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Beyond traditional approaches to understanding the functional role of neuromodulators in sensory cortices  [PDF]
Jean-Marc Edeline
Frontiers in Behavioral Neuroscience , 2012, DOI: 10.3389/fnbeh.2012.00045
Abstract: Over the last two decades, a vast literature has described the influence of neuromodulatory systems on the responses of sensory cortex neurons (review in Gu, 2002; Edeline, 2003; Weinberger, 2003; Metherate, 2004, 2011). At the single cell level, facilitation of evoked responses, increases in signal-to-noise ratio, and improved functional properties of sensory cortex neurons have been reported in the visual, auditory, and somatosensory modality. At the map level, massive cortical reorganizations have been described when repeated activation of a neuromodulatory system are associated with a particular sensory stimulus. In reviewing our knowledge concerning the way the noradrenergic and cholinergic system control sensory cortices, I will point out that the differences between the protocols used to reveal these effects most likely reflect different assumptions concerning the role of the neuromodulators. More importantly, a gap still exists between the descriptions of neuromodulatory effects and the concepts that are currently applied to decipher the neural code operating in sensory cortices. Key examples that bring this gap into focus are the concept of cell assemblies and the role played by the spike timing precision (i.e., by the temporal organization of spike trains at the millisecond time-scale) which are now recognized as essential in sensory physiology but are rarely considered in experiments describing the role of neuromodulators in sensory cortices. Thus, I will suggest that several lines of research, particularly in the field of computational neurosciences, should help us to go beyond traditional approaches and, ultimately, to understand how neuromodulators impact on the cortical mechanisms underlying our perceptual abilities.
Interhemispheric Interactions between the Human Primary Somatosensory Cortices  [PDF]
Patrick Ragert,Till Nierhaus,Leonardo G. Cohen,Arno Villringer
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0016150
Abstract: In the somatosensory domain it is still unclear at which processing stage information reaches the opposite hemispheres. Due to dense transcallosal connections, the secondary somatosensory cortex (S2) has been proposed to be the key candidate for interhemispheric information transfer. However, recent animal studies showed that the primary somatosensory cortex (S1) might as well account for interhemispheric information transfer. Using paired median nerve somatosensory evoked potential recordings in humans we tested the hypothesis that interhemispheric inhibitory interactions in the somatosensory system occur already in an early cortical processing stage such as S1. Conditioning right S1 by electrical median nerve (MN) stimulation of the left MN (CS) resulted in a significant reduction of the N20 response in the target (left) S1 relative to a test stimulus (TS) to the right MN alone when the interstimulus interval between CS and TS was between 20 and 25 ms. No such changes were observed for later cortical components such as the N20/P25, N30, P40 and N60 amplitude. Additionally, the subcortically generated P14 response in left S1 was also not affected. These results document the existence of interhemispheric inhibitory interactions between S1 in human subjects in the critical time interval of 20–25 ms after median nerve stimulation.
Somatosensory-Motor Adaptation of Orofacial Actions in Posterior Parietal and Ventral Premotor Cortices  [PDF]
Krystyna Grabski, Laurent Lamalle, Marc Sato
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0049117
Abstract: Recent studies have provided evidence for sensory-motor adaptive changes and action goal coding of visually guided manual action in premotor and posterior parietal cortices. To extend these results to orofacial actions, devoid of auditory and visual feedback, we used a repetition suppression paradigm while measuring neural activity with functional magnetic resonance imaging during repeated intransitive and silent lip, jaw and tongue movements. In the motor domain, this paradigm refers to decreased activity in specific neural populations due to repeated motor acts and has been proposed to reflect sensory-motor adaptation. Orofacial movements activated a set of largely overlapping, common brain areas forming a core neural network classically involved in orofacial motor control. Crucially, suppressed neural responses during repeated orofacial actions were specifically observed in the left ventral premotor cortex, the intraparietal sulcus, the inferior parietal lobule and the superior parietal lobule. Since no visual and auditory feedback were provided during orofacial actions, these results suggest somatosensory-motor adaptive control of intransitive and silent orofacial actions in these premotor and parietal regions.
Are somatosensory evoked potentials of the tibial nerve the most sensitive test in diagnosing multiple sclerosis?
