Probing short-latency cortical inhibition in the visual cortex with transcranial magnetic stimulation: A reliability study.
Dalia Khammash, Molly Simmonite, Thad A Polk, Stephan F Taylor, Sean K Meehan
Author Information
Dalia Khammash: School of Kinesiology, University of Michigan, 401 Washtenaw Ave, 41809, Ann Arbor, MI, USA; Department of Psychology, University of Michigan, 530 Church Street, 48109, Ann Arbor, MI, USA. Electronic address: daliak@umich.edu.
Molly Simmonite: Department of Psychology, University of Michigan, 530 Church Street, 48109, Ann Arbor, MI, USA. Electronic address: molsim@umich.edu.
Thad A Polk: Department of Psychology, University of Michigan, 530 Church Street, 48109, Ann Arbor, MI, USA. Electronic address: tpolk@umich.edu.
Stephan F Taylor: Department of Psychiatry, University of Michigan, 4250 Plymouth Rd, 48109, Ann Arbor, MI, USA. Electronic address: sftaylor@med.umich.edu.
Sean K Meehan: School of Kinesiology, University of Michigan, 401 Washtenaw Ave, 41809, Ann Arbor, MI, USA. Electronic address: skmeehan@uwaterloo.ca.
BACKGROUND: Transcranial magnetic stimulation (TMS) is a non-invasive method to stimulate localized brain regions. Despite widespread use in motor cortex, TMS is seldom performed in sensory areas due to variable, qualitative metrics. OBJECTIVE: Assess the reliability and validity of tracing phosphenes, and to investigate the stimulation parameters necessary to elicit decreased visual cortex excitability with paired-pulse TMS at short inter-stimulus intervals. METHODS: Across two sessions, single and paired-pulse recruitment curves were derived by having participants outline elicited phosphenes and calculating resulting average phosphene sizes. RESULTS: Phosphene size scaled with stimulus intensity, similar to motor cortex. Paired-pulse recruitment curves demonstrated inhibition at lower conditioning stimulus intensities than observed in motor cortex. Reliability was high across sessions. CONCLUSIONS: TMS-induced phosphenes are a valid and reliable tool for measuring cortical excitability and inhibition in early visual areas. Our results also provide appropriate stimulation parameters for measuring short-latency intracortical inhibition in visual cortex.
