Environmental enrichment alters dentate granule cell morphology in oldest-old rat

One day away from mum has lifelong consequences on brain and behaviour

This chapter presents a brief overview of attachment theory and discusses the importance of the neonatal period in shaping an individual's physiological and behavioural responses to stress later in life, with a focus on the role of the parent-infant relationship, particularly in rodents. In rodents, the role of maternal behaviours goes far beyond nutrition, thermoregulation and excretion, acting as hidden regulators of the pup's physiology and development. In this review, we will discuss the inhibitory role of specific maternal behaviours on the ACTH and corticosterone (CORT) stress response. The interest of our group to explore the long-term consequences of maternal deprivation for 24 h (DEP) at different ages (3 days and 11 days) in rats was sparked by its opposite effects on ACTH and CORT levels. In early adulthood, DEP3 animals (males and females alike) show greater negative impact on affective behaviours and stress related parameters than DEP11, indicating that the latter is more resilient in tests of anxiety-like behaviour. These findings create an opportunity to explore the neurobiological underpinnings of vulnerability and resilience to stress-related disorders. The chapter also provides a brief historical overview and highlights the relevance of attachment theory, and how DEP helps to understand the effects of childhood parental loss as a risk factor for depression, schizophrenia, and PTSD in both childhood and adulthood. Furthermore, we present the concept of environmental enrichment (EE), its effects on stress responses and related behavioural changes and its benefits for rats previously subjected to DEP, along with the clinical implications of DEP and EE.

Providing height to pullets does not influence hippocampal dendritic morphology or brain-derived neurotrophic factor at the end of the rearing period

Pullets reared with diverse behavioral experiences are faster to learn spatial cognition tasks and acclimate more successfully to laying environments with elevated structures. However, the neural underpinnings of the improved spatial abilities are unclear. The objective of this study was to determine whether providing structural height in the rearing environment affected the development of the hippocampus and whether hippocampal neural metrics correlated with individual behavior on spatial cognition tasks. Female Dekalb White pullets were reared in a floor pen (FL), single-tiered aviary (ST), or two-tiered aviary (TT; 5 pens/treatment). Pullets completed floor-based Y-maze and elevated visual cliff tasks to evaluate depth perception at 15 and 16 wk, respectively. At 16 wk, brains were removed for Golgi-Cox staining (n = 12 for FL, 13 for ST, 13 total pullets for TT; 2 to 3 pullets/pen) and qPCR to measure gene expression of brain-derived neurotrophic factor (BDNF; n = 10 for FL, 11 for ST, and 9 pullets for TT). Rearing environment did not affect various morphometric outcomes of dendritic arborization, including Sholl profiles; mean dendritic length; sum dendritic length; number of dendrites, terminal tips, or nodes; soma size; or BDNF mRNA expression (P > 0.05). Hippocampal subregion did affect dendritic morphology, with multipolar neurons from the ventral subregion differing in several characteristics from multipolar neurons in the dorsomedial or dorsolateral subregions (P < 0.05). Neural metrics did not correlate with individual differences in behavior during the spatial cognition tasks. Overall, providing height during rearing did not affect dendritic morphology or BDNF at 16 wk of age, but other metrics in the hippocampus or other brain regions warrant further investigation. Additionally, other structural or social components or the role of animal personality are areas of future interest for how rearing environments influence pullet behavior.

Environmental enrichment and the aging brain: is it time for standardization?

Aging entails a progressive decline of cognitive abilities. However, since the brain is endowed with considerable plasticity, adequate stimulation can delay or partially compensate for age-related structural and functional impairment. Environmental enrichment (EE) has been reported to determine a wide range of cerebral changes. Although most findings have been obtained in young and adult animals, research has recently turned to aged individuals. Notably, EE can contribute identifying key lifestyle factors whose change can help extend the "mind-span", i.e., the time an individual lives in a healthy cognitive condition. Here we discuss specific methodological issues that can affect the outcomes of EE interventions applied to aged rodents, summarize the main variables that would need standardization (e.g., timing and duration, enrichment items, control animals and setting), and offer some suggestions on how this goal may be achieved. Reaching a consensus on EE experiment design would significantly reduce differences between and within laboratories, enable constructive discussions among researchers, and improve data interpretation.

