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Karlene Stoby, Sara Rafique, Georg Oeltzschner, Jennifer Steeves; cTBS to V1 alters GABA and Glx. Journal of Vision 2019;19(10):49c. doi: https://doi.org/10.1167/19.10.49c.
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Theta Burst Stimulation (TBS), an increasingly popular non-invasive neuromodulation technique, is used in a variety of experimental research exploring its effects on healthy controls as well as a number of neurological disorders including depression and schizophrenia. TBS can produce similar effects as repetitive transcranial magnetic stimulation (rTMS) but has the advantage that stimulation can be achieved in a much shorter amount of time. Our lab previously investigated the effects of single and accelerated (multiple) sessions of low-frequency (1 Hz “inhibitory”) rTMS to V1 on levels of the inhibitory neurotransmitter GABA and excitatory neurotransmitter Glutamate (Glx) using magnetic resonance spectroscopy (MRS). We found that the single session protocol had little effect on GABA and Glx, while accelerated sessions unexpectedly decreased GABA levels compared to baseline for 24 hours following stimulation. Here, we sought to measure the effects of cTBS (“inhibitory” TBS) to V1 on GABA and Glx compared to a sham cTBS condition. Our data show that cTBS increases GABA levels and decreases Glx levels. This contrasts our previous finding where accelerated 1 Hz rTMS reduces GABA levels. While 1 Hz rTMS and TBS may share similar behavioural inhibitory effects, they have comparatively different effects on neurotransmitter levels. This study demonstrates the short-term neural mechanisms of cTBS at V1 and highlights critical neurochemical differences between TBS and rTMS at the visual cortex.
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