Wait I might have to dig up the sources. But it is generally accepted in the “Keto sphere” that the brain runs on glucose. Even in ketosis the body creates some glucose for this purpose.
I don't have sources handy, but IIRC the brain will generally to run on about a 60/40 or 70/30 mix of ketones/glucose, but in some experiment they gave people in ketosis a does of insulin to drop their blood sugar to near 0, and they didn't pass out and were otherwise fine.