Somatosensory Evoked Responses Research Articles

Long-Term Plasticity in Mouse Sensorimotor Circuits after Rhythmic Whisker Stimulation

Mice actively explore their environment by rhythmically sweeping their whiskers. As a consequence, neuronal activity in somatosensory pathways is modulated by the frequency of whisker movement. The potential role of rhythmic neuronal activity for the integration and consolidation of sensory signals, however, remains unexplored. Here, we show that a brief period of rhythmic whisker stimulation in anesthetized mice resulted in a frequency-specific long-lasting increase in the amplitude of somatosensory-evoked potentials in the contralateral primary somatosensory (barrel) cortex. Mapping of evoked potentials and intracortical recordings revealed that, in addition to potentiation in layers IV and II/III of the barrel cortex, rhythmic whisker stimulation induced a decrease of somatosensory-evoked responses in the supragranular layers of the motor cortex. To assess whether rhythmic sensory input-based plasticity might arise in natural settings, we exposed mice to environmental enrichment. We found that it resulted in somatosensory-evoked responses of increased amplitude, highlighting the influence of previous sensory experience in shaping sensory responses. Importantly, environmental enrichment-induced plasticity occluded further potentiation by rhythmic stimulation, indicating that both phenomena share common mechanisms. Overall, our results suggest that natural, rhythmic patterns of whisker activity can modify the cerebral processing of sensory information, providing a possible mechanism for learning during sensory perception.

N30 somatosensory evoked potentials in patients with unilateral Parkinson's disease.

The N30 component of the somatosensory evoked responses (SEP) was reported as absent or abnormally low in various basal ganglia disorders, including Parkinson's disease (PD), but its relationship to the more affected side in asymmetric disease has not been assessed systematically. In 14 patients with unilateral PD and 10 controls, SEP were performed by stimulating each upper limb and recording from the parietal and frontal contralateral cortex. N30 was symmetric in 4 patients and 4 controls; it was asymmetric in 2 controls and in 8 patients (in 4 the responses were of lower amplitude over the affected hemisphere); no response was elicited in 2 patients and 4 controls. In all patients SEP were recorded off medication; in 9 of them the test was repeated following administration of L-dopa and did not show any significant changes. In conclusion, the N30 was asymmetric in a similar proportion of PD patients and controls. No correlation was found between the affected side and N30 latencies or amplitudes; no change was seen following L-dopa administration as well. The motor deficits and SEP abnormalities in PD probably reflect pathologies in different anatomical structures or functional circuits.

Evoked response studies of the thalamic pain syndrome.

Human and animal studies have suggested that the occurrence of thalamic pain (hyperpathia) is not simply a manifestation of a functional deficit in the major lemniscal pathway mediated through the ventral posterior (VP) thalamic nucleus. More effective relief of this pain has occurred following stereotaxic lesions of the centromedianum (CM) than after lesions restricted to VP. Median nerve stimulation has evoked abnormal contralateral somatosensory evoked responses (SER) in patients with lesions of VP. In this study the SERs evoked by contra-lateral stimulation in two patients with thalamic pain secondary to infarction were normal. These results support the hypothesis that thalamic pain can be caused by thalamic lesions sparing VP. The minor change noted in the ipsilateral SER when the abnormal hand was stimulated was consistent with a lesion involving CM or adjacent nonspecific thalamic nuclei.

Pain Ratings and Somatosensory Evoked Responses to Repetitive Intramuscular and Intracutaneous Stimulation in Fibromyalgia Syndrome

To determine the presence of perceptual sensitization and related brain responses we examined 15 patients with fibromyalgia syndrome and 15 healthy controls comparable in age and sex. Multichannel EEG recordings and pain ratings were obtained during the presentation of 800 painful electrical intramuscular and intracutaneous stimuli to the left m. erector spinae and the left m. extensor digitorum. The stimulus intensity was adjusted to 50% between pain threshold and tolerance. Detection and pain thresholds were significantly lower in the fibromyalgia syndrome group. Sensitization occurred for both groups during intramuscular stimulation. In the EEG data the fibromyalgia syndrome patients showed higher N80 amplitudes compared with the healthy controls. Arm stimulation and intramuscular stimulation yielded higher N80 and N150 amplitudes compared with intracutaneous stimulation or stimulation of the back. These results indicate lower pain thresholds in the fibromyalgia syndrome patients after electrical stimulation and a higher N80 amplitude both indicative of enhanced sensory processing in this group.

