Showing papers on "Somatosensory system published in 2006"
TL;DR: This review will concentrate on sensory and motor inputs to the superior colliculus, on its internal circuitry, and on its connections with other brainstem gaze centers, as well as its extensive outputs to those structures with which it is reciprocally connected.
Abstract: The superior colliculus is a laminated midbrain structure that acts as one of the centers organizing gaze movements. This review will concentrate on sensory and motor inputs to the superior colliculus, on its internal circuitry, and on its connections with other brainstem gaze centers, as well as its extensive outputs to those structures with which it is reciprocally connected. This will be done in the context of its laminar arrangement. Specifically, the superficial layers receive direct retinal input, and are primarily visual sensory in nature. They project upon the visual thalamus and pretectum to influence visual perception. These visual layers also project upon the deeper layers, which are both multimodal, and premotor in nature. Thus, the deep layers receive input from both somatosensory and auditory sources, as well as from the basal ganglia and cerebellum. Sensory, association, and motor areas of cerebral cortex provide another major source of collicular input, particularly in more encephalized species. For example, visual sensory cortex terminates superficially, while the eye fields target the deeper layers. The deeper layers are themselves the source of a major projection by way of the predorsal bundle which contributes collicular target information to the brainstem structures containing gaze-related burst neurons, and the spinal cord and medullary reticular formation regions that produce head turning.
563 citations
TL;DR: It is hypothesized that spatial-selective attention enhances the saliency of sensory representations by synchronizing neuronal responses in early somatosensory cortex and thereby enhancing their impact on downstream areas and facilitating interareal processing.
Abstract: We investigated the effects of spatial-selective attention on oscillatory neuronal dynamics in a tactile delayed-match-to-sample task. Whole-head magnetoencephalography was recorded in healthy subjects while dot patterns were presented to their index fingers using Braille stimulators. The subjects9 task was to report the reoccurrence of an initially presented sample pattern in a series of up to eight test stimuli that were presented unpredictably to their right or left index finger. Attention was cued to one side (finger) at the beginning of each trial, and subjects performed the task at the attended side, ignoring the unattended side. After stimulation, high-frequency gamma-band activity (60–95 Hz) in presumed primary somatosensory cortex (S1) was enhanced, whereas alpha- and beta-band activity were suppressed in somatosensory and occipital areas and then rebounded. Interestingly, despite the absence of any visual stimulation, we also found time-locked activation of medial occipital, presumably visual, cortex. Most relevant, spatial tactile attention enhanced stimulus-induced gamma-band activity in brain regions consistent with contralateral S1 and deepened and prolonged the stimulus induced suppression of beta- and alpha-band activity, maximal in parieto-occipital cortex. Additionally, the beta rebound over contralateral sensorimotor areas was suppressed. We hypothesize that spatial-selective attention enhances the saliency of sensory representations by synchronizing neuronal responses in early somatosensory cortex and thereby enhancing their impact on downstream areas and facilitating interareal processing. Furthermore, processing of tactile patterns also seems to recruit visual cortex and this even more so for attended compared with unattended stimuli.
435 citations
TL;DR: No evidence for a focal representation of single muscles in M1 is found, and the overlap and intermingling among the different populations of CM cells may be the neural substrate to create a wide variety of muscle synergies.
Abstract: How are the neurons that directly influence the motoneurons of a muscle distributed in the primary motor cortex (M1)? To answer this classical question we used retrograde transneuronal transport of rabies virus from single muscles of macaques. This enabled us to define cortico-motoneuronal (CM) cells that make monosynaptic connections with the motoneurons of the injected muscle. We examined the distribution of CM cells that project to motoneurons of three thumb and finger muscles. We found that the CM cells for these digit muscles are restricted to the caudal portion of M1, which is buried in the central sulcus. Within this region of M1, CM cells for one muscle display a remarkably widespread distribution and fill the entire mediolateral extent of the arm area. In fact, CM cells for digit muscles are found in regions of M1 that are known to contain the shoulder representation. The cortical territories occupied by CM cells for different muscles overlap extensively. Thus, we found no evidence for a focal representation of single muscles in M1. Instead, the overlap and intermingling among the different populations of CM cells may be the neural substrate to create a wide variety of muscle synergies. We found two additional surprising results. First, 15–16% of the CM cells originate from area 3a, a region of primary somatosensory cortex. Second, the size range of CM cells includes both “fast” and “slow” pyramidal tract neurons. These observations are likely to lead to dramatic changes in views about the function of the CM system.
