Threshold Tracking Method Research Articles

The recovery cycle of excitability assessed by a conventional electrodiagnostic machine: A study in healthy volunteers and in Charcot-Marie-Tooth 1A patients

ObjectiveTo validate the ‘paired pulses’ technique with a conventional electrodiagnostic machine (CEM) for studying the axonal excitability recovery cycle (ERC). MethodsPaired pulses, with a variable inter-stimulus interval, were delivered at the wrist along the median nerve. The CEM repeatability was verified in a group of 15 healthy volunteers (test/retest analysis). ERC was then applied in 40 healthy volunteers and 10 patients with Charcot-Marie-Tooth type 1A (CMT1A), using both the threshold tracking (TT) reference method and CEM (basal condition, during and after ischemia). ResultsCEM parameters evaluating absolute refractory and supernormal periods were reproducible (interclass correlation coefficient > 0.75). CEM results were consistent with TT method and literature data. In CMT1A, refractory and superexcitable periods were significantly reduced. According to receiving operator characteristic analysis, the CEM supernormal period area was the most relevant parameter for discriminating CMT1A from healthy volunteers (area under the curve = 0.98). ConclusionsCEM was a valid procedure for studying ERC. CMT1A patients exhibited ERC alterations due to modifications in passive membrane properties and of nodal ion channel distribution resulting from demyelination. SignificanceStudying ERC with CEM could be performed in routine practice in patients with peripheral neuropathies to provide information on motor axonal excitability.

Classical, spaced, or accelerated transcranial magnetic stimulation of motor cortex for treating neuropathic pain: A 3-arm parallel non-inferiority study

BackgroundRepetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) at high frequency (HF) is an effective treatment of neuropathic pain. The classical HF-rTMS protocol (CHF-rTMS) includes a daily session for one week as an induction phase of treatment followed by more spaced sessions. Another type of protocol without an induction phase and based solely on spaced sessions of HF-rTMS (SHF-rTMS) has also been shown to produce neuropathic pain relief. However, CHF-rTMS and SHF-rTMS of M1 have never been compared regarding their analgesic potential. Another type of rTMS paradigm, called accelerated intermittent theta burst stimulation (ACC-iTBS), has recently been proposed for the treatment of depression, the other clinical condition for which HF-rTMS is proposed as an effective therapeutic strategy. ACC-iTBS combines a high number of pulses delivered in short sessions grouped into a few days of stimulation. This type of protocol has never been applied to M1 for the treatment of pain. Methods/DesignThe objective of this single-centre randomized study is to compare the efficacy of three different rTMS protocols for the treatment of chronic neuropathic pain: CHF-rTMS, SHF-rTMS, and ACC-iTBS. The CHF-rTMS will consists of 10 stimulation sessions, including 5 daily sessions of 10Hz-rTMS (3,000 pulses per session) over one week, then one session per week for 5 weeks, for a total of 30,000 pulses delivered in 10 stimulation days. The SHF-rTMS protocol will only include 4 sessions of 20Hz-rTMS (1,600 pulses per session), one every 15 days, for a total of 6,400 pulses delivered in 4 stimulation days. The ACC-iTBS protocol will comprise 5 sessions of iTBS (600 pulses per session) completed in half a day for 2 consecutive days, repeated 5 weeks later, for a total of 30,000 pulses delivered in 4 stimulation days. Thus, CHF-rTMS and ACC-iTBS protocols will share a higher total number of TMS pulses (30,000 pulses) compared to SHF-rTMS protocol (6,400 pulses), while CHF-rTMS protocol will include a higher number of stimulation days (10 days) compared to ACC-iTBS and SHF-rTMS protocols (4 days). In all protocols, the M1 target will be defined in the same way and stimulated at the same intensity using a navigated rTMS (nTMS) procedure. The evaluation will be based on clinical outcomes with various scales and questionnaires assessed every week, from two weeks before the 7-week period of therapeutic stimulation until 4 weeks after. Additionally, three sets of neurophysiological outcomes (resting-state electroencephalography (EEG), nTMS-EEG recordings, and short intracortical inhibition measurement with threshold tracking method) will be assessed the week before and after the 7-week period of therapeutic stimulation. DiscussionThis study will make it possible to compare the analgesic efficacy of the CHF-rTMS and SHF-rTMS protocols and to appraise that of the ACC-iTBS protocol for the first time. This study will also make it possible to determine the respective influence of the total number of pulses and days of stimulation delivered to M1 on the extent of pain relief. Thus, if their analgesic efficacy is not inferior to that of CHF-rTMS, SHF-rTMS and especially the new ACC-iTBS protocol could be an optimal compromise of a more easy-to-perform rTMS protocol for the treatment of patients with chronic neuropathic pain.

