Showing papers on "Somatosensory system published in 2004"
TL;DR: It is suggested that the interaction between movement-triggered sensory feedback signals and self-organized spindle oscillations shapes the formation of cortical connections required for sensorimotor coordination.
Abstract: Sensorimotor coordination emerges early in development. The maturation period is characterized by the establishment of somatotopic cortical maps, the emergence of long-range cortical connections, heightened experience-dependent plasticity and spontaneous uncoordinated skeletal movement. How these various processes cooperate to allow the somatosensory system to form a three-dimensional representation of the body is not known. In the visual system, interactions between spontaneous network patterns and afferent activity have been suggested to be vital for normal development. Although several intrinsic cortical patterns of correlated neuronal activity have been described in developing somatosensory cortex in vitro, the in vivo patterns in the critical developmental period and the influence of physiological sensory inputs on these patterns remain unknown. We report here that in the intact somatosensory cortex of the newborn rat in vivo, spatially confined spindle bursts represent the first and only organized network pattern. The localized spindles are selectively triggered in a somatotopic manner by spontaneous muscle twitches, motor patterns analogous to human fetal movements. We suggest that the interaction between movement-triggered sensory feedback signals and self-organized spindle oscillations shapes the formation of cortical connections required for sensorimotor coordination.
555 citations
TL;DR: In this paper, the extent to which activity on chronically severed motor nerve fibers could be controlled by human amputees and whether distally referred tactile and proprioceptive sensations could be induced by stimulation of sensory axons in the nerve stumps was examined.
Abstract: Purpose It is not known whether motor and sensory pathways associated with a missing or denervated limb remain functionally intact over periods of many months or years after amputation or chronic peripheral nerve transection injury. We examined the extent to which activity on chronically severed motor nerve fibers could be controlled by human amputees and whether distally referred tactile and proprioceptive sensations could be induced by stimulation of sensory axons in the nerve stumps. Methods Amputees undergoing elective stump procedures were invited to participate in this study. Longitudinal intrafascicular electrodes were threaded percutaneously and implanted in severed nerves of human amputees. The electrodes were interfaced to an amplifier and stimulator system controlled by a laptop computer. Electrophysiologic tests were conducted for 2 consecutive days after recovery from the surgery. Results It was possible to record volitional motor nerve activity uniquely associated with missing limb movements. Electrical stimulation through the implanted electrodes elicited discrete, unitary, graded sensations of touch, joint movement, and position, referring to the missing limb. Conclusions These findings indicate that both central and peripheral motor and somatosensory pathways retain significant residual connectivity and function for many years after limb amputation. This implies that peripheral nerve interfaces could be used to provide amputees with prosthetic limbs that have more natural feel and control than is possible with current myoelectric and body-powered control systems.
343 citations
TL;DR: The present study systematically examined the capability of individual neurons in visual, auditory, and somatosensory cortex to be activated by stimuli from other senses and suggested a parcellation scheme in which modality-specific cortical domains are separated from one another by transitional multisensory zones.
Abstract: Traditional cortical parcellation schemes have emphasized the presence of sharply defined visual, auditory, and somatosensory domains populated exclusively by modality-specific neurons (i.e., neurons responsive to sensory stimuli from a single sensory modality). However, the modality-exclusivity of this scheme has recently been challenged. Observations in a variety of species suggest that each of these domains is subject to influences from other senses. Using the cerebral cortex of the rat as a model, the present study systematically examined the capability of individual neurons in visual, auditory, and somatosensory cortex to be activated by stimuli from other senses. Within the major modality-specific domains, the incidence of inappropriate (i.e., nonmatching) and/or multisensory neurons was very low. However, at the borders between each of these domains a concentration of multisensory neurons was found whose modality profile matched the representations in neighboring cortices and that were able to integrate their cross-modal inputs to give rise to enhanced and/or depressed responses. The results of these studies are consistent with some features of both the traditional and challenging views of cortical organization, and they suggest a parcellation scheme in which modality-specific cortical domains are separated from one another by transitional multisensory zones.
333 citations
TL;DR: Evidence in support of the hypothesis that an internal prediction of the consequences of the authors' actions is compared to the actual sensory input to cancel the resultant self-generated activation is obtained for early stages of sensory processing in the vestibular, visual and somatosensory systems.
