement of the various somatic inputs. Although reduced, there were consistent light tactile inputs from the damaged sciatic nerve giving rise to roughly normal neuronal responses, and simultaneously a noticeable increase in tactile signals from the saphenous nerve territory. There was also a significant increase in joint inputs from the paw with the ligated sciatic nerve. The possible functional role of such input rearrangement is discussed. The dramatic changes in the responses of “nociceptive” neurones to stimuli applied to the paw with the ligated sciatic nerve and the clear decrease in their activation threshold to mechanical and thermal stimuli could account for some of the abnormal pain-related behaviours that were exhibited. These data emphasize, again, that the primary sensory cortex is involved in nociceptive processing.
TL;DR: The responsiveness of individual neurons in the second somatosensory area (SII) in association with SI inactivation was examined to evaluate the relative importance for tactile processing of the direct thalamocortical projection to S II and the indirect projection from the thalamus to SII via an intracortical path through SI.
Abstract: 1. Localized cortical cooling was employed in anesthetized cats for the rapid reversible inactivation of the distal forelimb region within the primary somatosensory cortex (SI). The aim was to exam...
TL;DR: Horseradish peroxidase-labeled fibers in mouse somatosensory barrel cortex, which is patterned like the whiskers on the contralateral face from which it receives inputs, were evaluated by automated image analysis and demonstrated anatomically that the normal pattern of intracortical connections, like the normal sensory map, is dependent upon the sensory periphery four synapses away.
Abstract: The processes underlying development, refinement, and retention of the intracortical connections critical for the function of the mammalian brain are unknown. Horseradish peroxidase-labeled fibers in mouse somatosensory barrel cortex, which is patterned like the whiskers on the contralateral face from which it receives inputs, were evaluated by automated image analysis. The sensory nerve to the whiskers was sectioned on postnatal day 7, after the whisker map is set. The deprived barrel cortices, examined in adults, showed drastically diminished intracortical projections relative to normal controls, although the map of the whiskers in the cortex was unchanged. This demonstrates anatomically that the normal pattern of intracortical connections, like the normal sensory map, is dependent upon the sensory periphery four synapses away.