Levels Of Stimulation Intensity Research Articles

Usefulness of electronic stimulation in restless legs syndrome: a pilot study

Purpose This study aims to investigate the effect of electronic stimulation (ES) as a non-pharmacological treatment in restless legs syndrome (RLS). Methods This is a randomized, single-blind study. A total of 46 patients were included, consisting of an active group and a sham group with 22 and 24 members, respectively. The stimulation was administered to bilateral lower legs using the tapping mode (3 Hz) on a handheld ES device, and symptom changes were measured in both groups. The effects of the stimuli were analyzed with repeated measures ANOVA. Results The symptom severity was significantly reduced in the active group, and showed significant interaction effects in the time * group (F = 4.441, p = 0.031). Although both the active and sham groups reported improved symptoms upon receiving longer periods of treatment, the effect of the ES was greater in the active group. Conclusions ES treatment resulted in symptom improvement when using ideal levels of stimulation intensity. ES can be considered as a non-pharmacological treatment option for RLS.

Effects of Functional Electrical Stimulation Intensity Level on Corticomuscular Coherence during Action Observation

Purpose: This study examined the effects of changes in the intensity of Functional Electrical Stimulation (FES) on CorticoMuscular Co herence (CMC) during action observation. This paper presents a neurophysiological basis for the effective intensity of FES. Methods: Twenty-seven healthy volunteers were asked to observed a video with FES. The FES was provided with a sensory stimulation level, nerve stimulation level, and motor stimulation level. Simultaneously, an electroencephalogram (EEG) of the sensorimotor cortex and electromyogram (EMG) from the wrist extensor muscle were recorded. The peak CMC and average CMC were analyzed to compare the differences caused by the FES intensity. Results: The peak CMC showed a significant increase in the alpha band during motor stimulation (p<0.05). The average CMC showed a significant increase in the beta band during motor stimulation (p<0.05). Conclusion: The intensity of FES, which causes actual movement, increased the CMC during action observation. These results show that the intensity of the FES can affect the functional connection between the sensorimotor cortex and muscle.

Seismic Design of Steel Structures with Special Flexural Frame Based on Performance by Durability Method

Equivalent static, response spectrum and time history analysis are the well-known analysis methods that traditionally proposed. These methods are highly accurate but requires a great deal of time to match accelerations and the number of analyses, in the other words these methods are time consuming methods. Hence recently the structures are investigated using the durability time method, which plays an essential role in reducing the number of analyses that needs to be created; In fact, the durability time method is a new method of seismic analysis that is presented with a minimum number of time histories analysis. In this method the structure is placed under the influence of an increasing dynamic stimulation, structural response has been investigated over time and evaluated according to the corresponding response to different levels of stimulation intensity, strengths and weaknesses, and structural performance. In this study, steel folding frameworks with 5, 10 and 15 floors were investigated under two analytical methods (Time durability and Time histories methods). At first, the frameworks will be exposed under history of Imperial Governor, Kobe and Lumaprita earthquakes and analysis by finite element software ABAQUS. Then, based on the three analytical functions, the durability is investigated and the results are compared with each other. Finally, the behavior of the structures discussion and conclusion. The results show that the durability analysis method for earthquakes with higher intensity and time is more efficient, and for the Time-less earthquakes by time history method parametrically have a parametrical difference of 5%.

Evaluation Of ES-induced Fatigue In Relation To Muscle Size And Fiber Recruitment

