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Stimulus Intensity (stimulus + intensity)
Selected AbstractsThe Comparative Effects of Drive and Test Stimulus Intensity on Myocardial Excitability and VulnerabilityPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1 2000HOWARD S. FRIEDMAN The number and intensity of stimuli that set basic cycle length in cardiac electrophysiological studies can influence the electrical properties assessed by extrastimuli. The relative contribution of drive (S1) and test (S2) stimulus intensity in defining myocardial excitability and vulnerability has not been reported. The purpose of this investigation was to assess this interaction and to determine whether a trial and ventricular findings differed. The effects of S1 and S2 intensity on a trial and ventricular stimulus-intensity-refractory-period curves were determined in open-chest dogs: comparisons were made between curves with S1 intensity varied between diastolic threshold (DT) and 10 mA and S2 intensity maintained at DT and those with S, intensity maintained at DT and S2 intensity varied between DT and 10 mA. S1 -S2 was held constant and S1 -S2 varied. The effects of different stimulation sites, cycle length, number of stimulations, and neural blockade were assessed. S3 intensity amplification shifted atrial stimulus-intensity-refractory period curves in the direction of increased excitability and vulnerability; the changes were, more pronounced than those obtained by modulating S2 intensity. The changes produced by increasing S1 intensity were evident at different cycle lengths and were enhanced by an increased number of stimulations, but were not evident when S1 and S2 were delivered at different atrial sites. Although beta-blockade attenuated the effects of increasing S1 intensity somewhat, the addition of cholinergic blockade virtually abolished it. Ventricular refractoriness was also changed by modulation of S1 intensity, but the changes were less striking. In the atrium, modulation of S1 intensity has greater effects of stimulus-intensity-refractory-period relations than modulation ofS2 intensity; in the ventricle, the converse is true. [source] Cooling Abolishes Neuronal Network Synchronization in Rat Hippocampal SlicesEPILEPSIA, Issue 6 2002Sam P. Javedan Summary: ,Purpose: We sought to determine whether cooling brain tissue from 34 to 21°C could abolish tetany-induced neuronal network synchronization (gamma oscillations) without blocking normal synaptic transmission. Methods: Intracellular and extracellular electrodes recorded activity in transverse hippocampal slices (450,500 ,m) from Sprague,Dawley male rats, maintained in an air,fluid interface chamber. Gamma oscillations were evoked by afferent stimulation at 100 Hz for 200 ms. Baseline temperature in the recording chamber was 34°C, reduced to 21°C within 20 min. Results: Suprathreshold tetanic stimuli evoked membrane potential oscillations in the 40-Hz frequency range (n = 21). Gamma oscillations induced by tetanic stimulation were blocked by bicuculline, a ,-aminobutyric acid (GABA)A -receptor antagonist. Cooling from 34 to 21°C reversibly abolished gamma oscillations in all slices tested. Short, low-frequency discharges persisted after cooling in six of 14 slices. Single-pulse,evoked potentials, however, were preserved after cooling in all cases. Latency between stimulus and onset of gamma oscillation was increased with cooling. Frequency of oscillation was correlated with chamber cooling temperature (r = 0.77). Tetanic stimulation at high intensity elicited not only gamma oscillation, but also epileptiform bursts. Cooling dramatically attenuated gamma oscillation and abolished epileptiform bursts in a reversible manner. Conclusions: Tetany-induced neuronal network synchronization by GABAA -sensitive gamma oscillations is abolished reversibly by cooling to temperatures that do not block excitatory synaptic transmission. Cooling also suppresses transition from gamma oscillation to ictal bursting at higher stimulus intensities. These findings suggest that cooling may disrupt network synchrony necessary for epileptiform activity. [source] CLINICAL STUDY: Abnormalities in cortical and transcallosal inhibitory mechanisms in subjects at high risk for alcohol dependence: a TMS studyADDICTION BIOLOGY, Issue 3-4 2008Kesavan Muralidharan ABSTRACT Central nervous system (CNS) hyperexcitability and a resulting state of behavioral undercontrol are thought to underlie the vulnerability to early-onset alcohol dependence (AD). The aim of this study was to explore the differences in the functioning of cortical inhibitory systems, utilizing transcranial magnetic stimulation (TMS), in subjects at high risk (HR) and low risk (LR) for AD and to examine the relationship between CNS inhibition and behavioral undercontrol. Right-handed HR (n = 15) and LR (n = 15) subjects, matched for age, gender, height, weight and education, were assessed for psychopathology and family history of alcoholism using the Semi-Structured Assessment for the Genetics of Alcoholism and the Family