Interaction between age and perceptual similarity in olfactory discrimination learning in F344 rats: relationships with spatial learning

Abstract

Emerging evidence suggests that aging is associated with a reduced ability to distinguish perceptually similar stimuli in one’s environment. As the ability to accurately perceive and encode sensory information is foundational for explicit memory, understanding the neurobiological underpinnings of discrimination impairments that emerge with advancing age could help elucidate the mechanisms of mnemonic decline. To this end, there is a need for preclinical approaches that robustly and reliably model age-associated perceptual discrimination deficits. Taking advantage of rodents’ exceptional olfactory abilities, the present study applied rigorous psychophysical techniques to the evaluation of discrimination learning in young and aged F344 rats. Aging did not influence odor detection thresholds or the ability to discriminate between perceptually distinct odorants. In contrast, aged rats were disproportionately impaired relative to young on problems that required discriminations between perceptually similar olfactory stimuli. Importantly, these disproportionate impairments in discrimination learning did not simply reflect a global learning impairment in aged rats, as they performed other types of difficult discriminations on par with young rats. Among aged rats, discrimination deficits were strongly associated with spatial learning deficits. These findings reveal a new, sensitive behavioral approach for elucidating the neural mechanisms of cognitive decline associated with normal aging.

Rodent age‐related impairments in discriminating perceptually similar objects parallel those observed in humans

“…Given that age‐related discrimination deficits can be predictive of memory loss, both in elderly humans (Stark et al, ) and animal models (La Sarge et al, 2007; Yoder et al, preliminary acceptance Yoder et al, ), rats were cross‐characterized for spatial learning and memory abilities using a Morris water maze task (Bizon et al, ; Gallagher et al, ; Johnson et al, ). Cumulative integrated path length (CIPL) values across the 4 blocks of training trials are shown in Figure A.…”

“…These observations are consistent with our findings that aged F344 × BN rats in the present cohort did not show spatial learning or memory impairments relative to their young counterparts, even though these aged rats showed consistent, correlated deficits on similar object discriminations across Experiments 1 and 2. Interestingly, in F344 rats that show more robust water maze deficits with advancing age, as compared to hybrid strains (LaSarge & Nicolle, ), sensory discrimination abilities are highly predictive of spatial memory impairments (LaSarge et al, ; Yoder et al, ). Together, these data suggest application of the rodent target–lure discrimination task could permit detection of the earliest signs of age‐related neurobiological change across cortical–hippocampal circuits.…”

Emergence of β-Band Oscillations in the Aged Rat Amygdala during Discrimination Learning and Decision Making Tasks

“…Because the β oscillations that we found were primarily time locked to head entry into the food cup and well before reward delivery, the data suggest that this is an event of particular relevance to aged rats. Importantly, aged rats show intact thresholds for olfactory cue detection ( Yoder et al, 2017 ). It is possible that aged rats may have formed an association between the residual vanilla scent of the food cup area and upcoming rewards, although not required for accurate performance in any of the tasks administered here.…”

Decline of prefrontal cortical-mediated executive functions but attenuated delay discounting in aged Fischer 344 × brown Norway hybrid rats

“…Second, because attrition resulted in a relatively small number of rats cross-characterized on some tasks, aged rats were divided (based on a median split) to create subgroups corresponding to the upper and lower halves of the distribution on each behavioral measure. Performance on the intertemporal choice task was then compared between these subgroups and young rats using a two-factor ANOVA (subgroup × delay) as in previous work from our laboratories and others (e.g., Beas et al, 2013; Bizon et al, 2009; Leal et al, 2017; Lee et al, 2005; Yoder et al, 2017). …”