Neurocognitive Aging: Prior memories hinder new hippocampal encoding

ArticleinTrends in Neurosciences 29(12):662-70 · January 2007with11 Reads
DOI: 10.1016/j.tins.2006.10.002 · Source: PubMed
Abstract
Normal aging is often accompanied by impairments in forming new memories, and studies of aging rodents have revealed structural and functional changes to the hippocampus that might point to the mechanisms behind such memory loss. In this article, we synthesize recent neurobiological and neurophysiological findings into a model of the information-processing circuit of the aging hippocampus. The key point of the model is that small concurrent changes during aging strengthen the auto-associative network of the CA3 subregion at the cost of processing new information coming in from the entorhinal cortex. As a result of such reorganization in aged memory-impaired individuals, information that is already stored would become the dominant pattern of the hippocampus to the detriment of the ability to encode new information.
    • "Older individuals, relative to young adults, also have a greater incidence of improper source identification, or information about the circumstances or context within which learning occurred (Dodson, Bawa, & Slotnick, 2007). Improper source identification is thought to reduce the ability to prevent false memories and misinformation from impeding veridical information (Dodson, Koutstaal, & Schacter, 2000; Wilson, Gallagher, Eichenbaum, & Tanila, 2006). Thus, learning and recall are impacted by this fault. "
    [Show abstract] [Hide abstract] ABSTRACT: Sleep is an offline period during which newly acquired semantic information is transformed into longer-lasting memories. Language acquisition, which requires new word learning and semantic integration, is preferentially benefitted by a period of sleep in children and young adults. Specific features of sleep (e.g., sleep stage characteristics) have been associated with enhanced language acquisition and generalization. However, with increasing age, even in healthy individuals, sleep quality and quantity decrease. Simultaneously, deficits in word retrieval and new word learning emerge. Yet it is unknown whether age-related alterations in language ability are linked with alterations in sleep. The goal of this review is to examine changes in language learning and sleep across the lifespan. We consider how sleep detriments that occur with aging could affect abilities to learn novel words and semantic generalization and propose hypotheses to motivate future research in this area.
    Article · Jun 2016
    • "Furthermore, it is important to note that acetylcholine and dopamine levels are reduced in the hippocampi of older adults. These changes are correlated with a reduced ability to store new information, contributing significantly to age-associated memory impairment [118]. Moreover, noradrenaline levels are also attenuated during aging, thereby affecting emotional memory [125]. "
    [Show abstract] [Hide abstract] ABSTRACT: Major depressive disorder (MDD) is one of the most prevalent and life-threatening forms of mental illnesses affecting elderly people and has been associated with poor cognitive function. Recent evidence suggests a strong relationship between MDD and neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Amyotrophic Lateral Sclerosis (ALS), as well as natural processes of aging. Changes in the neuroplasticity, morphology, and neurotransmission in the brain are seem to be associated to both, MDD and neurodegenerative diseases. In addition, there is evidence that psychological stress and MDD are associated with molecular and cellular signs of accelerated aging. This review will highlight the relationship between MDD, the aging process, and neurodegenerative diseases, emphasizing the neurochemical processes involved.
    Full-text · Article · Jun 2016
    • "However, aging-related degradation in this form of memory cannot be viewed as entirely due to defects in mnemonic retention mechanisms. Indeed, it has been shown in both aged humans (Leal and Yassa, 2015) and animals (Gallagher et al., 2010; Wilson et al., 2006), that the formation of new memories of everyday life experiences is also hampered by interference from similar memories, produced by the combination of a diminished ability to discriminate between similar experiences, and overexpression of old memories (Stark et al., 2010). Hence, the lack of positive influence of E2 on mnemonic organization here demonstrated in male mice undermines potential therapeutic interest of estrogen supplementation, even though this result has yet to be reproduced in females and in humans. "
    [Show abstract] [Hide abstract] ABSTRACT: Because estrogens have mostly been studied in gonadectomized females, effects of chronic exposure to environmental estrogens in the general population are underestimated. Estrogens can enhance hippocampus-dependent memory through the modulation of information storage. However, declarative memory, the hippocampus-dependent memory of facts and events, demands more than abilities to retain information. Specifically, memory of repetitive events of everyday life such as "where I parked" requires abilities to organize/update memories to prevent proactive interference from similar memories of previous "parking events". Whether such organizational processes are estrogen-sensitive is unknown. We here studied, in intact young and aged adult mice, drinking-water (1μM) estradiol effects on both retention and organizational components of hippocampus-dependent memory, using a radial-maze task of everyday-like memory. Demand on retention vs organization was manipulated by varying the time-interval separating repetitions of similar events. Estradiol increased performance in young and aged mice under minimized organizational demand, but failed to improve the age-associated memory impairment and diminished performance in young mice under high organizational demand. In fact, estradiol prolonged mnemonic retention of successive events without improving organization abilities, hence resulted in more proactive interference from irrelevant memories. c-Fos imaging of testing-induced brain activations showed that the deterioration of young memory was associated with dentate gyrus dysconnectivity, reminiscent of that seen in aged mice. Our findings support the view that estradiol is promnesic but also reveal that such property can paradoxically impair memory. These findings have important outcomes regarding health issues relative to the impact of environmental estrogens in the general population.
    Full-text · Article · Mar 2016
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