Effects of acute stimulation through contacts placed on the motor cortex for chronic stimulation.
OBJECTIVE
We tried to determine which neural elements were activated in awake subjects by stimulation through contacts placed chronically on the motor cortex.


METHODS
We recorded the motor effects of stimulation through 4 disc contacts placed in the subdural space over the motor cortex in 9 patients undergoing chronic stimulation for the control of pain or for the control of the rigidity of multiple system atrophy.


RESULTS
Single stimuli could elicit short latency motor evoked potentials or facilitate active motoneurons in the contralateral limbs. The responsible neural elements had a short chronaxie (the pulse duration necessary to reach threshold with a stimulus intensity twice that required to reach threshold at the longest pulse duration used) and refractory period implying that they were myelinated axons. The facilitation was larger with cathodal than with anodal monopolar stimulation. The short latency facilitation in response to the second of two stimuli was greater at condition test intervals of 2-5 ms. This enhancement could be demonstrated with conditioning stimuli subthreshold for the excitation of active motoneurons suggesting that it arose, in part, at the level of the cortex. Single cortical stimuli could result in inhibition of voluntarily activated motoneurons. The inhibition was larger with cathodal than anodal monopolar stimulation. The responsible neural elements also had a short chronaxie and refractory period.


CONCLUSIONS
Stimulation in awake subjects through contacts placed chronically over the motor cortex appears to activate axons in the cortex, which excite both corticospinal neurons and inhibitory neurons.
Hanajima
R
R
University Health Network Research Institute, MP 13-319 Toronto Western Hospital, University of Toronto, 399 Bathurst Street, Ont., Canada M5T 2S8.
Ashby
P
P
Lang
A E
AE
Lozano
A M
AM
D000328:Adult; D000368:Aged; D001364:Awareness; D017097:Electric Impedance; D004599:Electric Stimulation Therapy; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000166:cytology / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology; D009069:Movement Disorders / Q000503:physiopathology* / Q000628:therapy*; D019578:Multiple System Atrophy / Q000503:physiopathology* / Q000628:therapy*; D009433:Neural Inhibition; D011930:Reaction Time