The hippocampal formation and action at a distance

Lost in time: Relocating the perception of duration outside the brain

It is well-accepted in neuroscience that animals process time internally to estimate the duration of intervals lasting between one and several seconds. More than 100 years ago, Henri Bergson nevertheless remarked that, because animals have memory, their inner experience of time is ever-changing, making duration impossible to measure internally and time a source of change. Bergson proposed that quantifying the inner experience of time requires its externalization in movements (observed or self-generated), as their unfolding leaves measurable traces in space. Here, studies across species are reviewed and collectively suggest that, in line with Bergson's ideas, animals spontaneously solve time estimation tasks through a movement-based spatialization of time. Moreover, the well-known scalable anticipatory responses of animals to regularly spaced rewards can be explained by the variable pressure of time on reward-oriented actions. Finally, the brain regions linked with time perception overlap with those implicated in motor control, spatial navigation and motivation. Thus, instead of considering time as static information processed by the brain, it might be fruitful to conceptualize it as a kind of force to which animals are more or less sensitive depending on their internal state and environment.

Cross-stage neural pattern similarity in the hippocampus predicts false memory derived from post-event inaccurate information

The misinformation effect occurs when people's memory of an event is altered by subsequent inaccurate information. No study has systematically tested theories about the dynamics of human hippocampal representations during the three stages of misinformation-induced false memory. This study replicates behavioral results of the misinformation effect, and investigates the cross-stage pattern similarity in the hippocampus and cortex using functional magnetic resonance imaging. Results show item-specific hippocampal pattern similarity between original-event and post-event stages. During the memory-test stage, hippocampal representations of original information are weakened for true memory, whereas hippocampal representations of misinformation compete with original information to create false memory. When false memory occurs, this conflict is resolved by the lateral prefrontal cortex. Individuals' memory traces of post-event information in the hippocampus predict false memory, whereas original information in the lateral parietal cortex predicts true memory. These findings support the multiple-trace model, and emphasize the reconstructive nature of human memory.

Spatial navigation and memory: A review of the similarities and differences relevant to brain models and age

Spatial navigation and memory are often seen as heavily intertwined at the cognitive and neural levels of analysis. We review models that hypothesize a central role for the medial temporal lobes, including the hippocampus, in both navigation and aspects of memory, particularly allocentric navigation and episodic memory. While these models have explanatory power in instances in which they overlap, they are limited in explaining functional and neuroanatomical differences. Focusing on human cognition, we explore the idea of navigation as a dynamically acquired skill and memory as an internally driven process, which may better account for the differences between the two. We also review network models of navigation and memory, which place a greater emphasis on connections rather than the functions of focal brain regions. These models, in turn, may have greater explanatory power for the differences between navigation and memory and the differing effects of brain lesions and age.

Transcriptomic and metabolomic studies on the protective effect of molecular hydrogen against nuclear electromagnetic pulse-induced brain damage

Background

Excessive doses of electromagnetic radiation pose a negative impact on the central nervous system and lead to mental disorders. Molecular hydrogen can scavenge intracellular hydroxyl radicals, acting as an antioxidant, anti-apoptotic and anti-inflammatory agent. We seek to assess the capability of molecular hydrogen to ameliorate brain damage induced by electromagnetic radiation.

Methods

NEMP (nuclear electromagnetic pulse), a subset of electromagnetic pulse with high voltage value that could cause severe brain injury, was applied to this study. Male wild-type rats were divided into four groups: the control group, the H₂ (Molecular hydrogen) group, the NEMP group and the NEMP+H₂ group. Rats in the H₂ group and the NEMP+H₂ group were fed with saturated hydrogen-rich water from 3 days before NEMP exposure (electromagnetic field intensity 400 kV/m, rising edge 20 ns and pulse width 200 ns) to the day of sacrifice. One day after exposure, animal behavior experiments were performed, and samples for transcriptomics and metabolomics analysis were collected. Seven days after exposure, histopathological experiments were conducted.

Results

The data from the elevated plus maze and the open field test showed that NEMP exposure elicited anxiety-like behavior in rats, which could be alleviated by H₂ treatment. Histopathological results manifested that NEMP exposure-induced injuries of the neurons in the hippocampus and amygdala could be attenuated by H₂ treatment. Transcriptomic results revealed that NEMP exposure had a profound effect on microtubule structure in the brain. And the combined analysis of transcriptomics and metabolomics showed that H₂ has a significant impact on the neuroactive ligand-receptor interaction, synaptic vesicle cycle and synapse etc. Moreover, it was indicated that the glutathione metabolic pathway played a vital role in the NEMP exposure-induced damage and the protective activity of H₂.

Conclusions

H₂ is identified as a potent agent against NEMP exposure-induced brain damage and has the potential to be a promising electromagnetic radiation protectant.

Readiness to remember: predicting variability in episodic memory

Learning and remembering are fundamental to our lives, so what causes us to forget? Answers often highlight preparatory processes that precede learning, as well as mnemonic processes during the act of encoding or retrieval. Importantly, evidence now indicates that preparatory processes that precede retrieval attempts also have powerful influences on memory success or failure. Here, we review recent work from neuroimaging, electroencephalography, pupillometry, and behavioral science to propose an integrative framework of retrieval-period dynamics that explains variance in remembering in the moment and across individuals as a function of interactions among preparatory attention, goal coding, and mnemonic processes. Extending this approach, we consider how a 'readiness to remember' (R2R) framework explains variance in high-level functions of memory and mnemonic disruptions in aging.