Environmental enrichment preserves a young DNA methylation landscape in the aged mouse hippocampus

The decline of brain function during aging is associated with epigenetic changes, including DNA methylation. Lifestyle interventions can improve brain function during aging, but their influence on age-related epigenetic changes is unknown. Using genome-wide DNA methylation sequencing, we here show that experiencing a stimulus-rich environment counteracts age-related DNA methylation changes in the hippocampal dentate gyrus of mice. Specifically, environmental enrichment prevented the aging-induced CpG hypomethylation at target sites of the methyl-CpG-binding protein Mecp2, which is critical to neuronal function. The genes at which environmental enrichment counteracted aging effects have described roles in neuronal plasticity, neuronal cell communication and adult hippocampal neurogenesis and are dysregulated with age-related cognitive decline in the human brain. Our results highlight the stimulating effects of environmental enrichment on hippocampal plasticity at the level of DNA methylation and give molecular insights into the specific aspects of brain aging that can be counteracted by lifestyle interventions.

Housing quality and behavior affect brain health and anxiety in healthy Japanese adults

Countless studies in animals have shown how housing environments and behaviors can significantly affect anxiety and brain health, giving valuable insight as to whether this is applicable in the human context. The relationship between housing, behavior, brain health, and mental wellbeing in humans remains poorly understood. We therefore explored the interaction of housing quality, weekend/holiday sedentary behavior, brain structure, and anxiety in healthy Japanese adults. Whole-brain structural magnetic resonance imaging (MRI) methods based on gray matter volume and fractional anisotropy were used as markers for brain health. Correlation tests were conducted, and then adjusted for multiple comparisons using the False Discovery Rate method. Housing quality and weekend/holiday sedentary behavior were associated with fractional anisotropy, but not with gray matter volume. Fractional anisotropy showed significant associations with anxiety. Lastly, both weekend/holiday sedentary behavior and housing quality were indirectly associated with anxiety through fractional anisotropy. These results add to the limited evidence surrounding the relationship among housing, behavior, and the brain. Furthermore, these results show that behavior and housing qualities can have an indirect impact on anxiety through neurobiological markers such as fractional anisotropy.

Enriching hippocampal memory function in older adults through video games

Healthy aging is accompanied by a steady cognitive decline with clear losses in memory. Animal studies have consistently demonstrated that simply modifying an animal's living environment (known as environmental enrichment) can have a positive influence on age-related cognitive decline in the hippocampus. Previously, we showed that playing immersive 3D video games can improve hippocampal-based memory in young healthy adults, suggesting that the exploration of the large open worlds of modern-day video games may act as proxy for environmental enrichment in humans. Here, we replicated our previous video game study in healthy older adults, showing that playing video games for four weeks can improve hippocampal-based memory in a population that is already experiencing age-related decline in memory. Furthermore, we showed that the improvements last for up to four weeks past the intervention, highlighting the potential of video games as intervention for age-related cognitive decline.

The Social Component of Environmental Enrichment Is a Pro-neurogenic Stimulus in Adult c57BL6 Female Mice

In rodents, the hippocampal dentate gyrus gives rise to newly generated dentate granule cells (DGCs) throughout life. This process, named adult hippocampal neurogenesis (AHN), converges in the functional integration of mature DGCs into the trisynaptic hippocampal circuit. Environmental enrichment (EE) is one of the most potent positive regulators of AHN. This paradigm includes the combination of three major stimulatory components, namely increased physical activity, constant cognitive stimulation, and higher social interaction. In this regard, the pro-neurogenic effects of physical activity and cognitive stimulation have been widely addressed in adult rodents. However, the pro-neurogenic potential of the social aspect of EE has been less explored to date. Here we tackled this question by specifically focusing on the effects of a prolonged period of social enrichment (SE) in adult female C57BL6 mice. To this end, 7-week-old mice were housed in groups of 12 per cage for 8 weeks. These mice were compared with others housed under control housing (2–3 mice per cage) or EE (12 mice per cage plus running wheels and toys) conditions during the same period. We analyzed the number and morphology of Doublecortin-expressing (DCX⁺) cells. Moreover, using RGB retroviruses that allowed the labeling of three populations of newborn DGCs of different ages in the same mouse, we performed morphometric, immunohistochemical, and behavioral determinations. Both SE and EE increased the number and maturation of DCX⁺ cells, and caused an increase in dendritic maturation in certain populations of newborn DGCs. Moreover, both manipulations increased exploratory behavior in the Social Interaction test. Unexpectedly, our data revealed the potent neurogenesis-stimulating potential of SE in the absence of any further cognitive stimulation or increase in physical activity. Given that an increase in physical activity is strongly discouraged under certain circumstances, our findings may be relevant in the context of enhancing AHN via physical activity-independent mechanisms.

