Abstract
Previous studies have shown that the neural mechanisms underlying visual spatial attention rely on top-down control information from the frontal and parietal cortexes, which ultimately amplifies sensory processing of stimulus occurred at the attended location relative to those at unattended location. However, the modulations of effective brain networks in response to stimulus at attended and unattended location are not yet clear. In present study, we collected event-related potentials (ERPs) from 15 subjects during a visual spatial attention task, and a partial directed coherence (PDC) method was used to construct alpha-band effective brain networks of two conditions (targets at attended and nontargets at unattended location). Flow gain mapping, effective connectivity pattern, and graph measures including clustering coefficient (C), characteristic path length (L), global efficiency (Eglobal), and local efficiency (Elocal) were compared between two conditions. Flow gain mapping showed that the frontal region seemed to serve as the main source of information transmission in response to targets at attended location while the parietal region served as the main source in nontarget condition. Effective connectivity pattern indicated that in response to targets, there existed obvious top-down connections from the frontal, temporal, and parietal cortexes to the visual cortex compared with in response to nontargets. Graph theory analysis was used to quantify the topographical properties of the brain networks, and results revealed that in response to targets, the brain networks were characterized by significantly smaller characteristic path length and larger global efficiency than in response to nontargets. Our findings suggested that smaller characteristic path length and larger global efficiency could facilitate global integration of information and provide a substrate for more efficient perceptual processing of targets at attended location compared with processing of nontargets at ignored location, which revealed the neural mechanisms underlying visual spatial attention from the perspective of effective brain networks and graph theory for the first time and opened new vistas to interpret a cognitive process.
Highlights
We can voluntarily limit our visual attention to a specific location in the visual field without changing the direction of eye gaze, and this visual spatial attention can improve perceptual processing of stimulus at attended location compared with processing of stimulus at ignored location [1,2,3]
The dorsal attention network (DAN) is mainly composed of intraparietal sulcus (IPS), superior parietal lobule, and frontal eye field (FEF) and shows increased blood-oxygenation-level-dependent (BOLD) signal when subjects voluntarily deploy their visual attention towards a target [4, 6,7,8]
The experiment is a classical visual spatial attention task that is modified according to reference [41] (Figure 1): EEG data were collected from subjects who attended to randomized sequences of filled round disks appearing briefly inside one of the three empty squares that were constantly displayed 1.0 cm above a central fixation cross
Summary
We can voluntarily limit our visual attention to a specific location in the visual field without changing the direction of eye gaze, and this visual spatial attention can improve perceptual processing of stimulus at attended location compared with processing of stimulus at ignored location [1,2,3]. Studies utilizing functional magnetic resonance imaging (fMRI) have consistently shown that two attention networks including the dorsal attention network (DAN) and the ventral attention network (VAN) are involved in visuospatial attention [1, 4, 5]. The DAN is mainly composed of intraparietal sulcus (IPS), superior parietal lobule, and frontal eye field (FEF) and shows increased blood-oxygenation-level-dependent (BOLD) signal when subjects voluntarily deploy their visual attention towards a target [4, 6,7,8]. The VAN, mainly consisting of the temporoparietal junction (TPJ) and the ventral frontal cortex, is thought to facilitate stimulus detection, when unexpected stimuli are present [4,5,6,7, 9]
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