Interview for Genetic Studies. Following single-pulse TMS, an electromyogram recorded from the right opponens pollicis muscle was used to measure the silent periods at different stimulus intensities. HR subjects had significantly shorter contralateral and ipsilateral (iSP) silent periods and a relatively higher prevalence of ,absent' iSP. They had significantly higher mean externalizing symptoms scores (ESS) than LR subjects, and there was a significant negative correlation between iSP duration and ESS. These preliminary findings suggest that HR subjects have relative impairments in corticocortical and transcallosal inhibitory mechanisms. The consequent state of CNS hyperexcitability may be etiologically linked to the excess of externalizing behaviors observed in this population, which is thought to be a predisposition to a higher risk of developing early-onset alcoholism. [source] Task-induced modulation of motor evoked potentials in upper-leg muscles during human gait: a TMS studyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2002Mireille Bonnard Abstract The aim of this study was to determine the relative involvement of the corticospinal (CS) pathway in voluntarily controlled walking compared to unconstrained walking. In the voluntarily controlled walking condition, subjects had to walk at the same speed as in unconstrained walking with a mechanical constraint, which is known to affect specifically the upper-leg muscles. The motor cortex was activated transcranially using a focal magnetic stimulation coil in order to elicit motor evoked potentials (MEPs) in the rectus femoris (RF) and the biceps femoris (BF). The magnetic stimulation was delivered at the end of the swing (at 90% of the cycle duration), when the EMG backgrounds were similar in the two experimental conditions. For each subject in each condition, MEPs were measured for several stimulus intensities in order to establish the input/output (I/O) curve (MEPs amplitude plotted against stimulus strength). The results showed a significant increase in the MEPs amplitude of both the RF and BF in voluntarily controlled walking compared to unconstrained walking, which is the first evidence of cofacilitation of MEPs in antagonist upper-leg muscles during human gait. In conclusion, although a lot of studies have emphasized a privileged input of the corticospinal pathway to the distal lower-leg muscles, this study shows that, if a locomotory task requires fine control of the proximal upper-leg muscles, a selective facilitation of MEPs is observed in these muscles. [source] The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulationHUMAN BRAIN MAPPING, Issue 3 2004Soile Komssi Abstract To better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS-evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor-cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS-evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure-of-eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 ± 5 msec (Peak I), 44 ± 10 msec (II), 102 ± 18 msec (III), and 185 ± 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid-shaped curve modeling the strength of TMS-evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response-stimulus intensity curve may be an indicator of the activation state of the brain. Hum. Brain Mapp. 21:154,164, 2004. © 2004 Wiley-Liss, Inc. [source] Effects of stimulus intensity on the efficacy and safety of twice-weekly, bilateral electroconvulsive therapy (ECT) combined with antipsychotics in acute mania: a randomised controlled trialBIPOLAR DISORDERS, Issue 2 2009Titus SP Mohan Objectives:, To examine differences in speed of improvement and remission in people with mania undergoing bilateral, brief-pulse, twice-weekly electroconvulsive therapy (ECT) at stimulus intensities administered just above and 2.5 times their individually titrated seizure threshold. Methods:, Consecutive, eligible subjects with mania, prescribed ECT, were randomised to receive treatments at stimulus doses either just above or 2.5 times their individually titrated seizure thresholds. Main outcomes were the speed of improvement and remission as measured by the Young Mania Rating Scale (YMRS) and the Clinical Global Impressions,Improvement scale (CGI-I) and cognitive side effects assessed by the Mini-Mental State Exam, the Wechsler Memory Scale, and a scale for autobiographical memory. Results:, A total of 24/26 subjects (92.3%) given threshold ECT and 22/24 subjects (91.7%) given suprathreshold ECT were significantly improved [CGI = 2; odds ratio (OR) = 1.1, 95% confidence interval (CI): 0.1,8.4; p = 1.0] at the end of ECT. A total of 88% of the sample had remitted [YMRS < 10; threshold 23/26 (88.5%) versus suprathreshold 21/24 (87.5%)], with no significant differences between interventions (OR = 1.1, 95% CI: 0.2, 6.0; p = 1.0). The interventions did not differ significantly in the time or number of ECT treatments required for improvement or remission. Both interventions were equally safe. Conclusions:, Bilateral, twice-weekly ECT delivered at stimulus intensities just above