Cortical inhibition of laser pain and laser-evoked potentials by non-nociceptive somatosensory input.

Although the inhibitory action that tactile stimuli can have on pain is well documented, the precise timing of the interaction between the painful and non-painful stimuli in the central nervous system is unclear. The aim of this study was to investigate this issue by measuring the timing of the amplitude modulation of laser evoked potentials (LEPs) due to conditioning non-painful stimuli. LEPs were recorded from 31 scalp electrodes in 10 healthy subjects after painful stimulation of the right arm (C6-C7 dermatomes). Non-painful electrical stimuli were applied by ring electrodes on the second and third finger of the right hand. Electrical stimuli were delivered at +50, +150, +200 and +250 ms interstimulus intervals (ISIs) after the laser pulses. LEPs obtained without any conditioning stimulation were used as a baseline. As compared to the baseline, non-painful electrical stimulation reduced the amplitude of the vertex N2/P2 LEP component and the laser pain rating when electrical stimuli followed the laser pulses only at +150 and +200 ms ISIs. As at these ISIs the collision between the non-painful and painful input is likely to take place at the cortical level, we can conclude that the late processing of painful (thermal) stimuli is partially inhibited by the processing of non-painful (cutaneous) stimuli within the cerebral cortex. Moreover, our results do not provide evidence that non-painful inputs can inhibit pain at a lower level, including the spinal cord.

Robot-assisted walking training for individuals with Parkinson's disease: a pilot randomized controlled trial.

BACKGROUND: Over the last years, the introduction of robotic technologies into Parkinson's disease rehabilitation settings has progressed from concept to reality. However, the benefit of robotic training remains elusive. This pilot randomized controlled observer trial is aimed at investigating the feasibility, the effectiveness and the efficacy of new end-effector robot training in people with mild Parkinson's disease. METHODS: Design. Pilot randomized controlled trial. RESULTS: Robot training was feasible, acceptable, safe, and the participants completed 100% of the prescribed training sessions. A statistically significant improvement in gait index was found in favour of the EG (T0 versus T1). In particular, the statistical analysis of primary outcome (gait speed) using the Friedman test showed statistically significant improvements for the EG (p = 0,0195). The statistical analysis performed by Friedman test of Step length left (p = 0,0195) and right (p = 0,0195) and Stride length left (p = 0,0078) and right (p = 0,0195) showed a significant statistical gain. No statistically significant improvements on the CG were found. CONCLUSIONS: Robot training is a feasible and safe form of rehabilitative exercise for cognitively intact people with mild PD. This original approach can contribute to increase a short time lower limb motor recovery in idiopathic PD patients. The focus on the gait recovery is a further characteristic that makes this research relevant to clinical practice. On the whole, the simplicity of treatment, the lack of side effects, and the positive results from patients support the recommendation to extend the use of this treatment. Further investigation regarding the long-time effectiveness of robot training is warranted. TRIAL REGISTRATION: ClinicalTrials.gov NCT01668407.

Habituation to pain in "medication overuse headache": a CO2 laser-evoked potential study.

OBJECTIVE: Our aim was to investigate CO(2) laser-evoked potential (LEP) habituation to experimental pain in a group of patients affected by medication-overuse headache, with a history of episodic migraine becoming chronic, before and after treatment, consisting in acute medication withdrawal and a preventive treatment cycle. BACKGROUND: One of the main features of LEPs in migraineurs is a lower habituation to repetitive noxious stimuli during the interictal phase. METHODS: LEPs were recorded to stimulation of both the right hand and the right perioral region in 14 patients and in 14 healthy subjects. The habituation of both the N1 and the vertex N2/P2 components was assessed by measuring the LEP amplitude changes across 3 consecutive repetitions of 30 trials each. RESULTS: In the 8 patients who had clinically improved after treatment, the N2/P2 amplitude habituation was significantly higher after treatment than before treatment following both hand (F = 43.2, P < .0001) and face stimulation (F = 6.9, P = .01). In these patients, the N2/P2 amplitude habituation after treatment was not different from that obtained in healthy controls (P = .18 and P = .73 for hand and face stimulation, respectively). On the contrary, in the patients who did not improve, the N2/P2 amplitude still showed reduced habituation after both hand (F = 3.1, P = .08) and face (F = 0.7, P = .4) stimulation. CONCLUSION: The deficient habituation of the vertex N2/P2 complex was partly restored after successful treatment of medication-overuse headache, reflecting a modification in pain-processing pathways.