394 citations
TL;DR: A beta2 frequency oscillation occurring in vitro in networks of layer V pyramidal cells, the cells of origin of the corticospinal tract, depends on gap junctional coupling, but it survives a cut through layer 4 and, hence, does not depend on apical dendritic electrogenesis.
Abstract: Beta2 frequency (20–30 Hz) oscillations appear over somatosensory and motor cortices in vivo during motor preparation and can be coherent with muscle electrical activity We describe a beta2 frequency oscillation occurring in vitro in networks of layer V pyramidal cells, the cells of origin of the corticospinal tract This beta2 oscillation depends on gap junctional coupling, but it survives a cut through layer 4 and, hence, does not depend on apical dendritic electrogenesis It also survives a blockade of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors or a blockade of GABAA receptors that is sufficient to suppress gamma (30–70 Hz) oscillations in superficial cortical layers The oscillation period is determined by the M type of K+ current
310 citations
TL;DR: It is concluded that patterns of cortical reorganization in SI and SII seem to parallel impaired tactile discrimination and the amount of reorganization and tactile impairment appeared to be linked to characteristics of CRPS pain.
300 citations
TL;DR: The laminar pattern of corticocortical connections suggests that AI receives primarily cortical feedback-type inputs and projects in a feedforward manner to its target areas, and supports the notion that AI is not merely involved in the analysis of auditory stimulus properties but also in processing of other sensory and multisensory information.
268 citations
TL;DR: It is shown that the strength of the covariations between neuronal activity and perceptual judgments progressively increases across cortical areas as the activity is transmitted from the primary somatosensory cortex to the premotor areas of the frontal lobe.
Abstract: When a sensory stimulus is presented, many cortical areas are activated, but how does the representation of a sensory stimulus evolve in time and across cortical areas during a perceptual judgment? We investigated this question by analyzing the responses from single neurons, recorded in several cortical areas of parietal and frontal lobes, while trained monkeys reported the presence or absence of a mechanical vibration of varying amplitude applied to the skin of one fingertip. Here we show that the strength of the covariations between neuronal activity and perceptual judgments progressively increases across cortical areas as the activity is transmitted from the primary somatosensory cortex to the premotor areas of the frontal lobe. This finding suggests that the neuronal correlates of subjective sensory experience gradually build up across somatosensory areas of the parietal lobe and premotor cortices of the frontal lobe.
252 citations
TL;DR: Data indicate that unilateral touch of fingers is associated, in addition to the well known activation of the contralateral SI cortex, with deactivation of the ipsilateral SI cortex and of the MI cortex of both hemispheres.
Abstract: The whole human primary somatosensory (SI) cortex is activated by contralateral tactile stimuli, whereas its subarea 2 displays neuronal responses also to ipsilateral stimuli. Here we report on a transient deactivation of area 3b of the ipsilateral SI during long-lasting tactile stimulation. We collected functional magnetic resonance imaging data with a 3 T scanner from 10 healthy adult subjects while tactile pulses were delivered at 1, 4, or 10 Hz in 25 s blocks to three right-hand fingers. In the contralateral SI cortex, activation [positive blood oxygenation level-dependent (BOLD) response] outlasted the stimulus blocks by 20 s, with an average duration of 45 s. In contrast, a transient deactivation (negative BOLD response) occurred in the ipsilateral rolandic cortex with an average duration of 18 s. Additional recordings on 10 subjects confirmed that the deactivation was not limited to the right SI but occurred in the SI cortex ipsilateral to the stimulated hand. Moreover, the primary motor cortex (MI) contained voxels that were phasically deactivated in response to both ipsilateral and contralateral touch. These data indicate that unilateral touch of fingers is associated, in addition to the well known activation of the contralateral SI cortex, with deactivation of the ipsilateral SI cortex and of the MI cortex of both hemispheres. The ipsilateral SI deactivation could result from transcallosal inhibition, whereas intracortical SI-MI connections could be responsible for the MI deactivation. The shorter time course of deactivation than activation would agree with stronger decay of inhibitory than EPSP at the applied stimulus repetition rates.