Djuric S,Djuric V,Zivkovic M,Milosevic V
Neurology India , 2010,
Abstract: Background : Multiple sclerosis (MS) is mostly diagnosed clinically, but the diagnosis has significantly improved through the use of brain magnetic resonance imaging (MRI), testing of cerebrospinal fluid, and multimodal evoked potentials (MEPs). Even though MRI is the superior method in diagnosing this illness, MEPs remain important because they can detect clinically silent lesions in the sensory and motor pathways of the central nervous system (CNS). Aim : The aim of the study is to test the diagnostic sensitivity of MEPs and MRI and the ratio of their sensitivity in patients with MS. Materials and Methods : The study subjects included 293 patients with MS with disease duration of two to six years: 249 patients with relapsing-remitting (RR) MS and 44 with primary-progressive (PP) MS. All patients were subjected to an MRI brain scan, visual evoked potentials (VEPs), median somatosensory evoked potentials (SEPs), tibial somatosensory evoked potentials (SEPs), and auditory evoked potentials (AEPs). Abnormal Findings Included : changed wave morphology, interside difference in wave amplitude, absolute and interwave latency increased by 2.5 SD as compared with the control group. The control group comprised of 35 healthy subjects. Results : In this study the most abnormal findings were tibial SEPs, median SEPs, and VEPs. Our results suggest different sensitivity of MEPs in patients suffering from different forms of MS. In RR-MS the sensitivity of tibial SEPs was statically significant (Fischer′s exact probability test) as compared to other evoked potential modalities. Similarly VEPs were more sensitive as compared to AEPs. In the PP-MS, median SEPs have been found to be more sensitive than VEPs, while tibial SEPs have been found to be more sensitive than AEPs. There was no significant difference in the sensitivity of MRI and MEPs both the forms of MS. Conclusion : Tibial SEPs produce the most abnormal results and the highest sensitivity in the RR-MS. We propose that this test as useful criterion for the diagnosis of MS.
Somatosensory evoked potentials by paraspinal stimulation in acute transverse myelitis.  [cached]
Murthy J
Neurology India , 1999,
Abstract: Somatosensory evoked potentials by paraspinal stimulation were studied in 6 patients with acute transverse myelitis. In one patient in whom posterior tibial somatosensory evoked potentials were not recordable, a poorly formed response was seen with paraspinal stimulation. Slowing of conduction across the involved segment was seen in the remaining 5 patients and fairly correlated with the clinical localization.
Pudendal somatosensory evoked potentials in normal women
Cavalcanti, Geraldo A.;Bruschini, Homero;Manzano, Gilberto M.;Nunes, Karlo F.;Giuliano, Lydia M.;Nobrega, Joao A.;Srougi, Miguel;
International braz j urol , 2007, DOI: 10.1590/S1677-55382007000600010
Abstract: objective: somatosensory evoked potential (ssep) is an electrophysiological test used to evaluate sensory innervations in peripheral and central neuropathies. pudendal ssep has been studied in dysfunctions related to the lower urinary tract and pelvic floor. although some authors have already described technical details pertaining to the method, the standardization and the influence of physiological variables in normative values have not yet been established, especially for women. the aim of the study was to describe normal values of the pudendal ssep and to compare technical details with those described by other authors. materials and methods: the clitoral sensory threshold and pudendal ssep latency was accomplished in 38 normal volunteers. the results obtained from stimulation performed on each side of the clitoris were compared to ages, body mass index (bmi) and number of pregnancies. results: the values of clitoral sensory threshold and p1 latency with clitoral left stimulation were respectively, 3.64 ± 1.01 ma and 37.68 ± 2.60 ms. results obtained with clitoral right stimulation were 3.84 ± 1.53 ma and 37.42 ± 3.12 ms, respectively. there were no correlations between clitoral sensory threshold and p1 latency with age, bmi or height of the volunteers. a significant difference was found in p1 latency between nulliparous women and volunteers who had been previously submitted to cesarean section. conclusions: the ssep latency represents an accessible and reproducible method to investigate the afferent pathways from the genitourinary tract. these results could be used as normative values in studies involving genitourinary neuropathies in order to better clarify voiding and sexual dysfunctions in females.
