RA. Hawkins and JF. Biebuyck (1979). Ketone bodies are selectively used by individual brain regions. Science (New York, N.Y.), 205(4403), 325-7. https://doi.org/10.1126/science.451608

PubMed 451608

[Abstract]
Close study of 3-hydroxybutyrate uptake by brain suggests that its metabolism is limited by permeability. Furthermore, the permeability characteristics vary from region to region; areas known to have no blood-brain barrier show the highest rate of utilization. The results imply that rather than substitute fuels, ketone bodies should be considered supplements which partially supply specific areas but are incapable of supporting the entire energy requirement of all brain regions.