Exploring the Variability of Single Trials in Somatosensory Evoked Responses Using Constrained Source Extraction and RMT

This paper describes the theoretical background of a new data-driven approach to encephalographic single-trial (ST) data analysis. Temporal constrained source extraction using sparse decomposition identifies signal topographies that closely match the shape characteristics of a reference signal, one response for each ST. The correlations between these ST topographies are computed for formal Correlation Matrix Analysis (CMA) based on Random Matrix Theory (RMT). The RMT-CMA provides clusters of similar ST topologies in a completely unsupervised manner. These patterns are then classified into deterministic set and noise using well established RMT results. The efficacy of the method is applied to EEG and MEG data of somatosensory evoked responses (SERs). The results demonstrate that the method can recover brain signals with time course resembling the reference signal and follow changes in strength and/or topography in time by simply stepping the reference signal through time.

Parallel input makes the brain run faster

In serial sensory processing, information flows from the thalamus via primary sensory cortices to higher-order association areas. However, association cortices also receive, albeit weak, direct thalamocortical sensory inputs of unknown function. For example, while information proceeds from primary (SI) to secondary (SII) somatosensory cortex in a serial fashion, both areas are known to receive direct thalamocortical sensory input. The present study examines the potential roles of such parallel input arrangements. The subjects were presented with median nerve somatosensory stimuli with the instruction to respond with the contralateral hand. The locations and time courses of the activated brain areas were first identified with magnetoencephalography (MEG). In a subsequent session, these brain areas were modulated with single-pulse transcranial magnetic stimulation (TMS) at 15–210 ms after the somatosensory stimulus while electroencephalography (EEG) was recorded. TMS pulses at 15–40 ms post-stimulus significantly speeded up reaction times and somatosensory-evoked responses, with largest facilitatory effects when the TMS pulse was given to contralateral SII at about 20 ms. To explain the results, we propose that the early somatosensory-evoked physiological SII activation exerts an SII→SI influence that facilitates the reciprocal SI→SII pathway – with TMS to SII we apparently amplified this mechanism. The results suggest that the human brain may utilize parallel inputs to facilitate long-distance cortico-cortical connections, resulting in accelerated processing and speeded reaction times. This arrangement could also allow very early top–down modulation of the bottom–up stream of sensory information.

Aberrant somatosensory-evoked responses imply GABAergic dysfunction in Angelman syndrome

A role for γ-aminobutyric acid (GABA)ergic inhibition in cortical sensory processing is one of the principle concerns of brain research. Angelman syndrome (AS) is thought to be one of the few neurodevelopmental disorders with GABAergic-related genetic involvement. AS results from a functional deficit of the imprinted UBE3A gene, located at 15q11–q13, resulting mainly from a 4-Mb deletion that includes GABA A receptor subunit genes. These genes are believed to affect the GABAergic system and modulate the clinical severity of AS. To understand the underlying cortical dysfunction, we have investigated the primary somatosensory-evoked responses in AS patients. Subjects included eleven AS patients with a 15q11–q13 deletion (AS Del), two AS patients without a 15q11–q13 deletion, but with a UBE3A mutation (AS non-Del), six epilepsy patients (non-AS) and eleven normal control subjects. Somatosensory-evoked fields (SEFs) in response to median nerve stimulation were measured by magnetoencephalography. The N1m peak latency in AS Del patients was significantly longer (34.6 ± 4.8 ms) than in non-AS patients (19.5 ± 1.2 ms, P < 0.001) or normal control subjects (18.4 ± 1.8 ms, P < 0.001). The next component, P1m, was prolonged and ambiguous and was only detected in patients taking clonazepam. In contrast, SEF waveforms of AS non-Del patients were similar to those of control individuals, rather than to AS Del patients. Thus, GABAergic dysfunction in AS Del patients is likely due to hemizygosity of GABA A receptor subunit genes, suggesting that GABAergic inhibition plays an important role in synchronous activity of human sensory systems.