246 citations
TL;DR: It is reported that visual deprivation produces opposite changes in synaptic function in primary visual and somatosensory cortices in rats, which are rapidly reversed by visual experience.
Abstract: Lack of a sensory input not only alters the cortical circuitry subserving the deprived sense, but also produces compensatory changes in the functionality of other sensory modalities. Here we report that visual deprivation produces opposite changes in synaptic function in primary visual and somatosensory cortices in rats, which are rapidly reversed by visual experience. This type of bidirectional cross-modal plasticity is associated with changes in synaptic AMPA receptor subunit composition.
201 citations
TL;DR: Interestingly, lip and toe stimulation also produced post-stimulus increases in beta rhythms in the bilateral motor hand areas for all subjects, suggesting that common neural systems in the primary motor cortex are activated during tactile stimulation of different body regions.
196 citations
TL;DR: The pattern of cortical deactivation during allodynia may hint at a shift of activation from tonically active sensory systems, like visual and vestibular cortices, into somatosensory-related brain areas.
Abstract: Objective: To investigate cerebral activations underlying touch-evoked pain (dynamic–mechanical allodynia) in patients with neuropathic pain. Methods: fMRI was used in 12 patients with complex regional pain syndromes (CRPSs). Allodynia was elicited by gently brushing the affected CRPS hand. Elicited pain ratings were recorded online to obtain pain-weighted predictors. Both activations and deactivations of blood oxygenation level–dependent signals were investigated. Results: Nonpainful stimulation on the nonaffected hand activated contralateral primary somatosensory cortex (S1), bilateral insula, and secondary somatosensory cortices (S2). In contrast, allodynia led to widespread cerebral activations, including contralateral S1 and motor cortex (M1), parietal association cortices (PA), bilateral S2, insula, frontal cortices, and both anterior and posterior parts of the cingulate cortex (aACC and pACC). Deactivations were detected in the visual, vestibular, and temporal cortices. When rating-weighted predictors were implemented, only few activations remained (S1/PA cortex, bilateral S2/insular cortices, pACC). Conclusions: Allodynic stimulation recruits a complex cortical network. Activations include not only nociceptive but also motor and cognitive processing. Using a covariance approach (i.e., implementation of rating-weighted predictors) facilitates the detection of a neuronal matrix involved in the encoding of allodynia. The pattern of cortical deactivation during allodynia may hint at a shift of activation from tonically active sensory systems, like visual and vestibular cortices, into somatosensory-related brain areas.
TL;DR: Sensory processing in patients with trigeminal neuropathic pain is associated with distinct activation patterns consistent with sensitization within and outside of the primary sensory pathway, which is consistent with the allodynia to brush and cold.
Abstract: Functional magnetic resonance imaging was used to study patients with chronic neuropathic pain involving the maxillary region (V2) of the trigeminal nerve in patients with spontaneous pain and evoked pain to brush (allodynia). Patients underwent two functional scans (2-3 months apart) with mechanical and thermal stimuli applied to the affected region of V2 and to the mirror site in the unaffected contralateral V2 region, as well as bilaterally to the mandibular (V3) division. Patients were stimulated with brush, noxious cold, and noxious heat. Significant changes were observed in regions within and outside the primary trigeminal sensory pathway. Stimulation to the affected (neuropathic) side resulted in predominantly frontal region and basal ganglia activation compared with the control side. The differences were consistent with the allodynia to brush and cold. A region of interest-based analysis of the trigeminal sensory pathway revealed patterns of activation that differentiated between the affected and unaffected sides and that were particular to each stimulus. Activation in the spinal trigeminal nucleus was constant in location for all pain stimuli. Activation in other brainstem nuclei also showed differences in the blood oxygenation level-dependent signal for the affected versus the unaffected side. Thus, sensory processing in patients with trigeminal neuropathic pain is associated with distinct activation patterns consistent with sensitization within and outside of the primary sensory pathway.
TL;DR: This study shows the existence of three distinct somatosensory maps in the suprasylvian, opercular and insular regions, and separate pain representations in SII andinsular cortex.
