No difference in LRP amplitude was found between familiar and unfamiliar sequences (see Fig. 5). This implies that the difference between the preparation of familiar and unfamiliar sequences concerns the involvement of general motor preparation and the load on visual-working memory, being enlarged for unfamiliar sequences. The differences between familiar and unfamiliar sequences were already present during preparation. This suggests that behavioral differences between familiar and unfamiliar sequences are not only due to execution, but also

to preparation. Regarding the interpretation of the CNV several options were posed Daporinad molecular weight in the introduction. Schröter and Leuthold (2009) suggested that the CNV reflects the amount of prepared keypresses or parameters. This was not confirmed by the present results, as there was no increased CNV for familiar sequences. In contrast, we observed an increased selleck chemicals llc CNV before unfamiliar sequences as compared with familiar sequences. Therefore we interpret the CNV effect as a reflection of the difference in preparation of unfamiliar (complex) and familiar (simple) responses (Cui et al., 2000). The complexity of the sequences per se was identical for familiar and unfamiliar sequences, as these were counterbalanced. However, during preparation of familiar sequences segments

of responses could be presetted, which is less demanding as compared with unfamiliar sequences where each individual response has to be presetted. Thus, we suggest that with practice the complexity of preparation decreases, as segments of responses can be presetted instead of individual responses. Previous studies in monkeys (e.g. Shima & Tanji, 1998) and humans (e.g. Ashe, Lungu, Basford, & Lu, 2006) indicated that higher order movement areas like the premotor area and the supplementary motor area (SMA) are involved in abstract movement preparation. More

specifically, Nachev, Kennard, and Husain (2008) relate the function of the supplementary motor complex to the complexity of actions. It was suggested that the pre-SMA is more active during complex or cognitive situations, whereas the SMA is more tightly related to actions (Nachev et al., 2008). In the present study ioxilan we suggest that sequence preparation becomes less complex with practice, as segments of responses can be presetted instead of individual responses. Therefore it may be argued that with practice activity related to general motor preparation shifts from pre-SMA to SMA. In our study the CNV displayed a parietal maximum, whereas other studies revealed a central maximum (e.g. Schröter & Leuthold, 2009). This suggests that the CNV is a mix of different processes with different topographies. The parietal CNV may be used to index visual-spatial processes, whereas the central CNV may be used to index general motor processes. In the present study the visual-spatial format of the stimuli is highly important and therefore the contribution of the parietal component is large.