Preservation of brainstem neurophysiological function in hydranencephaly

The preservation of central neurophysiological function was assessed in a 32-year-old woman with hydranencephaly using brainstem auditory evoked responses (BAER), auditory middle latency responses (MLR), cortical auditory evoked responses (CER), strobe electroretinograms (ERG), strobe-flash visual evoked responses (VER) and median and tibial nerve somatosensory evoked responses (SER). The BAER to the right ear stimulation revealed wave peaks I through VII with normal thresholds, morphology and latencies, while the BAER in the left ear was abnormal. The auditory MLR and CER were absent. Grossly normal strobe ERGs were acquired bilaterally with peak waves at 20 and 50 ms. Strobe VERs were poorly defined and abnormal bilaterally. Left and right median nerve SER revealed significant conduction defects in the large fiber sensory system caudal to the thalamus, above the lower pontine level. Bilateral tibial nerve stimulation revealed normal knee popliteal fossa potentials, but distinct conduction defects in the large fiber sensory system rostral to the lower spinal cord. Brainstem electrophysiological measures revealed functional auditory afferent tracts and nuclei, in the absence of cortical influence, suggesting intact unilateral auditory function, which would support clinical observations of behavioral auditory responses in hydranencephaly.

Electrophysiologic Monitoring During Surgery to Repair the Thoraco-Abdominal Aorta

Prevention of paraplegia during the repair of thoraco-abdominal aortic aneurysms and dissections present a substantial challenge to the operative team. The value of intraoperative electrophysiological monitoring (IOM) is to identify spinal cord ischemia that occurs during the procedure and guide the intraoperative management to reduce the risks of paralysis. The usefulness of IOM techniques requires an understanding of spinal cord blood flow and the spinal cord physiology, the surgical technique and their interaction. This paper will integrate these factors to review the laboratory and clinical experience with somatosensory evoked responses (SSEP) and motor evoked potentials (MEP) during thoraco-abdominal aorta surgery.

Evoked response amplitudes from somatosensory cortices do not determine reaction times to tactile stimuli

Sensory events cause changes in brain activity, which underlie the perception of and behavioural responses to sensory stimuli. Evoked cortical responses are an important measure of these stimulus-evoked changes in brain activity. However, evidence on the relationship between behavioural responses and evoked responses is inconsistent. Therefore, we used magnetoencephalography to reinvestigate the relationship between evoked responses from somatosensory cortices and behavioural responses to somatosensory stimuli. We characterized modulations of somatosensory-evoked responses exerted by preceding painful and tactile conditioning stimuli (CS), and related these modulations of evoked responses to modulations of reaction times. Our results show that painful CS yield a long-lasting (> 4 s) facilitation of evoked responses, whereas tactile CS result in a shorter lasting (1-2 s) suppression of evoked responses to tactile stimuli. These contrary physiological effects were both associated with a significant shortening of reaction times. These findings indicate that the conditioning effects of painful and tactile stimuli represent essentially different modulatory mechanisms. Moreover, our results show that amplitudes of evoked responses from somatosensory cortices do not determine reaction times to tactile stimuli.

A comparison of random field theory and permutation methods for the statistical analysis of MEG data

We describe the use of random field and permutation methods to detect activation in cortically constrained maps of current density computed from MEG data. The methods are applicable to any inverse imaging method that maps event-related MEG to a coregistered cortical surface. These approaches also extend directly to images computed from event-related EEG data. We determine statistical thresholds that control the familywise error rate (FWER) across space or across both space and time. Both random field and permutation methods use the distribution of the maximum statistic under the null hypothesis to find FWER thresholds. The former methods make assumptions on the distribution and smoothness of the data and use approximate analytical solutions, the latter resample the data and rely on empirical distributions. Both methods account for spatial and temporal correlation in the cortical maps. Unlike previous nonparametric work in neuroimaging, we address the problem of nonuniform specificity that can arise without a Gaussianity assumption. We compare and evaluate the methods on simulated data and experimental data from a somatosensory-evoked response study. We find that the random field methods are conservative with or without smoothing, though with a 5 vertex FWHM smoothness, they are close to exact. Our permutation methods demonstrated exact specificity in simulation studies. In real data, the permutation method was not as sensitive as the RF method, although this could be due to violations of the random field theory assumptions.

