The relationship between hippocampal-dependent task performance and hippocampal grey matter myelination and iron content

Abstract

Individual differences in scene imagination, autobiographical memory recall, future thinking and spatial navigation have long been linked with hippocampal structure in healthy people, although evidence for such relationships is, in fact, mixed. Extant studies have predominantly concentrated on hippocampal volume. However, it is now possible to use quantitative neuroimaging techniques to model different properties of tissue microstructure in vivo such as myelination and iron. Previous work has linked such measures with cognitive task performance, particularly in older adults. Here we investigated whether performance on scene imagination, autobiographical memory, future thinking and spatial navigation tasks was associated with hippocampal grey matter myelination or iron content in young, healthy adult participants. Magnetic resonance imaging data were collected using a multi-parameter mapping protocol (0.8 mm isotropic voxels) from a large sample of 217 people with widely-varying cognitive task scores. We found little evidence that hippocampal grey matter myelination or iron content were related to task performance. This was the case using different analysis methods (voxel-based quantification, partial correlations), when whole brain, hippocampal regions of interest, and posterior:anterior hippocampal ratios were examined, and across different participant sub-groups (divided by gender and task performance). Variations in hippocampal grey matter myelin and iron levels may not, therefore, help to explain individual differences in performance on hippocampal-dependent tasks, at least in young, healthy individuals.

Conduction velocity along a key white matter tract is associated with autobiographical memory recall ability

“…These results offer a new perspective on individual differences in autobiographical memory recall ability. This is especially welcome given the current lack of a clear biological explanation for such variations in the healthy population ( Clark et al, 2020 ; Clark et al, 2021a ; LePort et al, 2012 ; Maguire et al, 2003 ; Palombo et al, 2018 ; Van Petten, 2004 ).…”

“…There is no doubt that the hippocampus is central to the processing of autobiographical memories, and hippocampal damage is linked with autobiographical memory impairments ( McCormick et al, 2018 ; Scoville and Milner, 1957 ; Winocur and Moscovitch, 2011 ). However, no consistent relationship between autobiographical memory recall ability and hippocampal grey matter volume or microstructure has been identified in healthy individuals ( Clark et al, 2020 ; Clark et al, 2021a ; LePort et al, 2012 ; Maguire et al, 2003 ; Van Petten, 2004 ). The hippocampus does not act alone, and functional neuroimaging studies have revealed that a distributed set of brain areas supports autobiographical memory recall along with the hippocampus, including the parahippocampal, retrosplenial, parietal and medial prefrontal cortices ( Andrews-Hanna et al, 2014 ; Maguire, 2001 ; Spreng et al, 2009 ; Svoboda et al, 2006 ).…”

Exercise Training Improves Memory Performance in Older Adults: A Narrative Review of Evidence and Possible Mechanisms

“…The higher cardiorespiratory fitness and physical activity in aged subjects, have been found to be associated with greater brain structures integrity, and better memory performance (Burzynska et al, 2015). Previous studies confirmed that, exercise training increases gray matter integrity in brain, and volume of brain regions, particularly entorhinal cortex and hippocampus in both human and animal studies (Voss et al, 2013;Ten Brinke et al, 2015;Chieffi et al, 2017;Firth et al, 2018;Tsai S.-F. et al, 2018;Clark et al, 2021), and also, brain white matter of memoryrelated regions in people with mild cognitive impairment (Amjad et al, 2019). In addition, reduced hippocampal atrophy together with improved memory were reported following 6-12 weeks of exercise training in early stage of Alzheimer's disease with this finding (Chirles et al, 2017;Ma et al, 2017;Morris et al, 2017).…”

Conduction velocity along a key white matter tract is associated with autobiographical memory recall ability

“…These results offer a new perspective on the neural instantiation of autobiographical memories, and in particular on drivers of individual differences in recall ability. This is especially welcome given the dearth of consistent findings linking hippocampal grey matter volume or microstructure with autobiographical memory recall ability in the healthy population (Clark et al, 2020;Clark et al, 2021a;LePort et al, 2012;Maguire et al, 2003;Van Petten, 2004).…”

“…There is no doubt that the hippocampus is central to the processing of autobiographical memories, and hippocampal damage is linked with autobiographical memory impairments (McCormick et al, 2018;Scoville and Milner, 1957;Winocur and Moscovitch, 2011). However, no consistent relationship between autobiographical memory recall ability and hippocampal grey matter volume or microstructure has been identified in healthy individuals (Clark et al, 2020;Clark et al, 2021a;LePort et al, 2012;Maguire et al, 2003;Van Petten, 2004). The hippocampus does not act alone, and functional neuroimaging studies have revealed that a distributed set of brain areas supports autobiographical memory recall along with the hippocampus, including the parahippocampal, retrosplenial, parietal and medial prefrontal cortices (Andrews-Hanna et al, 2014;Maguire, 2001;Spreng et al, 2009;Svoboda et al, 2006).…”