ABSTRACT
Brain activation includes many events but all can be grouped into two basic physiological processes: neuronal signaling and brainmetabolism.Neuronal signaling refers to themovement of ions across the cellmembrane, and brainmetabolism refers to changes in oxygen and glucose consumption. These processes of metabolism and neuronal signaling occur continually, but their rate of activity varies across brain regions and during different states (e.g., sleeping, awake, cognitive demands). Some of these cellular changes, such as movement of oxygen molecules, produce patterns of electromagnetic signals that radiate to the outside of the brain and can be detected bymeasurement devices. Other cellular changes, such as increased glucose consumption, can be tracked and measured with radioactive substances that are attached to glucose molecules and taken up by active neurons. Thus, neuroimaging techniques measure either metabolism (glucose, oxygen consumption, or changes in blood volume) or neural
signaling (flow of ions, release of neurotransmitters, or density of receptors). Other techniques, such as CT and MRI measure brain structure, not function, and provide information about the morphology of the brain. Physiological techniques such as EEG measure the summed postsynaptic activity of many individual neurons at the level of the cortex.