Baseline robot-measured kinematic metrics predict discharge rehabilitation outcomes in individuals with subacute stroke.

Background: The literature on upper limb robot-assisted therapy showed that robot-measured metrics can simultaneously predict registered clinical outcomes. However, only a limited number of studies correlated pre-treatment kinematics with discharge motor recovery. Given the importance of predicting rehabilitation outcomes for optimizing physical therapy, a predictive model for motor recovery that incorporates multidirectional indicators of a patient's upper limb abilities is needed. Objective: The aim of this study was to develop a predictive model for rehabilitation outcome at discharge (i.e., muscle strength assessed by the Motricity Index of the affected upper limb) based on multidirectional 2D robot-measured kinematics. Methods: Re-analysis of data from 66 subjects with subacute stroke who underwent upper limb robot-assisted therapy with an end-effector robot was performed. Two least squares error multiple linear regression models for outcome prediction were developed and differ in terms of validation procedure: the Split Sample Validation (SSV) model and the Leave-One-Out Cross-Validation (LOOCV) model. In both models, the outputs were the discharge Motricity Index of the affected upper limb and its sub-items assessing elbow flexion and shoulder abduction, while the inputs were the admission robot-measured metrics. Results: The extracted robot-measured features explained the 54% and 71% of the variance in clinical scores at discharge in the SSV and LOOCV validation procedures respectively. Normalized errors ranged from 22% to 35% in the SSV models and from 20% to 24% in the LOOCV models. In all models, the movement path error of the trajectories characterized by elbow flexion and shoulder extension was the significant predictor, and all correlations were significant. Conclusion: This study highlights that motor patterns assessed with multidirectional 2D robot-measured metrics are able to predict clinical evalutation of upper limb muscle strength and may be useful for clinicians to assess, manage, and program a more specific and appropriate rehabilitation in subacute stroke patients.

Effect of balance training using virtual reality-based serious games in individuals with total knee replacement: A randomized controlled trial.

BACKGROUND: Virtual reality (VR) and serious games (SGs) are widespread in rehabilitation for many orthopedic and neurological diseases. However, few studies have addressed the effects of rehabilitation with VR-based SGs on clinical, gait, and postural outcomes in individuals with total knee replacement (TKR). OBJECTIVE: The primary objective was the efficacy of balance training using non-immersive VR-based SGs compared to conventional therapy in TKR patients on the Time Up and Go test. Secondary objectives included the efficacy on clinical, gait, and postural outcomes. METHODS: We randomly allocated 56 individuals with unilateral TKR to the experimental group (EG) or control group (CG) for 15 sessions (45 min; 5 times per week) of non-immersive VR-based SGs or conventional balance training, respectively. The primary outcome was functional mobility measured by the Timed Up and Go test; secondary outcomes were walking speed, pain intensity, lower-limb muscular strength, independence in activities of daily living as well as gait and postural parameters. RESULTS: We found significant within-group differences in all clinical outcomes and in a subset of gait (p<0.0001) and postural (p ≤ 0.05) parameters. Analysis of the stance time of the affected limb revealed significant between-group differences (p = 0.022): post-hoc analysis revealed within-group differences in the EG (p = 0.002) but not CG (p = 0.834). We found no significant between-group differences in other outcomes. CONCLUSIONS: Balance training with non-immersive VR-based SGs can improve clinical, gait, and postural outcomes in TKR patients. It was not superior to the CG findings but could be considered an alternative to the conventional approach and can be added to a regular rehabilitation program in TKR patients. The EG had a more physiological duration of the gait stance phase at the end of the treatment than the CG. CLINICALTRIALS: GOV: NCT03454256.

Factors Influencing Functional Outcome at Discharge: A Retrospective Study on a Large Sample of Patients Admitted to an Intensive Rehabilitation Unit.

