Magnetic resonance spectroscopy (MRS)
- MRS measures neurotransmitter metabolism and can be used to examine the neural basis of the fMRI signal by correlating changes in neuroenergetics — cerebral metabolic rate of oxygen (CMRO2) — with neural activity and estimating the fraction of total brain activity accounted for by changes in a task.
- A large proportion of the energy costs of neuronal activity are related to glutamate release. Modern models of neuroenergetics support the view that functional activity accounts for 85 percent of brain energy metabolism. The relationship between glutamate release and CMRO2 is linear and provides an index of neuronal signaling.
- Changes in fMRI signal are proportional to changes in neuroenergetics (and thus, neural activity).
- The amount of brain activity in the resting state is many times greater than the change in signal induced by a particular task.
- Researchers have used MRS to examine changes associated with disease:
- Disturbances in glutamate flux between neurons and glia can lead to excitotoxicity and impaired neurotransmission.
- Lower concentrations of GABA have been detected in depression, while certain treatments result in increases in GABA.
- MRS methodology has limitations. For example, it is unknown how glutamate metabolism changes during development.
