Effects of aging on activity of the prefrontal cortex and autonomic nervous system during mental stress task.

We evaluated the effect of aging on the prefrontal cortex (PFC) activity and heart rate during the task. Employing near infrared spectroscopy (NIRS), we measured hemoglobin concentration changes in the bilateral PFC during a mental arithmetic task in young and older females. We selected the subjects who exhibited an increase in oxyhemoglobin with a decrease in deoxyhemoglobin during the task. We observed that right PFC activity predominantly modulates sympathetic effects during the task in both groups. However, the changes of oxyhemoglobin and heart rate during the task in older subjects were significantly smaller than those in young subjects. These results indicate that aging affects evoked cerebral blood oxygenation (CBO) response patterns of the PFC during a mental stress task. Aging did not affect the laterality of PFC activity in modulation of ANS function in the subjects who exhibited increases of oxyhemoglobin and deoxyhemoglobin associated with a decrease of deoxyhemoglobin during the task. However, aging reduced the heart rate increase during the task.