Referral of Touch and Ownership between the Hands and the Role of the Somatosensory Cortices  [PDF]
Michael Schaefer, Franziska Konczak, Hans-Jochen Heinze, Michael Rotte
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0052768
Abstract: Recent studies have shown that the feeling of body ownership can be fooled by simple visuo-tactile manipulations. Perceptual illusions have been reported in which participants sense phantom touch seen on a rubber hand (rubber hand illusion). While previous studies used homologous limbs for those experiments, we here examined an illusion where people feel phantom touch on a left rubber hand when they see it brushed simultaneously with brushes applied to their right hand. Thus, we investigated a referral of touch from the right to the left hand (across the body midline). Since it is known from animal studies that tactile illusions may alter early sensory processing, we expected a modulation of the primary somatosensory cortex (SI) corresponding to this illusion. Neuromagnetic source imaging of the functional topographic organization in SI showed a shift in left SI, associated with the strength of the referral of touch. Hence, we argue that SI seems to be closely associated with this perceptual illusion. The results suggest that the transfer of tactile information across the body midline could be mediated by neurons with bilateral tactile receptive fields (most likely BA2).
The effect of water immersion on short-latency somatosensory evoked potentials in human
Daisuke Sato, Koya Yamashiro, Hideaki Onishi, Yoshimitsu Shimoyama, Takuya Yoshida, Atsuo Maruyama
BMC Neuroscience , 2012, DOI: 10.1186/1471-2202-13-13
Abstract: Water immersion significantly reduced the amplitudes of the short-latency SEP components P25 and P45 measured from electrodes over the parietal region and the P45 measured by central region.Water immersion reduced short-latency SEP components known to originate in several cortical areas. Attenuation of short-latency SEPs suggests that water immersion influences the cortical processing of somatosensory inputs. Modulation of cortical processing may contribute to the beneficial effects of aquatic therapy.UMIN-CTR (UMIN000006492)Water immersion activates several distinct somatosensory modalities, including tactile, pressure, and thermal sensations. Somatosensory inputs can induce a variety of cardiovascular and respiratory responses, including decreased heart rate, increased stroke volume [1], and reduced functional residual capacity [2]. These physiological responses can have therapeutic benefits; indeed, water immersion is used as part of rehabilitation regimes for orthopedic, cardiovascular, and respiratory disorders. Water immersion once a week also improved the activities of daily living (ADL) in some frail elderly and hemiplegic patients after stroke [3]. Benefits to neurological patients suggest that water immersion may influence cerebrocortical processing, but this remains to be determined. Elucidating the cortical somatosensory processes induced by water immersion and the effects of water immersion on the processing of other sensory inputs will help delineate the mechanisms of sensory integration and could facilitate the development of improved aquatic therapies for neurology patients.Somatosensory input from peripheral nerves activates several cortical areas. This modulation of somatosensory input can be evaluated by somatosensory-evoked potentials (SEPs). SEPs are divided into short-latency and long latency types. Short-latency SEPs (with latencies of 20 to 40 ms) are generated in area 3b and/or area 1 during thalamocortical inputs [4] and reflect the first s
Using Variations of Somatosensory Evoked Potentials to Quantify Spinal Cord Injury Level  [PDF]
Hasan Mir, Hasan Al-Nashash, Douglas Kerr, Angelo All, Nitish Thakor
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.510B020

Existing work indicates that the degree of variation of somatosensory evoked potential (SEP) signals between a healthy spinal pathway and spinal pathway affected by spinal cord injury (SCI) can be used to evaluate the integrity of the spinal pathway. This paper develops a metric that exploits the time-domain features of SEP signals (relative amplitude, time scaling, and time duration) in order to quantify the level of SCI. The proposed method is tested on actual SEP signals collected from rodents afflicted with focal demyelination SCI. Results indicate that the proposed method provides a robust assessment of the different degrees of demyelination in the spinal cord.

Low-frequency oscillations in human tibial somatosensory evoked potentials
Tierra-Criollo, Carlos Julio;Infantosi, Antonio Fernando Catelli;
Arquivos de Neuro-Psiquiatria , 2006, DOI: 10.1590/S0004-282X2006000300010
Abstract: oscillatory cerebral electric activity has been related to sensorial and perceptual-cognitive functions. the aim of this work is to investigate low frequency oscillations (<300 hz), particularly within the gamma band (30-110 hz), during tibial stimulation. twenty-one volunteers were subjected to 5 hz stimulation by current pulses of 0.2 ms duration and the minimum intensity to provoke involuntary twitch. eeg signals without (spontaneously) and during stimulation were recorded at primary somatosensory area. a time-frequency analysis indicated the effect of the stimulus artifact in the somatosensory evoked potential (sep) frequencies up to 5 ms after the stimulus. the oscillations up to 100 hz presented the highest relative power contribution (approximately 99%) for the sep and showed difference (p<0.01) from the frequencies of the spontaneously eeg average. moreover, the range 30-58 hz was identified as the band with the highest contribution for the tibial sep morphology (p<0.0001).
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