OBJECTIVE: Functional outcome represents the most central objective of rehabilitation programs. Understanding which factors could affect functional status at discharge is crucial for the planning of appropriate treatments in both neurologic and orthopedic patients. The aim of this study was to investigate which clinical and demographic variables, collected at the patient's admission, could influence the functional outcome, assessed by the modified Barthel Index (mBI), at discharge. DESIGN: A retrospective study was conducted on a large cohort (n = 3548) of orthopedic and neurologic patients. Functional, demographic, and clinical records at patient admission and mBI score at discharge were collected. General linear model analysis was performed to assess the influence of these variables on functional outcome at discharge. RESULTS: The results reported a significant effect of mBI score at admission (P < 0.0001), age (P < 0.0001), and time from the acute event (P < 0.0001) on mBI score at discharge. Moreover, the disease type (neurologic or orthopedic) adjusted by sex (male or female) and presence of different impairments (cognitive and behavioral impairments) and complications (hypertension and cardiovascular diseases) significantly influenced mBI score at discharge (P < 0.05) (R2 = 0.497). No significant interactions between other factors were found (P > 0.05). CONCLUSION: Several prognostic factors should be considered when planning an appropriate tailored rehabilitation program.

Gait Recovery with an Overground Powered Exoskeleton: A Randomized Controlled Trial on Subacute Stroke Subjects.

BACKGROUND: Overground Robot-Assisted Gait Training (o-RAGT) provides intensive gait rehabilitation. This study investigated the efficacy of o-RAGT in subacute stroke subjects, compared to conventional gait training. METHODS: A multicenter randomized controlled trial was conducted on 75 subacute stroke subjects (38 in the Experimental Group (EG) and 37 in the Control Group (CG)). Both groups received 15 sessions of gait training (5 sessions/week for 60 min) and daily conventional rehabilitation. The subjects were assessed at the beginning (T1) and end (T2) of the training period with the primary outcome of a 6 Minutes Walking Test (6MWT), the Modified Ashworth Scale of the Affected lower Limb (MAS-AL), the Motricity Index of the Affected lower Limb (MI-AL), the Trunk Control Test (TCT), Functional Ambulation Classification (FAC), a 10 Meters Walking Test (10MWT), the modified Barthel Index (mBI), and the Walking Handicap Scale (WHS). RESULTS: The 6MWT increased in both groups, which was confirmed by both frequentist and Bayesian analyses. Similar outcomes were registered in the MI-AL, 10MWT, mBI, and MAS-AL. The FAC and WHS showed a significant number of subjects improving in functional and community ambulation in both groups at T2. CONCLUSIONS: The clinical effects of o-RAGT were similar to conventional gait training in subacute stroke subjects. The results obtained in this study are encouraging and suggest future clinical trials on the topic.

Ultrasound guidance increases diagnostic yield of needle EMG in plegic muscle.

OBJECTIVES: To increase the specificity of motor unit potential (MUPs) detection by using ultrasound guided electromyography (USG-EMG) in patients with muscle plegia due to traumatic nerve lesions. METHODS: Forty-six patients with recent nerve trauma underwent baseline standard EMG (ST-EMG) evaluation with evidence of absent MUPs. In 41 of them, ST-EMG was repeated after 2-3 months (T1) and the patients were accordingly divided in two groups: ST-EMG+ (if MUPs were detected) or ST-EMG- (MUPs not detected). Then, ST-EMG- patients underwent muscle ultrasound evaluation (M-US) and, if isles of muscular contractility were found, they also had USG-EMG. The same protocol was repeated 4-6 months after baseline (T2). RESULTS: At T1, 22/41 patients were ST-EMG+. While 19/41 were ST-EMG-; 9 of these patients had M-US consistent with residual muscular activity, for that reasons underwent USG-EMG with 7 of 9 demonstrating MUPs (at T2 all of these 7 patients resulted ST-EMG). In the other 2 patients, we found no MUPs at T1 but they became ST-EMG+ or USG-EMG positive at T2. The remaining 10 ST-EMG- patients had no EMG or US evidence of muscle contraction at T1, but at T2 2 of 10 became ST-EMG+ and 2 had USG-EMG showing MUPs. In the remaining 6 patients still M-US negative at T2, complete denervation was diagnosed. Concerning the 22 patients who were ST-EMG+ at T1, all but one showed increase of MUPs at T2. CONCLUSIONS: In this study, we demonstrated the utility of US guidance when performing EMG evaluation in locating isles of muscular contractility in patients who have no detectable MUPs on EMG after nerve trauma. SIGNIFICANCE: USG-EMG significantly increases the specificity of needle EMG allowing earlier detection of MUPs.