individually titrated seizure threshold was as effective and safe as ECT administered at stimulus intensities 2.5 times seizure threshold in rapidly resolving the symptoms of acute mania. [source] 4122: Exploring new strategies to record and analyse clinical electroretinogramsACTA OPHTHALMOLOGICA, Issue 2010P LACHAPELLE Purpose Investigate if the combination of time-frequency domain analysis and ERG dipole rotation reveals hidden features of the normal ERG that could be instrumental in the interpretation of nearly extinguished ERG responses. Methods Analyses were conducted on photopic ERGs (Photopic Hills: PH) obtained from normal subjects (n=75) and patients (n=65) affected with various retinopathies. A Discrete Wavelet Transform (DWT) was done on each ERGs and key descriptors (Holder exponent and wavelet coefficient maxima) were calculated. Dipole rotation was obtained by combining 11 gaze positions (0, 8, 16, 24, 32 and 40 degrees nasal or temporal to center) with 4 electrode locations [corneal (CE), lower lid (LL), external (EC) and internal canthi (IC)]. Results The Holder exponent follows a parabola, while some of the local wavelet maxima seem to follow a PH-like like distribution (b-wave and OPs) or a logistic growth function (a-wave). In still recordable pathological ERGs, the wavelet maxima matched that found in normal ERGs evoked at low stimulus intensities while in nearly extinguished ERGs (<10% of normal) the wavelet coefficients were significantly lower. Irrespective of the direction of gaze, there was little variation in DTL ERGs. EC ERGs were the only ones to reverse in polarity (seen 5 degrees nasal to fixation in nasal to temporal shift). Conclusion The parameters obtained with the DWT offers useful and reproducible tools to help identify subtle features of residual ERGs and therefore should allow for a more accurate quantification of low-voltage ERGs responses. Finally, our results suggest that varying the gaze and electrode positions would represent a valuable addition to the recording of clinical ERGs. Funded by NSERC. [source] Scaling the structure,function relationship for clinical perimetryACTA OPHTHALMOLOGICA, Issue 4 2005Ronald S. Harwerth Abstract. Purpose:,The full ranges of glaucomatous visual field defects and retinal ganglion cell losses extend over several orders of magnitude and therefore an interpretation of the structure,function relationship for clinical perimetry requires scaling of both variables. However, the most appropriate scale has not been determined. The present study was undertaken to compare linear and logarithmic transformations, which have been proposed for correlating the perimetric defects and neural losses of glaucoma. Methods:,Perimetry, by behavioural testing, and retinal histology data were obtained from rhesus monkeys with significant visual field defects caused by experimental glaucoma. Ganglion cell densities were measured in histologic sections of retina that corresponded to specific perimetry test locations for the treated and control eyes. The linear (percentage) and logarithmic (decibel) relationships for sensitivity loss as a function of ganglion cell loss were analysed. Results:,With decibel scaling, visual sensitivity losses and ganglion cell densities were linearly correlated with high coefficients of determination (r2), although the parameters of the functions varied with eccentricity. The structure,function relationships expressed as linear percentage-loss functions were less systematic in two respects. Firstly, the relationship exhibited considerable scatter in the data for small losses in visual sensitivity and, secondly, visual sensitivity losses became saturated with larger losses in ganglion cell density. The parameters of the percentage-loss functions also varied with eccentricity, but the variation was less than for the decibel-loss functions. Conclusions:,Linear scaling of perimetric defects and ganglion cell losses might potentially improve the structure,function relationship for visual defects associated with small amounts of cell loss, but the usefulness of the relationship is limited because of the high variability in that range. With log,log co-ordinates, the structure,function relationship for clinical perimetry is relatively more accurate and precise for cell losses greater than about 3 dB. The comparatively greater accuracy and precision of decibel loss functions are a likely consequence of the logarithmic scale of stimulus intensities for perimetry measurements and because the relationship between visual sensitivity and the number of neural detectors is a form of probability summation. [source] NEURAL CONTROL OF RENAL MEDULLARY PERFUSIONCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 5-6 2004Gabriela A Eppel Summary 1.,There is strong evidence that the renal medullary circulation plays a key role in long-term blood pressure control. This, and evidence implicating sympathetic overactivity in development of hypertension, provides the need for understanding how sympathetic nerves affect medullary blood flow (MBF). 