Strength-duration time constant and rheobase measurements: Comparison of the threshold tracking method and a manual procedure

ObjectiveTo compare the strength-duration time constant (SDTC) and rheobase measurements obtained by the threshold tracking method (TT) and by a non-automated method (MM). MethodsThe MM procedure involved measuring, using a routine electrodiagnostic device, the intensity required to evoke a motor response whose amplitude corresponds to 40% of the maximum amplitude for four stimulus duration (1.0, 0.7, 0.5, 0.2 ms), and studying the linear relationship between stimulus charge and stimulus duration (slope = rheobase, intercept on the x-axis = SDTC). Using TT and MM, 30 successive healthy subjects (mean age = 38 years old) underwent a prospective evaluation of SDTC and rheobase of the median nerve motor axons at the wrist. Nerve stimulation and bipolar recording of evoked motor responses were performed with disposable self-adhesive surface electrodes. ResultsThe Spearman correlations between the two methods were 0.78 (p < 0.0001) for SDTC and 0.96 (p < 0.0001) for the rheobase. The Bland-Altman analysis did not reveal any systematic bias of MM compared to TT. ConclusionsThe MM procedure was reliable for strength-duration relationship analysis. SignificanceWe encourage neurophysiologists, who do not have dedicated threshold tracking equipment, not to hesitate to use these simple tools to assess peripheral nerve excitability.

N°43 – Strength-duration time constant and rheobase measurements: Comparison of the threshold tracking method and a non-automated procedure

N°43 – Strength-duration time constant and rheobase measurements: Comparison of the threshold tracking method and a non-automated procedure

The test–retest reliability of large and small fiber nerve excitability testing with threshold tracking

ObjectiveStandard nerve excitability testing (NET) predominantly assesses Aα- and Aβ-fiber function, but a method examining small afferents would be of great interest in pain studies. Here, we examined the properties of a novel perception threshold tracking (PTT) method that preferentially activates Aδ-fibers using weak currents delivered by a novel multipin electrode and compared its reliability with NET. MethodsEighteen healthy subjects (mean age:34.06 ± 2.0) were examined three times with motor and sensory NET and PTT in morning and afternoon sessions on the same day (intra-day reliability) and after a week (inter-day reliability). NET was performed on the median nerve, while PTT stimuli were delivered through a multipin electrode located on the forearm. During PTT, subjects indicated stimulus perception via a button press and the intensity of the current was automatically increased or decreased accordingly by Qtrac software. This allowed changes in the perception threshold to be tracked during strength-duration time constant (SDTC) and threshold electrotonus protocols. ResultsThe coefficient of variation (CoV) and interclass coefficient of variation (ICC) showed good–excellent reliability for most NET parameters. PTT showed poor reliability for both SDTC and threshold electrotonus parameters. There was a significant correlation between large (sensory NET) and small (PTT) fiber SDTC when all sessions were pooled (r = 0.29, p = 0.03). ConclusionsThreshold tracking technique can be applied directly to small fibers via a psychophysical readout, but with the current technique, the reliability is poor. SignificanceFurther studies are needed to examine whether Aβ-fiber SDTC may be a surrogate biomarker for peripheral nociceptive signalling.