Clinical effects of robot-assisted gait training and treadmill training for Parkinson's disease. A randomized controlled trial.

BACKGROUND: Although gait disorders strongly contribute to perceived disability in people with Parkinson's disease, clinical trials have failed to identify which task-oriented gait training method can provide the best benefit. Freezing of gait remains one of the least investigated and most troublesome symptoms. OBJECTIVE: We aimed to compare the effects of robot-assisted gait training and treadmill training on endurance and gait capacity in people with Parkinson disease; the secondary aim was to compare the effect of the treatments in people with freezing and/or severe gait disability and assess changes in overall disease-related disability and quality of life. METHODS: Outpatients with Parkinson disease (Hoehn and Yahr stage≥2) were randomly assigned to receive 20 sessions of 45-min gait training assisted by an end-effector robotic device (G-EO System) or treadmill training. Outcome assessments were the 6-min walk test, Timed Up and Go test, Freezing of Gait Questionnaire, Unified Parkinson's Disease Rating Scales and Parkinson's Disease Quality of Life Questionnaire-39 administered before (T0) and after treatment (T1). RESULTS: We included 96 individuals with Parkinson disease: 48 with robot-assisted gait training and 48 treadmill training. Both groups showed significant improvement in all outcomes. As compared with baseline, with robot-assisted gait training and treadmill training, endurance and gait capacity were enhanced by 18% and 12%, respectively, and motor symptoms and quality of life were improved by 17% and 15%. The maximum advantage was observed with the Freezing of Gait Questionnaire score, which decreased by 20% after either treatment. On post-hoc analysis, dependent walkers benefited more than independent walkers from any gait training, whereas freezers gained more from robot-assisted than treadmill training in terms of freezing reduction. CONCLUSIONS: Repetitive intensive gait training is an effective treatment for people with Parkinson disease and can increase endurance and gait velocity, especially for those with severe walking disability. Advantages are greater with robot-assisted gait training than treadmill training for individuals with freezing of gait - related disability.

Abnormal Circadian Modification of Aδ-Fiber Pathway Excitability in Idiopathic Restless Legs Syndrome.

Restless legs syndrome (RLS) is characterized by unpleasant sensations generally localized to legs, associated with an urge to move. A likely pathogenetic mechanism is a central dopaminergic dysfunction. The exact role of pain system is unclear. The purpose of the study was to investigate the nociceptive pathways in idiopathic RLS patients. We enrolled 11 patients (mean age 53.2 ± 19.7 years; 7 men) suffering from severe, primary RLS. We recorded scalp laser-evoked potentials (LEPs) to stimulation of different sites (hands and feet) and during two different time conditions (daytime and nighttime). Finally, we compared the results with a matched control group of healthy subjects. The Aδ responses obtained from patients did not differ from those recorded from control subjects. However, the N1 and the N2-P2 amplitudes' night/day ratios after foot stimulation were increased in patients, as compared to controls (N1: patients: 133.91 ± 50.42%; controls: 83.74 ± 34.45%; p = 0.016; Aδ-N2-P2: patients: 119.15 ± 15.56%; controls: 88.42 ± 23.41%; p = 0.003). These results suggest that RLS patients present circadian modifications in the pain system, which are not present in healthy controls. Both sensory-discriminative and affective-emotional components of pain experience show parallel changes. This study confirms the structural integrity of Aδ nociceptive system in idiopathic RLS, but it also suggests that RLS patients present circadian modifications in the pain system. These findings could potentially help clinicians and contribute to identify new therapeutic approaches.

Nociceptive contribution to the evoked potentials after painful intramuscular electrical stimulation.

