The medial temporal lobe functional connectivity patterns associated with forming different mental representations

Abstract

The medial temporal lobes (MTL), and more specifically the hippocampus, are critical for forming mental representations of past experiences-autobiographical memories-and for forming other "nonexperienced" types of mental representations, such as imagined scenarios. How the MTL coordinate with other brain areas to create these different types of representations is not well understood. To address this issue, we performed a task-based functional connectivity analysis on a previously published dataset in which fMRI data were collected as participants created different types of mental representations under three conditions. One condition required forming and relating together details from a past event (autobiographical task), another required forming and relating together details of a spatial context (spatial task) and another condition required relating together conceptual/perceptual features of an object (conceptual task). We contrasted the connectivity patterns associated with a functionally defined region in the parahippocampal cortex (PHC) and anatomically defined anterior and posterior hippocampal segments across these tasks. Examining PHC connectivity patterns revealed that the PHC seed was distinctly connected to other MTL structures during the autobiographical task, to posterior parietal regions during the spatial task and to a distributed network of regions for the conceptual task. Examining hippocampal connectivity patterns revealed that the anterior hippocampus was preferentially connected to regions of default mode network during the autobiographical task and to areas implicated in semantic processing for the conceptual task whereas the posterior hippocampus was preferentially connected to medial-posterior regions of the brain during the spatial task. We interpret our findings as evidence that there are MTL-guided networks for forming distinct types of mental representations that align with functional distinctions within the hippocampus.

What does the functional organization of cortico-hippocampal networks tell us about the functional organization of memory?

“…Sheldon and Levine (2018) recently reported results that align well with the above account. Briefly, in this study, participants were tasked with creating mental representations under conditions of autobiographical retrieval, generating a spatial framework, or relating conceptual/perceptual features of objects.…”

Hemispheric Regional Based Analysis of Diffusion Tensor Imaging and Diffusion Tensor Tractography in Patients with Temporal Lobe Epilepsy and Correlation with Patient outcomes

“…The supramarginal gyrus is not part of the limbic system like the other structures showing significant decreases in DTI values. However, the supramarginal gyrus is located in the parietal lobe which is adjacent to the temporal lobe 21 . With extension of the sclerotic structure beyond the temporal lobe in the pathologic hemisphere into surrounding areas, the supramarginal gyrus may be affected, as in this case, Additionally, as neuronal connections traverse the brain to reach the mesial temporal lobe, fibers may cross through or near the supramarginal gyrus as well leading to the significant decrease in the DTT versus the DTI value on the diseased side.…”

The ratio of posterior–anterior medial temporal lobe volumes predicts source memory performance in healthy young adults

“…Much of the important evidence supporting a posterior–anterior organization of episodic retrieval processes come from task fMRI studies (Lacot et al, 2017; Mugikura et al, 2016; Ritchey et al, 2015; Ritchey, Wang, Yonelinas, & Ranganath, 2019; Rosenbaum, Ziegler, Winocur, Grady, & Moscovitch, 2004; Sheldon & Levine, 2018). In examining functional activation in the MTL cortex during source and item memory trials, a classic fMRI study conducted by Davachi, Mitchell, and Wagner (2003), observed that activity in the PRC during encoding predicted subsequent item recognition, but not source retrieval.…”

“…While evidence from task and resting‐state fMRI studies supporting the posterior–anterior division of labor in the MTL is plentiful (Epstein, Harris, Stanley, & Kanwisher, 1999; Maass et al, 2015; Murray et al, 2007; Nadel et al, 2012; Olsen & Robin, 2020; Ritchey et al, 2015; Ryan et al, 2012; Sheldon & Levine, 2018; Staresina et al, 2011), there is little support from structural MRI studies in healthy young adults. Indeed, much of the evidence linking the amount of gray matter (GM) in MTL regions of interest (ROIs) with their proposed functions has been collected from studies in aging or clinical populations (Bohbot et al, 2015; Kivisaari, Tyler, Monsch, & Taylor, 2012; Olsen et al, 2013; Olsen et al, 2017; Palombo et al, 2013;Yeung et al, 2017; Yeung et al, 2019).…”