260 citations
TL;DR: Results from a juvenile mouse thalamocortical slice preparation with whole cell recording conclude that the input from layer 6 to both nuclei acts as a modulator but that the layer 5 input to the posterior medial nucleus serves as a driver.
Abstract: We used a juvenile mouse thalamocortical slice preparation with whole cell recording to investigate synaptic properties of corticothalamic inputs from somatosensory cortex to the ventral posterior ...
244 citations
TL;DR: Early primates retained this basic organization and also had a larger posterior parietal region that mediated sensorimotor functions via connections with motor and premotor areas, and Posterior parietal cortex expanded into more areas that related to frontal cortex.
Abstract: Inferences about how the complex somatosensory systems of anthropoid primates evolved are based on comparative studies of such systems in extant mammals. Experimental studies of members of the major clades of extant mammals suggest that somatosensory cortex of early mammals consisted of only a few areas, including a primary area, S1, bordered by strip-like rostral and caudal somatosensory fields, SR and SC. In addition, the second somatosensory area, S2, and the parietal ventral area, PV, were probably present. S1, S2, and PV were activated independently via parallel projections from the ventroposterior nucleus, VP. Little posterior parietal cortex existed, and it was unlikely that a separate primary motor area, M1, existed until placental mammals evolved. Early primates retained this basic organization and also had a larger posterior parietal region that mediated sensorimotor functions via connections with motor and premotor areas. The frontal cortex included M1, dorsal and ventral premotor areas, supplementary motor area, and cingulate motor fields. Ventroposterior superior and ventroposterior inferior nuclei were distinct from the ventroposterior nucleus in the thalamus. In early anthropoid primates, areas S1, SR, and SC had differentiated into the fields now recognized as areas 3b, 3a, and 1. Areas 3b and 1 contained parallel mirror-image representations of cutaneous receptors and a parallel representation in area 2 was probable. Serial processing became dominant, so that neurons in areas 1, S2, and PV became dependent on area 3b for activation. Posterior parietal cortex expanded into more areas that related to frontal cortex. Less is known about changes that might have occurred with the emergence of apes and humans, but their brains were larger and posed scaling problems most likely solved by increasing the number of cortical areas and reducing the proportion of long connections.
213 citations
TL;DR: It is suggested that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing.
Abstract: Ensemble neuronal activity was recorded in each layer of the whisker area of the primary somatosensory cortex (SI) while rats performed a whisker-dependent tactile discrimination task. Comparison of this activity with SI activity evoked by similar passive whisker stimulation revealed fundamental differences in tactile signal processing during active and passive stimulation. Moreover, significant layer-specific functional differences in SI activity were observed during active discrimination. These differences could not be explained solely by variations in ascending thalamocortical input to SI. Instead, these results suggest that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing.
210 citations
TL;DR: The results show that observation of somatosensory stimulation alone is sufficient to cause significant modulation of motor cortex activity, and add further details as to what stimuli can activate the human mirror neuron system.
207 citations
TL;DR: It is suggested that TOR involves a complex network including parietal and insular somatosensory association cortices, as well as occipitotemporal visual areas, prefrontal, and medial temporal supramodal areas, and lateral and lateral secondary motor cortices.
Abstract: A functional magnetic resonance imaging (fMRI) study was conducted during which seven subjects carried out naturalistic tactile object recognition (TOR) of real objects. Activation maps, conjunctions across subjects, were compared between tasks involving TOR of common real objects, palpation of "nonsense" objects, and rest. The tactile tasks involved similar motor and sensory stimulation, allowing higher tactile recognition processes to be isolated. Compared to nonsense object palpation, the most prominent activation evoked by TOR was in secondary somatosensory areas in the parietal operculum (SII) and insula, confirming a modality-specific path for TOR. Prominent activation was also present in medial and lateral secondary motor cortices, but not in primary motor areas, supporting the high level of sensory and motor integration characteristic of object recognition in the tactile modality. Activation in a lateral occipitotemporal area associated previously with visual object recognition may support cross-modal collateral activation. Finally, activation in medial temporal and prefrontal areas may reflect a common final pathway of modality-independent object recognition. This study suggests that TOR involves a complex network including parietal and insular somatosensory association cortices, as well as occipitotemporal visual areas, prefrontal, and medial temporal supramodal areas, and medial and lateral secondary motor cortices. It confirms the involvement of somatosensory association areas in the recognition component of TOR, and the existence of a ventrolateral somatosensory pathway for TOR in intact subjects. It challenges the results of previous studies that emphasize the role of visual cortex rather than somatosensory association cortices in higher-level somatosensory cognition.