Our study aimed at investigating the nociceptive contribution to the somatosensory evoked potentials after electrical intramuscular stimulation (mSEPs) at painful intensity. Scalp mSEPs were recorded in 10 healthy subjects after electrical stimulation of the left brachioradialis muscle at three intensities: non-painful (I2), slightly painful (I4) and moderately painful (I6). For each intensity, mSEPs were recorded in a neutral condition (NC) in which subjects did not have any task, and in an attention condition (AC) in which subjects were asked to count the number of stimuli. In both NC and AC, the N120 and P220 amplitudes were significantly higher at I6 than at I2. While the N120 amplitude did not vary between NC and AC, the P220 amplitude was significantly higher in AC than in NC at all stimulus intensities. Our results suggest that nociceptive inputs contribute to the N120 amplitude increase at painful stimulus intensity, while the P220 amplitude is more sensitive to changes of subjects' attention level. Therefore, the N120 amplitude increase to moderately painful stimuli, as compared to non-painful stimuli, may represent a marker of the activation of the muscular thin myelinated afferents.

Pre-stimulus alpha power affects vertex N2-P2 potentials evoked by noxious stimuli.

It is well known that scalp potentials evoked by nonpainful visual and auditory stimuli are enhanced in amplitude when preceded by pre-stimulus low-amplitude alpha rhythms. This study tested the hypothesis that the same holds for the amplitude of vertex N2-P2 potentials evoked by brief noxious laser stimuli, an issue of interest for clinical perspective. EEG data were recorded in 10 subjects from 30 electrodes during laser noxious stimulation. The artifact-free vertex N2-P2 complex was spatially enhanced by surface Laplacian transformation. Pre-stimulus alpha power was computed at three alpha sub-bands according to subject's individual alpha frequency peak (i.e. about 6-8Hz for alpha 1, 8-10Hz for alpha 2 and 10-12Hz for alpha 3 sub-band). Individual EEG single trials were divided in two sub-groups. The strong-alpha sub-group (high band power) included halfway of all EEG single trials, namely those having the highest pre-stimulus alpha power. Weak-alpha sub-group (low band power) included the remaining trials. Averaging procedure provided laser evoked potentials for both trial sub-groups. No significant effect was found for alpha 1 and alpha 2 sub-bands. Conversely, compared to strong-alpha 3 sub-group, weak-alpha 3 sub-group showed vertex N2-P2 potentials having significantly higher amplitude (p<0.05). These results extend to the later phases of pain processing systems the notion that generation mechanisms of pre-stimulus alpha rhythms and (laser) evoked potentials are intrinsically related and subjected to fluctuating "noise". That "noise" could explain the trial-by-trial variability of laser evoked potentials and perception.

Parallel spinal pathways generate the middle-latency N1 and the late P2 components of the laser evoked potentials.

OBJECTIVE: To investigate the possible presence of multiple spino-thalamic pathways with different conduction velocities (CVs) in the human spinal cord. METHODS: Laser evoked potentials (LEPs) were recorded in 10 healthy subjects after stimulation of the dorsal midline at four vertebral level: C5, T2, T6, and T10. This method allowed us to minimize the influence of the conduction in the peripheral fibers and to calculate the spinal CV in two different ways: (1) the reciprocal of the slope of the regression line was obtained from the latencies of the different LEP components, and (2) the distance between C5 and T10 was divided by the latency difference of the responses at the two sites. In particular, we considered the middle-latency N1 potential (latencies of around 135, 150, 157, and 171 ms after stimulation at C5, T2, T6, and T10 levels, respectively), which is generated in the second somatosensory (SII) area, and the late P2 response (latencies of around 336, 344, 346, and 362 ms after stimulation at C5, T2, T6, and T10 levels, respectively), which is generated in the anterior cingulate cortex (ACC). RESULTS: The calculated CV of the spinal fibers generating the N1 potential (around 9 m/s) was significantly different (P<0.05) from the one of the pathway producing the P2 response (around 13 m/s). CONCLUSIONS: Our results suggest that the N1 and the P2 LEP components are generated by two parallel spinal pathways. SIGNIFICANCE: Both the N1 and P2 potentials should be recorded in the clinical routine since a dissociated abnormality of either response may be found in lesions of the nociceptive system not only in the brain, but also at spinal cord level.

