bioRxiv Science⌕ Search

Biology subjects

Hoy, K. E.

Publications and source records attributed to Hoy, K. E..

2 recordsLinked to original sources
bioRxiv2021

No evidence for changes in GABA concentration, functional connectivity, or working memory following continuous theta burst stimulation over dorsolateral prefrontal cortex

Continuous theta burst stimulation (cTBS) is thought to reduce cortical excitability and modulate functional connectivity, possibly by altering cortical inhibition at the site of stimulation. However, most evidence comes from the motor cortex and it remains unclear whether similar effects occur following stimulation over other brain regions. We assessed whether cTBS over left dorsolateral prefrontal cortex altered gamma aminobutyric acid (GABA) concentration, functional connectivity and brain dynamics at rest, and brain activation and memory performance during a working memory task. Seventeen healthy individuals participated in a randomised, sham-controlled, cross-over experiment. Before and after either real or sham cTBS, magnetic resonance spectroscopy was obtained at rest to measure GABA concentrations. Functional magnetic resonance imaging (fMRI) was also recorded at rest and during an n-back working memory task to measure functional connectivity, regional brain activity (low-frequency fluctuations), and task-related patterns of brain activity. We could not find evidence for changes in GABA concentration (P=0.66, Bayes factor [BF10]=0.07), resting-state functional connectivity (P(FWE)>0.05), resting-state low-frequency fluctuations (P=0.88, BF10=0.04), blood-oxygen level dependent activity during the n-back task (P(FWE) >0.05), or working memory performance (P=0.13, BF10=0.05) following real or sham cTBS. Our findings add to a growing body of literature suggesting the effects of cTBS are highly variable between individuals and question the notion that cTBS is a universal inhibitory paradigm.

neuroscience↗
bioRxiv2017

Impact of different intensities of intermittent theta burst stimulation on the cortical properties during TMS-EEG and working memory performance

IntroductionIntermittent theta burst stimulation (iTBS) is a non-invasive brain stimulation technique capable of increasing cortical excitability beyond the stimulation period. Due to the rapid induction of modulatory effects compared to conventional repetitive transcranial magnetic stimulation (rTMS) paradigms, prefrontal application of iTBS is gaining popularity as a therapeutic tool for psychiatric disorders such as depression. In an attempt to increase efficacy, higher than conventional intensities are currently being applied. The assumption that this increases neuromodulatory effect is well established for the standard rTMS paradigms but may be mechanistically false for iTBS. This study examined the influence of intensity on the neurophysiological and behavioural effects of iTBS in the prefrontal cortex.\n\nMethods16 healthy participants received iTBS over prefrontal cortex (F1 electrode) at either 50, 75 or 100% resting motor threshold (rMT) in separate sessions. Single-pulse TMS and concurrent electroencephalography (EEG) was used to assess changes in cortical reactivity measured as TMS-evoked potentials (TEPs) and TMS-evoked oscillations. The n-back task (2-back and 3-back) were used to assess changes in working memory (accuracy and reaction time).\n\nResultsThe data can be summarised as an inverse U-shape relationship between intensity and iTBS plastic effects, where 75% iTBS resulted in the largest neurophysiological changes both in TMS-EEG and working memory. Even though 75% iTBS showed significantly decreased reaction time in the 3-back task, between condition comparisons revealed no significant differences.\n\nConclusionsThe assumption that higher intensity results in greater neuromodulatory effects is false, at least in healthy individuals, and should be carefully considered for clinical populations. Neurophysiological changes associated with working memory following iTBS suggest functional relevance. However, the effects of different intensities on behavioural performance remain elusive in the present healthy sample.\n\nHighlightsO_LIEffects of prefrontal iTBS at 50, 75 and 100% rMT were investigated\nC_LIO_LIInverse U-shape relationship between intensity and neurophysiological effects\nC_LIO_LIEffects on the behavioural performance remain elusive in healthy individuals\nC_LI\n\nDisclosures and conflict of interestsSWC was supported by a Monash Graduate Scholarship. NCR is supported by a NHMRC Early Career Fellowship (1072057). KEH is supported by a NHMRC Career Development Fellowship (1082894). PBF is supported by a NHMRC Practitioner Fellowship (1078567). PBF has received equipment for research from MagVenture A/S, Medtronic Ltd, Cervel Neurotech and Brainsway Ltd and funding for research from Neuronetics and Cervel Neurotech. He is on the scientific advisory board for Bionomics Ltd. There are no other conflicts.

neuroscience↗