Electrical stimulation (ES) has been used to strengthen muscles in athletic training and rehabilitation programs. ES is an effective stimulus to increase muscle force by evoking contraction via the application of electrical current. However, fast neuromuscular fatigue development limits its application in the clinical setting. The rapid fatigue onset has been attributed to differences in ES parameters and motor unit (MU) recruitment pattern compared to voluntary contractions. PURPOSE: To evaluate the ES intensity needed to generate predetermined force in two muscles of varying size and fiber type (proportion of type I and type II fibers) during isometric contractions, as well as to investigate the fatigue characteristics and time to fatigue under these conditions. METHODS: ES-induced fatigue was initiated in the small, type I abductor pollicis brevis (APB) and large, type II vastus lateralis (VL) muscles of three healthy individuals (mean age: 22.33±2.36 years). ES was delivered at three frequencies (10, 30, 50Hz) in randomized order, with a duty cycle of 4s on/4s off, pulse duration of 300μs, and stimulation intensity level required to achieve an initial tetanic force equal to 25% of the pre-fatigue MVC. ΔMVC values, required intensity, and %drop in force during ES were compared between APB and VL. RESULTS: ΔMVC values were relatively low, though higher in the VL with no apparent association to frequency (VL mean ΔMVC: 10Hz = 16.8N; 35Hz = 28.3N; 50Hz = 6.0N, APB mean ΔMVC: 10Hz = -4.0N; 35Hz = 0.32N; 50Hz = 2.38N). ES at 10Hz requires a higher intensity to achieve 25%MVC force than at 35Hz or 50Hz for both the APB (mean intensity: 10Hz = 20.3mA; 35Hz = 17mA; 50Hz = 15.3mA) and VL (mean intensity: 10Hz = 54mA; 35Hz = 46.7mA; 50Hz = 46.7mA). The %drop in force was greatest at 50Hz (APB = 21% drop; VL = 18% drop), then 35Hz (APB = 17.5% drop; VL = 19.9% drop), then 10Hz (APB = 14.75% drop; VL = 16.35% drop) at the first quartile of time to fatigue, while the second quartile values were consistent among frequencies. CONCLUSIONS: Fatigue is a major limiting factor for application of ES in sports injury and rehabilitation. Muscles with different fiber type composition respond differently to stimulation frequencies and fatigue development. These differences should be considered when developing treatment plans. Supported by NSF EFRI 1332329.

P174 Effects of transcranial direct current stimulation (tDCS) intensity on vigilance performance

Introduction Previously, evidence suggests that transcranial direct current stimulation (tDCS) can preserve vigilance performance for up to 6 h. However, the stimulation paradigm utilized in these studies may not be optimal. For example, Cuypers et al. (2013) found there may be more pronounced performance effects at lower tDCS intensities. The goal was to elucidate these effects and attempt to uncover biomarkers that correlate with performance. Objectives The purpose of this effort was to (1) quantify the effects of transcranial direct current stimulation (tDCS) intensity on vigilance performance, (2) measure the duration of tDCS after effects on vigilance, and (3) survey changes in biomarkers found in breath and establish correlations between biomarkers and tDCS intensity and vigilance performance. Patients & methods A within subjects experimental design was utilized with factor “stimulation intensity level” tested at 6 levels. The levels included tDCS at: (1) 0.5 mA, (2) 1 mA, 3) 1.5 mA, (4) 2 mA, (5) Sham, and (6) no electrodes/stimulation applied for 30 min. Participants performed a vigilance test during each visit. On each visit, they arrived at 0800 and performed the vigilance task while receiving one of the 6 randomized tDCS treatments. They provided breath samples before and after the test. Participants returned at 1600 for follow-up testing (no tDCS) and provided another breath sample. Results A one-way ANOVA revealed there was a significant effect of tDCS intensity on vigilance target detection accuracy ( p Conclusions The evidence suggests tDCS applied at 2 mA significantly improves vigilance performance. However, this effect is completely gone 8 h later. This supports previous evidence suggesting the effect of tDCS on vigilance is approximately 6 h. Additionally, a protein in breath was discovered whose concentrations correlate with performance and tDCS intensity. Hence, this could be a biomarker capable of monitoring operator vigilance state.

EP 65. DBS-induced alpha desynchronization in the subthalamic nucleus of PD patients

Question Deep brain stimulation of the subthalamic nucleus (STN DBS) has developed into a standard therapy for treatment refractory stages of Parkinson’s disease (PD). Oscillatory components play an important role in the functioning of the brain through the control of neuronal firing ( Engel and Fries, 2010 ). The power of the beta-band (12–30 Hz) in the STN is an informative biomarker for PD. It is reduced under L-Dopa medication and DBS ( [Kuhn et al., 2008] , [Bronte-Stewart et al., 2009] ). However, the impact of DBS onto other oscillatory components and their relevance as PD biomarkers is less explored ( [Rosa et al., 2014] , [Beudel and Brown, 2016] ). In the present contribution, we investigate the effect of DBS upon the power of the alpha-band (8–12 Hz). Methods For three PD patients (S1–S3), intraoperative microelectrode recordings were acquired as part of the implantation procedure for DBS. For one hemisphere three MER electrodes were lowered into the target region simultaneously (anterior, central, lateral) over a Ben’s gun approach (FHC, USA). Stimulating on a singular macro-tip of the telescopic FHC electrode (FHC, USA) with increasing currents allowed to record signals with 5 kHz sampling rate from two other MER positions. Overall, seven recording constellations were measured. Starting with stimulation off, stimulation intensity was ramped up in steps of 0.5 mA and 1 mA. Each intensity was delivered for at least 20 s at a rate of 130 Hz. Five out of seven recording constellations showed a clear alpha baseline activity prior to stimulation onset. These were used for an offline bandpower analysis. The analyzed frequency band was centered onto the individual alpha frequency of each patient and had a width of 3 Hz. The log-bandpower intensity was extracted from 10 non-overlapping consecutive time windows of one second duration each, overall covering the interval of [0,10]s relative to the onset of a novel stimulation intensity. To represent baseline activity, ten values were extracted from the interval [−15, −5]s relative to the stimulus onset. Results For 2 out of 3 patients and 2 out of 5 recording constellations (see plots for S2 left and S3 right in Fig. 1 ), DBS onset caused a significant reduction of the alpha power relative to the baseline activity. Increasing the stimulation current (and overall stimulation time) beyond 2 mA for S2 and beyond 5 mA for S3 lead to a rebound effect. The resulting higher alpha power of higher stimulation intensities, however, still remained significantly below the baseline level. For recordings of S1 [left] and S3 [left], an alpha reduction was observed after stimulation onset as well, but it did not reach significance over all levels of stimulation intensity. Conclusions Alpha band power of the STN may represent a biomarker for PD, which is sensitive to DBS and deserves further investigation along with the classical biomarkers beta and gamma. The rebound effect observed in this pilot study, however, suggests to test nonlinear analysis methods to assess the alpha activity.

A test method for quantification of stimulus-induced depression effects on perceptual threshold in epiretinal prosthesis

As part of a clinical trial, an investigational epiretinal implant (IMI Intelligent Medical Implant) was implanted in a retinitis pigmentosa patient. The prosthesis was wirelessly controlled by a visual interface containing a microcamera, providing wireless data and energy transmission. Forty-nine (49) electrodes were used for pattern recognition. This study examined the changes of perceptual thresholds over time and its relation to long-term stimulation. The goal of the study was to introduce stimulus-related depression of perceptual threshold (StirDepth) measurements as a method to gain further insight into the safety profile of electrical stimulation. The perceptual threshold was defined as the level of stimulation intensity at which a phosphene perception with a probability of 50% was detected using the Best-PEST method. StirDepth was measured by comparing the threshold changes immediately before and after a stimulation session of using three active electrodes and one passive electrode, which served as control. The initial threshold of the day remained stable over the observed period. In StirDepth measurement all thresholds raised significantly after the stimulation sessions. The threshold increase of the active electrodes never exceeded that of the inactive control electrode. StirDepth measurement is feasible in epiretinal implants. The prolonged stimulation raised no safety concerns in the patient. The threshold increase of both the active electrodes and the control electrode leads one to hypothesise that cognitive or neurophysiological effects are the cause rather than the desensitizing of the retinal network or incipient retinal damage.