Attentional training in elderly subjects affects voluntarily oriented, but not automatic attention: a neurophysiological study.

OBJECTIVES: Our study aimed at investigating the effect of repetitive recordings on somatosensory evoked potentials (SEPs) related to spatial attention in a population of healthy elderly subjects. METHODS: Fifteen healthy elderly subjects were tested for six consecutive days using a somatosensory oddball paradigm, in which target stimuli were applied above the elbow and the non-target stimuli on the ipsilateral shoulder. Brain electrical activity was recorded from six scalp electrodes (Fz, Cz, F3, F4, T3 and T4). RESULTS: The N140 response to target stimuli showed a significantly decreased amplitude across the sessions with the lowest value during the fourth day of recording and with a partial recovery at the sixth day. On the contrary, the amplitude of the N140 response to non-target stimuli and that of the P300 potential to target stimuli were not significantly modified. CONCLUSIONS: The significant amplitude reduction of the N140 potential in target, but not in non-target recordings across sessions, suggests that the voluntarily oriented attention is reduced by stimulus repetition, while the automatic attention is not.

Cortical neuroplastic changes to painful colon stimulation in patients with irritable bowel syndrome.

The aim of this study was to model the cerebral generators following painful electrical stimulation of the sigmoid colon in 10 healthy controls and 10 patients with visceral pain due to the irritable bowel syndrome. The evoked brain potentials to 30 painful electrical stimuli from the sigmoid colon were recorded from 31 surface electrodes and subjected to electrical dipole source modelling. Two dipoles in the bilateral insular cortex, one dipole in the anterior cingulate gyrus and two dipoles in the bilateral second somatosensory area were found. The anterior cingulate dipole showed a more posterior position in patients than in control subjects. This finding suggests that the cortical representation of painful stimuli can be modified in presence of chronic visceral pain and that this change involves the anterior cingulate gyrus.

Reduction in amplitude of the subcortical low- and high-frequency somatosensory evoked potentials during voluntary movement: an intracerebral recording study.

OBJECTIVE: To investigate whether the reduction of amplitude of the scalp somatosensory evoked potentials (SEPs) during movement (gating) is due to an attenuation of the afferent volley at subcortical level. METHODS: Median nerve SEPs were recorded from 9 patients suffering from Parkinson's disease, who underwent implant of intracerebral (IC) electrodes in the subthalamic nucleus or in the globus pallidum. SEPs were recorded from Erb's point ipsilateral to stimulation, from the scalp surface and from the IC leads, at rest and during a voluntary flexo-extension movement of the stimulated wrist. The recorded IC traces were submitted to an off-line filtering by a 300-1500 bandpass to obtain the high-frequency SEP bursts. RESULTS: IC leads recorded a triphasic component (P1-N1-P2) from 14 to 22 ms of latency. The amplitudes of the scalp N20, P20 and N30 potentials and of the IC triphasic component were significantly decreased during movement, while the peripheral N9 amplitude remained unchanged. Also the IC bursts, whose frequency was around 1000 Hz, were reduced in amplitude by the voluntary movement. CONCLUSIONS: Since the IC triphasic component is probably generated by neurons of the thalamic ventro-postero-lateral nucleus, which receive the somatosensory afferent volley, the P1-N1 amplitude reduction during movement suggests that the gating phenomenon involves also the subcortical structures.

Different neuronal contribution to N20 somatosensory evoked potential and to CO2 laser evoked potentials: an intracerebral recording study.

OBJECTIVE: To investigate the possible contribution of the primary somatosensory area (SI) to pain sensation. METHODS: Depth recordings of CO2 laser evoked potentials (LEPs) and somatosensory evoked potentials (SEPs) were performed in an epileptic patient with a stereotactically implanted electrode (Talairach coordinates y=-23, z=40) that passed about 10 mm below the hand representation in her left SI area, as assessed by the source of the N20 SEP component. RESULTS: The intracerebral electrode was able to record the N20 SEP component after non-painful electrical stimulation of her right median nerve. The N20 potential showed a phase reversal in the bipolar montage (at about 31 mm from the midline), which confirms that the electrode was located near its generator in area 3b. In contrast, no reliable response was recorded from the SI electrode after painful CO2 laser stimulation of the right hand. An N2-P2 response was evoked at the vertex electrode (Cz), thus demonstrating the effectiveness of the delivered CO2 laser stimuli. CONCLUSIONS: Since the N20 SEP component originates from the anterior bank of the post-central gyrus (area 3b), our result suggests that this part of SI does not participate in LEP generation. In fact, the previously published LEP sources in the SI area estimated from scalp recordings are about 10-17 mm posterior of the electrode in our patient, suggesting that they are more likely located in area 1, 2 or posterior parietal cortex.

