Abstract
Mental imagery is the process through which we retrieve and recombine information from our memory to elicit the subjective impression of “seeing with the mind’s eye”. In the social domain, we imagine other individuals while recalling our encounters with them or modelling alternative social interactions in future. Many studies using imaging and neurophysiological techniques have shown several similarities in brain activity between visual imagery and visual perception, and have identified frontoparietal, occipital and temporal neural components of visual imagery. However, the neural connectivity between these regions during visual imagery of socially relevant stimuli has not been studied. Here we used electroencephalography to investigate neural connectivity and its dynamics between frontal, parietal, occipital and temporal electrodes during visual imagery of faces. We found that voluntary visual imagery of faces is associated with long-range phase synchronisation in the gamma frequency range between frontoparietal electrode pairs and between occipitoparietal electrode pairs. In contrast, no effect of imagery was observed in the connectivity between occipitotemporal electrode pairs. Gamma range synchronisation between occipitoparietal electrode pairs predicted subjective ratings of the contour definition of imagined faces. Furthermore, we found that visual imagery of faces is associated with an increase of short-range frontal synchronisation in the theta frequency range, which temporally preceded the long-range increase in the gamma synchronisation. We speculate that the local frontal synchrony in the theta frequency range might be associated with an effortful top-down mnemonic reactivation of faces. In contrast, the long-range connectivity in the gamma frequency range along the fronto-parieto-occipital axis might be related to the endogenous binding and subjective clarity of facial visual features.
Highlights
Mental imagery is the process through which we retrieve and recombine information from our memory to elicit the subjective impression of “seeing with the mind’s eye”
Ganis and Schendan investigated whether visual perception and visual imagery of faces recruit the same early perceptual processes, as assessed by the event-related potentials (ERPs) N170 and vertex positive potential (VPP) using a rapid adaptation p aradigm[18]
We propose that dynamic topdown interactions between cortical sites may drive two fundamental components of visual imagery—working memory and feature binding
Summary
Mental imagery is the process through which we retrieve and recombine information from our memory to elicit the subjective impression of “seeing with the mind’s eye”. We used electroencephalography to investigate neural connectivity and its dynamics between frontal, parietal, occipital and temporal electrodes during visual imagery of faces. The long-range connectivity in the gamma frequency range along the fronto-parieto-occipital axis might be related to the endogenous binding and subjective clarity of facial visual features. Top-down reactivation and active maintenance of visual images involve multiple mnemonic processes, e.g. when we imagine a known face, we need to recall and maintain it in our working memory for the duration of a mental image. The visuospatial working memory of mental images involves a broader neural network of occipital and temporal visual areas under executive frontal lobe c ontrol[19]. One of the functional roles of such long-range dynamic interactions between cortical regions could be visual feature binding of sensory images reactivated and stored in working memory. Kottlow et al reported a link between an increase in gamma synchronisation and feature binding during a face integration task[36]
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