Combined effect of motor imagery and peripheral nerve electrical stimulation on the motor cortex

Although motor imagery enhances the excitability of the corticospinal tract, there are no peripheral afferent inputs during motor imagery. In contrast, peripheral nerve electrical stimulation (ES) can induce peripheral afferent inputs; thus, a combination of motor imagery and ES may enhance the excitability of the corticospinal tract compared with motor imagery alone. Moreover, the level of stimulation intensity may also be related to the modulation of the excitability of the corticospinal tract during motor imagery. Here, we evaluated whether a combination of motor imagery and peripheral nerve ES influences the excitability of the corticospinal tract and measured the effect of ES intensity on the excitability induced during motor imagery. The imagined task was a movement that involved touching the thumb to the little finger, whereas ES involved simultaneous stimulation of the ulnar and median nerves at the wrist. Two different ES intensities were used, one above the motor threshold and another above the sensory threshold. Further, we evaluated whether actual movement with afferent input induced by ES modulates the excitability of the corticospinal tract as well as motor imagery. We found that a combination of motor imagery and ES enhanced the excitability of the motor cortex in the thenar muscle compared with the other condition. Furthermore, we established that the modulation of the corticospinal tract was related to ES intensity. However, we found that the excitability of the corticospinal tract induced by actual movement was enhanced by peripheral nerve ES above the sensory threshold.

Effect of Neuromuscular Electrical Muscle Stimulation on Energy Expenditure in Healthy Adults

Weight loss/weight control is a major concern in prevention of cardiovascular disease and the realm of health promotion. The primary aim of this study was to investigate the effect of neuromuscular electrical stimulation (NMES) at different intensities on energy expenditure (oxygen and calories) in healthy adults. The secondary aim was to develop a generalized linear regression (GEE) model to predict the increase of energy expenditure facilitated by NMES and identify factors (NMES stimulation intensity level, age, body mass index, weight, body fat percentage, waist/hip ratio, and gender) associated with this NMES-induced increase of energy expenditure. Forty sedentary healthy adults (18 males and 22 females) participated. NMES was given at the following stimulation intensities for 10 minutes each: sensory level (E1), motor threshold (E2), and maximal intensity comfortably tolerated (E3). Cardiopulmonary gas exchange was evaluated during rest, NMES, and recovery stage. The results revealed that NMES at E2 and E3 significantly increased energy expenditure and the energy expenditure at recovery stage was still significantly higher than baseline. The GEE model demonstrated that a linear dose-response relationship existed between the stimulation intensity and the increase of energy expenditure. No subject’s demographic or anthropometric characteristics tested were significantly associated with the increase of energy expenditure. This study suggested NMES may be used to serve as an additional intervention for weight loss programs. Future studies to develop electrical stimulators or stimulation electrodes to maximize the comfort of NMES are recommended.

Perceptual threshold and neuronal excitability as long‐term safety evaluation in retinal implants

Abstract Purpose Despite the recent progress of retinal implants the effects of continuing stimulation still remains an open issue. Sofar the established safety limits are based on laboratory findings and clinical observations.This study examined the changes of perceptual threshold over time and its relation to longterm stimulation. The goal of the study was to establish stimulus induced depression of neuronal excitability (SIDNE) measurements as a method to gain further insight on the safety profile of epiretinal implants. Methods As part of a clinical trial a prototype of an epiretinal implant ( IMI Intelligent medical implant) with 61 active platinum electrodes was implanted in a retinitis pigmentosa (RP) patient. The threshold was defined as the level of stimulation intensity at which the patient had a visual perception in a defined probability of 50% using the Best‐PEST method. SIDNE is measured by comparing the thresholds of two electrodes obtained at the beginning and at the end of a stimulation session. One electrode is actively used during the stimulation, the other remains passive. The stimulation is regarded as safe when the threshold raise of active electrodes is not significantly higher than of the inactive electrode. Results The threshold remained stable over the observation period. The threshold raise of the active electrodes never exceeded that of the inactive electrode. Conclusion SIDNE measurement is feasible in epiretinal implants. After prolonged stimulation the thresholds may increase by more than 16 % due to the patients fading concentration, however the stimulation was performed within the safety limits.

