title: The effect of current direction induced by transcranial magnetic stimulation on the corticospinal excitability in human brain.
abstract: Evoked spinal cord potentials (ESCPs) from the cervical epidural space and motor evoked potentials (MEPs) from the hand muscles were recorded simultaneously in 6 subjects following transcranial magnetic stimulation in two different coil orientations on motor cortex. The onset latency of the MEPs was approximately 1 ms shorter when the induced current flowed in a latero-medial direction (L-M stimulation) on the motor cortex as compared to a postero-anterior direction (P-A stimulation). Hence, L-M stimulation elicited an earlier component of the ESCPs than that induced by P-A stimulation. During general anesthesia with Sevoflurane, only the first component of the ESCPs could be elicited routinely following L-M stimulation. In contrast, all components of the ESCPs were dramatically attenuated following P-A stimulation. Moreover, first component latency of the ESCPs induced by L-M stimulation was almost the same as that induced by transcranial anodal electrical stimulation. These results suggest that if the induced current following transcranial magnetic stimulation flows in a latero-medial direction on motor cortex, it preferentially stimulates the corticospinal tract non-synaptically (producing a D-wave). However, if the induced current flows in a postero-anterior direction, it preferentially stimulates the corticospinal tract trans-synaptically (producing I-waves). Therefore, the direction of magnetically induced current is crucial in determining corticospinal excitability in the human brain.
authors.affiliation: Department of Orthopedic Surgery, University of Yamaguchi, School of Medicine, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kaneko
authors.forename: S
authors.initials: S
authors.lastname: Kawai
authors.forename: Y
authors.initials: Y
authors.lastname: Fuchigami
authors.forename: H
authors.initials: H
authors.lastname: Morita
authors.forename: A
authors.initials: A
authors.lastname: Ofuji
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000502:physiology*; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013116:Spinal Cord / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation