Middle-latency Somatosensory Evoked Potentials Research Articles

Facilitation of Early and Middle Latency SEP after tDCS of M1: No Evidence of Primary Somatosensory Homeostatic Plasticity

Homeostatic plasticity is a mechanism that stabilizes cortical excitability within a physiological range. Most homeostatic plasticity protocols have primed and tested the homeostatic response of the primary motor cortex (M1). This study investigated if a homeostatic response could be recorded from the primary sensory cortex (S1) after inducing homeostatic plasticity in M1. In 31 healthy participants, homeostatic plasticity was induced over M1 with a priming and testing block of transcranial direct current stimulation (tDCS) in two different sessions (anodal and cathodal). S1 excitability was assessed by early (N20, P25) and middle-latency (N33-P45) somatosensory evoked potentials (SEP) extracted from 4 electrodes (CP5, CP3, P5, P3). Baseline and post-measures (post-priming, 0-min, 10-min, and 20-min after homeostatic induction) were taken. Anodal M1 homeostatic plasticity induction significantly facilitated the N20-P25, P45 peak, and N33-P45 early SEP components up to 20-min post-induction, without any indication of a homeostatic response (i.e., reduced SEP). Cathodal homeostatic induction did not induce any significant effect on early or middle latency SEPs. M1 homeostatic plasticity induction by anodal stimulation protocol to the primary motor cortex did not induce a homeostatic response in SEPs.

The Impact of Micro RNA-320a Serum Level on Severity of Symptoms and Cerebral Processing of Pain in Patients with Fibromyalgia.

The aim of this work was to explore the expression of miR-320a level in fibromyalgia patients in comparison to healthy controls, and to clarify its impact on the severity of symptoms and the cerebral processing of pain assessed by middle latency somatosensory evoked potentials (SSEPs). Case-control study. Rheumatology and Neurology outpatient clinics. Seventy-four fibromyalgia patients and seventy-four normal healthy controls. The included patients were subjected to detailed history taking, assessment of severity of fibromyalgia symptoms using the Fibromyalgia Impact Questionnaire Revised (FIQR), assessment of pain intensity using the Neuropathic Pain Symptom Inventory (NPSI), measurement of the serum level of miR-320a in addition to of measurement peak latencies and amplitudes of middle latency SSEPs. Fibromyalgia patients had significantly higher micro-RNA-320a levels (0.907 ± 0.022) in comparison to controls (0.874 ± 0.015) (P-value < .001). The mean values of micro-RNA-320a levels were significantly higher in fibromyalgia patients with insomnia, chronic fatigue syndrome, persistent depressive disorder, and primary headache disorder than those without (P-value = .024, <.001, .006, .036 respectively). There were statistically significant positive correlations between micro-RNA-320a levels, and disease duration, FIQR, and NPSI total scores (P-value <0.001, 0.003, 0.002 respectively). There were no statistically significant correlations between micro-RNA-320a levels and middle latency SSEPs. Micro-RNA-320a level is significantly upregulated in fibromyalgia patient. It has a crucial impact on the severity of symptoms but not related to the cerebral processing of pain.

S103. Description of short and middle latency somatosensory evoked potentials in adult patients with ischemic cerebrovascular accident

Introduction In the United States, cerebrovascular accidents (CVAs) are the fourth most common cause of death with a general prevalence of 2.6%. Approximately 85% of all CVAs are of the ischemic type. Somatosensory evoked potentials (SSEPs) evoked through transcutaneous bipolar electrical stimulation applied to the selected nerve, this is one of the most informative neurophysiological techniques available, since it provides an evaluation of brain function. In turn, the middle latency somatosensory evoked potentials (MLSEP) between 35 and 100 ms after stimulation of the median nerve. SSEPs are abnormal in patients with lesions in the brainstem, diencephalon or cerebral hemispheres, when lemniscal pathways are involved, with similar patterns for brainstem, thalamic and thalamic-capsular lesions. The SSEPs have been studied in an attempt to prove their usefulness as a tool for clinical evaluation and prognosis in ischemic CVA. Methods Observational, cross-sectional, exploratory study enrolled 7 adult patients with corroborated ischemic stroke by imaging study (computed tomography CT or magnetic resonance imaging MRI) within the first 24 h of evolution. Short and middle latency somatosensory evoked potentials were performed at the American British Cowdray Medical Center, with Sierra Wave 4 channels electromyograph, recording and quantifying its latencies of N35, P45 and N60 ipsi and contralateral responses to the site of injury taking into account clinical and paraclinical variables. Results In this study 7 patients were recorded; the group had a median age of 61 years, with a minimum age of 25 years and maximum of 84 years. With their respective controls, the study showed the MLSEP in patients with CVA being of cardioembolic, atherothrombotic, prothrombotic and indeterminate etiology; in the short latency potentials peripheral response was found in all cases (N9), N60 was absent in patients with CVAs of different etiologies, the proportion of waves absent in lesion-ipsilateral MLSEP was greater than in contralateral MLSEP. Conclusion The clinical use of the middle latency responses has been limited by the incomplete knowledge of their generators, since the specific utility of this neurophysiological study is based on the evaluation of neurological pathways which can be interrupted in their journey by other pathologies such as ischemic stroke. The use of MLSEP shows that in patients with CVA they are present unilaterally, contralaterally and bilaterally, so the usefulness of performing them has future implications to determine the frequency of each of them related to the type of etiology, treatment and prognostic outcome.

