n-Hexane-induced changes in nerve conduction velocities and somatosensory evoked potentials

Summary Fifteen women from a shoe factory were examined clinically and their cerebral evoked responses to 256 electrical stimulations of the median nerve were averaged. Neurophysiological investigations included maximal motor (MCV) and distal sensory (dSCV) nerve conduction velocity measurement on ulnar, median, and peroneal nerves. A referent group was composed of 15 age-matched women without exposure to neurotoxic chemicals. MCVs and dSCVs of the exposed workers were significantly reduced vs referents, while P₁₅ and N₂₀ components of the somatosensory evoked potentials (SEP) showed an increased latency. A negative linear relationship was found between dSCV and P₁₅ latency. However, two subjects with an abnormally low dSCV showed normal SEP latency, and two other subjects displayed abnormal SEP latency, while their dSCV was in the normal range. Therefore, SEP investigation may give additional information on nervous system function, even in subjects with peripheral neuropathy. The later SEP components were much flatter in the exposed than in the referent group, suggesting some neurotoxic effects of n-hexane on the central nervous system too.This work was supported in part by the Department of Social Security, Region Emilia-Romagna.     

Pediatric polysomnography—A review of indications,technical aspects,and interpretation

Polysomnography is an elaborate diagnostic test composed of numerous data-collecting sensors working concomitantly to aid in the evaluation of varied sleep disorders in all age groups. Polysomnography is the study of choice for the assessment of pediatric sleep-disordered breathing, including obstructive sleep apnea syndrome, central apnea, and hypoventilation disorders, and is used to help determine treatment efficacy. Beyond the purview of snoring and breathing pauses, polysomnography can elucidate the etiology of hypersomnolence, when associated with a multiple sleep latency test, and abnormal movements or events, whether nocturnal seizure or complex parasomnia, when a thorough patient history cannot provide clear answers. This review will highlight the multitudinous indications for pediatric polysomnography and detail its technical aspects by describing the multiple neurophysiologic and respiratory parametric sources. Knowledge of these technical aspects will provide the practitioner with a thoughtful means to understand the limitations and interpretation of polysomnography.     

Auditory neurophysiological development in early childhood: A growth curve modeling approach

ObjectiveDuring early childhood, the development of communication skills, such as language and speech perception, relies in part on auditory system maturation. Because auditory behavioral tests engage cognition, mapping auditory maturation in the absence of cognitive influence remains a challenge. Furthermore, longitudinal investigations that capture auditory maturation within and between individuals in this age group are scarce. The goal of this study is to longitudinally measure auditory system maturation in early childhood using an objective approach.MethodsWe collected frequency-following responses (FFR) to speech in 175 children, ages 3–8 years, annually for up to five years. The FFR is an objective measure of sound encoding that predominantly reflects auditory midbrain activity. Eliciting FFRs to speech provides rich details of various aspects of sound processing, namely, neural timing, spectral coding, and response stability. We used growth curve modeling to answer three questions: 1) does sound encoding change across childhood? 2) are there individual differences in sound encoding? and 3) are there individual differences in the development of sound encoding?ResultsSubcortical auditory maturation develops linearly from 3-8 years. With age, FFRs became faster, more robust, and more consistent. Individual differences were evident in each aspect of sound processing, while individual differences in rates of change were observed for spectral coding alone.ConclusionsBy using an objective measure and a longitudinal approach, these results suggest subcortical auditory development continues throughout childhood, and that different facets of auditory processing follow distinct developmental trajectories.SignificanceThe present findings improve our understanding of auditory system development in typically-developing children, opening the door for future investigations of disordered sound processing in clinical populations.     

Neurophysiologie clinique en psychiatrie : 4 – Réalisation et interprétation des explorations du sommeil pour les pathologies du sommeil comorbides des troubles mentaux

Sleep disorders like sleep-related breathing disorders, sleep-related movement disorders, parasomnias, and central hypersomnia are frequently associated with psychiatric disorders. It is thus important to detect patients with comorbid sleep disorders and to refer them for an appropriate sleep exploration if necessary. Sleep explorations are noninvasive electrophysiological diagnostic tests to assess brain function and more generally to assess the cardiopulmonary, motor and behavioral functions that are major physiologic functions modified during sleep. Sleep explorations allow diagnosis of sleep disorders and the assessment of their severity. The objective of this article is: to provide basic knowledge to psychiatrists on the conduct, the interpretation, and the results of the main sleep explorations, and to highlight the principles of clinical screening of sleep disorders evaluated by the sleep explorations. Close collaboration between psychiatry and sleep medicine is needed to promote access to subjects suffering from mental disorder to sleep explorations with the aim to ensure quality of care.     

Neurophysiological approach to central pain modulation in primary headaches

The study of CNS painmodulating pathways has led to important discoveries about the role of central nociceptive structures such as PAG and hypothalamus in the pathophysiology of episodic and chronic primary headaches. Functional neuroimaging studies have revealed that primary headaches are characterised by different patterns of activation of central pain modulatory structures. A future model of headache pathophysiology investigating the contribution of CNS pain–modulating pathways will probably increase our understanding of pain processing in primary headaches. Herein we review the neurophysiological approaches to assess central pain modulation in primary headaches with emphasis on the diffuse noxious inhibitory control, a form of endogenous pain inhibition. In addition, patients’ data will be presented that highlights the utility of such methods for primary headache’s pathophysiology and clinical monitoring.     

