Movie S1.

Grand average syllable-related potential. All conditions and all subjects are pulled together. Top Row: time series of the 256 channels (left) and 2D map of the voltage topography (right). Middle row: 3D projection of the same data on a 3-month-old infant template (26). Bottom row: brain sources projected on the 3-month-template brain. The grand average voltage has been modelled using 15000 distributed dipoles assigned to each vertex of the cortical surface. Their orientation was not constrained and the norm was computed from the x, y and z axes and projected on the template brain. EEG forward modelling was computed using three overlapping spheres with conductivity parameters adjusted according to the tissue properties typical for the infant head. Cortical current maps were computed from the EEG time series using a linear inverse estimator (weighted minimum-norm current estimate). All these procedures were conducted with BrainStorm Matlab toolkit (http://neuroimage.usc.edu/brainstorm).