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.
    • "(Simkin et al., 2015; Wilson et al., 2005 Wilson et al., , 2006), our whole-cell experiments indicated that aging is associated with an increase in the intrinsic excitability without changes in the passive membrane properties of CA3 pyramidal neurons. We also found a reduction in the amplitude but not in the frequency of spontaneous glutamatergic postsynaptic currents and a systematic decrease in the amplitude and frequency of spontaneous GABAergic currents. "
    [Show abstract] [Hide abstract] ABSTRACT: The network interaction between the dentate gyrus and area CA3 of the hippocampus is responsible for pattern separation, a process that underlies the formation of new memories, and which is naturally diminished in the aged brain. At the cellular level, aging is accompanied by a progression of biochemical modifications that ultimately affects its ability to generate and consolidate long-term potentiation (LTP). Although the synapse between dentate gyrus via the mossy fibers (MF) onto CA3 neurons has been subject of extensive studies, the question of how aging affects the MF-CA3 synapse is still unsolved. Extracellular and whole cell recordings from acute hippocampal slices of aged Wistar rats (34 ± 2 months old) shows that aging is accompanied by a reduction in the interneuron-mediated inhibitory mechanisms of area CA3. Several MF-mediated forms of short-term plasticity, MF LTP and at least one of the critical signaling cascades necessary for potentiation are also compromised in the aged brain. An analysis of the spontaneous glutamatergic and GABAergic currents on CA3 cells reveal a dramatic alteration in amplitude and frequency of the non-evoked events. CA3 cells also exhibited increased intrinsic excitability. Together, these results demonstrate that aging is accompanied by a decrease in the GABAergic inhibition, reduced expression of short- and long-term forms of synaptic plasticity, and increased intrinsic excitability.
    Full-text · Article · Sep 2016
    • "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.
    Full-text · 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
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