brain surgery

  I am doing a report for class and I need to know: Why do you
  keep the patients awake during surgery??
=====================================================================
Thanks for your question.  The main reason to keep a patient awake during
a neuro-surgical procedure is when it involves the resection of a tumor,
or of a focus of epilepsy that is very close or actually within a so-called
"eloquent" brain region.  These are regions where the resection would result
in significant motor, or sensory impairment, and they include: the primary
motor cortex, and adjacent suplementary motor cortices; the primary somatosensory
cortex; the visual cortex; and the auditory cortex.  One method of "mapping"
these areas intra-operatively (thus avoiding their damage) is by using
small focal eletric stimulation over the brain tissue and rely on the
patient's perception of the stimulus.  A modification of this method is
to ask the patient to execute a simple task (such as saying words) and
observe interruption/disruption of the task during electric simulation.
Since the brain tissue itself does not contain pain receptors, all these
manipulation are painless to the patient.
I hope this information is helpful.  Best of luck.