Hemispheric Differences within the Fronto-Parietal Network Dynamics Underlying Spatial Imagery

Alexander T Sack,Teresa Schuhmann

doi:10.3389/fpsyg.2012.00214

Abstract

Spatial imagery refers to the inspection and evaluation of spatial features (e.g., distance, relative position, configuration) and/or the spatial manipulation (e.g., rotation, shifting, reorienting) of mentally generated visual images. In the past few decades, psychophysical as well as functional brain imaging studies have indicated that any such processing of spatially coded information and/or manipulation based on mental images (i) is subject to similar behavioral demands and limitations as in the case of spatial processing based on real visual images, and (ii) consistently activates several nodes of widely distributed cortical networks in the brain. These nodes include areas within both, the dorsal fronto-parietal as well as ventral occipito-temporal visual processing pathway, representing the “what” versus “where” aspects of spatial imagery. We here describe evidence from functional brain imaging and brain interference studies indicating systematic hemispheric differences within the dorsal fronto-parietal networks during the execution of spatial imagery. Importantly, such hemispheric differences and functional lateralization principles are also found in the effective brain network connectivity within and across these networks, with a direction of information flow from anterior frontal/premotor regions to posterior parietal cortices. In an attempt to integrate these findings of hemispheric lateralization and fronto-to-parietal interactions, we argue that spatial imagery constitutes a multifaceted cognitive construct that can be segregated in several distinct mental sub processes, each associated with activity within specific lateralized fronto-parietal (sub) networks, forming the basis of the here proposed dynamic network model of spatial imagery.

Highlights

A mentally generated inner image can be mentally transformed, distorted, or rotated in our mind. This can help to reason about the consequences of a potential corresponding physical manipulation (Kosslyn et al, 1998). (Visuo)Spatial imagery refers to the inspection and evaluation of spatial features and/or the spatial manipulation of mentally generated visual images
When we speak about spatial imagery in the remainder of this article, we refer to the mental representation of visual objects, events, or scenes which are either mainly defined by spatial characteristics and/or which require in addition to the mere generation of the mental representation, a spatial analysis or manipulation to be mentally performed upon this mental visual image
Numerous neuropsychological (Levine et al, 1985; Farah et al, 1988) and neuroimaging studies (Cohen et al, 1996;Mellet et al, 1996, 1998; D’Esposito et al, 1997; Richter et al, 1997; Knauff et al, 2000; Trojano et al, 2000) have aimed at unraveling the neural foundations of mental imagery using a wide variety of imagery tasks. These imaging studies have consistently revealed that the pure imagination and mental representation of a specific mental object results in neural activity within category-specific occipital-temporal regions of the ventral visual processing pathway (Ishai et al, 2000, 2002; O’Craven and Kanwisher, 2000), including superior occipital areas (Mellet et al, 1995, 1996; D’Esposito et al, 1997; de Borst et al, 2011), inferior temporal regions (Carpenter et al, 1999; Mechelli et al, 2004; de Borst et al, 2012), parahippocampal cortex, HEMISPHERIC LATERALIZATION DURING SPATIAL IMAGERY As can be seen in Figure 1, most functional imaging studies show bilateral fronto-parietal networks to be activated during the execution of spatial imagery