Most importantly,

however, we also observed that alpha power is significantly larger over ipsi- as compared to contralateral recordings. In contrast to the P1 which is interpreted as evoked alpha activity (that is short and transient), alpha power can be monitored over the entire time course of a trial. According to our hypothesis that alpha reflects (functional) inhibition, we expected significant differences during the poststimulus period that are due to the side where the target is presented. In general, MG-132 ipsilateral alpha power should be larger than contralateral alpha power. For the prestimulus period, we expect differences in alpha power that are induced by the cue. In invalid trials subjects will expect the target at the ‘wrong’ location. Thus, for invalid trials, the target is expected in the ipsilateral hemisphere (with respect to actual target presentation) and hence the power in the contralateral hemisphere will be larger. As an example, if in the invalid condition the cue points to the P450 inhibitor left hemifield, we expect larger prestimulus alpha power over the left hemisphere which is contralateral to the actual target presentation. Thus, for the prestimulus period, we expected larger power over ipsilateral

sites in the valid condition but larger power over contralateral sites in the invalid condition. This expected pattern of results could be confirmed statistically and is illustrated in Fig. 7. It should be noted that around 100 ms poststimulus (cf. the black vertical line in Fig. 7) there is the

‘crossing point’ (and, thus, no power difference) between invalid ipsi- and contralateral upper alpha Amylase power. Beyond that time, ipsilateral alpha power increases, whereas contralateral power decreases, indicating most likely the (delayed) reorientation of attention to the hemifield where the target appeared. Indirect evidence for a positive relationship between alpha power and P1 amplitude comes from research about schizophrenia and frontal lobe dysfunction. The prefrontal cortex is considered to play an important role for the inhibition of irrelevant information and the modulation of the P1–N1 complex in attentional cuing paradigms. Studies with schizophrenic patients have shown reliably that resting EEG is characterized by diminished alpha power and increased theta and delta power (e.g., Itil et al., 1972, Itil et al., 1974, Miyauchi et al., 1990, Sponheim et al., 1994 and Sponheim et al., 2000). Sponheim et al. (2000) have demonstrated that even within a group of schizophrenic patients, diminished alpha power is related to increased negative symptomatology and deviant brain morphology. Haenschel et al. (2007) observed that during the encoding of items in a memory scanning task, the P1 is decreased in schizophrenic patients, but increases with load in healthy control subjects.