Case of the Month #32 Brain Stem Death

Published 03/10/2022

How does the “M” score of the GCS assessment correlate with neurological function?

The motor response to verbal or painful stimulus directly correlates with the complexity of neurological function required to produce it. 

M Score


Required Brain Function


Obeys Command

Complex polysynaptic, bilateral hemisphere pathways involving higher brain centres


Localises to pain

Unconscious response but still requires pre-motor and motor cortex to be functional


Withdrawal from pain

As above but without the pre-motor areas functioning


Flexion to pain

Corticospinal tract not functioning and the more primitive rubrospinal tract in the midbrain takes over


Extension to pain

Loss of midbrain function reduces the motor response to vestibulospinal/reticulospinal tracts in the medulla


No response

All centres and tracts including and above brain-stem non functioning


This linear relationship between motor score and brain function is the reason neurosurgical centres place more onus on this part of the GCS when prognosticating or monitoring for deteriorations [1].   Conversely, the cause of changes in Eye or Voice scores can represent an array of clinical conditions aside from interruptions in brain function.