[Problem]It is intended to quantitatively evaluate deterioration in
brain function associated with a
disease such as
dementia, with a high degree of accuracy by a simplified method using signals acquired from a few sensors arranged on the
scalp.[Solution]The present invention relates to a brain
activity measurement device comprising: a
signal acquisition part configured to acquire a
signal from a brain of the subject, using three sensors attached to different locations on the surface of the head of a subject; a
data extraction part configured to extract, from each of the three signals acquired from respective ones of the sensors, a deep-brain potential
signal having a specific
frequency band arising from an activity of a deep
brain region, and acquire data from the extracted deep-brain potential signal with a sampling period; a correlation value calculation part configured to calculate a correlation value indicative of a correlative relationship among the deep-brain potential signals acquired from each respective sensors, based on a
phase relationship among three pieces of time-
series data each extracted from the respective sensors by the
data extraction part; and an index value calculation part configured to analyze the deep-brain potential signals from the deep
brain region, based on the calculated correlation value, to calculate an index value for determining a
brain function.