The role of instantaneous relations in the estimation of brain effective connectivity and a modified measure

As a developing field of investigation, exploring the causal relations (effective connectivity) among brain regions, helps the neurologists to understand the brain function. Most of effective connectivity measures are model-based but in the recent years some nonparametric measures like Transfer Entropy (TE) have been proposed. TE is based on the conditional mutual information concept. However in the presence of strong instantaneous relations that are observed extensively among cortical activity of brain regions, TE may estimate the causal (delayed) relations inaccurately. In this paper we present a novel information-theoretic based measure called Instantaneous Interaction (II) to estimate the brain instantaneous relations. Then we present a novel measure called Modified Transfer Entropy (MTE) to estimate the causal (delayed) relations when II is significant. The performance of these new measures is evaluated on 3 simulated models and experimental EEG data.