2.,The precise vascular elements that regulate MBF under physiological conditions are unknown, but likely include the outer medullary portions of descending vasa recta and afferent and efferent arterioles of juxtamedullary glomeruli, all of which receive dense sympathetic innervation. 3.,Many early studies of the impact of sympathetic drive on MBF were flawed, both because of the methods used for measuring MBF and because single and often intense neural stimuli were tested. 4.,Recent studies have established that MBF is less sensitive than cortical blood flow (CBF) to electrical renal nerve stimulation, particularly at low stimulus intensities. Indeed, MBF appears to be refractory to increases in endogenous renal sympathetic nerve activity within the physiological range in all but the most extreme cases. 5.,Multiple mechanisms appear to operate in concert to blunt the impact of sympathetic drive on MBF, including counter-regulatory roles of nitric oxide and perhaps even paradoxical angiotensin II-induced vasodilatation. Regional differences in the geometry of glomerular arterioles are also likely to predispose MBF to be less sensitive than CBF to any given vasoconstrictor stimulus. 6.,Failure of these mechanisms would promote reductions in MBF in response to physiological activation of the renal nerves, which could, in turn, lead to salt and water retention and hypertension. [source] The interaction of age and unconditioned stimulus intensity on long-trace conditioned flavor aversion in ratsDEVELOPMENTAL PSYCHOBIOLOGY, Issue 2 2002James R. Misanin Abstract To see if the neural representation of the conditioned stimulus (CS) is available to old-age rats beyond the time it is available to young adults, the intensity of the unconditioned stimulus (US) and the length of the CS,US interval were systematically varied in a trace conditioning experiment. Results indicated that increasing US intensity extends the interval over which trace conditioning is evident in old-age rats but not in young adults, suggesting that trace decay occurs more rapidly in young rats. Results were interpreted in terms of age differences in the workings of hypothesized biochemical timing mechanisms that may directly influence the ability to associate stimuli over trace intervals in conditioned taste-aversion procedures. © 2002 Wiley Periodicals, Inc. Dev Psychobiol 40: 131,137, 2002. DOI 10.1002/dev.10018 [source] Effect of Dipotassium Clorazepate on Ainygdaloid-Kiiidling and Comparison Between Amygdaloid- and Hippocampal-Kindled Seizures in RatsEPILEPSIA, Issue 2000Kouichiro Amano Purpose: We reportcd previously that dipotassium clorazcpate (potassium 7-chloro-2, 3-dihydro-2-oxo-S-phcnyI- l H- l, 4-bcnzodiazepinc-3-carboxylate potassium hydroxide: DC), an antianxiety drug, suppressed hippocampel kindled scizures in rats i n a dose-dependent manner (Amano et al. Psychiatry Clin Neuroscienccs 1998; 52: 459,462). Its effect on kindling, howcver, has not been evaluated. Moreover, differcnces in the anticonvulsive effccts of conventional anticonvulsants bctween amygdaloid-and hippocampal-kindlcd seizures have becn reportcd (Kamci et al. Arch. Int. Pharmacodyn I98 1; 249: 164,176). To clarify the anticonvulsive propcrties of DC, we examined its effects on amygdaloid kindling and compared it for 7 succcssive days against amygdaloid- and hippocampal-kindled seizures using thc rat kindling model of epilcpsy. Methods: Adult inale Wistar rata weighing 220,330 g werc used. Electrodes were implanted stereotaxically into thc left basoiatcfiil amygdala or the left dorsal hippocampus under pcntobarhital ancsthesia. Expcriment 1: Anticonvulsive effect on amygdaloid-kindled seizurcs. Rats having >5 consecutive stage-5 seimrcs were htimulated at the generalizcd seizure-triggering threshold (GST) intensity 30 minutes after i.p. administration or DC or saline. Experiment 2: Effect on amygdala kindling. In other groups of Tiits, the amygdala was stimulated once daily following 30 minutes i.p. administration or DC at 5 mg/kg or saline until the first stage-5 seizure was attained. Experimcnt 3: Comparison of anticonvulsive effect bctween amygdaloid- and hippocampal-kindled scizures. In other groups of rats having 5 consecutive stage-5 seizures, the GST was determined. Furthermorc, rats having >I0 stage-5 scizures induced at thc GST intensity were testcd once a day for 7 consecutive days. Thc stimulation was delivercd 30 minutes aftcr i.p. administration of DC or saline. Results: Expcriment I: DC suppresscd amygdaloid-kindled scizures in a dose-depcndent manner. Significant reduction of aftcr-discharge duration compared with the control group was observed at dosagcs of 2 mg/kg or more, hut complete suppression of after-discharges was observed in only I of 7 sessions at the highcst dose. Expcriment 2: Thc number of stimulations rcquired for the first stage-5 seiiurc in the 5 mg/kg dosage group was 14.1+1.4 stimulations, which was significantly greater than the 10.2+1.7 stimulations in the control group (P4.01). The contralateral cortical afterdischarge duration i n the DC treated