Voluntary and Reflex Influences on the Initiation of Swallowing Reflex in Man

The electrophysiological features of voluntarily induced and reflexive/spontaneous swallows were investigated. In normal subjects, swallows were elicited by infusing water either into the mouth (1–3 ml) or directly into the oropharyngeal region through a nasopharyngeal cannula (0.3–1 ml). For water infused orally, subjects were either requested to swallow voluntarily or instructed to resist swallowing and maintain the horizontal head position until swallowing occurred reflexively. Spontaneous saliva swallowing was investigated in patients with severe dysphagia who had a prominent clinical picture of suprabulbar palsy. Comparisons between different swallowing types were made by measuring the time interval between the onset of submental electromyographic activity (SM-EMG) and the onset of the upward movement of the larynx recorded by a movement sensor. This interval was less than 100 ms, even frequently less than 50 ms, in reflexive/spontaneous swallows, while in voluntarily induced swallows it was substantially longer. The rising time of submental muscle's excitation was also shorter in reflexive/spontaneous swallows. It was suggested that the triggering of voluntarily induced swallows commences more than 100 ms before the onset of swallowing reflex and that this mechanism is under the control of corticobulbar–pyramidal pathways. If the swallowing reflex is triggered within such a short period of time following the onset of SM-EMG, the central control by the bulbar swallowing center should be effective until the end of oropharyngeal swallowing.     

Comparison of electric stimulation methods for reduction of triceps surae spasticity in spinal cord injury

OBJECTIVES: To compare the effect of 3 methods of electric stimulation to reduce spasticity of the triceps surae in patients with complete spinal cord injury (SCI) and to investigate the carryover effect. DESIGN: Placebo-controlled study with repeated measurements after the interventions. SETTING: Research department affiliated with a rehabilitation hospital in the Netherlands. PARTICIPANTS: Ten patients with a complete SCI were recruited from the outpatient population of the rehabilitation hospital. All subjects had American Spinal Injury Association grade A impairment scores, except for one, who had grade C. The patients had no voluntary triceps surae contractibility. INTERVENTIONS: Forty-five minutes of cyclic electric stimulation of the agonist, antagonist, or dermatome of the triceps surae or a placebo approach. MAIN OUTCOME MEASURES: Outcome measures were the Modified Ashworth Scale (MAS), clonus score, and the H-reflex and M wave (H/M) ratio. The electromyographic response to a stretch of the soleus over the whole range of motion was also determined. The magnitude and ankle angle at which the electromyographic response started were calculated. RESULTS: Stimulation of the agonist provided a significant reduction in the MAS compared with the placebo approach (P<.001). There was no significant change in the H/M ratio or the electromyographic response amplitude after any of the stimulation methods, whereas stimulation of the antagonist muscle resulted in a significant reduction in the ankle angle at which the electromyographic response started, compared with the placebo approach (P<.037). CONCLUSIONS: Triceps surae stimulation reduces the MAS for that specific muscle, whereas the angle at which the reflex starts changes after antagonist stimulation.     

High incidence of absent nerve conduction in older patients with bilateral carpal tunnel syndrome

INTRODUCTION

Carpal tunnel syndrome has been reported by some to have a less satisfactory outcome in older patients following surgery. However, this impression is not supported by other investigators but no objective explanation has been suggested for these differences. In our department, such patients are routinely treated with night wrist splints and, if this is unsatisfactory, they are investigated with nerve conduction studies prior to surgery.

PATIENTS AND METHODS

This paper reports the neurophysiological outcome in a young (< 40 years of age) and an older (> 60 years of age) group of patients with clinical bilateral carpal tunnel syndrome who did not benefit from splints.

RESULTS

The results showed that both the motor and sensory conduction speeds are significantly lower in the older age group. More importantly in the older group, half had one or more hands where the sensory conduction was absent. In four out of these 10 patients this finding was bilateral and three patients had unilateral absent motor conduction. In the younger group, no patient had absent conduction.

CONCLUSIONS

Poor surgical outcome in some older patients may be because of irreversibly damaged nerves prior to surgery and pre-operative neurophysiology is, therefore, recommended both for clinical and medicolegal reasons.     

A new tool for assessing human movement: The Kinematic Assessment Tool

The study of human behaviour ultimately requires the documentation of human movement. In some instances movements can be recorded through a simple button press on a computer input device. In other situations responses can be captured through questionnaire surveys. Nevertheless, there is a need within many neuroscience settings to capture how complex movements unfold over time (human kinematics). Current methods of measuring human kinematics range from accurate but multifarious laboratory configurations to portable but simplistic and time-consuming paper and pen methods. We describe a new system for recording the end-point of human movement that has the power of laboratory measures but the advantages of pen-and-paper tests: the Kinematic Assessment Tool. KAT provides a highly portable system capable of measuring human movement in configurable visual-spatial tasks. The usefulness of the system is shown in a study where 12 participants undertook a tracing and copying task using their preferred and non-preferred hand. The results show that it is possible to capture behaviour within complex tasks and quantify performance using objective measures automatically generated by the KAT system. The utility of these measures was indexed by our ability to distinguish the performance of the preferred and non-preferred hand using a single variable.