title: Intra-operative recording of motor tract potentials at the cervico-medullary junction following scalp electrical and magnetic stimulation of the motor cortex.
abstract: Activity in descending motor pathways after scalp electrical and magnetic brain stimulation of the motor cortex was recorded from the exposed cervico-medullary junction in six patients having trans-oral surgery of the upper cervical spine. Recordings during deep anaesthesia without muscle paralysis revealed an initial negative potential (D wave) at about 2 ms with electrical stimulation in five of the six patients. This was followed by a muscle potential which obscured any later waveforms. Magnetic stimulation produced clear potentials in only one patient. The earliest wave to magnetic stimulation during deep anaesthesia was 1-2 ms later than the earliest potential to electrical stimulation. Following lightening of the anaesthetic and the administration of muscle relaxants a series of later negative potentials (I waves) were more clearly seen to both electrical and magnetic stimulation. More I waves were recorded to magnetic stimulation during light anaesthesia than during deep anaesthesia. Increasing the intensity of electrical stimulation also produced an extra late I wave. At the highest intensity of magnetic stimulation the latency of the earliest potential was comparable to the D wave to electrical stimulation. The intervals between these various D and I waves corresponded to those previously described for the timing of single motor unit discharge after cortical stimulation.
authors.affiliation: MRC Human Movement and Balance Unit, University Department of Clinical Neurology, National Hospitals for Neurology and Neurosurgery, London, UK.
authors.forename: P D
authors.initials: PD
authors.lastname: Thompson
authors.forename: B L
authors.initials: BL
authors.lastname: Day
authors.forename: H A
authors.initials: HA
authors.lastname: Crockard
authors.forename: I
authors.initials: I
authors.lastname: Calder
authors.forename: N M
authors.initials: NM
authors.lastname: Murray
authors.forename: J C
authors.initials: JC
authors.lastname: Rothwell
authors.forename: C D
authors.initials: CD
authors.lastname: Marsden
mesh_terms: D000328:Adult; D000368:Aged; D002574:Cervical Vertebrae / Q000503:physiopathology / Q000601:surgery*; D004525:Efferent Pathways / Q000503:physiopathology; D004558:Electric Stimulation / Q000295:instrumentation; D004574:Electromagnetic Fields; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006225:Hand / Q000294:innervation; D006801:Humans; D008297:Male; D008526:Medulla Oblongata / Q000503:physiopathology; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation*; D009044:Motor Cortex / Q000503:physiopathology*; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000294:innervation; D011149:Pons / Q000503:physiopathology; D013116:Spinal Cord / Q000503:physiopathology*; D013117:Spinal Cord Compression / Q000503:physiopathology / Q000601:surgery*; D013122:Spinal Diseases / Q000503:physiopathology / Q000601:surgery*; D009435:Synaptic Transmission / Q000502:physiology