Our brains make up only about 2% of our body mass, but when it comes to metabolism they are real energy guzzlers. About 20% of the oxygen we breath and 25% of our glucose supply goes straight to our heads, keeping the brain's 100 billion neurons, plus astrocytes and other cells, well nourished. And yet our brains use almost as much energy when they are seemingly doing very little as when they are firing away on complicated tasks or thoughts. In a keynote talk at a session entitled "Looking inside your brain," neuroscientist Pierre Magistretti of the University of Lausanne in Switzerland suggested some possible answers.
Magistretti's talk was actually about the neuroscience of brain imaging, particularly the mechanisms behind the metabolic changes detected in techniques such as positron emission tomography (PET) and functional MRI--techniques now routinely used in both medicine and basic research. But in the course of figuring those mechanisms out, Magistretti and others have begun to hypothesize about the high-energy brain states that make such imaging possible. Magistretti suggested three possible explanations for the high baseline rate of brain energy consumption, all of which could be part of the story. First, a lot of energy might be going into keeping the brain from getting over-stimulated: About 15% of the neurotransmitters in brain synapses are inhibitory molecules rather than excitatory. Second, new discoveries about the brain's plasticity--its ability to create new synapses in response to new experiences or situations--suggest that the brain is working away even when information is not being transmitted. And finally, Magistretti said, unconscious processes may keep the brain ticking away at a rapid rate even when we are inactive, such as during sleep.
All in all, a lot of food for thought before the meeting breaks for dinner tonight.
Photo: A 3-D view of a neuron by digital holographic microscopy