Three different short-interval intracortical inhibition methods in early diagnosis of amyotrophic lateral sclerosis

Objectives: To compare the utility of conventional amplitude measurements of short-interval intracortical inhibition (A-SICI) with two threshold-tracking (T-SICI) methods, as aids to early diagnosis of amyotrophic lateral sclerosis (ALS). The new parallel threshold-tracking method (T-SICIp) was compared with the previously used serial tracking method (T-SICIs). Methods: 112 consecutive patients referred with the suspicion of ALS and 40 healthy controls were prospectively included. Based on clinical follow-up, patients were divided into 67 patients with motor neuron disease (MND) comprising progressive muscular atrophy (PMA) as well as ALS, and 45 patient controls. SICI was recorded from first dorsal interosseus muscle using the three different protocols. Results: MND patients had significantly reduced T-SICIp, T-SICIs and A-SICI, compared with healthy controls and patient controls, while healthy and patient controls were similar. Paradoxically, T-SICIp was least affected in MND patients with the most upper motor neuron (UMN) signs (Spearman ρ = 0.537, P < 0.0001) whereas there was no correlation for T-SICIs or A-SICI. T-SICIp also provided the best discrimination between patient controls and MND as determined by the receiver operating characteristic (ROC) curves. For patients with no UMN signs, area under ROC curve for 2-3ms inter-stimulus intervals was 0.931 for T-SICIp, 0.771 for T-SICIs and 0.786 for A-SICI. Conclusions: SICI is a sensitive measure for detection of cortical involvement in ALS patients. T-SICIp has higher sensitivity and specificity than T-SICIs and A-SICI, particularly in patients without any upper motor neuron signs.

Short latency afferent inhibition: comparison between threshold-tracking and conventional amplitude recording methods.

Short-latency afferent inhibition (SAI), which is conventionally measured as a reduction in motor evoked potential amplitude (A-SAI), is of clinical interest as a potential biomarker for cognitive impairment. Since threshold-tracking has some advantages for clinical studies of short-interval cortical inhibition, we have compared A-SAI with a threshold-tracking alternative method (T-SAI). In the T-SAI method, inhibition was calculated by tracking the required TMS intensity for the targeted MEP amplitude (200 uV) both for the test (TMS only) and paired (TMS and peripheral stimulation) stimuli. A-SAI and T-SAI were recorded from 31 healthy subjects using ten stimuli at each of 12 inter-stimulus intervals, once in the morning and again in the afternoon. There were no differences between morning and afternoon recordings. When A-SAI was normalized by log conversion it was closely related to T-SAI. Between subjects, variability was similar for the two techniques, but within-subject variability was significantly smaller for normalized A-SAI. Conventional amplitude measurements appear more sensitive for detecting changes within-subjects, such as in interventional studies, but threshold-tracking may be as sensitive as detecting abnormal SAI in a patient.

A new parameter to discriminate amyotrophic lateral sclerosis patients from healthy participants by motor cortical excitability changes.

We sought a combination of abnormalities to define a more sensitive measure of cortical excitability in amyotrophic lateral sclerosis (ALS). The automatic threshold tracking method was employed to assess the resting motor threshold, intracortical facilitation (ICF), short-interval intracortical inhibition (SICI), and short-interval intracortical faciilitation (SICF) in patients and controls. SICF at interstimulus intervals (ISI) between 1 and 1.8 ms and 2 and 3 ms as well as average SICI and SICI at ISIs of 1 and 2.5 ms were significantly reduced in ALS. The SICI curve was altered, displaying a solitary peak. Discriminant analysis revealed that the combination of SICI 2.5 ms and the mean SICF between 1 and 1.8 ms ISIs was the most sensitive parameter to distinguish patients with ALS from healthy participants. Along with the reduced SICI and its altered shape, connectivity between motor cortical circuits is changed in ALS. Combination with SICF increases the diagnostic utility of SICI in ALS.

