title: Assessment of cortical excitability using threshold tracking techniques.
abstract: Conventional paired-pulse transcranial magnetic stimulation (TMS) techniques of assessing cortical excitability are limited by fluctuations in the motor evoked potential (MEP) amplitude. The aim of the present study was to determine the feasibility of threshold tracking TMS for assessing cortical excitability in a clinical setting and to establish normative data. Studies were undertaken in 26 healthy controls, tracking the MEP response from abductor pollicis brevis. Short-interval intracortical inhibition (SICI) occurred up to an interstimulus interval (ISI) of 7-10 ms, with two distinct peaks evident, at ISIs of < or =1 and 3 ms, followed by intracortical facilitation to an ISI of 30 ms. Long-interval intracortical inhibition (LICI) occurred at ISIs of 50-300 ms, peaking at 150 ms. The present study has confirmed the effectiveness of the threshold tracking TMS technique in reliably and reproducibly measuring cortical excitability. Simultaneous assessment of upper and lower motor neuronal function with threshold tracking techniques may help to determine the site of disease onset and patterns of progression in neurodegenerative diseases.
authors.affiliation: Prince of Wales Medical Research Institute and Prince of Wales Clinical School, University of New South Wales, Barker Street, Randwick, Sydney, NSW 2031, Australia.
authors.forename: Steve
authors.initials: S
authors.lastname: Vucic
authors.forename: James
authors.initials: J
authors.lastname: Howells
authors.forename: Louise
authors.initials: L
authors.lastname: Trevillion
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Kiernan
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D003627:Data Interpretation, Statistical; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D015203:Reproducibility of Results; D012684:Sensory Thresholds / Q000502:physiology; D050781:Transcranial Magnetic Stimulation