In the absence of pharmacological cure, finding the most sensitive early cognitive markers of Alzheimer's disease (AD) is becoming increasingly important. In this paper, we review evidence showing that brain mechanisms of spontaneous, but stimulus-dependent, cognition overlap with key hubs of the default mode network (DMN), which become compromised by amyloid pathology years before the clinical symptoms of AD. This leads to the formulation of a novel hypothesis, which predicts that spontaneous, but stimulus-dependent conscious retrieval processes, generally intact in healthy ageing, will be particularly compromised in people at the earliest stages of AD. Initial evidence for this hypothesis is presented across diverse experimental paradigms (e.g., prospective memory, mind-wandering), and new avenues for research in this area are outlined. Glossary Alzheimer's disease (AD): A progressive and irreversible neurodegenerative disease, affecting primarily older population, which is characterized by significant impairments in episodic memory and other cognitive abilities, leading to a loss of functional independence. Default mode network (DMN): A widely distributed functional network along the brain's midline that is important for self-referential information processing. It is characterized by high activations when people are engaged in processing internal thoughts and deactivations when individuals perform attentionally demanding experimental tasks. Intrusive memories: Memories that repeatedly intrude upon consciousness, often against one's will, are hard to control, and may disrupt one's ongoing activities. Although they can be sometimes about positive events, they are predominantly negative and disturbing, and constitute a core symptom of the Post-Traumatic Stress Disorder. Involuntary autobiographical memories: Memories of past events that pop into mind without any deliberate intention to recall anything, often when a person is engaged in some mundane everyday activities (e.g., driving, brushing teeth) and in response to easily identifiable triggers. They may refer to positive, negative, or completely neutral events such as remembering one's first romantic kiss, failing an exam, or buying food in a supermarket. Involuntary (or spontaneous) future thinking: Involves mental representations about the future, which may come to mind unintended (unexpectedly) while being engaged in other habitual activities, and in response to irrelevant stimuli in the environment. They can refer to planned events (e.g., buying a train ticket tomorrow), plausible future events (e.g., a trip to Japan) or hypothetical scenarios and wishful thinking (e.g., winning the lottery). Involuntary semantic memories: Fragments of semantic knowledge (e.g., someone's name, image of Big Ben, or a familiar song) that pop into mind unexpectedly, without any 5 accompanying contextual information (e.g., memory of when we last heard the song). Research on mind-pops has focussed mainly on 'earworms'-when a song or a tune gets stuck in one's mind and repeatedl...

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 We examined the interaction between MS and ΝΗΙ on emotionality and markers of plasticity. Both MS and NHI increased anxiety levels, but only NHI induced depressionlike behavior. Maternal separation did not further increase emotionality in HI-treated rats. Both MS and NHI decreased synaptophysin levels in dentate gyrus and CA3 hippocampal areas. BDNF expression in CA3 was decreased only in the HI animals that were maternally-separated. AbstractExposure to early-life stress is associated with long-term alterations in brain and behavior, and may aggravate the outcome of neurological insults. This study aimed at investigating the possible interaction between maternal separation, a model of early stress, and subsequent neonatal hypoxia-ischemia on emotional behavior and markers of synaptic plasticity in hippocampus. Therefore, rat pups (N=60) were maternally separated for a prolonged (MS 180min) or a brief (MS 15min) period during the first six postnatal days, while a control group was left undisturbed. Hypoxia-ischemia was applied to a subgroup of each rearing condition on postnatal day 7. Emotional behavior was examined at three months of age and included assessments of anxiety (elevated plus maze), depression-like behavior (forced swimming) and spontaneous exploration (open field). Synaptic plasticity was evaluated based on BDNF and synaptophysin expression in CA3 and dentate gyrus hippocampal regions. We found that neonatal hypoxia-ischemia caused increased levels of anxiety, depression-like behavior and locomotor activity (ambulation). Higher anxiety levels were also seen in maternally separated rats (MS180min) compared to non-maternally separated rats, but prolonged maternal separation prior to HI did not potentiate the HI-associated effect. No differences among the three rearing conditions were found regarding depression-like behavior or ambulation. Immunohistochemical evaluation of synaptophysin revealed that both prolonged maternal separation (MS180min) and neonatal hypoxia-ischemia significantly reduced its expression in the CA3 and dentate gyrus. Decreases in synaptophysin expression in these areas were not exacerbated in rats that were maternally separated for a prolonged period prior to HI. Regarding BDNF expression, we found a significant decrease in immunoreactivity only in the hypoxic-ischemic rats that were subjected to the prolonged maternal separation paradigm. The above findings suggest that early-life stress prior to neonatal hypoxia-ischemia leads to significant alterations in synaptic plasticity of the dorsal hippocampus during adulthood, but does not exacerbate HI-related changes in emotional behavior.

The COVID-19 pandemic created a unique set of circumstances in which to investigate collective memory and future simulations of events reported during the onset of a potentially historic event. Between early April and late June 2020, we asked over 4,000 individuals from 15 countries across four continents to report on remarkable (a) national and (b) global events that (i) had happened since the first cases of COVID-19 were reported, and (ii) they expected to happen in the future. Whereas themes of infections, lockdown, and politics dominated global and national past events in most countries, themes of economy, a second wave, and lockdown dominated future events. The themes and phenomenological characteristics of the events differed based on contextual group factors. First, across all conditions, the event themes differed to a small yet significant degree depending on the severity of the pandemic and stringency of governmental response at the national level. Second, participants reported national events as less negative and more vivid than global events, and group differences in emotional valence were largest for future events. This research demonstrates that even during the early stages of the pandemic, themes relating to its onset and course were shared across many countries, thus providing preliminary evidence for the emergence of collective memories of this event as it was occurring. Current findings provide a profile of past and future collective events from the early stages of the ongoing pandemic, and factors accounting for the consistencies and differences in event representations across 15 countries are discussed. Supplementary Information The online version contains supplementary material available at 10.3758/s13421-022-01329-8.