ANATOMICAL LEVEL (the level reached by progressive damage)

CONSCIOUSNESS

RESPIRATION

PUPILS

OCULOMOTOR-VESTIBULAR

MOTOR

Upper diencephalon

Drowsy (dull)

Eupnea with yawns and sighs

Small, reactive

Depression of ocular checking and fast component of nystagmus

Left hemiparesis, bilateral paratonia

Lower diencephalon

Coma

Cheyne-Stokes (CSR)

Small, reactive

Loss of above

Left hemiparesis, decorticate

Mesencephalon

Coma

CSR or central neurogenic hyperventilation (CNH)

Midposition, fixed (MPF)

Dysconjugate response; loss of medial rectus function on horizontal gaze; may see loss of lateral rectus function also (see text)

Decerebrate

Upper pons

Coma

CNH or ataxia

MPF

As above

Weak decrebrate

Lower pons

Coma

Ataxia or apnea

MPF

None

Flaccid, areflexic

Medulla

Coma

Apnea

MPF

None

Same