The effect of the anodal transcranial direct current stimulation over the cerebellum on the motor cortex excitability

This study was designed to investigate whether the cerebellum has an inhibitory effect on motor cortical excitability.Sixteen healthy adults (age range, 25–50 years, five female) participated in the study. Anodal cerebellar transcranial direct current stimulation (a-cTDCS) was used to modulate cerebellar excitability. A-cTDCS was given for 20 min at 1 mA intensity. The automatic threshold tracking method was used to investigate cortical excitability. Resting motor threshold (RMT), short interval intracortical inhibition (SICI), short interval intracortical facilitation (SICF), intracortical facilitation (ICF), and the input output curve (I-O curve) were motor cortical excitability parameters.a-cTDCS caused a reduction in overall SICI and the reduced SICF for interstimulus intervals (ISIs) to 2.4–4.4 ms. a-cTDCS has no effect on ICF, RMT, and the I-O curve. There were no significant changes in any of these cortical excitability parameters after sham cTDCS.Results of the study indicate that a-cTDCS has a dual (both inhibitory and excitatory) effect on motor cortical excitability, rather than a simple inhibitory effect. The cerebellum modulates both the inhibitory and facilitatory activities of motor cortex (M1) and suggest that cerebello–cerebral motor connectivity is more complex than solely inhibitory or facilitatory connections.

P237 Axonal excitability findings in type 1 diabetes mellitus – Median nerve versus tibial nerve comparison

Objective Length dependent peripheral neuropathy is the most common complication of diabetes mellitus (DM). As no curative treatment for diabetic polyneuropathy (DMP) is available, its prevention and early detection is very important. Axonal excitability is defined as the capability of nodal and paranodal pathological changes in DMP. The aim of present study was to determine alterations in axonal excitability findings in tibial nerve by comparing median nerve axonal excitability findings in Type 1 DMP. Methods The total 284 patients, who were followed up for Type 1 DM according to criteria of American Diabetes Association, were screened in this study. Six DMP patients, 10 random non-polyneuropathy cases and 14 healthy control subjects were examined by threshold tracking method (TROND protokol) from median and tibial nerve. Results Even if there is not prominent difference in median nerve axonal excitability studies in PNP and DM patients there was prominent pathological findings in tibial nerve. The strength–duration time constant was significantly longer in DPN Type 1 patients than in normal patients. Supernormality was significantly smaller in DPN patients. Threshold electrotonus studies showed abnormalities in patients with DPN that smaller threshold changes by long depolarizing and hyperpolarizing conditioning current named as “fanning-in”. Conclusion This study confirms that there was significantly alteration in axonal excitability findings in DMP in tibial nerve. Comparisons median and tibial nerve axonal excitability findings have potential to show the length dependent polyneuropathic pathological status in axonal excitability studies.

P344 Motor cortical excitability changes in early stage ALS patients using automatic threshold tracking method

Objectives to determine motor cortical excitability changes in early stage ALS patients. Methods Twenty-seven ALS patients were recruited the study. The mean age was 55.2 years and seven patients were female. Cortical excitability tests performed on the diagnostic stage of the disease. Investigated cortical excitability parameters were; resting motor threshold: (RMT), short interval intracortical inhibition (SICI), short interval intracortical facilitation (SICF) and intracortical facilitation (ICF). Results Mean RMT was 60.1 ± 2.2% MSO for ALS patients, 52.9 ± 3.1% for control group. There was not significant difference between two groups ( p > 0.05 ). Factor analysis of SICI resulted in two factors with eigenvalues more than 1. In the calculation of factor 1 (SICI1-2.5 ms) values, short ISI values have more weight than long ISI values. The opposite was true for factor 2. (SICI2.5-5 ms). Mean SICI1-2.5 msvalues were 11.3 ± 11.7 in ALS group and 74.3 ± 9.9 in control group ( p 0.05 ) while mean SICI2.5-5 ms were 10.6 ± 9.7 in ALS group and 67.8 ± 9.8 in control group ( p 0.05 ). Factor analysis of SICF and ICF resulted in two factor with eigenvalues more than 1. There were no significant difference between two groups any of these two factors both for SICF and ICF ( p > 0.05 ). Comment SICI values are significantly reduced in ALS patients at the early stage of the disease. Significance SICI analysis with automatic threshold tracking method may have potential role for diagnosis of ALS. Reliability and reproducibility of this test should be performed before using it as a diagnostic test.

