Time processing reflected by EEG surface Laplacians.

We previously described significant relationships between amplitude variations in slow brain potentials and timed between-press intervals (2.5 s). We suggested that these variations are neural traces of timing mechanisms. To determine which time processing stage is concerned, the current study examines whether these variations result from trial-to-trial memory updating controlled by feedback or from memory consolidation. EEG surface Laplacians (SL) were computed from the first trial on, with feedback (condition 1) and after feedback suppression (condition 2). Performance-dependent variations were related to the individual memory traces revealed by condition 2. As in our previous data, they were restricted to a site overlying the supplementary motor area (SMA). The data suggest that the SMA subserves timing functions, involving memory consolidation and cumulative activation processes as described by current models.