Where the brain spends its energy

In investigating a crime, to pinpoint the culprit, the saying goes, "follow the money." In science, the saying is (or at least, should be), "follow the ATP."

A six month old paper acts as a nice review on this topic. The authors stratify tissue types based on the degree of myelination (none, developing, and adult). This is shown here,

where:

• action potential use is on voltage-gated Na+/K+-ATPases

• synapse use is on postsynaptic membrane currents, presynaptic calcium entry, and neurotransmitter/vesicle cycling

• oligodendrocyte resting potential use is continuous Na+/K+ pumps

• housekeeping use is on protein/lipid synthesis and intracellular trafficking of molecules/organelles

That's way more than I would have expected on housekeeping. But by far their most surprising finding is that the cost of maintaining the resting potentials in oligodendrocytes is so large that myelination doesn't usually save energy on net--it depends on the firing rate of the neuron. That's a heterodox bomb.

I suppose that myelination not leading to energy saving is weak evidence in favor of it doing something else, aside from speeding up spikes. Like, allowing for plasticity.

Reference

Harris; Atwood (2012). "The Energetics of CNS White Matter". Journal of Neuroscience. DOI:10.1523/JNEUROSCI.3430-11.2012