An empirical Bayesian solution to the source reconstruction problem in EEG

Distributed linear solutions of the EEG source localisation problem are used routinely. In contrast to discrete dipole equivalent models, distributed linear solutions do not assume a fixed number of active sources and rest on a discretised fully 3D representation of the electrical activity of the brain. The ensuing inverse problem is underdetermined and constraints or priors are required to ensure the uniqueness of the solution. In a Bayesian framework, the conditional expectation of the source distribution, given the data, is attained by carefully balancing the minimisation of the residuals induced by noise and the improbability of the estimates as determined by their priors. This balance is specified by hyperparameters that control the relative importance of fitting and conforming to various constraints. Here we formulate the conventional “Weighted Minimum Norm” (WMN) solution in terms of hierarchical linear models. An “Expectation-Maximisation” (EM) algorithm is used to obtain a “Restricted Maximum Likelihood” (ReML) estimate of the hyperparameters, before estimating the “Maximum a Posteriori” solution itself. This procedure can be considered a generalisation of previous work that encompasses multiple constraints. Our approach was compared with the “classic” WMN and Maximum Smoothness solutions, using a simplified 2D source model with synthetic noisy data. The ReML solution was assessed with four types of source location priors: no priors, accurate priors, inaccurate priors, and both accurate and inaccurate priors. The ReML approach proved useful as: (1) The regularisation (or influence of the a priori source covariance) increased as the noise level increased. (2) The localisation error (LE) was negligible when accurate location priors were used. (3) When accurate and inaccurate location priors were used simultaneously, the solution was not influenced by the inaccurate priors. The ReML solution was then applied to real somatosensory-evoked responses to illustrate the application in an empirical setting.

Altered central somatosensory processing in chronic pain patients with "hysterical" anesthesia.

The authors hypothesized that central factors may underlie sensory deficits in patients with nondermatomal somatosensory deficits (NDSD) and that functional brain imaging would reveal altered responses in supraspinal nuclei. Patients with chronic pain frequently present with NDSD, ranging from hypoesthesia to complete anesthesia in the absence of substantial pathology and often in association with motor weakness and occasional paralysis. Patients with pain and such pseudoneurologic symptoms can be classified as having both a pain disorder and a conversion disorder (Diagnostic and Statistical Manual of Mental Disorders-IV classification). The authors tested their hypothesis with functional MRI (fMRI) of brush and noxious stimulation-evoked brain responses in four patients with chronic pain and NDSD. The fMRI findings revealed altered somatosensory-evoked responses in specific forebrain areas. Unperceived stimuli failed to activate areas that were activated with perceived touch and pain: notably, the thalamus, posterior region of the anterior cingulate cortex (ACC), and Brodmann area 44/45. Furthermore, unperceived stimuli were associated with deactivations in primary and secondary somatosensory cortex (S1, S2), posterior parietal cortex, and prefrontal cortex. Finally, unperceived (but not perceived) stimuli activated the rostral ACC. Diminished perception of innocuous and noxious stimuli is associated with altered activity in many parts of the somatosensory pathway or other supraspinal areas. The cortical findings indicate a neurobiological component for at least part of the symptoms in patients presenting with nondermatomal somatosensory deficits.

Neurophysiological evaluation of late paraphrenia: Comparison with chronic schizophrenia and dementia of the Alzheimer type

AbstractBackground: Late paraphrenia (LP) is a clinical entity first proposed by Roth in 1955. Recently, neuroimaging studies have described the organic changes in the brain that are associated with LP. We performed a neurophysiological study on patients with LP, chronic schizophrenics and patients with dementia of the Alzheimer type (DAT) to examine the cognitive function of patients with LP and to differentiate LP patients from these other groups.Methods: We investigated somatosensory‐evoked response (SER), contingent negative variation (CNV) and P300 in 30 LP patients, 22 chronic schizophrenics and 31 patients with DAT. Thirty‐four age‐matched healthy volunteers served as a control group. SER was performed by applying a mechanical stimulus to the right or left palm. CNV was performed by presenting a clicking sound (S1) and a flash of light (S2) to the subjects, with an interval between S1 and S2 of 2 s. P300 was performed using an auditory oddball paradigm.Results: The mean N3 peak latency of SER was significantly prolonged in patients with LP and in patients with DAT, compared with the control group. The mean CNV amplitude was significantly decreased in schizophrenics compared with the control group, but it did not decrease in patients with LP. The mean N200 and P300 latencies were significantly prolonged in patients with DAT compared with the control group, LP patients and schizophrenics, but the latencies of patients with LP were not prolonged compared with the control group.Conclusion: Based on these results, we propose that patients with LP have impaired cerebral reactivity to the stimulus, but their attention, motivation, recognition and differentiation are relatively intact. The present findings are consistent with former investigations, indicating that patients with LP are less likely to show negative symptoms, such as personality deterioration, and more likely to show organic changes in the brain relative to schizophrenics arising in early life.

