Lateralized Readiness Potential (LRP) and the Motor Related Amplitude Asymmetry in the beta band (beta MRAA). The

Lateralization was calculated over the second half of the preparation interval using the first cued response or the first actual response for neutral cues. To investigate the preparation of motor sequences we used a two-movement, two-response task with full, partial and non-informative (neutral) cues [4]. Subjects (N = 16) received cues in the form of two letters: ‘R ’ and ‘L ’ for the right and left index finger. The upper letter indicated the first and the lower letter the second response (fig. 1). For uncued movements the letter was replaced by an asterisk. A 1.5 second preparation interval preceded the stimulus that provided full information. Partial cues were intended to have subjects prepare a partial motor program. Measures reported here are the Contingent Negative Variation (CNV) and two lateralization measures: the Response Times (RT) on the first segment were most sensitive to the manipulations. RT was lower when cues were more informative. There was an interaction-effect of cueing the first response, cueing the second response and sequence type on first RT (fig. 2; F(1, 15) = 21, p =.000). An interaction effect between electrode (Fpz, Fz, Cz and Pz) and cue type (neutral, second, first, full-different, full-equal) on CNV during the second half of the preparation interval was found (F(12, 180) = 2.2, p =.047). This could be due to a division between full-different and both partial cues and the full-same and neutral cues at Cz (fig. 3A). The LRP (fig. 3B) only developed for full cues and sequences with two different responses (t(15) = 3.8, p = 0.002). There also was a significant effect of cue type on beta MRAA (fig. 3C; F(4, 60) = 9.4, p <.0005). Pairwise comparisons showed that this was due to differences between full cues with equal responses and the three non-full cues. Note the double dissociation between the LRP and beta MRAA for full cues. Discussio