Assessing the mechanism of response in the retrosplenial cortex of good and poor navigators

Abstract

The retrosplenial cortex (RSC) is consistently engaged by a range of tasks that examine episodic memory, imagining the future, spatial navigation, and scene processing. Despite this, an account of its exact contribution to these cognitive functions remains elusive. Here, using functional MRI (fMRI) and multi-voxel pattern analysis (MVPA) we found that the RSC coded for the specific number of permanent outdoor items that were in view, that is, items which are fixed and never change their location. Moreover, this effect was selective, and was not apparent for other item features such as size and visual salience. This detailed detection of the number of permanent items in view was echoed in the parahippocampal cortex (PHC), although the two brain structures diverged when participants were divided into good and poor navigators. There was no difference in the responsivity of the PHC between the two groups, while significantly better decoding of the number of permanent items in view was possible from patterns of activity in the RSC of good compared to poor navigators. Within good navigators, the RSC also facilitated significantly better prediction of item permanence than the PHC. Overall, these findings suggest that the RSC in particular is concerned with coding the presence of every permanent item that is in view. This mechanism may represent a key building block for spatial and scene representations that are central to episodic memories and imagining the future, and could also be a prerequisite for successful navigation.

Cortical Integration of Contextual Information across Objects

“…Therefore, more activation would be expected relative to single objects assuming independent processing for each element in the stimulus. This explanation seems consistent with previous reports (e.g., Auger & Maguire, 2013), suggesting that the cingulate retrieves information independently for each object. Auger and Maguire additionally showed that the activation levels in this region are affected also by the object's tendency to appear in a particular position in the three-dimensional space (see also Troiani, Stigliani, Smith, & Epstein, 2014).…”

“…Importantly, there was hardly any overlap between the cingulate RSC portions and these clusters (peak Talairach coordinates: left hemisphere: −19, −56, 19, right hemisphere: 16, −54, 23). This lack of overlap supports the results obtained with the context localizer ROI in the left hemisphere and the anatomical parcellation of the scene RSC ROIs in both hemispheres motivated by the memory literature (Auger & Maguire, 2013;Lundstrom et al, 2005). Other regions showing large clusters of significant relation effect were observed bilaterally in the inferior parietal cortex (left: −50, −56, 31, right: 38, −61, 47), the right supramarginal (36, −39, 34), the right posterior cingulate (far away from the ROI portion of the cingulate: 5, −12, 37), the left rostral-middle frontal region (−44, 29, 24), and bilaterally in the superior frontal cortex (left: −12, 46, 34, right: 15, 38, 41).…”

“…The precuneus seems to be sensitive to contextual relatedness and coherence, whereas the cingulate does not. The fact that we observed no relation effect in the cingulate despite the overall strong activation in this region suggests that whether the cingulate is involved in the retrieval of objects information from memory (Auger & Maguire, 2013) or in the analysis of information retrieved by a different brain region, it likely does so independently for each object; otherwise, we would expect to see a difference between the activation patterns caused by related and unrelated pairs. This finding can potentially explain the stronger activation for buildings than for single objects used to define this ROI (not presented).…”

“…This raises the possibility that the commonly used context and scene localizers might tap into multiple processes, each of those being performed by a different brain region. With the cingulate participating in the retrieval of information related to individual objects (e.g., Auger & Maguire, 2013) and the precuneus participating in retrieval of higher-order information such as objects relation via the retrieval of episodic memory information (e.g., Lundstrom, Ingvar, & Petersson, 2005). Another aim of the current study was therefore to investigate the potential different functions that subportions of the RSC perform in relation to contextual processing, as these processes necessarily involve retrieval of higher-order information from memory.…”

Evidencing a place for the hippocampus within the core scene processing network

“…Also, while the one‐back localiser task was sufficient to identify significant RSC voxels in individual brains, particularly at lower voxel‐wise thresholds, it is not necessarily attuned to the precise function of this brain region in scene processing (i.e., spatial navigation), which could account for the reduced inter‐individual consistency found here. In addition, there are inconsistencies in the field when defining the RSC [Knight and Hayman, 2014; Vann et al, 2009], to the extent that some researchers have restricted analysis to anatomical boundaries [Auger and Maguire, 2013], whereas others use the more liberal, and functionally‐defined retrosplenial complex [Bar and Aminoff, 2003; Epstein et al, 2007]. …”