P157 Reliability of threshold tracking technique for short interval intracortical inhibition

Introduction In threshold-tracking TMS, stimulation intensity is adjusted online to maintain a predefined target MEP response, thus allowing monitoring and controlling for the naturally occurring fluctuations in corticospinal excitability as well as technical errors. Although it is emerging as a useful clinical tool, little is known about its reliability and comparability with conventional techniques. Objectives To evaluate the reproducibility of the threshold-tracking (constant response ) TMS technique for short interval intracortical inhibition (SICI) and compare it with standard (constant stimulus ) measurements. Methods SICI was measured in 12 healthy volunteers (6 males, 31 ± 7.6 years) from the right FDI muscle using an automated stimulation protocol incorporating (i) conventional, fixed-intensity (A-SICI) and (ii) threshold tracking (T-SICI) methods at conditioning stimuli (CS) of 50–80% resting motor threshold (RMT) and interstimulus interval of 2.5 ms. RMT was defined as a stimulation intensity required to evoke a response of 0.2 mV and was determined by threshold tracking. Measurements were repeated on the same day and at least a week later by a single operator. Results No significant differences in mean RMT, A-SICI and T-SICI were observed between sessions. RMT and TS, measured by threshold-tracking technique, showed excellent intra- and adequate interday reproducibility. At 50% RMT CS both types of SICI had poor reproducibility. At all other CS intensities, T-SICI had excellent intraday (intraclass correlation coefficient, ICC 0.81–0.92) and adequate-to-excellent interday (ICC 0.61–0.88) reproducibility, while A-SICI showed poor intraday and poor-to-adequate interday reproducibility (ICC 0.29–0.37 and 0.37–0.51, respectively). Conclusion SICI measured by threshold tracking shows good intra- and interday reproducibility. Automation of the procedure and allowance for naturally occurring fluctuations in cortical excitability by threshold tracking may increase the reproducibility of SICI.

An Improved Sequential Smoothing Particle Filtering Method

In order to cope with the challenges of non-cooperative targets such as stealth targets to modern radar, especially when traditional threshold detection and tracking methods can hardly detect fast-moving stealth targets, technological innovation has long been required. In this paper we have proposed a new algorithm which can reduce computational cost and improve tracking accuracy. Firstly, the number of particles in the traditional particle filter is reduced and a small number of sampling points are derived from the possible distribution of the target to be tracked, each given a proper weight. Then, the transformed sampling points are sequentially smoothed. And finally, the target positions are estimated. The simulation results show that the proposed algorithm is more accurate than the traditional particle filter algorithm and has lower computational complexity. In the case when SNR is between 0dB to 15dB, a total of 100 Monte Carlo simulations are carried out, obtaining a high detection probability. The detection probability of the improved algorithm is higher than that of the existing particle filter at 7dB. Also, the computational cost is lower than the existing particle filter algorithm.

Membrane properties in small cutaneous nerve fibers in humans

Assessment of membrane properties is important for understanding the mechanisms of painful peripheral neuropathy, developing new diagnostic techniques, and screening/profiling of analgesics that target ion channels. Small cutaneous nerves were activated electrically by small diameter (0.2 mm) cathodes, and large nerves were activated by ordinary patch electrodes. This new perception threshold tracking method combines perception threshold assessment and stimulation paradigms from conventional threshold tracking. The strength-duration time-constant of large fibers (580 µs ± 160 µs) was lower than the time constant of small fibers (1060 µs ± 690 µs; P < 0.01, paired t-test). Threshold electrotonus showed similar threshold reductions to sub-threshold prepulses, except for 80 ms hyperpolarizing prepulses, to which small fibers showed less threshold reduction than large fibers (repeated-measures analysis of variance, Bonferroni, P = 0.006). This is a reliable method to investigate the membrane properties of small cutaneous nerve fibers in humans and may be used in clinical settings as a diagnostic or profiling tool. Muscle Nerve 55: 195-201, 2017.

