Corticospinal direct response in humans: identification of the motor cortex during intracranial surgery under general anaesthesia.

The corticospinal direct (D) response to stimulation of the motor cortex exposed for intracranial surgery was recorded in 20 cases from wire electrodes inserted into the spinal epidural space. The D response was obtained from stimulation of restricted areas of the cerebral cortex, that is, the hand, trunk and thigh areas of the motor cortex. The D response was resistant to anaesthesia and unaffected by muscle relaxants. Thus, recordings of the D response are useful for identifying the location of the motor cortex during intracranial surgery under general anaesthesia.