Effects of tDCS on spontaneous spike activity in a healthy ambulatory rat model

BackgroundThe neurophysiological effects of transcranial direct current stimulation (tDCS) are typically described with respect to changes in cortical excitability, defined by using transcranial magnetic stimulation pulses to determine changes in motor evoked potentials. However, how individual cortical neurons change firing patterns under the influence of tDCS is largely unknown. While the relatively weak currents produced in the brain by tDCS may not be adequate to directly depolarize neuronal membranes, ongoing neuronal activity, combined with subthreshold changes in membrane polarization might be sufficient to alter the threshold for neural firing.ObjectivesThe purpose of this study was to determine the effects of tDCS on neurophysiological activity in motor cortex of freely moving, healthy rats.MethodsIn nine healthy, ambulatory rats, each studied under six different stimulation conditions varying in current intensity (maximum current density = 39.8 A/m² at 0.4 mA) and polarity (anodal or cathodal), neural activity was analyzed in response to 20 min of tDCS applied through bone screws insulated from the overlying scalp.ResultsAfter analysis of 480 multi-unit channels that satisfied a rigid set of neurophysiological criteria, we found no systematic effect of tDCS stimulation condition on firing rate or firing pattern. Restricting the analysis to the most responsive units, subtle, but statistically significant changes occurred only in the highest intensity anodal condition.ConclusionsThese results confirm that at current densities typically used in human or animal tDCS studies, observed effects of tDCS are likely to occur via mechanisms other than direct neuronal depolarization.     

Electrophysiological findings in a case of congenital lower limb hypoplasia

Limb hypoplasia is a rare congenital disorder. Is usually encountered in patients with segmental spinal dysplasia (SSD), in progressive facial hemiatrophy (Parry-Romberg syndrome) and in other rare conditions. We performed an extensive electrophysiological study in a 18-year-old female with congenital left lower limb hypoplasia, but with no motor and sensory deficit. Electrophysiological investigation comprised motor and sensory nerve conduction velocities, needle EMG, quantitative sensory studies and SEP with standard techniques. The study showed markedly involved large diameter peripheral sensory nerve fibers and intact motor and small diameter peripheral sensory nerve fibers. Extensive electrophysiological investigation in cases of limb hypoplasia has not been previously performed. In this patient congentital hypoplasia of the muscles also involved the peripheral large diameter sensory nerve fibers.     

Semi-quantitative electromyography as a predictor of nerve transfer outcome

ObjectivesEvaluate correlation between donor nerve semi-quantitative electromyography (sqEMG) and strength outcome in nerve transfer surgery.MethodsRetrospective review of pre-operative donor nerve semi-quantitative neurophysiology and post-operative recipient muscle force after at least one-year follow-up. The semi-quantitative technique is the average motor unit number estimate associated with needle recorded interference patterns in the donor muscle (IP-AMUNE), which was correlated with hand-held manometry, standardized as a percent of the contralateral arm, using multivariable linear regression with backward selection.ResultsTwenty-eight nerve transfer cases were included. The correlation between the donor nerve IP-AMUNE and the recipient muscle strength was moderate to strong and highly significant (r = 0.67, p < 0.001). Medical Research Council (MRC) grading did not predict strength (p > 0.54).ConclusionsIP-AMUNE is a good predictor of strength after nerve transfer surgery and should be considered in the evaluation and planning of patients undergoing nerve transfer to aid in donor nerve selection.SignificanceIP-AMUNE may significantly benefit those undergoing nerve transfer surgery for the restoration of movement.     

Peripheral motor neuropathy caused by excessive intake of dapsone (Avlosulfon)

Summary A case of selective peripheral motor polyneuropathy caused by excessive intake of dapsone is described. The condition was characterized by a peripheral muscle weakness in all limbs, normal sensitivity and present, although weak, muscle reflexes. Neurophysiologically, low amplitude muscle responses, prolonged distal latencies and reduced motor conduction velocities were found together with electromyographic signs of denervation. Sensory neurography was normal. The patient showed a complete clinical recovery and a marked neurophysiological restitution after termination of the excessive drug intake. The patient was found to acetylate dapsone at a slow rate. The case is compared with those previously reported in the literature.     

Silicon-based microelectrodes for neurophysiology, micromachined from silicon-on-insulator wafers

A process is described for the fabrication of silicon-based microelectrodes for neurophysiology using bonded and etched-back silicon-on-insulator (BESOI) wafers. The probe shapes are defined without high levels of boron doping in the silicon; this is considered as a step towards producing probes with active electronics integrated directly beneath the electrodes. Gold electrodes, of 4μm by 4μm to 50μm by 50μm are fabricated on shanks (cantilever beams) 6μm thick and which taper to an area approximately 100μm wide and 200μm long, which are inserted into the tissue under investigation. The passive probes fabricated have been successfully employed to make acute recordings from locust peripheral nerve.     

灰质异位的功能磁共振成像研究(附3例报告)

目的:对灰质异位进行运动功能的功能磁共振成像研究,探讨异位灰质的神经生理功能及功能磁共振成像在神经外科中的作用。方法:采用功能磁共振成像技术对3例拟行手术治疗的灰质异位且伴癫痫症状的患者进行对指运动任务下的脑区反应观察。结果:2例顶叶灰质异位患者在对侧手指运动时异位灰质内出现明显的反应信号,否定外科手术治疗计划。1例额叶的灰质异位患者异位灰质内未出现反应。结论:异位的灰质可以具有运动中枢功能,对于靠近主要功能中枢的灰质异位患者在手术计划的拟定时要考虑异位灰质是否具有功能。功能磁共振成像可以用于评价灰质异位的神经生理,有助于治疗方法的选择。     