Aged rats with different performances at environmental enrichment onset display different modulation of habituation and aversive memory

A wide agreement exists that environmental enrichment (EE) is most beneficial if introduced early in life, but numerous studies reported that also aged animals remain responsive. As age-related memory and cognition impairments are not uniform, an open question is whether EE might exert different effects in animals with different age-related deficits. A 12-week EE protocol was applied to late adult rats pretested for habituation and aversive memory. Animals were classified as low (LP) and high (HP) performers according to percent exploration change in Open Field test (OF) and as impaired (I) and not impaired (NI) according to latency in Step-through Passive Avoidance test (PA). Standard housing (SH) animals pretested by OF and PA, and naïve (non-pretested) EE and SH rats were used as controls. In comparison to pretest, after the housing protocol, EE LP ameliorated while EE HP and both SH HP and LP worsened their habituation pattern. The positive influence of EE on LP was probably due to the more active interaction with and the faster adaptation to surroundings promoted by continuous, multiple stimuli provided during the enriched housing. Regarding HP, EE did not boost the basal behavior, which likely represented the maximum achievable for that age, and the post housing exploration change dropped, as in SH animals, because of the retesting. After EE, a significant percentage of NI animals became I and a significant percentage of I animals became NI. The changes evidenced in the NI group likely depended on EE-related reduction of anxiety and the consequent more efficient coping with fearful situations. This hypothesis was strengthened by the observation that naïve EE animals were almost all I. Pretested EE I rats were not influenced by the rearing condition: their behavior was comparable to SH animals' behavior and determined by retesting. In conclusion, these results demonstrated that, when applied to aging rats, EE produces different effects based on pre-housing cognitive performances. The issue needs further analyses, but the observation that not all animals are able to take advantage of EE to the same extent suggests the opportunity to design individually tailored approaches to optimize their efficacy and minimize possible unwanted consequences.

Improving Hippocampal Memory Through the Experience of a Rich Minecraft Environment

It is well known that the brain changes in response to the surrounding environment. The hippocampus has been shown to be particularly susceptible to environmental enrichment, with effects ranging from the generation of new hippocampal neurons and synapses to an increased expression of neurotrophic factors. While many of these changes in the hippocampus are well documented in animals, our understanding of how environmental enrichment can apply to humans is more ambiguous. In animals, spatial exploration has been shown to be a clear way to elicit the effects of environmental enrichment and considering the role of the hippocampus in spatial navigation, which has been shown in both animal models and humans, it suggests a viable avenue for translation of environmental enrichment to humans. Here, we test the hypothesis that the spatial exploration of a virtual video game environment, can impact the hippocampus and lead to an improvement in hippocampal-dependent memory. Using the video game Minecraft, we tested four groups of participants, each playing on custom servers and focusing on different aspects of Minecraft to test the effects of both building and exploration over the course of 2 weeks. We found an improvement in hippocampus-associated memory from pre-test to post-test and that the degree of improvement was tied to both the amount of exploration of the Minecraft world and the complexity of the structures built within Minecraft. Thus, the number of enrichment participants engaged in while playing Minecraft was directly correlated with improvements in hippocampal-dependent memory outside of the game.