ANESTHESIA AND TEMPERATURE EFFECTS ON SOMATOSENSORY EVOKED POTENTIALS PRODUCED BY TRAIN STIMULI

Objective: To determine the effect of anesthesia, temperature, and stimulus characteristics on the response of upper extremity somatosensory evoked responses (SSEP) to repetitive stimulation. Methods: Pairs and trains of electrical stimuli were used to elicit the upper extremity SSEP, and the amplitudes of the N20-P22, N13, and Erb s point potentials produced by each stimulus were measured. The ratio of the amplitude of the response to each stimulus to that produced by the first stimulus in a given train was computed. Recordings were also made directly from the cortical surface in a single patient. Results: There were only minimal effects of anesthesia, temperature, or stimulus characteristics on the amplitude ratios for the N13 and Erb s point potentials. The N20-P22 amplitude ratio demonstrated facilitation with interstimulus intervals in the 20 100 ms range and was markedly reduced with hypothermia. The degree of facilitation was strongly dependent on isoflurane and nitrous oxide concentrations. In response to stimulation with trains of four stimuli, increased amplitudes of the N20-P22 complex were seen maximally with the second response while the third and fourth responses were of lower amplitude. Conclusions: There are strong effects of anesthesia and temperature on the cortical responses to repetitive stimulation of the upper extremity. Speculations on the origin of these effects were made.

Postural responses to combinations of head and body displacements: vestibular-somatosensory interactions.

Postural responses to head displacements are triggered by the vestibular system; responses to body displacements are triggered by the somatosensory system. We examined the interaction of responses to combinations of head and support surface perturbations. Head displacements were always in the opposite direction of body displacements. The time between head and support surface perturbations was varied. We measured amplitude and latency of gastrocnemius and tibialis anterior EMGs for various head backward/body forward and head forward/body backward displacement combinations. These responses were compared to head-only or body-only displacement trials, which served as controls. Relative to controls, the latency of somatosensory-evoked responses to body displacement was longer and vestibular-evoked responses were absent or of low amplitude for combinations where head and support surface perturbations were presented closely in time (10-50 ms apart). These results illustrate complex integration of vestibular and somatosensory information, suggesting that the vestibulospinal and somatosensory-spinal pathways are not two isolated systems independently driving motor neurons. Rather, these pathways may influence one another at premotoneuronal levels where common circuitry may be shared by both systems.

Dipole localization of human induced focal afterdischarge seizure in simultaneous magnetoencephalography and electrocorticography.

Localizations were compared for the same human seizure between simultaneously measured MEG and iEEG, which were both co-registered to MRI. The whole-cortex neuromagnetometer localized a dipole in a sphere phantom, co-registered to the MEG sensor array, with an error of 1.4 mm. A focal afterdischarge seizure was induced in a patient with partial epilepsy, by stimulation at a subdural electrocorticography (ECoG) electrode with a known location, which was co-registered to the MRI and to the MEG sensor array. The simultaneous MEG and ECoG during the 30-second seizure was measured and analyzed using the single, moving dipole model, which is the localization model used clinically. The dipole localizations from simultaneous whole cortex 68-channel MEG and 64-channel ECoG were then compared for the repetitive spiking at six different times during the seizure. There were two main regions of MEG and ECoG activity. The locations of these regions were confirmed by determining the location clusters of 8,000 dipoles on ECoG at consecutive time points during the seizure. The mean distances between the stimulated electrode location versus the dipole location of the MEG and versus the dipole location of the ECoG were each about one (1) centimeter. The mean distance between the dipole locations of the MEG versus the dipole locations of the ECoG was about 2 cm. These errors were compared to errors of MEG and ECoG reported previously for phantoms and for somatosensory evoked responses (SER) in patients. Comparing the findings from the present study to those from prior studies, there appeared to be the expected stepwise increase in mean localization error progressing from the phantom, to the SER, to the seizure.

Effect of current frequency during electrical stunning in a water bath on somatosensory evoked responses in turkey’s brain