Maximal versus submaximal intensity stimulation with variable patterns

It is essential to determine optimal parameters of stimulation to maintain muscle force during neuromuscular electrical stimulation (NMES). Protocols that increase in frequency and include doublets can prolong force output over time. However, stimulation intensity level could differentially affect muscle force output during variable-frequency NMES. We compared three intermittent stimulation patterns at maximal and submaximal intensities of stimulation of the median nerve: (1) a constant 20-HZ pattern; (2) 90 s at 20 HZ followed by a 90-s increase from 20 to 40 HZ; and (3) 90 s at 20 HZ followed by 90 s of doublets at 20 HZ. At submaximal intensities, the doublet pattern produced the highest overall force-time integral (FTI). At maximal intensities, the doublet pattern produced the lowest FTI and the increasing frequency pattern produced the least amount of fatigue. Thus, double-pulse stimulation was more effective during submaximal than maximal intensity NMES. These data demonstrate that intensity level must be taken into consideration when programming frequency patterns for NMES devices.

Is mechanical pain threshold after transcutaneous electrical nerve stimulation (TENS) increased locally and unilaterally? A randomized placebo‐controlled trial in healthy subjects

It is not fully understood how transcutaneous electrical nerve stimulation (TENS) intensity affects mechanical pain threshold. Sixty-six healthy volunteers (13 male, 53 female; 132 hands) without prior experience of TENS participated in the study, which comprised a randomized single-blind controlled trial. TENS was administered for 20 minutes through electrodes (25 x 25 mm) placed on the hands and forearms with a fixed frequency of 100 Hz and pulse duration of 150 micros. TENS intensity was randomized and allocated in a concealed manner so that one arm received TENS with stimulation intensity set at participants' subjective sensory threshold and the other received TENS with stimulation intensity continuously adjusted by physiotherapists to a strong but comfortable non-painful stimulation. Observers were blinded to stimulation intensity levels. Mechanical pain threshold increased significantly, by a mean total of 0.79 kg/cm2 (95% confidence interval [95% CI]: 0.54-1.04) (p < 0.001) on the strong but comfortable non-painful stimulation side. The mean change in mechanical pain threshold on the sensory threshold side was 0.19 kg/cm2 and did not reach statistical significance (95% CI-0.15 to 0.51). The mean stimulation intensity level for sensory threshold was 6.7 mA (95% CI: 5.65 to 7.83) which was significantly lower (p < 0.001) than the mean stimulation intensity for the strong stimulation, which was 20.5 mA (95% CI 16.6 to 24.4), respectively. The strong stimulation levels were, on average, 3.05 times higher than sensory threshold, but individual variations were large (range 1.2-6.1). TENS administered at a strong but comfortable non-painful stimulation intensity increases mechanical pain threshold ipsi-laterally in healthy subjects, whereas TENS administered at sensory threshold intensity does not. TENS may be ineffective if electrodes are placed contralaterally or distant to the pain site and if stimulation intensity levels are not titrated to subjective strong levels. Further clinical trials are needed to clarify if these findings may also be generalized to populations of chronic pain sufferers.

Morphology and physiology of lamina I neurons of the caudal part of the trigeminal nucleus

It has been suggested that in mammals, trigeminal lamina I neurons play a role in the processing and transmission of sensory information from the orofacial region. We investigated the physiological and morphological properties of trigeminal subnucleus caudalis (Sp5C) lamina I neurons in slices prepared from the medulla oblongata of 13- to 15-day-old postnatal rats using patch-clamp recordings and subsequent biocytin–streptavidin–Alexa labeling. Twenty-five neurons were recorded and immunohistochemically stained. The Sp5C lamina I consisted of several types of neurons which, on the basis of their responses to somatic current injection, can be classified into four groups: tonic neurons, which fired throughout the depolarizing pulse; phasic neurons, which expressed an initial burst of action potentials; delayed onset neurons, which showed a significant delay of the first action potential; and single spike neurons, characterized by only one to five action potentials at the very beginning of the depolarizing pulse even at high levels of stimulation intensity. Electrical stimulation of the spinal trigeminal tract evoked AMPA receptor-mediated excitatory postsynaptic currents (EPSC) exhibiting a strong polysynaptic component. AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSC) were characterized by a 10–90% rise time of 0.50±0.06 ms and a decay time constant of 2.5±0.5 ms. The kinetic properties of NMDA receptor-mediated EPSCs were measured at +40 mV. The 10–90% rise time was 8±2 ms and the deactivation time constants were 94±31 and 339±72 ms, respectively. Intracellular staining and morphological analysis revealed three groups of neurons: fusiform, pyramidal, and multipolar. Statistical analysis indicated that the electrophysiological properties and morphological characteristics are correlated. Tonic and phasic neurons were fusiform or pyramidal and delayed onset and single spike neurons were multipolar. Our results show that both the physiological and morphological properties of Sp5C lamina I neurons exhibit significant differences, indicating their specific integration in the processing and transmission of sensory information from the orofacial region.

