Biology subjects

Caulfield, K. A.

Publications and source records attributed to Caulfield, K. A..

7 recordsLinked to original sources

bioRxiv2025

Accelerated rTMS for Enhancing Intact Cognition: An Examination of Dose Effects on Electrocortical Indicators of Attention and Working Memory

BACKGROUND AND AIMSImprovements in cognition (e.g., attention, working memory) are common after repetitive trans-cranial magnetic stimulation (rTMS) treatment and have also been observed in non-clinical samples. This study investigated whether rTMS can enhance cognitive resilience in individuals who perform in high-stress environments using cognitive measures and electroencephalography (EEG) to explore potential neural mechanisms of rTMS-induced cognitive change. METHODS40 college-educated adults not reporting cognitive or psychiatric concerns underwent a 5-day accelerated (10 sessions/ day) rTMS treatment and pre-post cognitive assessment. Participants were assigned to 1 of 10 doses defined as number of active vs. sham stimulation sessions/ day (total active pulses = 3,000 - 30,000). To assess cognitive effects, standard batteries (NIH Toolbox, Spaceflight Cognitive Assessment Tool for Windows [WinSCAT]) were administered - and a subset (n=21) also did an N-Back working memory task with EEG measurement - before, immediately after, and 1 month after rTMS. For all indices, linear and quadratic correlations of pre-to-post-rTMS change with dose were examined to test if an optimal dose was achieved. RESULTSFrom pre- to post-rTMS, participants improved in fluid cognition (working memory, processing speed) as measured by NIH toolbox, t(39)=8.4, p<.001, d=1.3, and WinSCAT, t(39)=4.1, p<.001, d=.65; and, improvement in the latter related linearly to rTMS dose, r(39)=.40, p=.01. Regarding EEG, subjects who received high (6+ active sessions/day) also showed increased amplitudes of an event-related marker of stimulus-directed attention (P300) whether it was elicited by simple task targets, t(10)=3.1, p=.01, d=.95, or task-unrelated noise stimuli played during the task as probes of peripheral attention, t(10)=3.6, p=.005, d=1.1. Additionally, there were linear relationships between change magnitude and rTMS dose for simple task target-related, r(20)=.45, p=.04, and peripheral noise-related, r(20)=.54, p=.009, P300s. CONCLUSIONSrTMS improved fluid reasoning abilities and also changed how dynamic attention is deployed during high-demand challenges as a potential mediator of fluid cognition improvements. While linear dose-response relationships support that changes were rTMS-elicited, absence of a response curve asymptote also suggests that still-higher doses could be warranted to achieve maximal effects in non-clinical samples.

neuroscience↗

bioRxiv2025

Focused ultrasound to the bilateral thalamus causally modulates human cognitive attention in a frequency- and intensity-dependent manner

The centromedian nucleus of the thalamus (CMT) is a core arousal center with potential for enhancing cognitive attention. While emergent focused ultrasound can reach this area, the stimulation paradigms which may enhance function in humans remain unknown. Here we performed bilateral stimulation of the CMT using a novel ultrasound neuromodulation wearable device using 3 distinct pulse frequencies. We found that a brief 25Hz stimulation enhanced reaction time in a in a directed attention Oddball task for at least 40 minutes. Pre-post task electrocortical EEG revealed a correlation between reaction time and the prevalence of arousal related alpha and theta cortical activity. Examination of dose dependence revealed bidirectional modulation of arousal state, with lower intensities preferentially enhancing cognitive function. Pre- and post-MRI scans showed no neuroradiological changes due to stimulation. Collectively, these findings demonstrate that targeted LIFU stimulation of the CMT can safely enhance cognitive function in healthy individuals with carefully designed parameters.

neuroscience↗

bioRxiv2023

From scalp to cortex, the whole isn't greater than the sum of its parts: introducing GetTissueThickness (GTT) to assess age and sex differences in tissue thicknesses