ID 108 – Reproducibility of short interval intracortical inhibition using threshold-tracking

Aim To evaluate the reproducibility of a threshold-tracking (constant response) TMS technique for short interval intracortical inhibition (SICI) and compare it with standard (constant stimulus) measurements. Methods SICI was measured in 12 healthy volunteers (31 ± 7.6 years) from the right FDI muscle using an automated stimulation protocol incorporating (i) conventional, fixed-intensity (A-SICI) and (ii) threshold tracking (T-SICI) methods at conditioning stimuli (CS) of 50–80% resting motor threshold (RMT) and interstimulus interval of 2.5 ms. Measurements were repeated on the same day and at least a week later by a single operator. Results No significant differences in RMT, A-SICI and T-SICI were observed between sessions. At 50% RMT CS both types of SICI had poor reproducibility. At all other CS intensities, T-SICI had excellent intraday (intraclass correlation coefficient, ICC 0.81–0.92) and adequate-to-excellent interday (ICC 0.61–0.88) reproducibility, while A-SICI showed poor intraday and poor-to-adequate interday reproducibility (ICC 0.29–0.37 and 0.37–0.51, respectively). Conclusion SICI measured by threshold tracking shows good intra- and interday reproducibility. Key message Automation of the procedure and allowance for naturally occurring fluctuations in cortical excitability by threshold tracking may increase the reproducibility of SICI.

Nerve excitability and structural changes in myelinated axons from diabetic mice.

The mechanisms associated with nerve dysfunction and axonal loss in diabetes has not been fully clarified. Excitability and pathological aspects in nerves from diabetic mice were studied in order to explore the pathophysiology of diabetic neuropathy. Myelinated nerve fibres from the sciatic nerve of BKS.Cg-m (+/+) Lepr (db) /J mice were studied by registering the CMAP controlled by an automated threshold tracking method. The sciatic nerve was also studied pathologically. Diabetic mice displayed longer latencies, higher thresholds and lower amplitudes compared to controls and had a rightward shift in the stimulus response curves. Strength-duration time constant was lower in diabetic mice but not reaching statistical significance (p=0.09). Diabetics displayed an increase in accommodation, with a smaller change in excitability in threshold electrotonus. Refractoriness, mean superexcitability and late subexcitability were reduced in diabetic mice. Diabetic mice had a larger number of myelinated fibres compared to controls (p<0.05), but larger than 9 μm were virtually absent, accounting for near 7% in control animals. Db/db mice develop electrophysiological changes suggestive of membrane depolarization as the result of Na(+)/K(+) pump impairment. Loss of large myelinated fibres might also contribute to the nerve excitability profiles in this model.

Inter-individual variation in the after-effect of paired associative stimulation can be predicted from short-interval intracortical inhibition with the threshold tracking method.