Abstract: Somatosensory and pain responses to direct intracerebral stimulations of the SII area were obtained in 14 patients referred for epilepsy surgery. Stimulations were delivered using transopercular electrodes exploring the parietal opercular cortex (SII area), the suprasylvian parietal cortex (SI area) and the insular cortex. SII responses were compared to those from adjacent SI and insular cortex. In the three areas we elicited mostly somatosensory responses, including paresthesiae, temperature and pain sensations. The rate of painful sensations (10%) was similar in SII and in the insula, while no painful sensation was evoked in SI. A few nonsomatosensory responses were evoked by SII stimulation. Conversely various types of non-somatosensory responses (auditory, vegetative, vestibular, olfacto-gustatory, etc.) were evoked only by insular stimulation, confirming that SII, like SI, are mostly devoted to the processing of somatosensory inputs whereas the insular cortex is a polymodal area. We also found differences in size and lateralization of skin projection fields of evoked sensations between the three studied areas, showing a spatial resolution of the somatotopic map in SII intermediate between those found in SI and insula. This study shows the existence of three distinct somatosensory maps in the suprasylvian, opercular and insular regions, and separate pain representations in SII and insular cortex.
TL;DR: This article examined patterns of thalamocortical and cortical connections in adult opossums that had been bilaterally enucleated neonatally, prior to the formation of retinogeniculate and geniculocortic connections.
TL;DR: The results show that a focally applied brief painful stimulus globally suppresses spontaneous oscillations in somatosensory, motor and visual areas and shows that pain induces a widespread change in cortical function and excitability.
Abstract: The neuronal activity of the resting human brain is dominated by spontaneous oscillatory activity of primary visual, somatosensory and motor areas. These spontaneous brain rhythms are related to the functional state of a system. A higher amplitude of oscillatory activity is thought to reflect an idling state, whereas a lower amplitude is associated with activation and higher excitability of the specific system. Here, we used magnetoencephalography to investigate the effects of pain on spontaneous brain rhythms. Our results show that a focally applied brief painful stimulus globally suppresses spontaneous oscillations in somatosensory, motor and visual areas. This global suppression contrasts with the regionally specific suppressions of other modalities and shows that pain induces a widespread change in cortical function and excitability. This global change in excitability may reflect the alerting function of pain which opens the gates for processing of and reacting to stimuli of existential relevance.
TL;DR: Results reveal a human anatomical-functional homologue to monkey inferior parietal areas that respond to aversive stimuli by producing nocifensive muscle and limb movements.
Abstract: The posterior parietal cortex of both human and non-human primates is known to play a crucial role in the early integration of visual information with somatosensory, proprioceptive and vestibular signals. However, it is not known whether in humans this region is further capable of discriminating if a stimulus poses a threat to the body. In this functional magnetic resonance imaging (fMRI) study, we tested the hypothesis that the posterior parietal cortex of humans is capable of modulating its response to the visual processing of noxious threat representation in the absence of tactile input. During fMRI, participants watched while we "stimulated" a visible rubber hand, placed over their real hand with either a sharp (painful) or a blunt (nonpainful) probe. We found that superior and inferior parietal regions (BA5/7 and BA40) increased their activity in response to observing a painful versus nonpainful stimulus. However, this effect was only evident when the rubber hand was in a spatially congruent (vs. incongruent) position with respect to the participants' own hand. In addition, areas involved in motivational-affective coding such as mid-cingulate (BA24) and anterior insula also showed such relevance-dependent modulation, whereas premotor areas known to receive multisensory information about limb position did not. We suggest these results reveal a human anatomical-functional homologue to monkey inferior parietal areas that respond to aversive stimuli by producing nocifensive muscle and limb movements.
TL;DR: Physiological observations suggest that one function of somatosensory input to the auditory system is to suppress responses to "expected" body-generated sounds such as vocalization or respiration, which would serve to enhance responses to 'unexpected' externally- generated sounds, such as the vocalizations of other animals.
TL;DR: In this paper, the effect of transcranial direct current stimulation (tDCS) on the excitability of the human motor cortex measured by motor evoked potentials (MEPs) after transcranial magnetic stimulation was investigated.
TL;DR: Results provide direct evidence that illusory somatosensory percepts can affect primary somatoensory cortex in a manner that corresponds somatotopically to the illusORY percept.
