Differential impacts of healthy cognitive aging on directed and random exploration.

Deciding whether to explore unknown opportunities or exploit well-known options is a ubiquitous part of our everyday lives. Extensive work in college students suggests that young people make explore-exploit decisions using a mixture of information seeking and random behavioral variability. Whether, and to what extent, older adults use the same strategies is unknown. To address this question, 51 older adults (ages 65-74) and 32 younger adults (ages 18-25) completed the Horizon Task, a gambling task that quantifies information seeking and behavioral variability as well as how these strategies are controlled for the purposes of exploration. Qualitatively, we found that older adults performed similar to younger adults on this task, increasing both their information seeking and behavioral variability when it was adaptive to explore. Quantitively, however, there were substantial differences between the age groups, with older adults showing less information seeking overall and less reliance on variability as a means to explore. In addition, we found a subset of approximately 26% of older adults whose information seeking was close to zero, avoiding informative options even when they were clearly the better choice. Unsurprisingly, these "information avoiders" performed worse on the task. In contrast, task performance in the remaining "information seeking" older adults was comparable to that of younger adults suggesting that age-related differences in explore-exploit decision making may be adaptive except when they are taken to extremes. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Transcranial magnetic stimulation reveals diminished homoeostatic metaplasticity in cognitively impaired adults.

Homoeostatic metaplasticity is a neuroprotective physiological feature that counterbalances Hebbian forms of plasticity to prevent network destabilization and hyperexcitability. Recent animal models highlight dysfunctional homoeostatic metaplasticity in the pathogenesis of Alzheimer's disease. However, the association between homoeostatic metaplasticity and cognitive status has not been systematically characterized in either demented or non-demented human populations, and the potential value of homoeostatic metaplasticity as an early biomarker of cognitive impairment has not been explored in humans. Here, we report that, through pre-conditioning the synaptic activity prior to non-invasive brain stimulation, the association between homoeostatic metaplasticity and cognitive status could be established in a population of non-demented human subjects (older adults across cognitive spectrums; all within the non-demented range). All participants (n = 40; age range, 65-74, 47.5% female) underwent a standardized neuropsychological battery, magnetic resonance imaging and a transcranial magnetic stimulation protocol. Specifically, we sampled motor-evoked potentials with an input/output curve immediately before and after repetitive transcranial magnetic stimulation to assess neural plasticity with two experimental paradigms: one with voluntary muscle contraction (i.e. modulated synaptic activity history) to deliberately introduce homoeostatic interference, and one without to serve as a control condition. From comparing neuroplastic responses across these experimental paradigms and across cohorts grouped by cognitive status, we found that (i) homoeostatic metaplasticity is diminished in our cohort of cognitively impaired older adults and (ii) this neuroprotective feature remains intact in cognitively normal participants. This novel finding suggests that (i) future studies should expand their scope beyond just Hebbian forms of plasticity that are traditionally assessed when using non-invasive brain stimulation to investigate cognitive ageing and (ii) the potential value of homoeostatic metaplasticity in serving as a biomarker for cognitive impairment should be further explored.

Impaired discrimination with intact crossmodal association in aged rats: A dissociation of perirhinal cortical-dependent behaviors.

The perirhinal cortex (PRC) supports associative memory and perception, and PRC dysfunction impairs animals' abilities to associate stimulus features across sensory modalities. PRC damage also leads to deficits in discriminating between stimuli that share features. Although PRC-dependent stimulus discrimination has been shown to be impaired with advanced age, data regarding the abilities of older adults and other animals to form PRC-dependent associations have been equivocal. Moreover, the extent to which similar neural computations within the PRC support associative memory versus discrimination abilities have not been directly examined. In the current study, young and aged rats were cross-characterized on two PRC-dependent crossmodal object recognition (CMOR) tasks to test associative memory, and a LEGO object discrimination task. In the CMOR tasks, rats were familiarized with an object with access to tactile input and then tested for recognition with visual input only. The relative exploration time of novel versus familiar objects indicated that aged rats showed preference for the novel over familiar object with and without an epoch of multimodal preexposure to the familiar object prior to the testing session. Furthermore, crossmodal recognition performance between young and aged rats was not significantly different. In contrast, for the LEGO object discrimination task, aged rats were impaired relative to young rats. Notably, aged rats that performed poorly on the LEGO object discrimination task had better performance on the CMOR tasks. The dissociation of discrimination and association abilities with age suggests that these behaviors rely on distinct neural computations within PRC-medial temporal lobe circuit. (PsycINFO Database Record