Biphasic dendritic growth of dorsolateral prefrontal cortex associative neurons and early cognitive development

Aim

To analyze postnatal development and life-span changes of apical dendrite side branches (oblique dendrites) from associative layer IIIC magnopyramidal neurons in the human dorsolateral prefrontal cortex and to compare the findings with the previously established pattern of basal dendrite development.

Methods

We analyzed dendritic morphology from 352 rapid-Golgi impregnated neurons (10-18 neurons per subject) in Brodmann area 9 from the post-mortem tissue of 25 subjects ranging in age from 1 week to 91 years. Data were collected in the period between 1994 and 1996, and the analysis was performed between September 2017 and February 2018. Quantitative dendritic parameters were statistically analyzed using one-way analysis of variance and two-tailed t tests.

Results

Oblique dendrites grew rapidly during the first postnatal months, and the increase in the dendrite length was accompanied by the outgrowth of new dendritic segments. After a more than one-year-long “dormant” period of only fine dendritic rearrangements (2.5-16 months), oblique dendrites displayed a second period of marked growth, continuing through the third postnatal year. Basal and oblique dendrites displayed roughly the same growth pattern, but had considerably different topological organization in adulthood.

Conclusion

Our analysis confirmed that a biphasic pattern of postnatal dendritic development, together with a second growth spurt at the age of 2-3 years, represents a unique feature of the associative layer IIIC magnopyramidal neurons in the human dorsolateral prefrontal cortex. We propose that these structural changes relate to rapid cognitive development during early childhood.

Exercising New Neurons to Vanquish Alzheimer Disease

Alzheimer disease (AD) is the most common type of dementia in individuals over 65 years of age. The neuropathological hallmarks of the condition are Tau neurofibrillary tangles and Amyloid-β senile plaques. Moreover, certain susceptible regions of the brain experience a generalized lack of neural plasticity and marked synaptic alterations during the progression of this as yet incurable disease. One of these regions, the hippocampus, is characterized by the continuous addition of new neurons throughout life. This phenomenon, named adult hippocampal neurogenesis (AHN), provides a potentially endless source of new synaptic elements that increase the complexity and plasticity of the hippocampal circuitry. Numerous lines of evidence show that physical activity and environmental enrichment (EE) are among the most potent positive regulators of AHN. Given that neural plasticity is markedly decreased in many neurodegenerative diseases, the therapeutic potential of making certain lifestyle changes, such as increasing physical activity, is being recognised in several non-pharmacologic strategies seeking to slow down or prevent the progression of these diseases. This review article summarizes current evidence supporting the putative therapeutic potential of EE and physical exercise to increase AHN and hippocampal plasticity both under physiological and pathological circumstances, with a special emphasis on neurodegenerative diseases and AD.

Biphasic dendritic growth of dorsolateral prefrontal cortex associative neurons and early cognitive development

AIM

To analyze postnatal development and life-span changes of apical dendrite side branches (oblique dendrites) from associative layer IIIC magnopyramidal neurons in the human dorsolateral prefrontal cortex and to compare the findings with the previously established pattern of basal dendrite development.

METHODS

We analyzed dendritic morphology from 352 rapid-Golgi impregnated neurons (10-18 neurons per subject) in Brodmann area 9 from the post-mortem tissue of 25 subjects ranging in age from 1 week to 91 years. Data were collected in the period between 1994 and 1996, and the analysis was performed between September 2017 and February 2018. Quantitative dendritic parameters were statistically analyzed using one-way analysis of variance and two-tailed t tests.

RESULTS

Oblique dendrites grew rapidly during the first postnatal months, and the increase in the dendrite length was accompanied by the outgrowth of new dendritic segments. After a more than one-year-long "dormant" period of only fine dendritic rearrangements (2.5-16 months), oblique dendrites displayed a second period of marked growth, continuing through the third postnatal year. Basal and oblique dendrites displayed roughly the same growth pattern, but had considerably different topological organization in adulthood.

CONCLUSION

Our analysis confirmed that a biphasic pattern of postnatal dendritic development, together with a second growth spurt at the age of 2-3 years, represents a unique feature of the associative layer IIIC magnopyramidal neurons in the human dorsolateral prefrontal cortex. We propose that these structural changes relate to rapid cognitive development during early childhood.