Evidence of oesophageal stimulus dependant response in the human anterior cingulate and primary somatosensory cortex

S. J. Coen, L. J. Gregory, L. Yaguez, D. Hall, E. Amaro, S. Smale, S. C. Williams, D. G. Thompson, Q. Aziz Institute of Psychiatry, London, United Kingdom, University of Manchester, Manchester, United Kingdom, Kings College Hospital, London, United Kingdom Synopsis Studies investigating the neural correlates of non-painful and painful oesophageal stimulation have produced variable results. Furthermore, regions involved in the encoding of stimulation intensity are not fully understood. Using a standardised method for establishing quantifiable intensities of oesophageal stimulation, the neural correlates of four levels of oesophageal stimulation were investigated. Stimulation resulted in a complex pattern of cerebral activation that was similar across different levels of stimulation intensity. The anterior cingulate gyrus (ACG) and primary somatosensory cortex (SI), both showed evidence of stimulus dependent response, which may be a result of encoding of intensity and unpleasantness or levels of attention. Introduction Although the functional correlates of non-painful and painful visceral stimulation have previously been investigated (1), the results have been variable. Furthermore, despite the fact that functional Magnetic Resonance Imaging (fMRI) can be used to objectively quantify perception of visceral sensation, regions involved in the encoding of stimulation intensity are not fully understood. By using a standardised method for determining varying intensities of oesophageal stimulation, the neural correlates of four levels of stimulation and the regions involved in encoding of intensity can be investigated. Aims: The purpose of this study was to determine the neural correlates of four intensities of oesophageal stimulation as well as investigating regions involved in the encoding of stimulation intensity, using fMRI. Methods Subjects: 7 healthy volunteers (5 male, mean age 22 years, +7 months) participated in the study. All subjects gave informed, written consent prior to intubation and scanning. The study was approved by our local ethics committee for research. Oesophageal stimulation: a standard manometry catheter with a silicone balloon attached was passed trans-nasally into the lower oesophagus (35cm from the nostril). The catheter was attached to a pump that inflated the balloon with air at regular intervals. The experiment examined four conditions. During each condition one of four balloon distension intensities, obtained by dividing the difference between sensory (the point at which volunteers first perceived a sensation) and pain thresholds (100%) into 4 levels at 25% increments (i.e. 25%, 50%, 75% and 100%), was used to stimulate the distal oesophagus. A modified block design was employed for each intensity, where each “active” and “rest” phase was repeated five times. Behavioural data measuring the subjective perception of the stimulus (0 = non-painful, 5 = discomfort, 10 = extreme pain) was acquired after each active epoch, using visual analogue scales (VAS). fMRI acquisition: Functional Magnetic Resonance Imaging was performed using a GE Neuro-optimised 1.5 Tesla system (General Electric, Milwaukee WI, USA), based at the Maudsley Hospital, London. Sixteen 7mm slices (0.7 mm gap) parallel to the bicomissural plane were acquired, with a repetition time (TR) of 3 seconds and an echo time (TE) of 40ms, flip angle 90o. A total of 122 T2* weighted images per slice, depicting BOLD contrast (Ogawa et al, 1990) were collected over a six minute and six second period of continuous acquisition during which, subjects received localised phasic distensions to the oesophagus. This procedure was performed on four occasions to collect data for four levels of intensity of oesophageal distension. Image Analysis: Spatially realigned BOLD responses were modelled as the weighted sum of the input function convolved with two Poisson functions. A goodness of fit statistic was computed and a voxel-wise inference was carried out non-parametrically. At the group level, individual statistic maps were transformed into standard stereotactic space and median activation images constructed. Results Mean VAS scores increased progressively with increasing stimulation intensities (χ2 = 10.9, df 3, P=0.001), (mean VAS (+SEM); 25% = 3+0.80, 50% = 3.68+0.91, 75% = 5.67+0.79, 100% = 7.34+0.48). In response to 100% and 75% stimulation intensity, activation was seen in the anterior cingulate gyrus (ACG) (BA 24, 32), bilateral insula, supplementary motor area (SMA), thalamus, bilateral primary and secondary sensory cortices (SIS 114: 559-578 2. Lowy AD. Central Autonomic Pathways. In: Lowey AD, Spyer KM eds. Central regulation of autonomic function (1990). New York: Oxford University Press, 4:88-103. 3. Porro CA, Cettolo V, Pia Francescato M, Baraldi P. Temporal and intensity coding in of pain in the human cortex. Journal neurophysiology 1998;80:3312-3320. 4. Tolle TR, Kaufmann T, Siessmeier T, Lautenbacher S, Berthele A, Munz F, Zieglgeansberger W, Willoch F, Schwaiger M, Conrad B, Bartenstien P. Region specific encoding of sensory and affective components of pain in the human brain: a positron emission tomography correlation analysis. Ann Neurol 1999;45: 4047. 5. Vogt BA, Watanabe H, Grootoonk S, Jones AKP. Topography of diprenorphine binding in human cingulate gyrus and adjacent cortex derived from co-registered PET and MR images. Human Brain Mapping 1995; 3:1-12.