Discrete functional contributions of cerebral cortical foci in voluntary swallowing: a functional magnetic resonance imaging (fMRI) “Go,No-Go” study

Brain-imaging studies have shown that visually-cued, voluntary swallowing activates a distributed network of cortical regions including the precentral and postcentral gyri, anterior cingulate cortex (ACC), insula, frontoparietal operculum, cuneus and precuneus. To elucidate the functional contributions of these discrete activation foci for swallowing, a Go, No-Go functional magnetic resonance imaging (fMRI) paradigm was designed. Brain activation associated with visually-cued swallowing was compared with brain activation evoked by a comparable visual cue instructing the subject not to swallow. Region-of-interest analyses performed on data from eight healthy subjects showed a significantly greater number of activated voxels within the precentral gyrus, postcentral gyrus, and ACC during the Go condition compared to the No-Go condition. This finding suggests that the precentral gyrus, postcentral gyrus, and ACC contribute primarily to the act of swallowing. In contrast, the numbers of activated voxels within the cuneus and precuneus were not significantly different for the Go and No-Go conditions, suggesting that these regions mediate processing of the cue to swallow. Together these findings support the view that the discrete cortical foci previously implicated in swallowing mediate functionally distinct components of the swallowing act.     

The effects of epidural application of allografted nucleus pulposus in rats on cytokine expression, limb withdrawal and nerve root discharge

This study investigated cytokine expression, behavioral and neurophysiologic changes in Lewis rats whose lumbar nerve roots were exposed to nucleus pulposus (NP). Allografted NP or fat was implanted over the left L5 nerve root. Sham rats had no NP or fat implantation. Control rats had no surgery. Rats were allowed to survive for 7 days and were tested daily for hind-paw mechanical and thermal withdrawal response (TWR). Granulation tissue was processed by immunohistochemistry for cytokines—interleukin 1 beta (IL-1), interleukin 6 (IL-6) and tumor necrosis factor (TNF). Neurophysiological response from the L5 nerve roots was also characterized after 7 days. Significant staining density for IL-1, IL-6 and TNF was observed in NP granulation tissue compared with fat and sham (p<0.05). However, there were no significant thermal and mechanical behavioral changes. TWR data computed as percentage-difference scores indicated no significant changes in withdrawal response between the four groups, although NP-treated group showed a trend of decreasing withdrawal latency. Comparison of combined percentage-difference scores revealed increased sensitivity in the NP group on days 4, 5 and 6, 7 when compared with control rats only, with no significant changes in the percentage-difference scores of fat and sham rats when compared to control. Neurophysiologically, the percentage increase in discharge rate in NP-treated rats was higher than control (p<0.05) but not higher than fat and sham rats. These results support the inflammatory nature of NP but offer limited support to NP-mediated thermal behavioral changes.     

Effect of periurethral denervation on smooth muscles of the lower urinary tract

OBJECTIVE: This study was undertaken to determine the effect of periurethral denervation on contractile function of the smooth muscle of the lower urinary tract of the female rat. STUDY DESIGN: Periurethral nerve transection or sham operation was performed in 35 young female rats. Contractile function of the bladder dome and base was determined as a function of time after surgery. Statistical analysis was conducted by Student t test. RESULTS: Periurethral denervation resulted in impaired contractile responses to electrical field stimulation in the bladder base (nerve-transected 45 +/- 11 g/cm 2 ; sham 84 +/- 10 g/cm 2 , P < .05) and dome (nerve-transected 179 +/- 16 g/cm 2 ; sham 334 +/- 29 g/cm 2 , P < .05) 2 weeks after nerve transection. The ability to respond to potassium chloride and the muscarinic agonist, carbachol, and the rates of contraction and relaxation, however, remained intact. Baseline phasic contractile activity was increased significantly in bladders from nerve-transected animals. Maximal field-stimulated contractions of the longitudinal urethra smooth muscle were not altered by periurethral denervation (sham 21 +/- 6 g/cm 2 , nerve-transected 19 +/- 5 g/cm 2 , P = .4). Compromised nerve-mediated contractions of the bladder dome and base improved significantly by 21 days. CONCLUSION: Periurethral nerve transection results in transient impairment of neurogenic contractile responses in the bladder base and dome, though the intrinsic ability of the bladder to contract remains intact. This compromised response of the dome, in conjunction with previous results demonstrating impaired urethral smooth muscle relaxation, suggests that transection of periurethral neurons may have complex effects on the entire lower urinary tract.     

Transcranial magnetic stimulation: studying motor neurophysiology of psychiatric disorders

Rationale. Transcranial magnetic stimulation (TMS) is a noninvasive tool that directly stimulates cortical neurons by inducing magnetic and secondary electric fields. Traditionally TMS has been used to study the motor neurophysiology of healthy subjects and those with neurological disorders.Objective. Given the known motor dysfunctions in many psychiatric disorders supplemental usage of TMS to study the underlying pathophysiology of certain psychiatric disorders and to assess treatment outcomes is underway. Such studies include examination of motor neuronal membrane, corticospinal and intracortical excitability. Our objective is to overview the past findings.Methods. We review the past literature that used TMS as an assessment tool in psychiatric disorders such as schizophrenia, mood disorders, Tourette's syndrome, obsessive-compulsive disorder, attention-deficit hyperactivity disorder, and substance abuse.Results. While the findings are still preliminary due to small sample-size, inconsistent patient population (diagnosis, medication), differences in methodology between research groups, studies restricted to the motor region and possible lack of sensitivity and specificity, the studies are yielding interesting results which could potentially lead to trait- and state-markers of psychiatric disorders.Conclusions. Future studies using TMS alone or in combination with other neuroimaging techniques promise to further expand the application of TMS from studies of motor excitability to higher cognitive functions.