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Alertness fluctuations when performing a task modulate cortical evoked responses to transcranial magnetic stimulation
Valdas Noreika1, Marc R Kamke2, Andrés Canales-Johnson3
1Queensland Brain Institute, University of Queensland, St Lucia, QLD 4072, Australia; Cambridge Consciousness and Cognition Lab, Department of Psychology, University of Cambridge, Cambridge CB2 3EB, United Kingdom; Department of Biological and Experimental Psychology, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
Alertness fluctuations significantly impact brain responses to Transcranial Magnetic Stimulation (TMS). This study reveals rapid, non-linear changes in neural activity during the wake-to-sleep transition, affecting motor and cortical reactivity.
Area of Science:
- Cognitive Neuroscience
- Neurophysiology
Background:
- Transcranial Magnetic Stimulation (TMS) is crucial for studying brain function.
- Variability in TMS responses is a known challenge.
- Spontaneous alertness fluctuations may explain this variability.
Purpose of the Study:
- Investigate how alertness changes during wake-to-sleep transition affect TMS responses.
- Quantify neurophysiological changes with objective alertness measures.
- Understand the neural basis of TMS variability.
Main Methods:
- Combined single-pulse TMS with electroencephalography (EEG) during natural sleep onset.
- Monitored motor evoked potentials and TMS-evoked potentials.
- Defined alertness levels based on EEG activity.
Main Results:
- Observed rapid, non-linear changes in TMS responses as alertness decreased.
- Motor evoked potential amplitude peaked during EEG flattening.
- TMS-evoked potentials increased during EEG flattening and early sleep onset (theta ripples).
Conclusions:
- Spontaneous alertness fluctuations significantly reorganize neural networks during wake-to-sleep transition.
- This reorganization impacts both motor and cortical reactivity to TMS.
- Findings provide insights into TMS response variability and neural dynamics during sleep onset.
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