Noninvasive techniques to record and stimulate the brain rely on passing through the tissues in between the scalp and cortex. Currently, there is no method to obtain detailed information about these scalp-to-cortex distance (SCD) tissues. We introduce GetTissueThickness (GTT), an open-source, automated approach to quantify SCD, and unveil how tissue thicknesses differ across age groups, sexes and brain regions (n = 250). We show that men have larger SCD in lower scalp regions and women have similar-to-larger SCD in regions closer to the vertex, with aging resulting in increased SCD in fronto-central regions. Soft tissue thickness varies by sex and age, with thicker layers and greater age-related decreases in men. Compact and spongy bone thickness also differ across sexes and age groups, with thicker compact bone in women in both age groups and an age-related thickening. Older men generally have the thickest cerebrospinal fluid layer and younger women and men having similar cerebrospinal fluid layers. Aging mostly results in grey matter thinning. Concerning SCD, the whole isnt greater than the sum of its parts. GTT enables rapid quantification of the SCD tissues. The distinctive sensitivity of noninvasive recording and stimulation modalities to different tissues underscores the relevance of GTT.

neuroscience↗

bioRxiv2023

A Systematic Review and Large-Scale tES and TMS Electric Field Modeling Study Reveals How Outcome Measure Selection Alters Results in a Person- and Montage-Specific Manner

BackgroundElectric field (E-field) modeling is a potent tool to examine the cortical effects of transcranial magnetic and electrical stimulation (TMS and tES, respectively) and to address the high variability in efficacy observed in the literature. However, outcome measures used to report E-field magnitude vary considerably and have not yet been compared in detail. ObjectivesThe goal of this two-part study, encompassing a systematic review and modeling experiment, was to provide an overview of the different outcome measures used to report the magnitude of tES and TMS E-fields, and to conduct a direct comparison of these measures across different stimulation montages. MethodsThree electronic databases were searched for tES and/or TMS studies reporting E-field magnitude. We extracted and discussed outcome measures in studies meeting the inclusion criteria. Additionally, outcome measures were compared via models of four common tES and two TMS modalities in 100 healthy younger adults. ResultsIn the systematic review, we included 118 studies using 151 outcome measures related to E-field magnitude. Structural and spherical regions of interest (ROI) analyses and percentile-based whole-brain analyses were used most often. In the modeling analyses, we found that there was an average of only 6% overlap between ROI and percentile-based whole-brain analyses in the investigated volumes within the same person. The overlap between ROI and whole-brain percentiles was montage- and person-specific, with more focal montages such as 4x1 and APPS-tES, and figure-of-eight TMS showing up to 73%, 60%, and 52% overlap between ROI and percentile approaches respectively. However, even in these cases, 27% or more of the analyzed volume still differed between outcome measures in every analyses. ConclusionsThe choice of outcome measures meaningfully alters the interpretation of tES and TMS E-field models. Well-considered outcome measure selection is imperative for accurate interpretation of results, valid between-study comparisons, and depends on stimulation focality and study goals. We formulated four recommendations to increase the quality and rigor of E-field modeling outcome measures. With these data and recommendations, we hope to guide future studies towards informed outcome measure selection, and improve the comparability of studies.

neuroscience↗

bioRxiv2021

Optimizing transcranial direct current stimulation (tDCS) electrode position, size, and distance doubles the on-target cortical electric field: Evidence from 3000 Human Connectome Project models

Transcranial direct current stimulation (tDCS) is a widely used noninvasive brain stimulation technique with mixed results and no FDA-approved therapeutic indication to date. So far, thousands of published tDCS studies have placed large scalp electrodes directly over the intended brain target and delivered the same stimulation intensity to each person. Inconsistent therapeutic results may be due to insufficient cortical activation in some individuals and the inability to determine an optimal dose. Here, we computed 3000 MRI-based electric field models in 200 Human Connectome Project (HCP) participants, finding that the largely unexamined variables of electrode position, size, and between-electrode distance significantly impact the delivered cortical electric field magnitude. At the same scalp stimulation intensity, smaller electrodes surrounding the neural target deliver more than double the on-target cortical electric field while stimulating only a fraction of the off-target brain regions. This new optimized tDCS method can ensure sufficient cortical activation in each person and could produce larger and more consistent behavioral effects in every prospective research and transdiagnostic clinical application of tDCS.

