The observed overall asymmetry in alpha ERD, as well as the lack of alpha ERD asymmetry in CHR patients, may be understood in the same context, given that the current task requirements involved unilateral responses. As most participants were right-handed, and left versus right hand responses have yielded opposite P3 source asymmetries during auditory oddball tasks (although not of comparable magnitude; e.g., Kayser & Tenke, 2006a, Kayser et al., 2010a; Tenke at al., 1998), one might speculate that asymmetric contributions of motor preparation, execution, and monitoring between 400 and 800 ms resulted in the observed alpha ERD asymmetry and its absence in CHR patients. Interestingly, Kayser et al. (2010a) found that the FRN-related source asymmetry linked to manual response versus silent count of target tones was reduced in schizophrenia. Predominant right parieto-occipital alpha ERD has also been reported for right-handed healthy adults during the anticipatory S1-S2 interval of a cued motor response task, particularly for participants with weak lateralization of sensorimotor alpha activity, suggesting distinct alpha asymmetry patterns associated with motor or attentional processes (Deiber et al., 2012). However, more research is required to clarify the mechanisms underlying these alpha ERD effects.