Paired associative stimulation (PAS), which is used to test a long term potentiation (LTP)-like effect, involves repeated pairing of peripheral somatosensory input with transcranial magnetic stimulation (TMS) given 25ms later over M1 (PAS25). The effect is usually quantified as an increase in amplitude of motor evoked potentials evoked by single pulse TMS. However, the effect varies greatly between individuals. We hypothesized that variability depends on either the individual level of GABAAergic activity in cortex, or on the proportion of late I-wave inputs that are evoked by TMS pulses during PAS25. Low levels of GABA facilitate LTP, whereas late I-waves are the site of facilitation after PAS25. GABAAergic inhibition was quantified using SICI measured with a threshold tracking method (SICI-TT) before and after PAS25 in 18 healthy volunteers. The PAS25 effect correlated with the level of SICI-TT (r=0.6) before PAS25. Contrary to the GABA hypothesis, people who had good facilitation after PAS25 had good inhibition measured by SICI-TT. On completion of the PAS25 protocol, SICI-TT was reduced by an amount correlated with the size of the PAS25 effect (r=0.5-0.6 at an interstimulus interval of 2.5-3.0ms). SICI is known to target late I-waves, thus SICI-TT will depend on the proportion of late I-waves evoked by the TMS test pulse. If the pulse recruits a large fraction of late I-waves, individuals will show good SICI-TT; they will also respond well to PAS25 since this relies on facilitation of late I-waves.

Opposite effects of weak transcranial direct current stimulation on different phases of short interval intracortical inhibition (SICI)

Short interval intracortical inhibition (SICI) is a common paired-pulse TMS technique that is used to measure GABAa-ergic inhibition in the cerebral motor cortex. However, inhibition evaluated with an interstimulus interval (ISI) between the TMS pulses of 2.5ms has quite different properties from that seen at 1ms. It is thought that the latter may represent either (or both) a different type of synaptic inhibition or refractoriness of neural membranes. The present experiments provide further evidence about the early and late components of SICI using transcranial direct current stimulation (tDCS), a technique thought to change neural excitability by polarising the nerve membranes. We assessed SICI using a threshold tracking method at a range of ISIs during concurrent application of tDCS in 11 healthy volunteers (8 males, 27-43years old). Each subject underwent both anodal and cathodal tDCS with two different intensities of stimulation (1 and 2mA). Because there was no significant difference between the results at the two intensities, the data were combined. Principal component analysis was used to separate the contributions of early and late SICI to the time course of inhibition from 1 to 5ms tDCS had opposite effects on early and late SICI. Anodal tDCS reduced late SICI but enhanced early SICI, whereas cathodal tDCS had the opposite effect. This is further evidence that the two phases of SICI are produced by different mechanisms, perhaps involving different sets of neurones or different locations on the same neurone that respond oppositely to tDCS.

P25.1 MTRACK, a software system to facilitate the development of threshold tracking methods

P25.1 MTRACK, a software system to facilitate the development of threshold tracking methods

Registering the Response of Tissues Exposed to an Interferential Electric Current Stimulation

Electrotherapy is a treatment method in which an electric stimulus is used to achieve physiological changes in the body. When increasing the level of the electric stimulus, three sensory, three motor and a pain response can be found. In this paper the three sensory threshold levels (1st just noticeable weak tingling sensation, 2nd a very fine but definite tingling and 3rd moderate strong tingling) were studied with an interferential electric current stimulus. The interferential electric current can be achieved by summing two alternating currents with little different frequencies with each other. As a current source, the study used a value intended for interferential electric current therapy. The threshold value measurements were performed on 5 days to 6 volunteers. The method of limits is a frequently used technique for determining sensory thresholds where ascending or descending stimuli is used and the observer reports of the appearance or disappearance of the sensation, respectively. A Bekesy's algorithm is a threshold tracking method with a variable stimulus. They were used for controlling the interferential electric current stimulus, and hence, for studying the,thresholds. By using the method of limits, the measurements were done at three sensory threshold levels at interferential frequencies deltaf of 10 Hz, 30 Hz, 50 Hz, and 100 Hz caused by two sine waves, one with a frequency between 2490 Hz and 2400 Hz, and the other constant 2500 Hz. In the method based on Bekésy's algorithm the interferential frequency deltaf was increased from 1 Hz to 100 Hz by changing the first frequency from 2499 Hz to 2400 Hz and the measurement was repeated for all three sensory thresholds. The sensory thresholds for interferential current stimuli seem to be quite unaffected by the interferential electric current frequency among the healthy test persons, and no distinct interferential electric current frequencies at which the threshold values should be measured were found in this study.