Sometimes you see them, sometimes you don't: IPSCs in the rat superficial superior colliculus.

Superficial superior colliculus (SSC) neurones were voltage-clamped and the current-voltage relationship of synaptically evoked currents analyzed in vitro. A strong interplay between excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) was identified. Glutamate receptor antagonists not only fully blocked EPSCs but IPSCs were also frequently reduced by the specific d,l,-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist (by 66.9%), indicative of glutamate-driven inhibitory projections. The GABA(A )receptor antagonist bicuculline enhanced EPSCs and either abolished or reduced (by 79.3%) IPSCs. The GABA(C) receptor antagonist 1,2,5,6-tetrahydro-(pyridin-4-yl)methylphosphinic acid decreased IPSCs in 80% of cells tested (by 24.1%), but had no effect on EPSCs. Varying the recording conditions influenced postsynaptic currents. At a holding potential of -60 mV, IPSCs were generally produced with intracellular chloride concentrations of both 5 and 10 mM (total n=24/30). However, with perforated-patch recordings using gramicidin, IPSCs were less frequently encountered (n=5/21), suggesting a higher intracellular chloride concentration in a large proportion of SSC neurones. Further assessment of experimental conditions revealed that two frequently used sodium channel blockers, QX-314 (bromide salt, intracellular) or tetrodotoxin (extracellular), shifted the IPSC reversal potential towards more positive values. Hence, IPSCs were not encountered at -60 mV in their presence. The level of stimulation intensity (minimal or maximal) did not influence IPSC production in these conditions. Thus, the current study describes the pharmacological properties of PSCs in the SSC and highlights the impact of experimental conditions on synaptic transmission, which requires consideration for past and present data reported in this preparation.

Spectroscopic Analysis of Neural Activity in Brain: Increased Oxygen Consumption Following Activation of Barrel Cortex