Abstract: We used functional magnetic resonance imaging (fMRI) to study neural correlates of a robust somatosensory illusion that can dissociate tactile perception from physical stimulation. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touches at intervening locations along the arm, as if a rabbit hopped along it. We examined brain activity in humans using fMRI, with improved spatial resolution, during this version of the classic cutaneous rabbit illusion. As compared with control stimulation at the same skin sites (but in a different order that did not induce the illusion), illusory sequences activated contralateral primary somatosensory cortex, at a somatotopic location corresponding to the filled-in illusory perception on the forearm. Moreover, the amplitude of this somatosensory activation was comparable to that for veridical stimulation including the intervening position on the arm. The illusion additionally activated areas of premotor and prefrontal cortex. These results provide direct evidence that illusory somatosensory percepts can affect primary somatosensory cortex in a manner that corresponds somatotopically to the illusory percept.
TL;DR: The concept of neuroplasticity and its applicability to oro-facial pain, to motor control and motor learning, and to adaptation to changes in the oral sensory environment such as may occur with the placement of dental implants are emphasized.
Abstract: This article provides a review of somatosensory and motor pathways and processes involved in oral sensorimotor function and dysfunction. It reviews somatosensory processes in peripheral tissues, brainstem and higher brain centres such as thalamus and cerebral cortex, with a particular emphasis on nociceptive mechanisms. It also outlines some of the circuits and processes involved in reflexes and motor control. In addition, it emphasizes the concept of neuroplasticity and its applicability to oro-facial pain, to motor control and motor learning, and to adaptation to changes in the oral sensory environment such as may occur with the placement of dental implants.
TL;DR: This study demonstrates the reliability of S-MMN recordings and indicates that subjects with cerebellar damage may be impaired in the cortical processing of incoming somatosensory inputs.
Abstract: Several recent studies support the view that the cerebellum's contribution to sensory processing is not limited to movement regulation. In a previous paper (Restuccia D, Valeriani M, Barba C, Le Pera D, Capecci M, Filippini V, Molinari M. Functional changes of the primary somatosensory cortex in patients with unilateral cerebellar lesions. Brain 2001; 124: 757-68) we showed that the cerebellum influences somatosensory input processing at very early stages. The present study was aimed at verifying whether an analogous influence is also exerted at higher levels. For some time it has been known that in the auditory modality a specific event-related potential (ERP), that is, mismatch negativity (MMN), reflects preattentive detection of changes in the incoming stimulus by comparing the new stimulus with sensory memory traces. To test the cerebellar influence on the processing of incoming somatosensory stimuli we first verified whether the electrical stimulation of fingers, according to an 'oddball' paradigm within a stimulus-ignored condition, was able to elicit event-related components specifically linked to the preattentive detection of change. We analysed scalp responses obtained from eight healthy volunteers during frequent and rare electrical stimulation of the first and fifth finger of the left hand, respectively. To ensure that responses to deviant stimuli were due to changes in detection mechanisms, rather than to activation of new afferents, we also analysed responses to rare stimulation alone ('standard-omitted' condition). The 'oddball' stimulation was able to elicit a parieto-occipital extra negativity that was different in scalp distribution and latency from the N140 response to the 'standard-omitted' stimulation. We considered that this response was related to changes in detection mechanisms and labelled it somatosensory mismatch negativity (S-MMN). When the same procedure was applied to six patients with unilateral cerebellar lesions we found that the S-MMN was clearly abnormal after stimulation of the affected hand (ipsilateral to the affected cerebellar hemisphere). Earlier ERPs, as well as ERPs elicited during the 'standard-omitted' condition, were fully normal. Present data indicate that cerebellar processing is involved in preattentive detection of somatosensory input changes. In conclusion, this study demonstrates the reliability of S-MMN recordings and indicates that subjects with cerebellar damage may be impaired in the cortical processing of incoming somatosensory inputs.
TL;DR: Early stimulus-evoked beta activity was more sensitive to ISI than temporally-overlapping gamma-band activity, and this effect was seen in both auditory and somatosensory studies, consistent with developing theories regarding the different roles of temporally overlapping oscillatory activity within cortical neuron populations at gamma and beta frequencies.
