Age-related decline in cognitive flexibility is associated with the levels of hippocampal neurogenesis

The neuroplastic brain: current breakthroughs and emerging frontiers

Neuroplasticity, the brain's capacity to reorganize itself by forming new neural connections, is central to modern neuroscience. Once believed to occur only during early development, research now shows that plasticity continues throughout the lifespan, supporting learning, memory, and recovery from injury or disease. Substantial progress has been made in understanding the mechanisms underlying neuroplasticity and their therapeutic applications. This overview article examines synaptic plasticity, structural remodeling, neurogenesis, and functional reorganization, highlighting both adaptive (beneficial) and maladaptive (harmful) processes across different life stages. Recent strategies to harness neuroplasticity, ranging from pharmacological agents and lifestyle interventions to cutting-edge technologies like brain-computer interfaces (BCIs) and targeted neuromodulation are evaluated in light of current empirical evidence. Contradictory findings in the literature are addressed, and methodological limitations that hamper widespread clinical adoption are discussed. The ethical and societal implications of deploying novel neuroplasticity-based interventions, including issues of equitable access, data privacy, and the blurred line between treatment and enhancement, are then explored in a structured manner. By integrating mechanistic insights, empirical data, and ethical considerations, the aim is to provide a comprehensive and balanced perspective for researchers, clinicians, and policymakers working to optimize brain health across diverse populations.

Cognition on the move: Examining the role of physical exercise and neurogenesis in counteracting cognitive aging

Structural and functional aspects of the hippocampus have been shown to be sensitive to the aging process, resulting in deficits in hippocampal-dependent cognition. Similarly, adult hippocampal neurogenesis (AHN), described as the generation of new neurons from neural stem cells in the hippocampus, has shown to be negatively affected by aging throughout life. Extensive research has highlighted the role of physical exercise (PE) in positively regulating hippocampal-dependent cognition and AHN. Here, by critically reviewing preclinical and clinical studies, we discuss the significance of PE in reversing age-associated changes of the hippocampus via modulation of AHN. We indicate that PE-induced changes operate on two main levels. On the first level, PE can potentially cause structural modifications of the hippocampus, and on the second level, it regulates the molecular and cellular pathways involved. These changes result in the vascular remodelling of the neurogenic niche, as well as the secretion of neurotrophic and antioxidant factors, which can in turn activate quiescent neural stem cells, while restoring their proliferation capacity and boosting their survival - features which are negatively impacted during aging. Understanding these mechanisms will allow us to identify new targets to tackle cognitive aging and improve quality of life.

Homocysteine Mediates Cognitive Inflexibility Induced by Stress via Targeting PIN1

BACKGROUND

Increasing evidence shows that HCY plays an important role in stress-induced cognitive dysfunction, and HCY significantly promotes the decline of cognitive function. Stress has been reported to cause elevated HCY in the hippocampus of mice. Cognitive flexibility refers to the ability of individuals to quickly adjust their neurobehavioral strategies to different situations or to solve different tasks.

AIMS

This study aims to explore the role of HCY in the impairment of cognitive flexibility induced by stress and its possible regulatory mechanism.

METHODS AND RESULTS

First, we examined changes in the protein and mRNA levels of the cognitive flexibility effector molecule, PIN1, during stress in mice. The results show that stress can cause a decline in cognitive flexibility in mice and lead to an increase in PIN1. Moreover, through the use of in vitro experiments, we found that HCY could induce an increase in PIN1 expression in neurons. Further in vivo experiments were used to investigate the effect of VitB on HCY and PIN1 and evaluated the therapeutic effect of VitB on stress-induced impairment of cognitive flexibility. The results show that VitB decreased the levels of HCY in plasma and the hippocampus, alleviated the stress-induced impairment of cognitive flexibility, and reduced the expression of PIN1.

CONCLUSIONS

These results suggest that the impairment of cognitive flexibility induced by stress can be inhibited by regulating the content of HCY. Collectively, our findings highlight therapeutic strategies aimed at improving HCY treatment for impairments in cognitive flexibility.

