Consistent

with this conjecture, the main driving input to pulvinar arises from cortical layer 5 (Sherman, 2007). Contrastingly, the alpha that has been reported in a large number of electroencephalographic/magnetoencephalographic (EEG/MEG) studies to be reduced by functional activation might be related to supragranular alpha sources. Supragranular alpha sources might be more readily detected by EEG/MEG methods, because the synaptic inputs generated by those alpha sources probably impinge on the dendrites of large pyramidal cells, resulting in vertical currents for which EEG/MEG measures are sensitive. Alternatively or in addition, the increased alpha-band coherence during the delay period described by Saalmann et al. (2012) could reflect effects related to short-term memory load, which have been related Imatinib to increased alpha-band power in several studies (Jensen and Mazaheri, 2010). Saalmann et al. (2012) further extend their core findings related to pulvinar-driven alpha-band synchronization to establish a functional relationship between alpha- and gamma-band synchronization during attentional allocation. At the cortical level, previous studies have reported increases Galunisertib molecular weight in gamma coherence primarily in the context of selective visual attention (Fries, 2009), with the idea that it promotes a more efficient communication

between cortical areas (Fries, 2009). Important questions mafosfamide follow regarding the circuits needed to generate gamma oscillations and the attentional mechanisms modulating the phase synchrony across neurons. Regarding the former, current evidence indicates the importance of inhibitory mechanisms provided by local GABAergic input (Fries, 2009). Regarding the latter, several theories have suggested that nonspecific circuits that exhibit low-frequency oscillations could mediate gamma synchrony via cross-frequency coupling (VanRullen and Koch, 2003; Fries, 2009). The Saalmann et al. (2012) paper provides important new information in this respect, as the authors

show that, unlike cortical circuits, the pulvinar engages in local synchrony in the alpha and not in the gamma range. This is not surprising given the evidence for alpha generators in the thalamus and for an absence of gamma sources in deep cortical layers, where the cortico-thalamic projection neurons are located (Buffalo et al., 2011). Moreover, a supplementary figure provided by Saalmann et al. (2012) shows increased cross-frequency coupling between cortical alpha- and gamma-band activity with attention. Clarifying the mechanistic details and functional implications of this alpha-gamma coupling deserves further consideration in future research. An attractive speculation is that alpha rhythms generated during wakefulness by pulvinar neurons reflect periodic perceptual sampling (VanRullen and Koch, 2003; Fries, 2009; Landau and Fries, 2012).