Abnormal Circadian Modification of A\u3b4-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\u2009\ub1\u200919.7 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 A\u3b4 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\u2009\ub1\u200950.42%; controls: 83.74\u2009\ub1\u200934.45%; p = 0.016; A\u3b4-N2-P2: patients: 119.15\u2009\ub1\u200915.56%; controls: 88.42\u2009\ub1\u200923.41%; 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 A\u3b4 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

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

Pain-related modulation of the human motor cortex

Pain is a complex multi-dimensional phenomenon that influences a wide variety of nervous system functions, including sensory-discriminative, affective-motivational and cognitive-evaluative components. So far, these components have been studied in both patients with chronic pain and in normal subjects in whom pain was induced experimentally. The interaction between pain and motor function is not fully understood, although from everyday life it is known that pain affects movements. The effects of pain on motor control are typically seen as a limited or impaired ability to perform movements. Most studies have dealt with the effects of pain on the spinal cord reflexes, but in recent years, several lines of evidence suggest that the interaction between motor and pain systems in conditions of pain induced experimentally, rather than a simple spinal reflex, is a more complex process that involves also supraspinal brain areas. Although pain-motor interaction shows different features and time course depending on different pain variables, such as duration (tonic versus phasic pain), submodalities (deep versus superficial pain) and location (distal versus proximal pain), a common finding is that pain is able to inhibit the motor cortex. This motor cortex inhibition may act as a sort of motor 'decerebration' so as to allow the spinal motor system to freely develop protective responses to noxious stimulation. Further studies are required to assess the effects of pain on the motor system in patients suffering from chronic pain, in order to develop innovative rational therapeutic strategies to reduce both pain and motor disability

Scalp distribution of the earliest cortical somatosensory evoked potential to tibial nerve stimulation: proposal of a new recording montage

Objective: to investigate the most reliable method to record the earliest cortical somatosensory evoked potential (SEP) after tibial nerve stimulation. The 'gating' phenomenon was used to dissociate the overlapping cortical SEP components. Methods: in 11 subjects we recorded the scalp SEPs at rest, during the voluntary (active gating) and passive (passive gating) foot movement and during the isometric calf muscle contraction (isometric gating). Results: at the vertex the P40 amplitude was reduced in all the gating conditions. Instead, both the P40 response recorded in the parietal region ipsilateral to the stimulation (indicated as P40par) and the fronto-temporal N37 potential were reduced in amplitude only during the passive foot movement. Conclusions: the same behaviour of the N37 and P40par potentials suggests that they can represent the opposite counterparts of the same dipolar generator. Instead, the real P40 amplitude, which is affected in all the gating conditions, is recorded at the vertex and might be generated by a different source. We conclude that the montage obtained by referring a temporal electrode contralateral to the stimulation to an ipsilateral parietal lead can reliably record the earliest cortical component (N37/P40par) after tibial nerve stimulation

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

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

The pathophysiology of giant SEPs in cortical myoclonus: a scalp topography and dipolar source modelling study

Somatosensory evoked potential (SEP) recordings in patients suffering from cortical myoclonus(CM) are characterised by evidence of abnormally enhanced scalp components. Our aim was to verify whether enhanced activity in giant SEPs arises from the same generators as in healthy subjects. We used the brain electrical source analysis (BESA) to compare scalp SEP generators of healthy subjects to those calculated in 3 patients with CM of varying causes. Firstly, we built a 4-dipole model explaining scalp distribution of early SEPs in normal subjects and then applied it to traces recorded from CM patients. Our model, issued from the right median nerve grand average and applied also to recordings from single individuals, included a dipole at the base of the skull and three other perirolandic dipoles. The first of the latter dipoles was tangentially oriented and was active at the same latencies as the N20/P20 potentials and, with opposite polarity, the P24/N24 responses; the second dipole explained the central P22 distribution and the third had a peak of activity corresponding to the N30 component. When we applied our 4-dipole model to CM recordings, the first perirolandic dipole had a third peak of activity in all patients at the same latency as a parietal negativity and a frontal positivity, both following giant P24/N24 components; on the other hand, in one patient the second perirolandic dipole showed a later activation corresponding to a high central negativity, following a giant P22 response. We suggest that only the initial giant SEPs correspond to physiological potentials evoked in healthy subjects. The occurrence of late giant SEPs could be explained by hyperpolarization, following the postsynaptic excitatory potentials responsible for the early giant components. (C) 1997 Elsevier Science Ireland Ltd

Sources of cortical responses to painful CO 2 laser skin stimulation of the hand and foot in the human brain

objectives: to investigate whether the same dipolar model could explain the scalp CO2 laser evoked potential (LEP) distribution after either hand or foot skin stimulation. methods: LEPs were recorded in 14 healthy subjects after hand and foot skin stimulation and brain electrical source analysis of responses obtained in each individual was performed. results: a 5 dipolar sources model explained the scalp LEP topography after both hand and foot stimulation. In particular, we showed that the co-ordinates of the two earliest activated dipoles were compatible with source locations in the upper bank of the sylvian fissure on both sides. these sources did not change their location when the stimulation site was moved from the upper to the lower limb. the other 3 dipoles of our model were activated in the late LEP latency range with a biphasic profile and a location compatible with activation of the cingulate gyrus and deep temporo-insular structures. conclusions: the dipolar model previously proposed for the hand stimulation LEPs can also satisfactorily explain the LEP distribution obtained after foot stimulation. the earliest activated sylvian dipolar sources did not change their location when the upper or lower limb was stimulated, as expected from the close projections of hand and foot in the second somatosensory area. no source in the primary somatosensory area was necessary to model the scalp topography of LEPs to hand and foot stimulation

The scalp to earlobe montage as standard in routine SEP recording. Comparison with the non-cephalic reference in patients with lesions of the upper cervical cord

We compared scalp somatosensory evoked potential (SEP) recordings by non-cephalic and earlobe reference in 14 healthy subjects and in 5 patients with lesions of the upper cervical cord. In healthy subjects, the scalp to earlobe montage tended to cancel all far-field potentials preceding the scalp P14. On the contrary, the P14 far-field was mon difficult to identify in scalp to non-cephalic recordings, because in 12/ 14 cases it followed another far-field (P13), which was very close in latency to the P14. In 4 patients, the scalp to non-cephalic traces showed a single positive wave (P13/P14 complex) in the P14 latency range. If this complex had been labelled as P14, the somatosensory dysfunction would have been localised above the foramen magnum. On the other hand, the scalp to earlobe recording allowed correct localisation of the lesion since it showed the 'real' and delayed P14 in two patients and no far-field response in the remaining two. Therefore, we propose the use of the scalp to earlobe montage as standard in routine examinations

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 NI 20 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