Plasma tryptophan levels are linked to hippocampal integrity and cognitive function in individuals with mild cognitive impairment

Tryptophan has been shown to improve cognitive functions, but whether these benefits emanate from changes in hippocampal structure or other mechanisms like enhanced serotonin pathways remains unclear. This study aimed to examine the relationship between tryptophan levels and hippocampal volumes in individuals with mild cognitive impairment (MCI) and to determine if changes in hippocampal volume correlate with cognitive function. A total of 499 individuals with MCI were recruited based on ADNI's clinical criteria. Cognitive function was assessed using the ADAS-Cog scale, and hippocampal volumes were measured through MRI using semi-automated Medtronic Surgical Navigation Technologies (SNT). Tryptophan levels in plasma were analyzed using a nuclear magnetic resonance (NMR)-based assay. This study used two models: One unadjusted and another adjusted for covariates such as age, gender, handedness, and ApoE ɛ3 and ɛ4. In both models, higher tryptophan levels were significantly associated with increased bilateral hippocampal volumes, with a stronger effect in the left hippocampus. Furthermore, larger hippocampal volumes were linked to improved cognitive performance. Mediation analysis showed that hippocampal volumes mediated the relationship between plasma tryptophan levels and cognitive function. These findings suggested that elevated plasma tryptophan levels support cognitive health by maintaining hippocampal structural integrity, underscoring its potential role in preserving cognitive function in individuals with MCI.

Reflections on the Role of Differentiation Processes in Forming Behavioral Phenotypes: Can These Processes Replace the Concepts of Plastic Phenotype and Reversible Plastic Phenotype?

This essay presents two lines of argument to suggest that the extension into adulthood of specific phenotypic differentiation processes, typical of early development, is fundamental to the evolution of cognition. The first of these two lines of argument is organized in three steps. The first step reviews various studies of human development, highlighting that it has slowed down throughout evolution compared to that of great apes. The second step explores the relationship between this slowed development and human cognition. The third step discusses evolutionary comparative analyses that show a correlation between the evolution of cognitive processes and developmental changes. The second line of argument examines concepts of phenotype. First, the concepts of phenotype are reviewed in correspondence to the two meanings of the word plasticity (i.e., as the ability to alternate or as the ability to shape), and it is concluded that all phenotypes -rigid, plastic, and reversible-fit the meaning of shaping. It is proposed that a phenotypical process can be seen as a continuous series of functional differentiations that occur at different times during the life of the organism and at different contextual points, both inside and outside the organism. Finally, a brief recapitulation is presented that is focused on supporting the formation of behavioral phenotypes as a sequence of differentiation processes shaping the environmental interactions from the most general to the most particular.

Alcohol, flexible behavior, and the prefrontal cortex: Functional changes underlying impaired cognitive flexibility

Cognitive flexibility enables individuals to alter their behavior in response to changing environmental demands, facilitating optimal behavior in a dynamic world. The inability to do this, called behavioral inflexibility, is a pervasive behavioral phenotype in alcohol use disorder (AUD), driven by disruptions in cognitive flexibility. Research has repeatedly shown that behavioral inflexibility not only results from alcohol exposure across species but can itself be predictive of future drinking. Like many high-level executive functions, flexible behavior requires healthy functioning of the prefrontal cortex (PFC). The scope of this review addresses two primary themes: first, we outline tasks that have been used to investigate flexibility in the context of AUD or AUD models. We characterize these based on the task features and underlying cognitive processes that differentiate them from one another. We highlight the neural basis of flexibility measures, focusing on the PFC, and how acute or chronic alcohol in humans and non-human animal models impacts flexibility. Second, we consolidate findings on the molecular, physiological and functional changes in the PFC elicited by alcohol, that may contribute to cognitive flexibility deficits seen in AUD. Collectively, this approach identifies several key avenues for future research that will facilitate effective treatments to promote flexible behavior in the context of AUD, to reduce the risk of alcohol related harm, and to improve outcomes following AUD. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Integrating adult neurogenesis and human brain organoid models to advance epilepsy and associated behavioral research