Whiplash and Concussion: Similar Acute Changes in Middle-Latency SEPs

Middle-latency somatosensory evoked potentials (SEPs) following median nerve stimulation can provide a sensitive measure of cortical function. We sought to determine whether the mechanical forces of whiplash injury or concussion alter normal processing of middle-latency SEPs. In a cross-sectional pilot study 20 subjects with whiplash were investigated (50% between 0.5-2 months and 50% between 6-41 months post injury) and compared to 83 healthy subjects using a standard middle-latency SEP procedure. In a subsequent prospective study subjects with either acute whiplash (n=13) or Grade 3 concussion (n=16) were investigated within 48 hours and again three months post injury. In the pilot study the middle-latency SEP component N60 was significantly increased in the ten subjects investigated within two months after whiplash. In contrast, the ten subjects examined more than six months after injury showed normal latencies. In the prospective study N60 latencies were increased after whiplash and concussion when tested within 48 hours of injury. At three months, latencies were improved though still significantly different from controls post whiplash and concussion. Both whiplash injury and concussion alter processing of the middle-latency SEP component N60 in the acute post traumatic period. The acute changes appear to normalize between three-six months post injury. The SEP similarities suggest that the overlapping clinical symptomatology post whiplash and concussion may reflect a similar underlying mechanism of rotational mild traumatic brain injury.

Effects of aging and sex on middle-latency somatosensory evoked potentials: normative data

Objectives: To investigate the exact relationship of middle-latency somatosensory evoked potential (SEP) components (in particular the third negative component N60) to age and sex in a normal population. Middle-latency SEPs are believed to show a considerable inter-individual variability and there is little published information on normative data of these components.Methods: Eighty-three healthy subjects aged 13–80 years were investigated using a standard SEP procedure.Results: Both latency and amplitude of N60 increased substantially with age. Least square polynomial regression analysis showed that a quadratic curve best described its relationship (r2=0.67 for the latency, r2=0.18 for the amplitude). Data did not differ significantly with reference to sex or side of stimulation.Conclusions: The use of polynomial regression analysis for the determination of the normal range of N60 latencies and amplitudes has to be highly recommended. It might improve the accuracy with which abnormal results are detected in studies investigating the value of middle-latency SEPs in various diseases.

Changes of middle latency somatosensory evoked potentials (SEPs) and alpha rythmicity associated with oculomotor processes

Objectives: To evaluate median nerve somatosensory evoked potentials (SEPs) and α waves during different eye conditions. Methods: Median SEPs and occipital electroencephalographs (EEG) were recorded in 6 eye conditions: eye-closed (EC), goggle (G), goggle+saccade (GS), saccade (S), eye-opened (EO) and pursuit (P), in 8 normal adults. Subjects saccaded their eyes reacting to auditory cues to watch a diode on the right or left side alternatively during the S condition, or imitated the same saccadic eye-movement as that in the S condition during the GS condition. In the P condition, subjects traced a small circle moving on a computer screen. Results: Compared with the EC and G conditions, N30 (P25-N30 or P14-N30) amplitudes in C4′ were significantly larger and the mean amplitude and power of the α band was significantly attenuated in the other 4 conditions. The amplitude and power of the α band differed significantly between the GS and S conditions, whereas N30 amplitudes were similar between the two conditions. N30-P45 or P45-N60 amplitudes in C4′ were significantly larger in the P condition than in other conditions. Conclusions: Present findings suggest that different neural mechanisms cause α blocking and the modification of middle latency SEPs associated with oculomotor control.

Scalp topographic mapping of middle-latency somatosensory evoked potentials in normal aging and dementia

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded in four groups of subjects: 13 normal young controls (mean age, 17.9 years). 11 normal elderly (mean age, 66.9 years), 11 patients with dementia of Alzheimer's type (DAT: mean age, 70.5), and four with vascular dementia (mean age, 79.3). MLSEPs in normal elderly showed an increase in the latency of P22, N30, P45, N60, and P100, and in the amplitude of N60. DAT patients also presented such changes; however, the increase in the amplitude of N60 was much more evident than that found in normal aging and was accompanied by a significant increase in amplitude of P45. Patients with vascular dementia tended to show longer latencies and larger amplitudes than the other groups. The increase in amplitude of P45 and N60 in MLSEPs seems to be characteristically associated with normal aging and the development of dementia. It is suggested that the mechanism of such functional changes might be correlated with the structural and neurochemical changes accompanying neuronal loss in these conditions.

