Threshold curves for transcranial magnetic stimulation to improve reliability of motor pathway status assessment

• Published in: Clinical neurophysiology Vol. 122; no. 5; pp. 975 - 983
• Main Authors: Julkunen, Petro, Ruohonen, Jarmo, Sääskilahti, Saara, Säisänen, Laura, Karhu, Jari
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ireland Ltd 01.05.2011; Elsevier
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Brain Mapping; Cortex; Differential Threshold; Electrodiagnosis. Electric activity recording; Electromyography; Evoked Potentials, Motor - physiology; Excitability; Female; Humans; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Middle Aged; Motor Cortex - physiology; Motor evoked potential; Motor threshold; Nervous system; Neurology; Neurons - physiology; Transcranial magnetic stimulation; Transcranial Magnetic Stimulation - methods; Vascular diseases and vascular malformations of the nervous system; Excitability; Motor evoked potential; Transcranial magnetic stimulation; Motor threshold; Cortex; Motor pathway; Central nervous system; Electrophysiology; Cardiovascular disease; Encephalon; Posture; Vascular disease; Motor cortex; Muscle; Excitation; Cerebrovascular disease; Monitoring; Human; Nervous system diseases; Stroke; Stimulator; Representation; Trauma; Cerebral disorder; Repeatability; Sensitivity; Central nervous system disease; Reliability
• ISSN: 1388-2457; 1872-8952; 1872-8952
• DOI: 10.1016/j.clinph.2010.09.005

► We present a straight-forward protocol for simultaneous determination of resting motor threshold and assessment of excitation-inhibition balance in motor cortex and pathways using navigated transcranial magnetic stimulation. ► The introduced protocol was found valid and repeatable, and sensitive to minor changes in stimulated cortical area. ► This stimulation protocol may be useful in the follow-up and monitoring of motor pathway recovery e.g. from stroke or trauma. To provide a new protocol for a simple determination of resting motor threshold (MT) and assessment of excitation-inhibition balance in motor cortex and pathways. Navigated TMS was used to map cortical representation area of the FDI muscle bilaterally in ten healthy subjects. Reference MTs were determined using a threshold hunting paradigm. Subsequently, a novel stimulation protocol was applied which included 70 stimuli (7 intensities, sub- and suprathreshold). The “MT-curve” was constructed by computing the MTs with several threshold amplitudes with the novel protocol. The measurements were repeated. Sensitivity of the MT-curve to stimulus location was also tested. The reference MTs agreed with those determined with the novel protocol ( R = 0.96–0.99, p < 0.001). Based on coefficient of repeatability derived from non-parametric one-way ANOVA, the repeatability was good ( ρ AO = 0.929, p < 0.05). Generally, the mean difference between the repeated MT-curves was <3% of the maximum stimulator output. Coil movement 10 mm medially from the optimal stimulus location increased that difference to >7%. The MTs derived using the MT-curve protocol concurred with the reference MTs. The MT-curve is highly reproducible and sensitive to the exact cortical location of stimulation. The MT-curves provide a simple way to assess motor pathway status using a single stimulation train. This may be useful in the follow-up and monitoring of motor pathway recovery e.g. from stroke or trauma.