203 citations
TL;DR: Enhanced or additional responses to innocuous stimuli in the ipsilateral hemisphere may contribute to the shift of perception from innocuous toward painful and ill-defined sensations.
Abstract: Objective: To investigate cerebral activity associated with allodynia in patients with neuropathic pain. Methods: The brain responses of 27 patients with peripheral (5), spinal (3), brainstem (4), thalamic (5), lenticular (5), or cortical (5) lesions were studied with fMRI as innocuous mechanical stimuli were addressed to either the allodynic territory or the homologous contralateral region. Results: When applied to the normal side, brush and cold rubbing stimuli did not evoke pain and activated a somatosensory “control” network including contralateral primary (SI) and secondary (SII) somatosensory cortices and insular regions. The same stimuli became severely painful when applied to the allodynic side and activated regions in the contralateral hemisphere that mirrored the “control” network, with, however, lesser activation of the SII and insular cortices. Increased activation volumes were found in contralateral SI and primary motor cortex (MI). Whereas ipsilateral responses appeared very small and restricted after control stimuli, they represented the most salient effect of allodynia and were observed mainly in the ipsilateral parietal operculum (SII), SI, and insula. Allodynic stimuli also recruited additional responses in motor/premotor areas (MI, supplementary motor area), in regions involved in spatial attention (posterior parietal cortices), and in regions linking attention and motor control (mid-anterior cingulate cortex). Conclusion: On a background of deafferentation in the hemisphere contralateral to stimuli, enhanced or additional responses to innocuous stimuli in the ipsilateral hemisphere may contribute to the shift of perception from innocuous toward painful and ill-defined sensations.
195 citations
TL;DR: The term chronic immune sensory polyradiculopathy (CISP) is suggested for this syndrome, which preferentially affects large myelinated fibers of the posterior roots, may respond favorably to treatment, and may be a restricted form of chronic inflammatory demyelinating poly Radiculoneuropathy.
Abstract: Background: Chronic inflammatory neuropathies can present with a sensory ataxia due to involvement of dorsal root ganglia (DRG) or sensory nerves. Selective inflammatory involvement of sensory nerve roots proximal to the DRG has been postulated. Methods: The authors identified 15 patients with a sensory syndrome and normal nerve conduction studies. Sensory nerve root involvement was suggested by either somatosensory evoked potential (SSEP) or imaging abnormalities. CNS disease was excluded. Results: All patients had gait ataxia, large fiber sensory loss, and paresthesias, and nine had frequent falls. The disease course was chronic and progressive (median duration 5 years, range 3 months to 18 years). Sural sensory nerve action potential amplitudes were preserved and SSEP abnormalities were consistent with sensory nerve root involvement. Five patients had enlargement of lumbar nerve roots on MRI with enhancement in three. The CSF protein was elevated in 13 of 14 patients tested. Three patients had lumbar sensory rootlet biopsies that showed thickened rootlets, decreased density of large myelinated fibers, segmental demyelination, onion-bulb formation, and endoneurial inflammation. Six patients who required aids to walk were treated with immune modulating therapy and all had marked improvement with four returning to normal ambulation. Conclusion: Based on the described clinical features, normal nerve conduction studies, characteristic somatosensory evoked potential (SSEP) abnormality, enlarged nerve roots, elevated CSF protein, and inflammatory hypertrophic changes of sensory nerve rootlet tissue, we suggest the term chronic immune sensory polyradiculopathy (CISP) for this syndrome. This condition preferentially affects large myelinated fibers of the posterior roots, may respond favorably to treatment, and may be a restricted form of chronic inflammatory demyelinating polyradiculoneuropathy.
TL;DR: Anodal tDCS over the sensorimotor cortex can induce a long-lasting increase in the size of ipsilateral cortical components of SEPs, and might be a useful tool to induce plasticity in cortical sensory processing.
TL;DR: The temporal relationship of activities among multiple cortical areas using magnetoencephalography in humans indicated the serial mode of processing both through the postcentral gyrus and through the primary and secondary somatosensory cortices.