TL;DR: It is speculated that protocols that involve repeated activation of motor cortical output lead to lasting changes in efficacy of synaptic connections in output circuits, whereas protocols that emphasize sensory inputs affect the strength of sensory inputs to motor circuits.
Abstract: Several experimental protocols induce lasting changes in the excitability of motor cortex. Some involve direct cortical stimulation, others activate the somatosensory system and some combine motor and sensory stimulation. The effects usually are measured as changes in amplitude of the motor-evoked-potential (MEP) or short-interval intracortical inhibition (SICI) elicited by a single or paired pulses of transcranial magnetic stimulation (TMS). Recent work has also tested sensorimotor organization within the motor cortex by recording MEPs and SICI during short periods of vibration applied to single intrinsic hand muscles. Here sensorimotor organization is focal: MEPs increase and SICI decreases in the vibrated muscle, whilst the opposite occurs in neighbouring muscles. In six volunteers we compared the after effects of three protocols that lead to lasting changes in cortical excitability: (i) paired associative stimulation (PAS) between a TMS pulse and an electrical stimulus to the median nerve; (ii) motor practice of rapid thumb abduction; and (iii) sensory input produced by semicontinuous muscle vibration, on MEPs and SICI at rest and on the sensorimotor organization. PAS increased MEP amplitudes, whereas vibration changed sensorimotor organization. Motor practice had a dual effect and increased MEPs as well as affecting sensorimotor organization. The implication is that different protocols target different sets of cortical circuits. We speculate that protocols that involve repeated activation of motor cortical output lead to lasting changes in efficacy of synaptic connections in output circuits, whereas protocols that emphasize sensory inputs affect the strength of sensory inputs to motor circuits.
TL;DR: It is found that in the principal sensory nucleus, the whisker-related map is contributed by rhombomere 3–derived neurons, whereas the rhombo-derived progeny supply the lower jaw and lip representation and Hoxa2 inactivation results in the absence of whiskers-related maps in the postnatal brain.
Abstract: In the mouse trigeminal pathway, sensory inputs from distinct facial structures, such as whiskers or lower jaw and lip, are topographically mapped onto the somatosensory cortex through relay stations in the thalamus and hindbrain. In the developing hindbrain, the mechanisms generating such maps remain elusive. We found that in the principal sensory nucleus, the whisker-related map is contributed by rhombomere 3-derived neurons, whereas the rhombomere 2-derived progeny supply the lower jaw and lip representation. Moreover, early Hoxa2 expression in neuroepithelium prevents the trigeminal nerve from ectopically projecting to the cerebellum, whereas late expression in the principal sensory nucleus promotes selective arborization of whisker-related afferents and topographic connectivity to the thalamus. Hoxa2 inactivation further results in the absence of whisker-related maps in the postnatal brain. Thus, Hoxa2- and rhombomere 3-dependent cues determine the whisker area map and are required for the assembly of the whisker-to-barrel somatosensory circuit.
TL;DR: It is shown that trial-by-trial relative frequency difference is represented linearly by activity changes in the left dorsolateral prefrontal cortex (DLPFC), the dorsal anterior cingulate cortex, and bilateral anterior insular cortices, and a circumscribed region within the left DLPFC showed a different response pattern.
Abstract: The neural processes underlying tactile decisions in the human brain remain elusive. We addressed this question in a functional magnetic resonance imaging study using a somatosensory discrimination task, requiring participants to compare the frequency of two successive tactile stimuli. Tactile stimuli per se engaged somatosensory, parietal, and frontal cortical regions. Using a statistical model that accounted for the relative difference in frequencies (i.e., Weber fraction) and discrimination accuracy (i.e., correct or incorrect), we show that trial-by-trial relative frequency difference is represented linearly by activity changes in the left dorsolateral prefrontal cortex (DLPFC), the dorsal anterior cingulate cortex, and bilateral anterior insular cortices. However, a circumscribed region within the left DLPFC showed a different response pattern expressed as activity changes that were monotonically related to relative stimulation difference only for correct but not for incorrect trials. Our findings suggest that activity in the left DLPFC encodes stimulus representations that underlie veridical tactile decisions in humans.
