This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
Primary mechanism responsible for cerebral protection effect of thiopentone is 
Select and explain. 
A. GABA action, calcium channel block and free radicle removal, B. Increased cerebral blood flow, C. Decreased (lowered) cerebn metabolism, D. Reduces cerebral 02 demand by limiting CBF
C: Decreased (lowered) cerebn metabolism
Answer: C: Decreased (lowered) cerebn metabolism 
Explanation: C i.e. Decreased (lowered) cerebn metabolism Barbiturates (thiopental), primarily decreases cerebral metabolismQ resulting in a dose related depression of cevebral metabolic oxygen consumption (CMR02).Reduced CMRO2 causes progressive slowing of EEG, a reduction in rate of ATP consumption, cerebral vasoconstriction (reducing cerebral blood flow and intracranial tension) and protection from incomplete cerebral ischemiaQ. Thiopentone Sodium* Thiopentone is a yellow coloured powder used as 2.5 % solution at 5 mg/kg dose for smooth induction. It is ultrasho actingQ due to rapid redistributionQ. It is contraindicated in porphyria.Q.