Threshold tracking primary motor cortex inhibition: the influence of current direction

Cirillo, John; Byblow, Winston D.

doi:10.1111/ejn.13369

Cited by 45 publications

(66 citation statements)

References 43 publications

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“…; Hamada et al . ; Cirillo & Byblow, ) and probably represent D‐wave recruitment following LM, early I‐wave recruitment following PA and late I‐wave recruitment following AP in both subject groups. Taken together, these findings suggest that the preferential recruitment of interneuronal circuits activated when varying the direction of the cortical current induced by TMS (i.e.…”

Section: Discussionmentioning

confidence: 84%

Age‐related changes in late I‐waves influence motor cortex plasticity induction in older adults

Opie

Cirillo

Semmler

2018

The Journal of Physiology

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Previous research shows that neuroplasticity assessed using transcranial magnetic stimulation (TMS) is reduced in older adults. While this deficit is often assumed to represent altered synaptic modification processes, age-related changes in the interneuronal circuits activated by TMS may also contribute. Here we assessed age-related differences in the characteristics of the corticospinal indirect (I) waves and how they influence plasticity induction in primary motor cortex. Twenty young (23.7 ± 3.4 years) and 19 older adults (70.6 ± 6.0 years) participated in these studies. I-wave recruitment was assessed by changing the direction of the current used to activate the motor cortex, whereas short-interval intracortical facilitation (SICF) was recorded to assess facilitatory I-wave interactions. In a separate study, I-wave periodicity TMS (iTMS) was used to examine the effect of I-wave latency on motor cortex plasticity. Data from the motor-evoked potential (MEP) onset latency produced using different coil orientations suggested that there were no age-related differences in preferential I-wave recruitment (P = 0.6). However, older adults demonstrated significant reductions in MEP facilitation at all 3 SICF peaks (all P values < 0.05) and a delayed latency of the second and third SICF peaks (all P values < 0.05). Using I-wave intervals that were optimal for young and older adults, these changes in the late I-waves were shown to influence the plasticity response in older adults after iTMS. These findings suggest that temporal characteristics are delayed for the late I-waves in older adults, and that optimising TMS interventions based on I-wave characteristics may improve the plasticity response in older adults.

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Section: Discussionmentioning

confidence: 84%

Age‐related changes in late I‐waves influence motor cortex plasticity induction in older adults

Opie

Cirillo

Semmler

2018

The Journal of Physiology

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“…In this study, the exclusion rate due to coil overheating was relatively high and biased towards subjects with high RMT 0.2mV , posing a potential limitation to the results. CS intensities for A-SICI were set based on RMT 0.2mV which, according to limited reports, is equal to about 109% RMT 0.05mV [ 50 , 51 ]. This should be kept in mind when comparing our results to the studies where RMT 0.05mV was used.…”

Section: Discussionmentioning

confidence: 99%

Short-interval intracortical inhibition: Comparison between conventional and threshold-tracking techniques

et al. 2018

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BackgroundShort-interval intracortical inhibition (SICI) is conventionally measured as the relative amplitude reduction of motor evoked potentials (MEPs) by subthreshold conditioning stimuli. In threshold-tracking SICI (T-SICI), stimulus intensity is instead adjusted repeatedly to maintain a constant MEP and inhibition is measured as the relative threshold increase. T-SICI is emerging as a useful diagnostic test, but its relationship to conventional amplitude SICI (A-SICI) is unclear.ObjectiveTo compare T-SICI and its reliability with conventional A-SICI measurements.MethodsIn twelve healthy volunteers (6 men, median age 30 years), conventional and T-SICI were recorded 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.ResultsAcross the CS range, mean group T-SICI showed a strong linear relationship to the mean group values measured by conventional technique (y = 29.7–0.3x, R2 = 0.99), but there was considerable interindividual variability. At CS 60–80% RMT, T-SICI had excellent intraday (intraclass correlation coefficient, ICC, 0.81–0.92) and adequate-to-excellent interday (ICC 0.61–0.88) reproducibility. Conventional SICI took longer to complete (median of 5.8 vs 3.8 min, p < 0.001) and tended to have poorer reproducibility (ICC 0.17–0.42 intraday, 0.37–0.51 interday). With T-SICI, smaller sample sizes were calculated for equally powered interventional studies.ConclusionThe close relationship between conventional and T-SICI suggests that both techniques reflect similar cortical inhibitory mechanisms. Threshold-tracking measurements of SICI may be able to improve reproducibility, to shorten acquisition time and to reduce sample sizes for interventional studies compared with the conventional technique.

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“…A further complicating factor which will need investigation is coil orientation. In common with the majority of TMS studies, our SICI measurements were obtained exclusively using the posterior-anterior current direction, whereas it has been reported that the anterior-posterior direction may result in more robust inhibition [23,24].…”

Section: Detection Of Abnormal Lack Of Sicimentioning

confidence: 99%

Short-interval intracortical inhibition as a function of inter-stimulus interval: Three methods compared

et al. 2021

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Background: Short-interval intracortical inhibition (SICI), as measured by threshold-tracking as a function of inter-stimulus interval (ISI), has been proposed as a useful biomarker for amyotrophic lateral sclerosis (ALS), but its relationship to conventional amplitude measurements has not been established. Methods: Serial tracking of SICI at increasing ISIs from 1 to 7 ms (T-SICIs) was compared in 50 healthy control subjects with the same ISIs tracked in parallel (T-SICIp), and with conventional amplitude measurements (A-SICI). For T-SICIp and A-SICI, pairs of conditioning and test stimuli with different ISIs were pseudo-randomised and interspersed with test-alone stimuli given at regular intervals. Thresholds were estimated by regression of log peak-to-peak amplitude on stimulus. Results: T-SICIp and A-SICI were closely related: a tenfold reduction in amplitude corresponding to an approximately 18% increase in threshold. Threshold increases were greater for T-SICIs than for T-SICIp at 3.5e5 ms (P < 0.001). This divergence depended on the initial settings and whether ISIs were progressively increased or decreased, and was attributed to the limitations of the serial tracking protocol. SICI variability between subjects was greatest for T-SICIs estimates and least for A-SICI, and only A-SICI estimates revealed a significant decline in inhibition with age. Conclusions: The serial tracking protocol did not accurately show the dependence of inhibition on ISI. Randomising ISIs gives corresponding SICI measures, whether tracking thresholds or measuring amplitude measurements. SICI variability suggested that A-SICI measurements may be the most sensitive to loss of inhibition.

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Threshold tracking primary motor cortex inhibition: the influence of current direction

Cited by 45 publications

References 43 publications

Age‐related changes in late I‐waves influence motor cortex plasticity induction in older adults

Age‐related changes in late I‐waves influence motor cortex plasticity induction in older adults

Short-interval intracortical inhibition: Comparison between conventional and threshold-tracking techniques

Short-interval intracortical inhibition as a function of inter-stimulus interval: Three methods compared

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