This research investigates the hemodynamic response to stimulation of the barrel cortex in anaesthetized rats using optical imaging and spectroscopy (Bonhoeffer and Grinvald, 1996; Malonek and Grinvald, 1996; Mayhew et al., 1999). A slit spectrograph was used to collect spectral image data sequences. These were analyzed using an algorithm that corrects for the wavelength dependency in the optical path lengths produced by the light scattering properties of tissue. The analysis produced the changes in the oxy- and deoxygenation of hemoglobin following stimulation. Two methods of stimulation were used. One method mechanically vibrated a single whisker, the other electrically stimulated the whisker pad. The electrical stimulation intensity varied from 0.4 to 1.6 mA. The hemodynamic responses to stimulation increased as a function of intensity. At 0.4 mA they were commensurate with those from the mechanical stimulation; however, the responses at the higher levels were greater by a factor of ∼10. For both methods of data collection, the results of the spectroscopic analysis showed an early increase in deoxygenated hemoglobin (Hbr) with no evidence for a corresponding decrease in oxygenated hemoglobin (HbO2). Evidence for increased oxygen consumption (CMRO2) was obtained by converting the fractional changes in blood volume (Hbt) into estimates of changes in blood flow (Grubb et al., 1974) and using the resulting time course to scale the fractional changes in Hbr. The results show an early increase CMRO2 peaking ∼2 s after stimulation onset. Using these methods, we find evidence for increased oxygen consumption following increased neural activity even at low levels of stimulation intensity.

Magnetic transcranial stimulation: dissociation of excitatory and inhibitory mechanisms in acute strokes

Magnetic transcranial stimulation was applied to 12 normal subjects and 30 patients (24 acute and 6 chronic) with hemiparesis contralateral to an ischaemic stroke. In the 24 acute patients, the recordings were made at the 7th day on the contralateral first dorsal interosseous (FDI) muscle. We studied the amplitudes of the motor evoked potential (MEP) responses and the post-MEP silent period durations (SPD) at different levels of stimulation intensity (SI) and voluntary isometric contraction (VIC). The evolution of these parameters was matched to the clinical status of the 24 acute patients evaluated 7, 30 and 90 days after the stroke (D 7, D 30 and D 90). Our results may be summarised as follows: (1) in all cases, the MEP-amplitudes increased with facilitation and SI; (2) in the normal subjects and in patients who did recover, the SPD augmented with stronger SI but was found to be independent on the strength of voluntary contraction; (3) in the acute patients with poor recovery, as well as in the chronic patients with spasticity, the SPD decreased with stronger VIC. It may be concluded that MEP-amplitudes and SPD patterns point out excitatory and inhibitory mechanisms which may be differently affected in cerebral injuries. The association between shortening of the SPD with increasing VIC of the target muscle and poor recovery of the stroke after 3 months could be a useful clinical test to predict eventual recovery early after a stroke.

Submaximal stimuli activate different nerve fiber populations at different sites.

Theoretically, the largest and fastest nerve fibers are preferentially stimulated with submaximal stimuli. However, it is also well known that intraneural fascicular topography changes substantially along a proximal to distal axis. Because of this change in fascicular topography, we hypothesized the percutaneous submaximal stimuli applied to a nerve at different locations would stimulate different subpopulations of large fibers. We performed a series of collision studies by stimulating the ulnar nerve submaximally at proximal and distal sites at varying levels of stimulation intensity from motor threshold to supramaximal stimulation. The results suggest that variation in intraneural topography at different sites allows different large diameter nerve fiber subpopulations to be activated at submaximal stimuli, and emphasizes the importance of supramaximal stimulation to determine a valid conduction velocity.

Optimization of single electrode tactile codes.

The effects of a frequency modulated electrocutaneous signal's (code's) characteristics on the interpretability of the signal were investigated using an electrocutaneous tracking approach. The characteristics investigated include the functional relationship (exponential and hybrid) between an informational signal and the stimulation frequency, the range of stimulation (2-50 Hz and 2-100 Hz), and the impact of pulse width compensation on a code's efficacy. The interpretability of six different single bipolar electrode codes was examined by 30 subjects using a balanced incomplete block experimental design. Codes with exponentially shaped transfer functions resulted in generally lower electrocutaneous tracking errors than codes utilizing hybrid-shaped transfer functions. Hybrid codes had a transfer function that was linear in the lower frequency range and exponential in the higher frequency range. Codes with a 2-100 Hz frequency range were interpreted better than codes with a 2-50 Hz frequency range. The use of pulse width compensation to maintain a more even level of stimulation intensity had a slightly negative effect on the subjects' abilities to cutaneously track the information signal.