The impact of experienced stress on aged spatial discrimination: Cortical overreliance as a result of hippocampal impairment

Abstract

A large body of neuroscientific work indicates that exposure to experienced stress causes damage to both cortical and hippocampal cells and results in impairments to cognitive abilities associated with these structures. Similarly, work within the domain of cognitive aging demonstrates that elderly participants who report experiencing greater amounts of stress show reduced levels of cognitive functioning. The present paper attempts to combine both findings by collecting data from elderly and young participants who completed a spatial discrimination paradigm developed by Reagh and colleagues (Reagh, Z. et al., Hippocampus 2013; 24:303-314) to measure hippocampal-mediated cognitive processes. In order to investigate the effect of stress on the cortex and, indirectly, the hippocampus, it paired the paradigm with electroencephalographic (EEG) recordings of the theta frequency band, which is thought to reflect cortical/hippocampal interactions. Findings revealed that elderly participants with high levels of experienced stress performed significantly worse on target recognition and lure discrimination and demonstrated heightened levels of cortical theta synchronization compared to young and elderly low stress counterparts. Results therefore provide further evidence for the adverse effect of stress on cognitive aging and indicate that impaired behavioral performance among high stress elderly may coincide with an overreliance on cortical cognitive processing strategies as a result of early damage to the hippocampus.3

Lost in Time and Space: States of High Arousal Disrupt Implicit Acquisition of Spatial and Sequential Context Information

“…In a subsequent surprise recall, participants viewed the same objects at either the same or stepwise vertically or horizontally displaced locations and had to decide whether the object had remained in the same location or whether it had been moved. Recently, this paradigm has been applied successfully to study early forms of hippocampal impairment in elderly humans (Reagh et al, 2014 ) and the impact of experienced life-time stress on age-related hippocampal function (Marshall et al, 2016 ). In addition, spatial discrimination ability in this spatial task was related to performance in the Rey Auditory Verbal Learning Test, a neuropsychological test of hippocampus related, declarative memory (Reagh et al, 2014 ).…”

“…The Spatial Mnemonic Discrimination Task (Reagh et al, 2014 ; Marshall et al, 2016 ) consists of 140 common objects and is structured in two sequences, an encoding and a retrieval phase. At first, participants had to judge whether each presented item is more likely to be used indoors or outdoors by responding with their right or left index finger.…”

“…At first, participants had to judge whether each presented item is more likely to be used indoors or outdoors by responding with their right or left index finger. The objects were located in a 5 × 7 grid due to the dimensions of common widescreen displays and appeared for 2500 ms, assigned pseudo randomly (Marshall et al, 2016 ). This first sequence conduces incidental learning (Reagh et al, 2014 ).…”

“…Diagonal displacements were excluded in the current setting (Reagh et al, 2014 ). This differentiation enables one to make parametric comparisons across levels of mnemonic interference (Marshall et al, 2016 ). Each space of the grid is equally likely to contain an object and direction of displacements also appeared for 2500 ms assigned pseudo randomly for each participant.…”

“…Our predictions were tested in two behavioral experiments using established experimental paradigms, assessing implicit acquisition of spatial relations (spatial discrimination paradigm; Marshall et al, 2016 ; Experiment 1) and predictive sequences (learned irrelevance paradigm; Orosz et al, 2008 , 2011 ; Experiment 2). The elicitation procedure comprised three cinematographic fragments: a social conversation, a violent encounter and sexual intercourse.…”