Neural Substrates of Visuospatial Processing in Distinct Reference Frames: Evidence from Unilateral Spatial Neglect

Abstract

There is evidence for different levels of visuospatial processing with their own frames of reference: viewer-centered, stimulus-centered, and object-centered. The neural locus of these levels can be explored by examining lesion location in subjects with unilateral spatial neglect (USN) manifest in these reference frames. Most studies regarding the neural locus of USN have treated it as a homogenous syndrome, resulting in conflicting results. In order to further explore the neural locus of visuospatial processes differentiated by frame of reference, we presented a battery of tests to 171 subjects within 48 hr after right supratentorial ischemic stroke before possible structural and/or functional reorganization. The battery included MR perfusion weighted imaging (which shows hypoperfused regions that may be dysfunctional), diffusion weighted imaging (which reveals areas of infarct or dense ischemia shortly after stroke onset), and tests designed to disambiguate between various types of neglect. Results were consistent with a dorsal/ventral stream distinction in egocentric/allocentric processing. We provide evidence that portions of the dorsal stream of visual processing, including the right supramarginal gyrus, are involved in spatial encoding in egocentric coordinates, whereas parts of the ventral stream (including the posterior inferior temporal gyrus) are involved in allocentric encoding.

Attributing awareness to oneself and to others

“…The TPJ, posterior superior temporal sulcus, and ventral prefrontal cortex are active in association with changes in one's own attentional state, especially when a novel or unexpected stimulus draws attention (31)(32)(33)(34). Moreover, lesions in the TPJ are associated with hemispatial neglect (35)(36)(37), and disruption of the TPJ has been found to induce visual extinction (38).…”

Where did you “left” Piazza del Popolo? At your “right” temporo-parietal junction

“…Neglect is a complex syndrome with several other dissociations (e.g., personal vs extrapersonal, egocentric vs allocentric, perceptual vs motor) and neural substrates have been described for all but the representational versus perceptual one (Committeri et al, 2007;Medina et al, 2009;Molenberghs, Sale, & Mattingley, 2012;Verdon, Schwartz, Lovblad, Hauert, & Vuilleumier, 2009). Besides a series of single-cases and sporadic small-group studies (see Table 1 in the recent review by Salvato et al, 2014), systematic anatomical investigations on the putative neural substrates of representational neglect are not available, therefore it is still unknown whether this disorder follows specific brain lesions.…”

The role of parieto-temporal connectivity in pure neglect dyslexia

“…These studies support the importance of the inferior parietal lobe for detection of unexpected, behaviourally relevant stimuli, and for attentional selection under conditions of competition in an egocentric reference frame. In contrast, studies examining which brain regions are important for the deployment of attention within objects (i.e., allocentric coding) support the importance of parts of the temporal lobe, such as the parahippocampal gyrus (Grimsen et al, 2008), the superior temporal sulcus and middle temporal gyrus (Chechlacz et al, 2010), or the posterior inferior temporal region (Medina et al, 2009). Interestingly, the lateral and inferior temporal cortex exhibits category-specific activity when subjects view pictures of tools or animals (Chao et al, 1999), suggesting that representations elaborated here rely on the coding of internal characteristics of objects.…”