Abstract: Although numerous anatomical and electrophysiological findings in animal studies have supported a hierarchical scheme of somatosensory processing, precise activation timings of each cortical area are not known. Therefore we examined the temporal relationship of activities among multiple cortical areas using magnetoencephalography in humans. We found activations in Brodmann’s areas 3b, 4, 1, 5 and the secondary somatosensory cortex region in the right hemisphere following transcutaneous electrical stimulation of the dorsum of the left hand. The mean onset latencies of each cortical activity were 14.4, 14.5, 18.0, 22.4 and 21.7 ms, respectively. The differences of onset latencies among these activations indicated the serial mode of processing both through the postcentral gyrus and through the primary and secondary somatosensory cortices.
TL;DR: Different mechanisms are therefore responsible for the state-dependence of PSP amplitude and the spike frequency response to the whisker stimulus, and the state dependence of action potential generation in response to whisker stimulation may in part be related to a shift in threshold.
Abstract: Changes in spontaneous activity within the cortex recognized by subthreshold fluctuations of the membrane potential of cortical neurons modified the response of cortical neurons to sensory stimuli....
TL;DR: It is shown that a 15 min intervention of vibration applied simultaneously to two hand muscles can lead to long‐term changes in the spatial pattern of sensorimotor interaction and that the effects are specific for the motor output to muscles involved in the intervention and that they are modulated by the subject's attention.
Abstract: Sensory input can remodel representations in the sensory cortex, and this effect is heavily influenced by attention to the stimulus. Here we ask whether pure sensory input can also influence the spatial distribution of sensory effects on motor cortical hand area (sensorimotor organization) and whether this is modulated by attention. Sensorimotor organization was tested by applying short (1.5 s) periods of low amplitude vibration to single intrinsic hand muscles and measuring motor cortex excitability with transcranial magnetic stimulation (TMS). In healthy subjects, sensorimotor organization in the hand is focal, with input from one hand muscle increasing motor-evoked potentials (MEPs), decreasing short and increasing long-interval intracortical inhibition (SICI and LICI) in the vibrated muscle (‘homotopic’ effects) and having opposite effects on neighbouring muscles (‘heterotopic’ effects). Here we show that a 15 min intervention of vibration applied simultaneously to two hand muscles can lead to long-term (> 30 min) changes in the spatial pattern of sensorimotor interaction. The amount and direction of the effects depended on the subject's attention during the intervention: if subjects attended to both muscles when they were receiving simultaneous vibration, subsequent short-term vibration applied to one of them produced ‘homotopic’ effects on both muscles. ‘Heterotopic’ effects on a muscle not vibrated during the intervention were unaffected. If subjects did not attend to simultaneous vibration, subsequent short-term vibration of the muscles involved in the intervention no longer had any effect on them although the ‘heterotopic’ effects on a muscle not involved in the intervention were unchanged. We conclude that a 15 min period of pure sensory input can remodel the way that subsequent sensory inputs interact with motor output, that the effects are specific for the motor output to muscles involved in the intervention and that they are modulated by the subject's attention.
01 Jan 2004
TL;DR: This article investigated the perceived size of finger-muscle twitches (MEPs) evoked by TMS in eight normal subjects and found that participants perceived the first test MEP to be smaller in trials where they made voluntary actions than on trials when they did not, demonstrating sensory suppression.
Abstract: Voluntary actions produce suppression of neural activity in sensory areas, and reduced levels of conscious sensation. Recent computational models of motor control have linked sensory suppression to motor prediction: an efferent signal from motor areas may cancel the sensory reafferences predicted as a consequence of movement. Direct evidence for the efferent mechanism in sensory suppression has been lacking. We investigated the perceived size of finger-muscle twitches (MEPs) evoked by TMS in eight normal subjects. Subjects freely chose on each trial whether to make or withhold a voluntary flexion of the right index finger, in synchrony with an instructional stimulus. A test MEP occurred at the instructed time of action. The subject then relaxed and a second reference MEP occurred a few seconds later. Subjects judged which of the two MEPs was larger. Subjects perceived the first test MEP to be smaller in trials where they made voluntary actions than on trials where they did not, demonstrating sensory suppression. On randomly selected trials, a conditioning prepulse was delivered over the supplementary motor area (SMA) 10 ms before the pulse producing the test MEP. The SMA prepulse reduced and almost abolished the sensory suppression effect in voluntary action trials. We suggest the SMA may provide an efferent signal which is used by other brain areas to modulate somatosensory activity during self-generated movement. D 2003 Elsevier B.V. All rights reserved. Theme: Motor systems and sensorimotor integration Topic: Cortex
TL;DR: It is reported that the transfer of adult rats reared in standard laboratory cages to a naturalistic habitat modifies the functional and morphological organization of the facial whisker representation in the somatosensory ‘barrel’ cortex.