group was signilicantly shortcr than thc afterdischarge duration in the amygdala at the first 7 stimulations, whereas it was significantly shorter only the first 3 stimulations i n the control group. Experiment 3: DC suppressed amygdaloid-kindled seizures at 2 and 5 mg/kg, whcreas I mg/kg or morc suppresscd hippocampal-kindlcd seizures. Conclusions: Thc result of the present study suggcst that thc principal anticonvulsive cffect of DC is likely to be relatcd mainly to attenuation of propagation of scizure activity rather than to an elevatcd seizure threshold, which may support our previously findings that increased stimulus intensity could not complctcly reverse thc anticonvulsive effects of DC. Thus, differences in effective dosages in both amygdaloid- and hippocampal-kindled seizures may suggcst a difference in the neuronal mechanisms that arc cvolved in this kindling. The present study dcmonstratcd that DC has a modest anticonvulsive effect without serious adverse effccts, which indicates thc clinical uscfulness of DC for treatment intractable epilepsy. [source] Lumbosacral spinal cord somatosensory evoked potentials for quantification of nociception in horsesEQUINE VETERINARY JOURNAL, Issue 3 2010J. P. A. M. Van LOON Summary Reasons for performing study: There is a need for objective evaluation and quantification of the efficacy of analgesic drugs and analgesic techniques in horses. Objectives: To determine whether lumbosacral spinal cord somatosensory evoked potentials (SSEP) can be a useful and reliable tool to assess nociception in equines. Methods: SSEPs and electromyograms (EMG) from the epaxial muscles were recorded simultaneously, following electrical stimulation applied to the distal hindlimb in lightly anaesthetised Shetland ponies (n = 7). In order to validate the model, the effect of increasing stimulus intensity was documented and the conduction velocities (CV) of the stimulated nerves were calculated. The effect of epidurally applied methadone (0.4 mg/kg bwt) in a randomised, crossover design was investigated. Results: Two distinct complexes (N1P1 and N2P2) were identified in the SSEP waveform. Based on their latency and conduction velocity and the depressant effect of epidurally applied methadone, the SSEP N2P2 was ascribed to nociceptive A,-afferent stimulation. The SSEP N1P1 originated from non-nociceptive A,-afferent stimulation and was not influenced by epidurally applied methadone. Conclusions and potential relevance: The nociceptive A, component of the SSEP, the N2P2 complex, is presented as a valid and quantitative parameter of spinal nociceptive processing in the horse. Validation of the equine SSEP model enables the analgesic effects of new analgesics/analgesic techniques to be quantified and analgesia protocols for caudal epidural analgesia in equidae improved. [source] Effects of insular cortex lesions on conditioned taste aversion and latent inhibition in the ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2007Christopher Roman Abstract The present study tested the hypothesis that lesions of the insular cortex of the rat retard the acquisition of conditioned taste aversions (CTAs) because of an impairment in the detection of the novelty of taste stimuli. Demonstrating the expected latent inhibition effect, nonlesioned control subjects acquired CTAs more rapidly when the conditioned stimulus (0.15% sodium saccharin) was novel rather than familiar (achieved by pre-exposure to the to-be-conditioned taste cue). However, rats with insular cortex lesions acquired taste aversions at the same slow rate regardless of whether the saccharin was novel or familiar. The pattern of behavioural deficits obtained cannot be interpreted as disruptions of taste detection or stimulus intensity, but is consistent with the view that insular cortex lesions disrupt taste neophobia, a dysfunction that consequently retards CTA acquisition because of a latent inhibition-like effect. [source] Hippocampal long-term depression as an index of spatial working memoryEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2002Kazuhito Nakao Abstract Long-term potentiation (LTP), a form of synaptic plasticity in the hippocampus, is a cellular model for the neural basis of learning and memory, but few studies have investigated the contribution of long-term depression (LTD), a counterpart of LTP. To address the possible relationship between hippocampal LTD and spatial performance, the spatial cognitive ability of a rat was assessed in a spontaneous alternation test and, thereafter, LTD in response to low-frequency burst stimulation (LFBS) was monitored in the dentate gyrus of the same rat under anaesthesia. To enhance a divergence in the ability for spatial performance, some of the animals received fimbria,fornix (FF) transection 14 days before the experiments. LTD was reliably induced by application of LFBS to the medial perforant path of intact rats, while no apparent LTD was elicited in rats with FF lesions. The behavioural parameters of spatial memory showed a significant correlation with the magnitude of LTD. We found