why does the brain need a constant supply of glucose?

Neurons are constantly using ATP and need to perform cellular respiration constantly. This requires a large amount of the bodies oxygen and glucose. In addition, the brain has low levels of Lactate dehydrogenase(LDH) which is in charge of converting pyruvate into lactate during anaerobic cellular respiration in humans. If the nervous system were to have a higher level of LDH then the cells would be able to operate better under conditions with little oxygen. Brain tissue is also unable to store glucose in the form of glycogen if levels get low having a storage of glucose could be beneficial to brain tissue. The brain is unable to break down fatty acids as a source of energy having a source of energy besides glucose could be beneficial when glucose is scarce.