Age- and height-dependent changes of amplitude and latency of somatosensory evoked potentials in children and young adults with Down's syndrome

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in 34 patients with Down's syndrome (DS) aged 7.4 to 35.7 years and in 16 normal control subjects aged 6.4 to 34.4 years. DS patients showed an increase in amplitude of P22, P45, and N60. P100 latency was significantly shortened. After normalization for height of subjects, N20 and N60 latencies were significantly longer in the patient group than in control subjects. On the other hand, it was possible to observe in both groups a significant trend for MLSEP amplitudes to decrease with age during the age period considered in this work. This study further confirms that the pattern of increase in amplitude of MLSEP components observed in DS is a finding peculiar of this syndrome and is not correlated with early aging processes.

Middle-latency somatosensory evoked potentials after stimulation of the radial and median nerves: component structure and scalp topography.

Somatosensory evoked potentials (SEPs) after radial nerve stimulation are studied less frequently than those after median nerve stimulation. Therefore, little is known about their component structure and scalp topography. We investigated radial nerve SEPs after electrical stimulation at the left wrist. For comparison, the median nerve was also stimulated at the wrist. SEPs were recorded with 15 scalp electrodes (bandpass 0.5-200 Hz) in 27 healthy subjects. The waveform of the radial nerve SEP at a contralateral parietal lead was comparable to that of the median nerve SEP, consisting of P14, N20, P30, and N60. In spite of comparable stimulus intensities, SEP amplitudes were smaller after radial than after median nerve stimulation. Significant latency differences were found only for N20 (earlier for median nerve) and P30 (earlier for radial nerve). The duration of the primary complex N20-P30 thus was significantly shorter for the radial nerve. Whereas N20 and P30 were present with either earlobe or frontal reference, N60 had a prerolandic maximum and was best recorded with a bipolar transverse derivation. In addition, another middle-latency negativity (N110) was found near the secondary somatosensory cortex, which had previously been described only for radial nerve stimulation. In standard SEP derivations, the N110 is riding on the ascending limb of the vertex negativity. It could best be recorded in low temporal leads versus a midline reference. The scalp topographies of P30, N60, and N110 were similar for radial and median nerve stimulation.

BIT-mapped somatosensory evoked potentials in the fragile X syndrome

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in ten male patients with the fragile X (fraX) syndrome and nine normal controls. One fraX patient was found presenting the so-called "giant" MLSEPs with an amplitude of N60 of about 60 microV and of 40 microV after stimulation of the right and left median nerves, respectively. Tapping of the right hand, in the same patient, induced the appearance of left parietal evoked EEG spikes. These findings further support the already suggested similarity between the epileptic picture of several fraX patients with that of the benign childhood epilepsy with centrotemporal spikes. Color mapping of the MLSEPs recorded in the remaining nine patients, when compared with the control group, showed an abnormally large N30 over the frontal regions, together with an increase in amplitude of P27, over the parietal areas, and of N60 and P100 which also presented abnormal field distributions, being represented preferentially over the frontal regions. These data could suggest the existence of a cortical dysfunction mostly involving the frontal lobes (supplementary motor area, in particular) in the fraX syndrome which could support many behavioral changes usually observed in these patients.

Bit-mapped somatosensory evoked potentials in Down's syndrome individuals

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in 19 patients with Down's syndrome (DS), in 13 age-matched normal controls and in 11 aged normal individuals. DS patients showed an increase in amplitude of P22, N30, P45, and N60. P100 latency was significantly shortened. After this potential, DS subjects showed the occurrence of a high voltage negative potential at around 100-110 msec followed by another high-voltage positive deflection; both these components showed a frontal-central distribution and were not observed in the two control groups. MLSEPs of DS subjects show peculiar alterations which could be supported by particular neurometabolic and/or neuropathologic changes.

Middle-latency somatosensory evoked potentials following median and posterior tibial nerve stimulation in Down's syndrome

Middle-latency somatosensory evoked potentials (SEPs) following median and posterior tibial nerve stimulation were studied in 40 patients with Down's syndrome and in age- and gender-matched healthy controls as well as in middle-aged and aged healthy subjects. In median nerve SEPs, latencies of the initial cortical potentials, N18 and P18, showed no significant difference, but the following potentials N22, P25, N32, P41 and P46 were relatively or significantly shorter in latency in Down's patients than in the controls. Amplitudes of all components in Down's patients were significantly larger than those of age- and gender-matched controls as well as of those of middle-aged healthy subjects, but there was only a small difference in their amplitudes from aged healthy subjects. Results of posterior tibial nerve SEPs were generally consistent with those of median nerve SEPs. Therefore, ‘short latency with large amplitude’ is the main characteristic of middle-latency SEPs in Down's syndrome, possibly related to accelerated physiological aging of the central nervous system.