Abnormal gating of somatosensory inputs in essential tremor.

OBJECTIVE: To study whether sensorimotor cortical areas are involved in Essential Tremor (ET) generation. BACKGROUND: It has been suggested that sensorimotor cortical areas can play a role in ET generation. Therefore, we studied median nerve somatosensory evoked potentials (SEPs) in 10 patients with definite ET. METHODS: To distinguish SEP changes due to hand movements from those specifically related to central mechanisms of tremor, SEPs were recorded at rest, during postural tremor and during active and passive movement of the hand. Moreover, we recorded SEPs from 5 volunteers who mimicked hand tremor. The traces were further submitted to dipolar source analysis. RESULTS: Mimicked tremor in controls as well as active and passive hand movements in ET patients caused a marked attenuation of all scalp SEP components. These SEP changes can be explained by the interference between movement and somatosensory input ('gating' phenomenon). By contrast, SEPs during postural tremor in ET patients showed a reduction of N20, P22, N24 and P24 cortical SEP components, whereas the fronto-central N30 wave remained unaffected. CONCLUSIONS: Our findings suggest that in ET patients the physiological interference between movement and somatosensory input to the cortex is not effective on the N30 response. This finding thus indicates that a dysfunction of the cortical generator of the N30 response may play a role in the pathogenesis of ET.

Short-term plastic changes of the human nociceptive system following acute pain induced by capsaicin.

OBJECTIVE: To investigate possible neuroplastic changes induced by pain in cerebral areas devoted to nociceptive input processing. METHODS: CO(2) laser-evoked potentials (LEPs) were recorded from 10 healthy subjects after stimulation of the right and left hand dorsum. Acute pain was obtained by topical application of capsaicin on the skin of right hand dorsum. LEPs were recorded after right and left hand stimulation before capsaicin, at the peak pain and 10-20 min after capsaicin removal. Right hand LEPs were evoked by laser stimuli delivered over the zone of secondary hyperalgesia during capsaicin and on both the zones of primary and secondary hyperalgesia after capsaicin removal. RESULTS: After right hand stimulation, the vertex LEPs, which are generated in the cingulate cortex, were significantly decreased in amplitude during capsaicin application and after capsaicin removal. Moreover, the topography of these potentials was modified after capsaicin removal, shifting from the central toward the parietal region. Dipolar modelling showed that the dipolar source in the anterior cingulate cortex moved backward after capsaicin removal. All these changes were not observed after stimulation of the left hand, contralateral to the application of capsaicin, thus suggesting that functional changes are selective for the painful skin and the adjacent territories. CONCLUSIONS: Our results suggest that acute cutaneous pain may inhibit the neural activity in regions of central nervous system processing nociceptive inputs and cortical representation of these inputs can be rapidly modified in presence of acute pain.

Dipolar source modelling of brain potentials evoked by painful electrical stimulation of the human sigmoid colon.

The aim of the study was to compare the cerebral generators following painful stimulation of the sigmoid colon and the abdominal skin in 11 healthy subjects. The evoked potentials (EPs) were recorded from 31 surface electrodes following painful electrical stimuli of the sigmoid colon, and of the referred pain area on the abdomen. Current dipole models estimating the EPs amplitude and topography were calculated. For colon stimulation, the earliest cortical activities were described by dipoles in the bilateral insula and in the anterior cingulate cortex, while both secondary somatosensory areas were activated later. When the skin was stimulated, early bilateral dipoles in the primary and secondary somatosensory areas were estimated, followed by a dipole in the frontal region. This suggests that painful cutaneous and visceral stimuli are processed differently in the brain.