Elucidation of causal relationships for multi-sourced activities in the human brain by directed transinformation between time series of equivalent dipoles.

Abstract

Visualizing the causal relationships among multi-sourced activities in the human brain non-invasively is important for the elucidation of the processing mechanism and for clinical application of the diagnosis of disease. We will show our preliminary results of estimating equivalent dipoles to show the multi-sourced brain activities and analyse directed transinformation through time series of dipoles with three-dimensional display. First, we estimated the equivalent dipoles from evoked potentials via a three-layered concentric spherical model and two-dipole estimation. Second, we analysed the directed transinformation between two time series of the first and second dipole moments by use of the derived two dipole positions and moments as the loci and magnitude of brain activities. Therefore, we obtained bi-directional information flow between the neuronal activities localized in three-dimensional space of the brain with respect to 21-ch somatosensory evoked potentials (SEPs). Our preliminary results can be interpreted as showing that the information, calculated based on our method, flows from the first dipole cluster located in the thalamus, to the second dipole cluster located in the somatosensory area. This does not go against the neurophysiological knowledge of SEPs that the activities move from the thalamus to the somatosensory area. With the above, we show the potential possibility of realizing the elucidation of causal relationships.