Somatosensory evoked responses (SEP) in a turkey’s brain were determined after water-bath stunning with a 150-mA (constant current) delivered with 50, 300 or 600 Hz, or with 75 mA, delivered with 50-Hz alternating current (AC) in order to evaluate the effectiveness of stunning. Ninety-four BUT 9 turkey hens 12 weeks of age were surgically implanted with EEG recording and left wing nerve stimulating electrodes 4 hours before stunning. They were individually stunned by immersion of the head and upper part of the neck in a water bath for 4 s. Using a 150-mA current, all birds stunned at 50 Hz showed cardiac arrest and a flat EEG immediately after the stun with no SEP recovery. The incidence of cardiac arrest at stunning decreased with increasing current frequency but SEP were lost in all birds. In birds that survived the stun, the duration of SEP abolition was on average 69 and 34 seconds at 300 and 600 Hz, respectively. Stunning with a 75-mA AC, delivered with 50 Hz, induced cardiac arrest in 32 per cent of turkeys.SEP were abolished in only 71 per cent of the birds that survived the stun, with an average duration of SEP of 66 seconds. The results indicate that increasing the frequency of a 150-mA AC current leads to a decreased stunning efficiency. A current of 75 mA per bird is unacceptable since 29 per cent of the birds do not show SEP abolition.

Impairment Tutorial: Rating Sensory and Motor Deficits of the Lower Extremities

Abstract Previous issues of The Guides Newsletter have presented overviews of electrodiagnostic evaluation, including electromyography, nerve conduction studies, and somatosensory-evoked responses. This article contains suggestions for nonelectromyographers who read reports and identify questionable uses of electrodiagnosis, specifically for the evaluation of radiculopathy and focal neuropathy (eg, nerve entrapments), the two most common presentations. Some subtle abnormalities (eg, changes in motor unit recruitment pattern, changes in firing rate, or reduction in motor units recruited) often are overinterpreted by poorly trained or inexperienced electromyographers. Nerve conduction studies often are overused and may accompany the electromyogram without apparent indication, but they are nearly useless in diagnosing radiculopathy and should be included only for nerve entrapment or differential diagnosis of plexus injury. Nerve conduction studies often are accompanied by F waves and H reflexes. The F wave helps assess proximal portions of nerves and is used primarily in the diagnosis of Landry-Guillain-Barré syndrome but has poor sensitivity and specificity in evaluation of radiculopathy or entrapment neuropathy. The H reflex is used primarily in S1 radiculopathy evaluation. The article includes six questions a clinician should bear in mind while interpreting the electrodiagnostic report. Improperly trained physicians may report false positive or negative results, so examiners should be aware of the qualifications of physicians to whom they refer their patients.

Subthalamic Prelemniscal Radiation Stimulation for the Treatment of Parkinson's Disease: Electrophysiological Characterization of the Area

BackgroundPrevious reports have provided evidence of a reticulo-thalamic system, extending from the mesencephalic reticular formation (MRF) to the ventrolateral thalamus (VL), involved in the production of tremor. In humans, a funnel of fibers in the posterior subthalamus named the prelemniscal radiations (Raprl) has been described as an exquisite target to treat tremor in cases of Parkinson's disease. MethodsIn the present study, a group of 14 patients suffering from Parkinson's disease, with prominent unilateral tremor and rigidity, were implanted with tetrapolar depth brain stimulation (DBS) electrodes in Raprl to perform chronic electrical stimulation (ES) for the treatment of patient symptoms. Electrodes were left externalized to corroborate their placement throughout MRI studies and also to perform the following electrophysiological battery: (a) recording of somatosensory-evoked responses (SEP) through different electrode contacts and scalp by means of a paradigm to study the attention process; (b) evoking scalp EEG responses by stimulation with low (3 cps, 6 cps) and high (60–120 cps) frequencies with stimuli delivered through different electrode contacts, and (c) studying recovery cycle (RC) potentials in the Raprl while the upper MRF was being stimulated and, conversely, the RC in MRF while Raprl was being stimulated, before and after subacute Raprl stimulation. Thereafter, the electrodes were internalized and connected to a pulse generator (IPG) to carry on chronic ES, while the effects of stimulation were determined through a quantitative evaluation that measured phasic and tonic muscular activity with EMG recordings during different motor tasks. ResultsResults indicate the following: (a) that late, but not early, SEP components were recorded in Raprl and modulated in different attentive conditions; (b) that bilateral recruiting responses and spike and wave complexes were elicited by Raprl through low-frequency stimulation, while bilateral positive DC shifts induced by high-frequency stimulation were recorded, similar to those obtained in animals from MRF, and (c) that Raprl-ES induced RC inhibition at Raprl, but Raprl ES did not change MRF-RC. Long-term Raprl-ES induced a significant decrease in tremor and rigidity. ConclusionsIt was concluded that Raprl represents a subthalamic circuit electrophysiologically related to MRF in the genesis of tremor and rigidity and in the process of selective attention. Raprl-ES induced a significant improvement in tremor and rigidity by causing inhibition of the stimulated area.