Forward MEEG problem and Fast Multipole Method Jan Kybic Magneto/electro-encephalography is a fast non-invasive in-vivo technique used to study processes in the brain. It is based on measuring weak electromagnetic fields outside the head produced by neuronal activities (mainly) in the cortex. The forward MEEG problem consists of solving the Maxwell equations to find the field outside the head, given the sources. We present briefly the Finite Difference and Finite Element Methods to concentrate on three distinct formulations of the Boundary Element Method (BEM) - single layer, double layer and symmetric, showing the superiority of the symmetric method. The BEM applied on a fine mesh needs to solve a large linear system of equation. This can be significantly accelerated using Fast Multipole Method, a hierarchical approximative technique taking advantage of the fact that the interaction between surface elements decreases sharply with distance and that effects on close triangles are similar. Some experiments and current state of the project (in collaboration with INRIA, Sophia-Antipolis) will be presented.