In accordance, correlation of the alpha rhythm with the BOLD signal during complete darkness revealed activity in right frontal cortical regions known to be related to attention allocation. Overall, these findings suggest that attention allocation might modulate the alpha rhythm independently of external sensory input. Given the known relation of alpha to arousal (Lansing et al., 1959; Barry et al., 2007; Sadaghiani et al., 2010), it
is further possible that attention-related alpha desynchronisation Proteasome inhibitor is a prerequisite for its known modulation by external sensory stimulation. This suggestion supports the inhibition hypothesis (Klimesch et al., 2007) and corresponds to earlier propositions, that it is the ‘looking’ and not the ‘seeing’ which causes alpha desynchronisation (Mulholland, 1974; Paskewitz, 1977). During complete darkness, negative correlation of the alpha rhythm with the BOLD signal revealed activity in the right IFG and medial frontal gyrus alongside the ACC. A network comprising right frontal regions and the ACC has been repeatedly shown as linked to intrinsic alertness (Sturm & Willmes, 2001; Sturm et al., 2004; Mottaghy
et al., 2006), which is defined as the internal control of arousal in the absence of an external cue (Sturm et al., 1999). In the current study, alpha-related BOLD activation in these regions was more robust in the dark condition, suggesting MG-132 in vivo a higher arousal state, most probably elicited by the complete darkness. Similarly, using EEG and fMRI, Laufs et al. PFKL (2006) suggested that frontoparietal regions negatively correlated with the alpha rhythm might imply a state of higher vigilance. In EEG research the alpha rhythm is a reliable measure of vigilance (e.g. in determining EEG vigilance states – Loomis et al., 1938; De Gennaro et al., 2001), also supported by skin conductance (Barry et al., 2007) as well as fMRI (Olbrich et al., 2009) studies. For example, a recent EEG–fMRI study revealed that drowsiness
caused a diminished ‘Berger effect’, i.e. alpha was not desynchronised due to eyes opening (Henning et al., 2006). This finding, much like the one reported in the current study, suggests a strong relation of the alpha band to ongoing arousal perhaps more so than to visual sensory input. In accordance, it is suggested that future combined imaging studies on the role of alpha would benefit from emphasising fluctuating arousal state (e.g. Foucher et al., 2004) while studying alpha rhythm modulations. During complete darkness, alpha modulation due to eyes open/closed paradigm is only associated with a change in the subject’s attention and less with sensory input (Yu & Boytsova, 2010). In accordance, the relation of alpha to intrinsic alertness might also be linked to its involvement in attention allocation.