An increasing number of studies have used the intermittent theta-burst stimulation (iTBS) protocol to investigate neural plasticity non-invasively in the prefontal cortex in healthy humans and in patients with psychiatric disorders. However, the variability in the neurophysiological response to iTBS stimulation is high. The cause of this variability is multifactorial and to some degree still unknown. Therefore, the current study explores inter- and intra-individual factors that are potentially moderating iTBS-induced excitability changes. A greater understanding of these determinants would be highly valuable for optimizing the therapeutic application of iTBS.
The investigators will measure the cortical excitability induced by iTBS with concurrent TBS/fNIRS technique in the same healthy individuals on multiple testing days. Meanwhile, several potential inter- (age, gender, etc.) and intra-individual factors (daily mood, daily physical activity levels, etc.) recently identified in non-invasive transcranial brain stimulation studies will be assessed before applying iTBS to the same individual on each testing day.
Study Type
INTERVENTIONAL
Allocation
NA
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
40
The iTBS protocol consists of 20 trains of stimulation. Each train comprises ten 3-pulse bursts, delivered at an intra-burst frequency of 50 Hz, with a 5 Hz overall frequency, followed by 8 seconds of rest. A total of 600 pulses (10\*3\*20) will be administered in this 3-minute iTBS protocol. Concurrent TBS/fNIRS stimulation will be applied over the left DLPFC at an intensity of 90% of the resting motor threshold (RMT), which is considered appropriate to ensure compliance and elicit robust DLPFC activation. Considering that the fNIRS optode beneath the coil increases the distance between the TMS coil and the skull by 10 mm, we will use the equation AdjMT% = MT + 2.8 \* (Dsitex - Dm1). Therefore, 2.8 \* 10 = 28% will be added to the normal intensity. The stimulation site over the DLPFC will be determined by the MNI coordinate (x-38, y+44, z+26) reported in previous studies.
The Hong Kong Polytechnic University
Hong Kong, Hong Kong
Oxygenated hemoglobin (HbO) change compared to baseline
iTBS-induced HbO change in the DLPFC before, during and after stimulation
Time frame: During and post TBS-fNIRS measurement, up to 3 months
Deoxygenated hemoglobin (HbR) change compared to baseline
iTBS-induced HbR change in the DLPFC before, during and after stimulation
Time frame: During and post TBS-fNIRS measurement, up to 3 months
Oxygen saturation change compared to baseline
iTBS-induced oxygen saturation change in the DLPFC before, during and after stimulation
Time frame: During and post TBS-fNIRS measurement, up to 3 months
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