no evidence that the cognitive ability correlated with other electrophysiological parameters, e.g. basal synaptic responses, stimulus intensity to produce half-maximal responses, paired-pulse facilitation or paired-pulse depression. These results suggest that the magnitude of LTD in the dentate gyrus serves as a reliable index of spatial cognitive ability, providing insights into the functional significance of hippocampal LTD. [source] Intensity modulation of TMS-induced cortical excitation: Primary motor cortexHUMAN BRAIN MAPPING, Issue 6 2006Peter T. Fox Abstract The intensity dependence of the local and remote effects of transcranial magnetic stimulation (TMS) on human motor cortex was characterized using positron-emission tomography (PET) measurements of regional blood flow (BF) and concurrent electromyographic (EMG) measurements of the motor-evoked potential (MEP). Twelve normal volunteers were studied by applying 3 Hz TMS to the hand region of primary motor cortex (M1hand). Three stimulation intensities were used: 75%, 100%, and 125% of the motor threshold (MT). MEP amplitude increased nonlinearly with increasing stimulus intensity. The rate of rise in MEP amplitude was greater above MT than below. The hemodynamic response in M1hand was an increase in BF. Hemodynamic variables quantified for M1hand included value-normalized counts (VNC), intensity (z-score), and extent (mm3). All three hemodynamic response variables increased nonlinearly with stimulus intensity, closely mirroring the MEP intensity-response function. VNC was the hemodynamic response variable which showed the most significant effect of TMS intensity. VNC correlated strongly with MEP amplitude, both within and between subjects. Remote regions showed varying patterns of intensity response, which we interpret as reflecting varying levels of neuronal excitability and/or functional coupling in the conditions studied. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source] The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulationHUMAN BRAIN MAPPING, Issue 3 2004Soile Komssi Abstract To better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS-evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor-cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS-evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure-of-eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 ± 5 msec (Peak I), 44 ± 10 msec (II), 102 ± 18 msec (III), and 185 ± 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid-shaped curve modeling the strength of TMS-evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response-stimulus intensity curve may be an indicator of the activation state of the brain. Hum. Brain Mapp. 21:154,164, 2004. © 2004 Wiley-Liss, Inc. [source] Development of Tactile Responses in Human Preterm and Full-Term Infants From 30 to 40 Weeks Postconceptional AgeINFANCY, Issue 1 2002Isabel Fearon Maturation of tactile sensitivity prior to term was examined in 36 preterm and 13 full-term infants using a fixed-trial, habituation procedure. Each infant was presented with a series of 8 habituation (arm stroke), 2 novel (arm lift), and 2 recovery (arm stroke) stimulus trials while heart rate and body movements were recorded. Maturation was observed with a gradual increase in the magnitude of the stimulus-elicited cardiac acceleration and cardiac-movement coupling from 30 to 40 weeks postconceptional age. The majority of infants displayed habituation,an excitatory response (heart rate acceleration and body movement),to the initial presentation of a tactile stimulus, response decline with repeated stimulations, and renewed response to a novel stimulus. A substantial number of infants (40%) failed to respond initially to the tactile stimulus, increased responding over several stimulus presentations, and failed to discriminate the presentation of a novel stimulus. We speculate that these differences in response patterns observed over all ages represent individual difference in the perception of stimulus intensity. [source] An aggression machine v. determinants in reactive aggression revisitedAGGRESSIVE BEHAVIOR, Issue 6 2001Petri Juujärvi Abstract The relations between reactive aggression, situational cues, and emotion regulation were examined by means of the Pulkkinen Aggression Machine (PAM) task. In the PAM, provocation and response were systematically varied under two conditions: the impulsive aggression condition and the controlled aggression condition. In the impulsive condition, no information about the attacker was provided, while in the controlled condition the attackers were specified in terms of sex, age, and physical strength. The task was administered to 109 children aged 8 to 13 years. Boys (n = 61) and girls (n = 48), as well as subgroups of Adjusted (n = 67) and Maladjusted (n = 26) children were compared. The results confirmed earlier findings showing that there is a strong relationship between attack and response intensity. However, this relationship was consistently modified by the effects of situation and personality-related variables. This meant that, while for the impulsive condition response intensity was closely tied to stimulus intensity, in the controlled condition this effect was modulated by the characteristics of the opponent: the more equal the opponent the stronger the retaliations displayed. The Maladjusted children reacted more intensively in the impulsive condition and to minor provocation in the controlled condition than the Adjusted children. This suggests that the intensity of the elicited aggression in the Maladjusted group was particularly dependent on contextual rather than internal control. Aggr. Behav. 