Abstract: Much of what is known about the functional organization and plasticity of adult sensory cortex is derived from animals housed in standard laboratory cages. Here we report that the transfer of adult rats reared in standard laboratory cages to a naturalistic habitat modifies the functional and morphological organization of the facial whisker representation in the somatosensory 'barrel' cortex. Cortical whisker representations, visualized with repeated intrinsic signal optical imaging in the same animals, contracted by 46% after four to six weeks of exposure to the naturalistic habitat. Acute, multi-site extracellular recordings demonstrated suppressed evoked neuronal responses and smaller, sharper constituent receptive fields in the upper cortical layers (II/III), but not in the thalamic recipient layer (IV), of rats with naturalistic experience. Morphological plasticity of the layer IV barrel field was observed, but on a substantially smaller scale than the functional plasticity. Thus, transferring animals to an environment that promotes the expression of natural, innate behaviours induces a large-scale functional refinement of cortical sensory maps.
TL;DR: FMRI data provides evidence that both SI and SII encode spatial information of nociceptive stimuli without additional information from the tactile system and highlights the concept of a redundant representation of basic discriminative stimulus features in human somatosensory cortices, which seems adequate in view of the evolutionary importance of pain perception.
TL;DR: The SMA may provide an efferent signal which is used by other brain areas to modulate somatosensory activity during self-generated movement, and is suggested to reduce and almost abolished the sensory suppression effect in voluntary action trials.
TL;DR: These findings demonstrate that somatosensory cortex can selectively regulate thalamic spatial response tuning by engaging topographically specific excitatory and inhibitory mechanisms in the thalamus.
TL;DR: It is reported that functional NMDA receptors are indeed present at or near the central terminals of primary afferent fibers and it is shown that activation of these presynaptic receptors results in an inhibition of glutamate release from the terminals.
Abstract: NMDA receptors have the potential to produce complex activity-dependent regulation of transmitter release when localized presynaptically. In the somatosensory system, NMDA receptors have been immunocytochemically detected on presynaptic terminals of primary afferents, and these have been proposed to drive release of substance P from central terminals of a subset of nociceptors in the spinal cord dorsal horn. Here we report that functional NMDA receptors are indeed present at or near the central terminals of primary afferent fibers. Furthermore, we show that activation of these presynaptic receptors results in an inhibition of glutamate release from the terminals. Some of these NMDA receptors may be expressed in the preterminal axon and regulate the extent to which action potentials invade the extensive central arborizations of primary sensory neurons.
TL;DR: It is demonstrated that ZI gates peripheral inputs to POm, enabling it to function both as a first-order and higher-order nucleus, and this gating mechanism may exert similar regulation of thalamic processing in other sensory systems.
Abstract: Sensory inputs are relayed to the neocortex by "first-order" thalamic nuclei, the responses of which are determined by ascending inputs from peripheral receptors. In contrast, "higher-order" thalamic nuclei respond poorly to peripheral inputs, and their responses are thought to be determined by descending cortical inputs. We tested this hypothesis by recording from neurons in the higher-order somatosensory posterior medial (POm) nucleus of narcotized rats. As reported previously, POm neurons responded to whisker stimuli with long-latency (median, 27 msec) and low-magnitude responses, consistent with cortically driven responses. However, when we suppressed inhibitory inputs from the subthalamic nucleus zona incerta (ZI), POm responses were of significantly higher magnitude and shorter latency, with many POm neurons responding at latencies consistent with ascending driving inputs from trigeminal nuclei. Our data suggest that POm comprises two neuronal populations: one population is driven by both peripheral and cortical inputs, and the second population responds only to cortical inputs. These findings demonstrate that ZI gates peripheral inputs to POm, enabling it to function both as a first-order and higher-order nucleus. Because ZI innervates all higher-order nuclei, this gating mechanism may exert similar regulation of thalamic processing in other sensory systems.