neuroscience↗

bioRxiv2020

Assessing the Intra- and Inter-Subject Reliability of the Perturbational Complexity Index (PCI) of Consciousness for Three Brain Regions Using TMS-EEG

BackgroundThe perturbational complexity index (PCI) is a useful measure of consciousness that combines transcranial magnetic stimulation (TMS) with electroencephalography (EEG). However, the PCI has not been assessed for reliability between sessions nor is there a clear best stimulation target to acquire a PCI. Objective/HypothesisWe assessed the reliability of within-subject PCIs between 3 sessions with stimulation over the same premotor, motor, and parietal targets between visits, hypothesizing that we could determine a most reliable TMS-EEG target to acquire PCIs in healthy, conscious adults. MethodsPCIs were acquired for 9 participants (5 women) over 3 sessions within a week. A 64 channel EEG system was used with all electrode impedances [≤] 10k{Omega}. Premotor, motor, and parietal stimulation targets were identified using a real-time Matlab graphical user interface (GUI). Neuronavigation using an MRI-template brain ensured that every TMS pulse was delivered within 3.0mm and 5{degrees} of the stimulation target. ResultsPremotor, motor, and parietal PCIs all had significant PCIs (all p < 0.05). However, parietal and motor PCIs had excellent reliability (ICCs = 0.927 and 0.857 respectively) whereas premotor PCIs had good reliability (ICC = 0.737). PCIs were similar between brain sites within each subject in a single visit, but with only a moderate effect (p = 0.024, ICC = 0.480). PCIs on a group level did not differ between brain sites (p = 0.589). ConclusionsThe PCI is a reliable measure over this timeframe within each subject for single brain targets. PCIs for parietal and motor sites are most similar between visits. Due to only moderate similarity between PCIs from three brain sites within each session, PCIs should be acquired over at least two brain sites, with parietal and motor regions as the top candidates.

neuroscience↗

bioRxiv2019

Transcranial Electrical Stimulation Motor Threshold Combined with Reverse-Calculated Electric Field Modeling Can Determine Individualized tDCS Dosage

BackgroundUnique amongst brain stimulation tools, transcranial direct current stimulation (tDCS) currently lacks an easy method for individualizing dosage.\n\nObjectiveCan one individually dose tDCS? We developed a novel method of reverse-calculating electric-field (E-field) models based on Magnetic Resonance Imaging (MRI) scans that can determine individualized tDCS dose. We also sought to develop an MRI-free method of individualizing tDCS dose by measuring transcranial magnetic stimulation (TMS) motor threshold (MT) and single pulse, suprathreshold transcranial electrical stimulation (TES) MT and regressing it against E-field modeling.\n\nMethodsIn 29 healthy adults, we acquired TMS MT, TES MT, and structural MRI scans with a fiducial marking the motor hotspot. We then computed a \"reverse-calculated tDCS dose\" of tDCS applied at the scalp needed to cause a 1.00V/m E-field at the cortex. Finally, we examined whether the predicted E-field values correlated with each participants measured TMS MT or TES MT.\n\nResultsWe were able to determine a reverse-calculated tDCS dose for each participant. The Transcranial Electrical Stimulation MT, but not the Transcranial Magnetic Stimulation MT, significantly correlated with the calculated tDCS dose determined by E-field modeling (R2 = 0.509, p < 0.001).\n\nConclusionsReverse-calculation E-field modeling, alone or in combination with TES MT, shows promise as a method to individualize tDCS dose. The large range of the reverse-calculated tDCS doses between subjects underscores the likely need to individualize tDCS dose. If these results are confirmed in future studies, TES MT may evolve into an inexpensive and quick method to individualize tDCS dose.

neuroscience↗