The effect of coil type and limb dominance in the assessment of lower-limb motor cortex excitability using TMS

• Published in: Neuroscience letters 2019-04, Vol.699, p.84-90
• Main Authors: Dharmadasa, Thanuja, Matamala, José M., Howells, James, Simon, Neil G., Vucic, Steve, Kiernan, Matthew C.
• Format: Article
• Language: English
• Subjects: Adult; Aged; Coil; Cortical Excitability - physiology; Corticomotoneuronal function; Evoked Potentials, Motor - physiology; Female; Functional Laterality - physiology; Humans; Intracortical facilitation; Lower Extremity - physiology; Lower-limb; Male; Middle Aged; Motor Cortex - physiology; Muscle, Skeletal - physiology; Resting motor threshold; Threshold tracking transcranial magnetic stimulation; Transcranial Magnetic Stimulation - instrumentation; Transcranial Magnetic Stimulation - methods; Young Adult
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2019.01.050

•Optimal coil type to assess lower-limb cortical function was determined with TT-TMS.•Key differences were found in generated cortical parameters between the coil types.•The double cone coil showed greatest efficacy, generating lowest motor thresholds.•Intracortical facilitation was comparatively greater using the double cone coil.•There was no cortical asymmetry between dominant and non-dominant hemispheres. Purpose: Clinical application of transcranial magnetic stimulation (TMS) has rapidly increased but the majority of studies have targeted upper limb muscles, with few exploring the lower-limb. Differences of coil choice have added to methodological difficulties of lower-limb studies and have challenged consistent interpretation of these parameters. The aims of this study were to determine the optimal coil choice for assessing lower-limb cortical excitability and assess laterality of normal cortical function. Methods: 69 recordings were undertaken from the tibialis anterior muscle from 48 healthy participants. Three coil types currently used in lower-limb studies (90 mm circular; 70 mm figure-of-8; and 110 mm double cone) were explored using single pulse TMS and paired-pulse threshold tracking TMS (TT-TMS) paradigms, with peripheral function also assessed. Cortical symmetry was ascertained with bilateral recordings (dominant versus non-dominant muscles). Results: The double-cone coil showed greatest efficacy, with significantly lower resting motor thresholds (49.0 ± 2.3%, p