USE OF NONLINEAR EEG MEASURES TO CHARACTERIZE EEG CHANGES DURING MENTAL ACTIVITY

Non-linear EEG analysis provides a possibility for studying the dynami cal changes in cortical networks related to mental activity. In this s tudy the correlation dimension D was used to study local changes in co mplexity, and the mutual dimension D-2 was used to assess changes in t he dynamical coupling between different brain areas. EEGs were recorde d in 25 healthy subjects under three conditions: (1) eyes closed, (2) eyes open, and (3) mental arithmetic with eyes closed (serial subtract ion of 7s from 1000). In the eyes-closed condition, D-2 was lower at p arieto-occipital sites. D-2 increased during the eyes-open and arithme tic conditions. Contrary to the D-2. the D-2 showed no regional differ ences in the eyes closed condition. A clear increase in D-2 was seen d uring eyes open and arithmetic. We conclude that both the correlation dimension and the mutual dimension are very sensitive to EEG changes d uring simple visual information processing and during mental arithmeti c. However, these measures seem to be relatively non-specific, and cor relate only weakly with performance on the arithmetic task.