27:430,445, 2001. © 2001 Wiley-Liss, Inc. [source] Characteristics of a jaw reflex in humans with temporomandibular disorders: a preliminary reportJOURNAL OF ORAL REHABILITATION, Issue 5 2007P. MAILLOU summary, Electromyography was used to compare characteristics of an inhibitory jaw reflex in 10 temporomandibular disorder patients and 10 age- and sex-matched healthy controls. The methodology was novel in that the reflex was that evoked in the active masseter muscle, by electrical stimulation of perioral skin. This response has advantages over those previously studied as it avoids problems associated with stimulating in the moist intra-oral environment and it is monophasic, thus permitting easy quantification. The results have shown that (i) with the stimulation parameters employed, the reflex was present in all 10 control subjects, but in only eight of 10 temporomandibular disorder patients. (ii) When stimulation intensities were expressed as multiples of sensory threshold, there was no significant difference in the minimum level of stimulation required to evoke the reflex between the groups, although there was a trend for the patients with temporomandibular disorders to require higher intensities. (iii) Comparison of data from subjects giving responses at the same stimulus intensity (6 × sensory threshold: seven temporomandibular disorder patients, eight controls), showed no significant differences in the latencies or magnitudes of the reflex between the groups. However, the overall duration of the reflex was significantly shorter for the patients with temporomandibular disorders, with the reflex finishing significantly earlier. Thus even within the limitations of this study, it appears that an inhibitory jaw reflex evoked from stimulation around the mouth, may be weaker in temporomandibular disorder patients. This conclusion is consistent with previous studies on more complex jaw reflexes evoked by intra-oral stimuli. [source] The Comparative Effects of Drive and Test Stimulus Intensity on Myocardial Excitability and VulnerabilityPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 1 2000HOWARD S. FRIEDMAN The number and intensity of stimuli that set basic cycle length in cardiac electrophysiological studies can influence the electrical properties assessed by extrastimuli. The relative contribution of drive (S1) and test (S2) stimulus intensity in defining myocardial excitability and vulnerability has not been reported. The purpose of this investigation was to assess this interaction and to determine whether a trial and ventricular findings differed. The effects of S1 and S2 intensity on a trial and ventricular stimulus-intensity-refractory-period curves were determined in open-chest dogs: comparisons were made between curves with S1 intensity varied between diastolic threshold (DT) and 10 mA and S2 intensity maintained at DT and those with S, intensity maintained at DT and S2 intensity varied between DT and 10 mA. S1 -S2 was held constant and S1 -S2 varied. The effects of different stimulation sites, cycle length, number of stimulations, and neural blockade were assessed. S3 intensity amplification shifted atrial stimulus-intensity-refractory period curves in the direction of increased excitability and vulnerability; the changes were, more pronounced than those obtained by modulating S2 intensity. The changes produced by increasing S1 intensity were evident at different cycle lengths and were enhanced by an increased number of stimulations, but were not evident when S1 and S2 were delivered at different atrial sites. Although beta-blockade attenuated the effects of increasing S1 intensity somewhat, the addition of cholinergic blockade virtually abolished it. Ventricular refractoriness was also changed by modulation of S1 intensity, but the changes were less striking. In the atrium, modulation of S1 intensity has greater effects of stimulus-intensity-refractory-period relations than modulation ofS2 intensity; in the ventricle, the converse is true. [source] Silent Functional Magnetic Resonance Imaging (fMRI) of Tonotopicity and Stimulus Intensity Coding in Human Primary Auditory Cortex,THE LARYNGOSCOPE, Issue 3 2004F. Zerrin Yetkin MD Abstract Objectives The aims of this study were to determine the feasibility of obtaining auditory cortex activation evoked by pure tones presented at threshold and suprathreshold hearing levels, to evaluate tonotopicity of the primary auditory cortex, and to determine the effect of