Vertex Stimulation as a Control Site for Transcranial Magnetic Stimulation: A Concurrent TMS/fMRI Study.
BACKGROUND
A common control condition for transcranial magnetic stimulation (TMS) studies is to apply stimulation at the vertex. An assumption of vertex stimulation is that it has relatively little influence over on-going brain processes involved in most experimental tasks, however there has been little attempt to measure neural changes linked to vertex TMS. Here we directly test this assumption by using a concurrent TMS/fMRI paradigm in which we investigate fMRI blood-oxygenation-level-dependent (BOLD) signal changes across the whole brain linked to vertex stimulation.


METHODS
Thirty-two healthy participants to part in this study. Twenty-one were stimulated at the vertex, at 120% of resting motor threshold (RMT), with short bursts of 1 Hz TMS, while functional magnetic resonance imaging (fMRI) BOLD images were acquired. As a control condition, we delivered TMS pulses over the left primary motor cortex using identical parameters to 11 other participants.


RESULTS
Vertex stimulation did not evoke increased BOLD activation at the stimulated site. By contrast we observed widespread BOLD deactivations across the brain, including regions within the default mode network (DMN). To examine the effects of vertex stimulation a functional connectivity analysis was conducted.


CONCLUSIONS
The results demonstrated that stimulating the vertex with suprathreshold TMS reduced neural activity in brain regions related to the DMN but did not influence the functional connectivity of this network. Our findings provide brain imaging evidence in support of the use of vertex simulation as a control condition in TMS but confirm that vertex TMS induces regional widespread decreases in BOLD activation.
Neuroscience and Aphasia Research Unit (NARU), School of Psychological Sciences, University of Manchester, UK; WCU Department of Brain and Cognitive Engineering, Korea University, South Korea.
JeYoung
J
Jung
Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, UK.
Andreas
A
Bungert
Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, UK.
Richard
R
Bowtell
WCU Department of Brain and Cognitive Engineering, Korea University, South Korea; School of Psychology, University of Nottingham, Nottingham, NG7 2RD, UK. Electronic address: stephen.jackson@nottingham.ac.uk.
Stephen R
SR
Jackson
D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
Concurrent TMS/fMRI; Transcranial magnetic stimulation; Vertex stimulation