Biology subjects

Hougland, J. R.

Publications and source records attributed to Hougland, J. R..

3 recordsLinked to original sources

bioRxiv2026

Brain-State-Resolved Consistency of Corticospinal Responses with EEG-TMS

BackgroundTranscranial magnetic stimulation (TMS) over the primary motor cortex (M1) elicits motor-evoked potentials (MEPs), a neurophysiological marker of corticospinal excitability. Ongoing brain activity at the time of stimulation, such as the phase and power of the sensorimotor mu rhythm (8-13 Hz), has a significant impact on MEP amplitudes. However, it remains unclear whether these endogenous excitability states also influence the consistency of MEP amplitudes across repeated trials. ObjectivesWe investigated whether instantaneous mu dynamics modulate not only the magnitude but also the consistency of corticospinal responses to TMS. MethodsTwenty-nine healthy participants received 1200 single TMS pulses over the left M1 during simultaneous EEG recording. Trials were stratified based on pre-stimulus mu power, phase, and interhemispheric M1-M1 functional connectivity. Brain-state-resolved MEP variability was quantified using the coefficient of variation (CV) within subsets of trials defined by similar pre-stimulus mu dynamics. ResultsTrial subsets characterized by high mu power or high M1-M1 functional connectivity were associated with reduced MEP variability, indicating more consistent corticospinal output. In contrast, the mu phase did not significantly influence response consistency. Brain-state-resolved MEP variability showed greater stability across sessions compared to MEP variability estimated from random trial subsampling. ConclusionsPre-stimulus mu dynamics shape not only magnitude but also consistency of corticospinal responses to TMS. We show that corticospinal response consistency reflects a structured, brain-state-dependent property of the sensorimotor network. These findings contribute to our mechanistic understanding of brain-state-dependent neuromodulation and may be leveraged to reduce variability and improve efficacy to TMS. HighlightsO_LIOngoing sensorimotor mu dynamics shape both magnitude and consistency of MEPs. C_LIO_LITrial subsets characterized by high mu power were associated with reduced MEP variability. C_LIO_LIMu phase modulated MEP amplitude but did not influence MEP consistency. C_LIO_LIBrain-state-resolved estimates of MEP variability were more reliable across sessions. C_LIO_LIFuture TMS protocols may reduce effect variability by targeting stable excitability states. C_LI

neuroscience↗

bioRxiv2026

Not Just Noise: Aperiodic Brain Activity Reflects Corticospinal Excitability

BackgroundElectroencephalography (EEG) can be combined with transcranial magnetic stimulation (TMS) to perform brain-state-dependent stimulation. EEG-TMS studies have shown that corticospinal excitability, as measured via motor evoked potentials (MEPs), is modulated by pre-stimulus periodic EEG features, such as sensorimotor mu-rhythm phase and power. However, the influence of aperiodic brain activity on corticospinal excitability is largely unexplored. ObjectivesWe evaluated the relationship between aperiodic and periodic mu-power, aperiodic exponent, and mu-phase on MEP amplitudes using EEG-TMS. MethodsWe applied 800 single TMS pulses to the left primary motor cortex in 78 healthy adults. We calculated aperiodic/periodic mu-power, aperiodic exponent, and mu-phase for each trial from the pre-stimulus C3-Hjorth transformed EEG. MEP amplitudes were extracted from the right first dorsal interosseous muscle. A linear mixed-effects model assessed relationships between MEP amplitudes and EEG features, with interactions between mu-phase and all other EEG features. ResultsAperiodic and periodic mu-power, aperiodic exponent, and mu-phase significantly modulated MEP amplitudes. Higher aperiodic/periodic mu-power was associated with larger MEP amplitudes, while higher aperiodic exponent was associated with smaller MEP amplitudes. We found a significant interaction effect of aperiodic exponent and mu-phase on MEP amplitude. Aperiodic exponent was negatively associated with MEPs for trough, rising, falling phases, but positively associated with MEPs for peak phase. ConclusionsAperiodic and periodic features of brain activity are reflective of dissociable corticospinal excitability states. Future brain-state-dependent TMS interventions may include aperiodic EEG features, such as aperiodic mu-power and exponent, in addition to the well-established periodic features.

neuroscience↗

bioRxiv2025

Cognitive and autonomic physiological responses to daily transcutaneous auricular vagus nerve stimulation in healthy adults

IntroductionThe vagus nerve regulates autonomic processes central to cognition. Transcutaneous auricular vagus nerve stimulation (taVNS) can acutely modulate executive function in healthy adults, but the effects of repeated dosing, roles of executive subdomains, and importance of sex as a biological variable require clarification. MethodIn a randomized, single-blind, sham-controlled, parallel group study, 12 healthy adults (six women) received 10 consecutive days of left monoaural taVNS (VNS) or sham (CON), with a two-week follow-up rechallenge. Stimulation (100Hz; 200{micro}s pulse width) was delivered continuously (online) at rest and during the Eriksen Flanker (inhibition), Wisconsin Card Sorting (shifting), and Sternberg (working memory) tasks. Resting autonomic measures included pupil diameter, skin conductance (SCL), mean R-R interval (mRR), respiration, and blood pressure. Primary outcomes were analyzed with linear mixed models and [S]idak-corrected contrasts. ResultsTen days of taVNS produced immediate and cumulative changes in multiple executive function subdomains that remained evident at rechallenge, with the strongest effects on accuracy. Across tasks, benefits were most pronounced in women; men displayed initial performance costs, but with greater longitudinal improvements. Cognitive effects were most evident on higher-difficulty trials. Autonomically, taVNS increased SCL during and after stimulation, amplified stimulus- and task-evoked pupil responses, and transiently lengthened mRR. Stimulation was well tolerated and blinding was acceptable. ConclusionsResolution of taVNS effects to higher-difficulty trials supports adaptive-gain modulation within executive function networks. The combination of larger evoked pupil/SCR, transient mRR lengthening, and increased SCL indicates that taVNS increased autonomic flexibility and arousal. Our findings identify biological sex and stimulation intensity as potentially important considerations for taVNS efficacy and provide longitudinal estimates to guide dosing, biomarker selection, and trial design. Collectively, the results support continued development of taVNS as a safe tool for the modulation of executive function and autonomic activity in healthy adults.

neuroscience↗