Enriched Environment Facilitates Anxiolytic Efficacy Driven by Deep-Brain Stimulation of Medial Prefrontal Cortex

Deep brain stimulation (DBS) is a widely used treatment for neurodegenerative disorders like Parkinson’s disease. Recently, several studies have used preclinical animal models to suggest that DBS has a potential to improve emotional symptoms in mental disorders such as treatment-resistant depression and post-traumatic stress disorder. An important difference between neurodegenerative and emotional disorders is the crucial role of environment in the ontogeny of the latter. Thus, it is important to understand the effects of DBS in the context of environmental variation. In this study, we show that DBS of ventromedial prefrontal cortex reduces anxiety in rats when it is coupled with simultaneous exposure to an enriched environment (EE). In contrast, effects of DBS on anxiety-like behaviors remained equivocal when animals were housed in standard laboratory conditions. These results suggest that the ability of DBS to treat anxiety and related phenotypes can be significantly enhanced by EE opportunities.

A Quantitative Golgi Study of Dendritic Morphology in the Mice Striatal Medium Spiny Neurons

In this study we have provided a detailed quantitative morphological analysis of medium spiny neurons (MSNs) in the mice dorsal striatum and determined the consistency of values among three groups of animals obtained in different set of experiments. Dendritic trees of 162 Golgi Cox (FD Rapid GolgiStain Kit) impregnated MSNs from 15 adult C57BL/6 mice were 3-dimensionally reconstructed using Neurolucida software, and parameters of dendritic morphology have been compared among experimental groups. The parameters of length and branching pattern did not show statistically significant difference and were highly consistent among groups. The average neuronal soma surface was between 160 μm² and 180 μm², and the cells had 5–6 primary dendrites with close to 40 segments per neuron. Sholl analysis confirmed regular pattern of dendritic branching. The total length of dendrites was around 2100 μm with the average length of individual branching (intermediate) segment around 22 μm and for the terminal segment around 100 μm. Even though each experimental group underwent the same strictly defined protocol in tissue preparation and Golgi staining, we found inconsistency in dendritic volume and soma surface. These changes could be methodologically influenced during the Golgi procedure, although without affecting the dendritic length and tree complexity. Since the neuronal activity affects the dendritic thickness, it could not be excluded that observed volume inconsistency was related with functional states of neurons prior to animal sacrifice. Comprehensive analyses of tree complexity and dendritic length provided here could serve as an additional tool for understanding morphological variability in the most numerous neuronal population of the striatum. As reference values they could provide basic ground for comparisons with the results obtained in studies that use various models of genetically modified mice in explaining different pathological conditions that involve MSNs.

Environmental enrichment as a viable neurorehabilitation strategy for experimental traumatic brain injury

Environmental enrichment (EE) emerged as a robust independent variable capable of influencing behavioral outcome in experimental studies after the fortuitous observation by renowned neuropsychologist Donald O. Hebb that rats raised as pets in his home performed markedly better on problem-solving tasks than those kept in the laboratory. In the subsequent years, numerous studies ensued demonstrating that EE was also capable of inducing neuroplasticity in normal (i.e., noninjured) rats. These behavioral and neural alterations provided the impetus for investigating EE as a potential therapy for traumatic brain injury (TBI), which, over the past two decades, has resulted in several reports. Hence, the aim of this review is to integrate the findings and present the current state of EE as a viable neurorehabilitation strategy for TBI. Using the specific key term searches "traumatic brain injury" and "environmental enrichment" or "enriched environment," 30 and 30 experimental TBI articles were identified by PubMed and Scopus, respectively. Of these, 27 articles were common to both search engines. An additional article was found on PubMed using the key terms "enriched environment" and "fluid percussion." A review of the bibliographies in the 34 articles did not yield additional citations. The overwhelming consensus of the 34 publications is that EE benefits behavioral and histological outcome after brain injury produced by various models. Further, the enhancements are observed in male and female as well as adult and pediatric rats and mice. Taken together, these cumulative findings provide strong support for EE as a generalized and robust preclinical model of neurorehabilitation. However, to further enhance the model and to more accurately mimic the clinic, future studies should continue to evaluate EE during more rehabilitation-relevant conditions, such as delayed and shorter time periods, as well as in combination with other therapeutic approaches, as we have been doing for the past few years.

