Traveling EEG slow oscillation along the dorsal attention network initiates spontaneous perceptual switching.

An ambiguous figure such as the Necker cube causes spontaneous perceptual switching (SPS). The mechanism of SPS in multistable perception has not yet been determined. Although early psychological studies suggested that SPS may be caused by fatigue or satiation of orientation, the neural mechanism of SPS is still unknown. Functional magnetic resonance imaging (fMRI) has shown that the dorsal attention network (DAN), which mainly controls voluntary attention, is involved in bistable perception of the Necker cube. To determine whether neural dynamics along the DAN cause SPS, we performed simultaneous electroencephalography (EEG) and fMRI during an SPS task with the Necker cube, with every SPS reported by pressing a button. This EEG-fMRI integrated analysis showed that (a) 3-4 Hz spectral EEG power modulation at fronto-central, parietal, and centro-parietal electrode sites sequentially appeared from 750 to 350 ms prior to the button press; and (b) activations correlating with the EEG modulation traveled along the DAN from the frontal to the parietal regions. These findings suggest that slow oscillation initiates SPS through global dynamics along the attentional system such as the DAN.

Frontal-to-parietal top-down causal streams along the dorsal attention network exclusively mediate voluntary orienting of attention.

Previous effective connectivity analyses of functional magnetic resonance imaging (fMRI) have revealed dynamic causal streams along the dorsal attention network (DAN) during voluntary attentional control in the human brain. During resting state, however, fMRI has shown that the DAN is also intrinsically configured by functional connectivity, even in the absence of explicit task demands, and that may conflict with effective connectivity studies. To resolve this contradiction, we performed an effective connectivity analysis based on partial Granger causality (pGC) on event-related fMRI data during Posner's cueing paradigm while optimizing experimental and imaging parameters for pGC analysis. Analysis by pGC can factor out exogenous or latent influences due to unmeasured variables. Typical regions along the DAN with greater activation during orienting than withholding of attention were selected as regions of interest (ROIs). pGC analysis on fMRI data from the ROIs showed that frontal-to-parietal top-down causal streams along the DAN appeared during (voluntary) orienting, but not during other, less-attentive and/or resting-like conditions. These results demonstrate that these causal streams along the DAN exclusively mediate voluntary covert orienting. These findings suggest that neural representations of attention in frontal regions are at the top of the hierarchy of the DAN for embodying voluntary attentional control.

Subsequent memory-dependent EEG theta correlates to parahippocampal blood oxygenation level-dependent response.

The 4-12 Hz (theta rhythm)-dependent neural dynamics play a fundamental role in the memory formation of the rat hippocampus. Although the power of human scalp electroencephalography theta (EEG theta) is known to be associated with a hippocampus-dependent memory encoding, it remains unclear whether the human hippocampus uses theta rhythm. In this study, we aim to identify the scalp EEG theta-related neural regions during memory encoding by using a simultaneous EEG-functional magnetic resonance imaging recording. We showed that the parahippocampal and the medial frontal and posterior regions were significantly correlated to subsequent memory-dependent EEG theta power. This evidence suggests that the human parahippocampal region and associated structures use theta rhythm during hippocampal memory encoding as in rodents.

Causality analysis defines neural streams of orienting and holding of attention.

Previous studies with effective connectivity analysis have revealed neural streams of orienting of attention. However, neural streams involved in holding of attention on the fovea remain unclear. To identify them, we performed event-related functional MRI with a cueing paradigm and Granger causality analysis. Typical regions along the dorsal attention network (DAN) showed greater activation during orienting than during holding of attention. However, causality analysis indicated that neural streams appeared along the DAN in a top-down manner during orienting, whereas streams from widely distributed regions to the left prefrontal cortex appeared and these were dissociable from the DAN during holding of attention. Our results suggest that dissociable neural streams contribute to orienting and holding of attention, respectively.

Dissociable neural correlates of reorienting within versus across visual hemifields.

Neural correlates of reorienting across visual hemifields have been extensively studied, however, those of reorienting within hemifields and if there are any differences remain unclear. Here, we performed a functional magnetic resonance imaging study to identify neural correlates of reorienting within and across hemifields using a variant of the cueing paradigm. Behavioral results showed that reorienting across hemifields showed significant validity effect, but reorienting within hemifields did not. Functional magnetic resonance imaging data revealed dissociable activations in the right posterior parietal region between reorienting within and across hemifields. The present results suggest that reorienting within hemifields differs from the 'classical reorienting' to some extent, whereas reorienting across hemifields does not.