Brain energy supply and usage

• Main Author: Howarth, C.
• Published: University College London (University of London) 2008
• Subjects: 612.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625149

Although a coupling between cerebral energy consumption and neuronal activity was initially suggested over a hundred years ago, the exact relationship remains unclear. This thesis addresses four aspects of the energy supply to the brain. First, blood flow is increased to areas where neurons are more active, and it is this blood flow increase which forms the basis of functional imaging techniques. In contrast to the common assumption that blood flow regulation occurs solely at the arteriole level, I have demonstrated experimentally that blood flow control, mediated by pericytes, also occurs in capillaries. Second, it has been proposed that glutamate transporters coordinate CNS glucose and oxygen usage: glutamate released from neurons is taken up into astrocytes, evoking glycolysis which is suggested to export lactate to power neuronal oxidative phosphorylation. I tested this hypothesis by measuring oxygen use when glial glutamate uptake was blocked, and found that this had little effect on the oxygen use evoked by neural activity, arguing against the idea that glutamate uptake and astrocyte lactate export regulate neuronal oxidative phosphorylation. Third, although it is known that most of the brain's energy is used on reversing the ion fluxes which generate action potentials and synaptic currents, in general it is unknown how the energetic resources to the brain are allotted to carry out different aspects of neuronal information processing. I constructed an energy budget for the cerebellum using the measured properties of cells in this area. This provides insight into how evolution has allocated energy at the cellular and subcellular levels to different parts of a neural computation. Finally, I estimated the amount of brain energy use expended on conscious perception of stimuli, as opposed to being used on unconscious information processing. Surprisingly, only a small percentage of brain energy is used on conscious perception.