TL;DR: Studies on the effects of stimuli from multiple sensory modalities on the brain of humans and some other higher primates are reviewed, striking that humans and other catarrhines interface the visual system to other sensory systems in the orbitofrontal cortex.
Abstract: In primates, stimuli to sensory systems influence motivational and emotional behavior via neural relays to the orbitofrontal cortex. This article reviews studies on the effects of stimuli from multiple sensory modalities on the brain of humans and some other higher primates. The primate orbitofrontal cortex contains the secondary taste cortex, in which the reward value of taste is represented. It also contains the secondary and tertiary olfactory cortical areas, in which information about the identity and also about the reward value of odors is represented. A somatosensory input is revealed by neurons that respond to the viscosity of food in the mouth, to the texture (mouth feel) of fat in the mouth, and to the temperature of liquids placed into the mouth. The orbitofrontal cortex also receives information about the sight of objects from the temporal lobe cortical visual areas. Information about each of these modalities is represented separately by different neurons, but in addition, other neurons show convergence between different types of sensory input. This convergence occurs by associative learning between the visual or olfactory input and the taste. In that emotions can be defined as states elicited by reinforcers, the neurons that respond to primary reinforcers (such as taste and touch), as well as learn associations to visual and olfactory stimuli that become secondary reinforcers, provide a basis for understanding the functions of the orbitofrontal cortex in emotion. In complementary neuroimaging studies in humans, it is being found that areas of the orbitofrontal cortex are activated by pleasant touch, by painful touch, by taste, by smell, and by more abstract reinforcers such as winning or losing money. Damage to the orbitofrontal cortex in humans can impair the learning and reversal of stimulus-reinforcement associations and thus the correction of behavioral responses when these are no longer appropriate because previous reinforcement contingencies change. It is striking that humans and other catarrhines, being visual specialists like other anthropoids, interface the visual system to other sensory systems (e.g., taste and smell) in the orbitofrontal cortex.
TL;DR: It is demonstrated that Merkel cells are excitable cells and suggested that they release neurotransmitters to shape touch sensitivity.
Abstract: Merkel cell-neurite complexes are somatosensory receptors that initiate the perception of gentle touch. The role of epidermal Merkel cells within these complexes is disputed. To ask whether Merkel cells are genetically programmed to be excitable cells that may participate in touch reception, we purified Merkel cells from touch domes and used DNA microarrays to compare gene expression in Merkel cells and other epidermal cells. We identified 362 Merkel-cell-enriched transcripts, including neuronal transcription factors, presynaptic molecules, and ion-channel subunits. Antibody staining of skin sections showed that Merkel cells are immunoreactive for presynaptic proteins, including piccolo, Rab3C, vesicular glutamate transporter 2, and cholecystokinin 26-33. These data indicate that Merkel cells are poised to release glutamate and neuropeptides. Finally, by using Ca2+ imaging, we discovered that Merkel cells have L- and P/Q-type voltage-gated Ca2+ channels, which have been shown to trigger vesicle release at synapses. These results demonstrate that Merkel cells are excitable cells and suggest that they release neurotransmitters to shape touch sensitivity.
TL;DR: Recurrent transcranial magnetic stimulation is used to probe the connection between primary somatosensory cortex (S1) and early visual cortex (V1 and neighboring areas), combining rTMS with positron emission tomography (PET).
Abstract: Crossmodal plasticity occurs when loss of input in one sensory modality leads to reorganization in brain representations of other sensory modalities. In congenital blindness the visual cortex becomes responsive to somatosensory input such as occurs during Braille reading. The route by which somatosensory information reaches the visual cortex is not known. Here, we used repetitive transcranial magnetic stimulation (rTMS) to probe the connection between primary somatosensory cortex (S1) and early visual cortex (V1 and neighboring areas), combining rTMS with positron emission tomography (PET). We applied stimulation over S1 in sighted, early blind and late blind individuals. Baseline regional cerebral blood flow in occipital cortex was highest in early blind and lowest in late blind individuals. Only the early blind group showed significant activation of early visual areas when rTMS was delivered over S1. This activation was significantly higher in early than in late blind, but not relative to sighted controls. These results are consistent with the hypothesis that tactile information may reach early visual areas in early blind humans through cortico-cortical pathways, possibly supporting enhanced tactile information processing.
