Blood Flow and Localization of Brain Function
The direct relation between an area’s neural activity and blood flow has recently been utilized to map the brain’s functional regions (mainly brain cortex) in conscious, responsive human subjects. A subject is injected with an inert radioactive gas such as xenon. As the blood flows through the varios brain regions, detectors in a helmet worn on the head measure the radioacivity. These studies revealed that regional brain blood flow pattern (hence neural activity) is dynamic changing depending on physiological and psychological conditions.
For example, at rest, only the frontal lobes, particularly the premotor regions, show higher than average activity. During bodily or mental activity, depending on the task involved, the regional activity pattern changes. Thus, clenching of the right hand increases activity in both the sensory and motor hand areas, although more in the left than right hemisphere.
Sensory stimulation of the hand alone, howerver, increases activity mostly in the sensory areas. Interestingly, whereas simple pronouncement of words increases activity mainly in the primary sensory/motor speech areas of both hemispheres (lips, tongue, face), creative speech involving thinking and ideas also increases activity in the Wernicke’s and Broca’s speech areas of the left hemisphere. Reading increases activity in a large area of the brain, including not only the expected visual and visual association areas but also the parieto-temporal areas, including the Wernicke’s area, which are involved in word comprehension. Activity in the frontal lobes is increased not only during contemplation, problem solving, and planning, but also during pain and anxiety.
Certain mental diseases such as schizophrenia and depression and the senile disorders such as the dementias (reduced cognitive and memory capacities) are associated with reduced blood flow/metabolic acitivity. Brain diseases such as epilepsy, in which convulsions are observed due to excessive electrical activity, are associated with increased blood flow and metabolic activity.
Regular exercise and proper nutrition are essential for keeping a healthy active brain. The increased blood and oxygen flow to the brain during exercise help strengthen the blood vessels and increase neuronal activation. A healthly brain keeps all of the systems of the body working effeciently throughout the aging process, and in fact, can reduce the aging affect.
Daryl Conant, M.Ed.