stimulus intensity on auditory cortex activation using silent functional magnetic resonance imaging (fMRI). Methods Sixteen subjects with normal hearing underwent silent fMRI. An audiometer was used to deliver pure tones of 1,000, 2,000, and 4,000 Hz to the left ear. Two levels of acoustic stimulation were used: 1) threshold, hearing level determined in the scanner room and 2) suprathreshold, 70 dB hearing loss (HL). Tonotopicity and stimulus intensity coding was assessed on the basis of the location, extent, and amount of the auditory cortex activation. Results The localization of activation moved to more medial and posterior regions of the primary auditory cortex as the frequency of the pure tone increased. Compared with a threshold stimulus, a suprathreshold stimulus evoked the same regions with increased spatial extent. The average increase in the right auditory cortex activation in response to suprathreshold stimulus was 57% at 1,000, 51% at 2,000, and 45% at 4,000 Hz compared with that activated by the threshold stimulus. Conclusions Silent fMRI can be used to evaluate auditory cortex activation using low-intensity stimuli. The level of stimulus intensity increases the amount of auditory cortex activation and influences the fMRI mapping of the tonotopic organization of the primary auditory cortex. [source] Variance of Vestibular-Evoked Myogenic Potentials,THE LARYNGOSCOPE, Issue 3 2001Kentaro Ochi MD Abstract Objectives/Hypothesis Vestibular-evoked myogenic potential (VEMP) has been thought to originate from sacculus. The variance of this potential and the effectiveness of the adjustments of pInII amplitudes using average muscle tonus of ipsilateral sternocleidomastoid muscle were evaluated. In addition, clinical application of VEMP was examined in patients with acoustic tumors (ATs) and vestibular neurolabyrinthitis (VNL). Study Design Prospective evaluation of the VEMP in 18 normal volunteers and 6 patients. Methods Variance and left,right difference of each parameter, including pI latency, nII latency, pInII amplitude, and threshold, was analyzed. Input, output function of pInII amplitude was evaluated. Average muscle tonus was calculated in 20 ears and applied for adjustment of pInII amplitude. Sensitivity of each parameter of VEMP was examined in 3 patients with ATs and 3 patients with VNL. Results VEMP was present in all 36 ears of 18 control subjects. Thresholds of VEMP for normal subjects were 80 to 95 dB normal hearing level (nHL). The muscle tonus affected pInII amplitude significantly; however, no statistically significant improvement was observed in test,retest investigation after adjustment using muscle tonus. The threshold of the affected side was elevated compared with the non-affected side in all patients with ATs, whereas 2 of 3 patients showed normal pInII-ratio. One patient with VNL presented normal VEMP, whereas 2 patients presented no VEMP to the highest stimulus intensity. Conclusions Interaural difference of thresholds might be the most useful parameters. Adjustment using average muscle tonus is not necessary when the subject is able to get sufficient muscle tonus. [source] Effects of stimulus intensity on the efficacy and safety of twice-weekly, bilateral electroconvulsive therapy (ECT) combined with antipsychotics in acute mania: a randomised controlled trialBIPOLAR DISORDERS, Issue 2 2009Titus SP Mohan Objectives:, To examine differences in speed of improvement and remission in people with mania undergoing bilateral, brief-pulse, twice-weekly electroconvulsive therapy (ECT) at stimulus intensities administered just above and 2.5 times their individually titrated seizure threshold. Methods:, Consecutive, eligible subjects with mania, prescribed ECT, were randomised to receive treatments at stimulus doses either just above or 2.5 times their individually titrated seizure thresholds. Main outcomes were the speed of improvement and remission as measured by the Young Mania Rating Scale (YMRS) and the Clinical Global Impressions,Improvement scale (CGI-I) and cognitive side effects assessed by the Mini-Mental State Exam, the Wechsler Memory Scale, and a scale for autobiographical memory. Results:, A total of 24/26 subjects (92.3%) given threshold ECT and 22/24 subjects (91.7%) given suprathreshold ECT were significantly improved [CGI = 2; odds ratio (OR) = 1.1, 95% confidence interval (CI): 0.1,8.4; p = 1.0] at the end of ECT. A total of 88% of the sample had remitted [YMRS < 10; threshold 23/26 (88.5%) versus suprathreshold 21/24 (87.5%)], with no significant differences between interventions (OR = 1.1, 95% CI: 0.2, 6.0; p = 1.0). The interventions did not differ significantly in the time or number of ECT treatments required for improvement or remission. Both interventions were equally safe. Conclusions:, Bilateral, twice-weekly ECT delivered at stimulus intensities just above individually titrated seizure threshold was as effective and safe as ECT administered at stimulus intensities 2.5 times seizure threshold in rapidly resolving the symptoms of acute mania. [source] | ||||||||||||||||