TL;DR: Increased tonic LC output generally decreased neuronal response latency measures for both BF cortical and VPM thalamic cells, and LC-mediated effects on target VPM and BF cortical neuron sensory processing are consistent with previous demonstrations of NE modulatory actions on central neurons but indicate that such actions are cell specific.
Abstract: In mammals, the pontine nucleus locus ceruleus (LC) is the sole source of norepinephrine (NE) projections to the forebrain. Increasing tonic discharge of LC neurons elevates extracellular levels of NE in the cortex and thalamus. Tonic LC discharge is linked to the level of wakefulness and behavioral performance, demonstrating an optimal firing rate during sustained attention tasks. Iontophoretic application of NE to target neurons in the forebrain has been shown to produce a diverse set of neuromodulatory actions, including augmentation of synaptically evoked discharge as well as suppression of spontaneous and stimulus-evoked firing patterns. Iontophoretic studies cataloged potential NE effects; however, the context in which such actions could occur in awake behaving animals remained controversial. To address this issue, the current study examined the effects of increasing tonic LC output on spontaneous and stimulus-evoked discharge of neurons within the ventroposterior medial (VPM) thalamus and barrel field (BF) somatosensory cortex of awake animals using multichannel extracellular recording strategies. The present findings indicate two primary outcomes that result from increasing frequencies of LC stimulation, either an inverted-U facilitating response profile or monotonic suppression of sensory-evoked neuronal responses. Increased tonic LC output generally decreased neuronal response latency measures for both BF cortical and VPM thalamic cells. LC-mediated effects on target VPM and BF cortical neuron sensory processing are consistent with previous demonstrations of NE modulatory actions on central neurons but indicate that such actions are cell specific. Moreover, clear differences were observed between the modulation of VPM and BF cortical cells. These data suggest that sensory signal processing is continually altered over the range of tonic LC discharge frequencies that occur in the waking animal. Such changes may account for LC-mediated shifts in sensory network performance across multiple stages of arousal and attention.
TL;DR: In the WAG/Rij model of absence epilepsy, a specific region of cortex is identified, in layer II-IV neurons on the lateral convexity of the cortex in the facial somatosensory area, where mRNA and protein expression of sodium channel genes Nav 1.1 and Nav1.6 are up-regulated, approximately matches the electrophysiologically determined region of seizure onset.
TL;DR: If sensory cortex can be considered a model system for cortex in general, because the use of sensory stimuli to activate neural circuits physiologically is helpful for understanding mechanisms of systems-level function and plasticity, is examined.
Abstract: Acetylcholine release in sensory neocortex contributes to higher-order sensory function, in part by activating nicotinic acetylcholine receptors (nAChRs). Molecular studies have revealed a bewildering array of nAChR subtypes and cellular actions; however, there is some consensus emerging about the major nAChR subtypes and their functions in sensory cortex. This review first describes the systems-level effects of activating nAChRs in visual, somatosensory, and auditory cortex, and then describes, as far as possible, the underlying cellular and synaptic mechanisms. A related goal is to examine if sensory cortex can be considered a model system for cortex in general, because the use of sensory stimuli to activate neural circuits physiologically is helpful for understanding mechanisms of systems-level function and plasticity. A final goal is to highlight the emerging role of nAChRs in developing sensory cortex, and the adverse impact of early nicotine exposure on subsequent sensory-cognitive function.
TL;DR: It is shown that the neural cell recognition molecule Close Homolog of L1 (CHL1) is required for neuronal positioning and dendritic growth of pyramidal neurons in the posterior region of the developing mouse neocortex.
TL;DR: It was found that a few hours of Hebbian coactivation evoked a significant increase of primary and secondary somatosensory cortical areas representing the stimulated body parts, and the amount of plastic changes was strongly correlated with improvement in spatial discrimination performance.
Abstract: Perceptual learning can be induced by passive tactile coactivation without attention or reinforcement. We used functional MRI (fMRI) and psychophysics to investigate in detail the specificity of this type of learning for different tactile discrimination tasks and the underlying cortical reorganization. We found that a few hours of Hebbian coactivation evoked a significant increase of primary (SI) and secondary (SII) somatosensory cortical areas representing the stimulated body parts. The amount of plastic changes was strongly correlated with improvement in spatial discrimination performance. However, in the same subjects, frequency discrimination was impaired after coactivation, indicating that even maladaptive processes can be induced by intense passive sensory stimulation.