Mapping motor cortex projections to single motor units in humans with transcranial magnetic stimulation

✍ Scribed by Kannan A. Nithi; Kerry R. Mills

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 329 KB
• Volume: 23
• Category: Article
• ISSN: 0148-639X
• DOI: 10.1002/1097-4598(200010)23:10<1542::aid-mus10>3.0.co;2-a

✦ Synopsis

We devised a method to investigate the cortical organization of corticomotoneurons (CMs) to upper limb muscles. A spike-triggering technique was used, in which a tonically discharging single motor unit (SMU) triggered transcranial magnetic stimulation (TMS) of motor cortex, and the probability of producing short-latency discharges (primary excitatory responses [PERs]) was measured. PER probabilities were mapped in 34 SMUs, using a 16 cm 2 scalp grid with the central reference point having a probability of 0.5. Maps showed a single optimum point of scalp stimulation and significant decreases in PER probability with shifts of 2 cm from this point, for all subjects. These findings suggest that the colony of CMs projecting to an individual SMN is contained within a small volume of motor cortex. Changes in PER probability with shifts in stimulation site may reflect the organization of other intracortical neurons mediating TMS activation of these CMs.