Epilepsy is a chronic neurological disorder characterized by recurring, unprovoked seizures, asymmetrical electroencephalogram patterns, and other pathological abnormalities. The hippocampus plays a pivotal role in learning, memory consolidation, attentional control, and pattern separation. Impairment of hippocampal network circuitry can induce long-term cognitive and memory dysfunction. In this review, we discuss how aberrant adult neurogenesis and plasticity collectively alter the network balance for information processing within the hippocampal neural network. Subsequently, we explore the potential of human brain organoids integrated into microelectrode array technology as an electrophysiological tool. We also discuss the utilization of a closed-loop platform that connects the brain organoid to a mobile robot in a virtual environment. While in vivo models provide valuable insights into some aspects of epileptogenesis, such as the impact of adult neurogenesis on hippocampal function, brain organoids are indispensable for comprehensively studying epileptogenesis involving genetic mutations that underlie human epilepsy. More importantly, a combinational approach using brain organoids on MEA paves the way for studying impaired plasticity and abnormal information processing within epileptic neural networks. This innovative in vitro approach may provide a new pathway for investigating the behavioral outcomes of aberrant neural networks when integrated with a mobile robot, closing the loop between the neural network in brain organoids and the mobile robot. In this review, we aim to discuss the use of each model to study the behavioral changes in epilepsy and highlight the benefits of both in vivo and in vitro models for understanding the behavioral aspects of epilepsy.

The Pgb1 locus controls glycogen aggregation in astrocytes of the aged hippocampus without impacting cognitive function

In aged humans and mice, aggregates of hypobranched glycogen molecules called polyglucosan bodies (PGBs) accumulate in hippocampal astrocytes. PGBs are known to drive cognitive decline in neurological diseases but remain largely unstudied in the context of typical brain aging. Here, we show that PGBs arise in autophagy-dysregulated astrocytes of the aged C57BL/6J mouse hippocampus. To map the genetic cause of age-related PGB accumulation, we quantified PGB burden in 32 fully sequenced BXD-recombinant inbred mouse strains, which display a 400-fold variation in hippocampal PGB burden at 16-18 months of age. A major modifier locus was mapped to chromosome 1 at 72-75 Mb, which we defined as the Pgb1 locus. To evaluate candidate genes and downstream mechanisms by which Pgb1 controls the aggregation of glycogen, extensive hippocampal transcriptomic and proteomic datasets were produced for aged mice of the BXD family. We utilized these datasets to identify Smarcal1 and Usp37 as potential regulators of PGB accumulation. To assess the effect of PGB burden on age-related cognitive decline, we performed phenome-wide association scans, transcriptomic analyses as well as conditioned fear memory and Y-maze testing. Importantly, we did not find any evidence suggesting a negative impact of PGBs on cognition. Taken together, our study demonstrates that the Pgb1 locus controls glycogen aggregation in astrocytes of the aged hippocampus without affecting age-related cognitive decline.

Age-related reductions in whole brain mass and telencephalon volume in very old white Carneau pigeons (Columba livia)

While studies have identified age-related cognitive impairment in pigeons (Columba livia), no study has detected the brain atrophy which typically accompanies cognitive impairment in older mammals. Instead, Coppola and Bingman (Aging is associated with larger brain mass and volume in homing pigeons (Columba livia), Neurosci. Letters 698 (2019) 39-43) reported increased whole brain mass and telencephalon volume in older, compared to younger, homing pigeons. One reason for this unexpected finding might be that the older pigeons studied were not old enough to display age-related brain atrophy. Therefore, the current study repeated Coppola and Bingman, but with a sample of older white Carneau pigeons that were on average 5.34 years older. Brains from young and old homing pigeons were weighed and orthogonal measurements of the telencephalon, cerebellum, and optic tectum were obtained. Despite having a heavier body mass than younger pigeons, older pigeons had a significant reduction in whole brain mass and telencephalon volume, but not cerebellum or optic tectum volume. This study is therefore the first to find that pigeons experience age-related brain atrophy.