TL;DR: Experimental evidence is provided that the neural control of stiffness or impedance--the resistance to displacement--provides for somatosensory precision in speech production.
TL;DR: It is demonstrated that functional magnetic resonance imaging can provide information of brain regions involved in opioid-induced central nervous system effects and the cingulate, orbitofrontal, posterior parietal and insular cortices, and amygdala showed activation, which was temporally closely related to most subjective sensations.
TL;DR: Findings support the theory that the input from oral structures converges hierarchically across the primary somatosensory cortex.
Abstract: Thetactilesensationoftheteethisinvolved invariousoralfunctions, such as mastication and speech. Using functional magnetic resonance imaging, we investigated the cortical sensory representation of the oral area, including the teeth. First, we identified the somatotopic representation of the lips, teeth and tongue in the postcentral gyrus (GpoC). Tactile stimuli were applied to the lower lip, tongue and teeth. The foci activated by each stimulus were characterized by the center of gravity (COG) of activated areas. Secondly, we examined the rostro-caudal changes in the somatotopic organization in the GPoC in terms of the overlap between each sensory representation. In the rostral portion of the GPoC, the COG of the representation of teeth was located significantly superior to that of the tongue and inferior to that of the lip, consistent with the classical ‘sensory homunculus’ proposed by Penfield; however, this somatotopic representation became unclear in the middle and caudal portions of the GPoC. The overlap between each representationinthemiddleandcaudalportionsoftheGPoCwassignificantly greater than that in the rostral portion of the GPoC. These findings support the theory that the input from oral structures converges hierarchically across the primary somatosensory cortex.
IBM1
TL;DR: The present studies were carried out to determine which measures of the evoked cortical responses could be correlated with behavioral measures, and therefore, were representative codes of psychological phenomena.
Abstract: Throughout the history of physiological psychology there has been existent a frustrated enthusiasm for direct comparisons between psychophysical responses and electrophysiological measures from the same verbally responsive human subjects. Unfortunately, experimental surgery, unrelated to pathological conditions, as it should have, remained an unacceptable course of action, and little could be made of the diffused and minute electrical signals which certainly existed below the myographic and resting encephalographic noise. It was the work of G. B. Dawson5 which opened up a whole new spectrum of possibilities of experimental inquiries. Professor Dawson devised techniques for recording signals from the major peripheral nerves by percutaneous recording as well as suggesting the techniques of statistical averaging which are used by all of the participants in this conference. Our earlier workg8l took advantage of the ability to measure peripheral nerve action potentials in the intact human arm and studied the temporal and spatial coding correlates of estimates of sensory magnitude. The success of these earlier studies led us to the present investigations which are directed at the coding of sensory intensity and space as they are reflected in the somatosensory evoked cortical potential. Since Dawson's original work, considerable attention has been directed towards the improvement of techniques and the associated instrumentation. The membership of this conference includes some of the contributors to this aspect of this work, and the reader is specifically directed to the work of W. A. Clark, Jr.,Io B. S. Rosner\" and Professor Rosenblith's Laboratory9 at MIT. Recent reviews by Davis and Ferris? and Rosenbliths are useful guides to the instrumentation complexities. As stated, the present studies were carried out to determine which measures of the evoked cortical responses could be correlated with behavioral measures, and therefore, were representative codes of psychological phenomena. Because of certain features of the recorded potentials it was also possible to tentatively associate certain portions of the averaged waveform with specific anatomic structures, Section A of our experiments and results section presents a description of the waveform which, along with the results of Section E, the effects of sleep on the evoked potential, contribute to this association. Section B presents the results of
TL;DR: Three subjects with unexplained sensory loss meeting criteria for conversion disorder are investigated using brain fMRI during unilateral and bilateral vibrotactile stimulation, finding selective alterations in primary sensorimotor cortex activity in conversion disorder.
Abstract: We investigated three subjects with unexplained sensory loss meeting criteria for conversion disorder using brain fMRI during unilateral and bilateral vibrotactile stimulation. In each subject, stimulation of the affected limb did not produce activation of the contralateral primary somatosensory (S1) region, whereas bilateral limb stimulation did. These findings implicate selective alterations in primary sensorimotor cortex activity in conversion disorder, and may also reconcile the discordant results of previous studies.