Structural dynamics of dendritic spines are influenced by an environmental enrichment: an in vivo imaging study

Sensory experience alters neuronal circuits, which is believed to form the basis for learning and memory. On a microscopic level, structural changes of the neuronal network are prominently observable as experience-dependent addition and removal of cortical dendritic spines. By environmental enrichment, we here applied broad sensory stimulation to mice and followed the consequences to dendritic spines in the somatosensory cortex utilizing in vivo microscopy. Additionally to apical dendrites of layer V neurons, which are typically analyzed in in vivo imaging experiments, we investigated basal dendrites of layer II/III neurons and describe for the first time experience-dependent alterations on this population of dendrites. On both classes of cortical dendrites, enriched environment-induced substantial changes determined by increases in density and turnover of dendritic spines. Previously established spines were lost after enriched stimulation. A fraction of experience-induced gained spines survived for weeks, which might therefore be functionally integrated into the neuronal network. Furthermore, we observed an increased density of spines that appeared only transiently. Together, we speculate that the cognitive benefits seen in environmental-enriched animals might be a consequence of both, a higher connectivity of the neuronal network due to more established synapses and an enhanced flexibility due to more transient spines.

Housing in environmental complexity following wheel running augments survival of newly generated hippocampal neurons in a rat model of binge alcohol exposure during the third trimester equivalent

BACKGROUND

Binge-like alcohol exposure in neonatal rats during the brain growth spurt causes deficits in adult neurogenesis in the hippocampal dentate gyrus (DG). Previous data from our laboratory demonstrated that 12 days of voluntary wheel running (WR) beginning on postnatal day (PD) 30 significantly increased the number of newly generated cells evident in the DG on PD42 in both alcohol-exposed (AE) and control rats, but 30 days later a sustained beneficial effect of WR was evident only in control rats. This study tested the hypothesis that housing rats in environmental complexity (EC) following WR would promote the survival of the newly generated cells stimulated by WR, particularly in AE rats.

METHODS

On PD4 to 9, pups were intubated with alcohol in a binge-like manner (5.25 g/kg/d), sham-intubated (SI), or reared normally. In Experiment 1, animals were either assigned to WR during PD30 to 42 or socially housed (SH). On PD42, animals were injected with bromodeoxyuridine (BrdU; 200 mg/kg) and perfused 2 hours later to confirm the WR-induced stimulation of proliferation. In Experiment 2, all animals received WR on PD30 to 42 and were injected with BrdU on the last full day of WR. On PD42, animals were randomly assigned either to EC (WR/EC) or to SH (WR/SH) for 30 days and subsequently perfused and brains were processed for immunohistochemical staining to identify BrdU+-, Ki67+-, and BrdU+/NeuN+-labeled cells in DG.

RESULTS

In Experiment 1, WR exposure significantly increased the number of proliferating cells in all 3 postnatal conditions. In Experiment 2, the AE rats given WR/SH had significantly fewer BrdU+ cells compared with control rats given WR/SH. However, WR/EC experience significantly increased the number of surviving BrdU+ cells in both the AE and SI groups compared with WR/SH rats of the same neonatal treatment. Approximately 80% of the surviving BrdU+ cells in the DG across the conditions were colabeled with NeuN.

CONCLUSIONS

WR followed by EC could provide a behavioral model for developing interventions in humans to ameliorate hippocampal-dependent impairments associated with fetal alcohol spectrum disorders.

Introduction to the fractality principle of consciousness and the sentyon postulate

Recently, consciousness research has gained much attention. Indeed, the question at stake is significant: why is the brain not just a computing device, but generates a perception from within? Ambitious endeavors trying to simulate the entire human brain assume that the algorithm will do the trick: as soon as we assemble the brain in a computer and increase the number of operations per time, consciousness will emerge by itself. I disagree with this simplistic representation. My argument emerges from the "atomism paradox": the irreducible space of the consciously perceived world, the endospace is incompatible with the reducible and decomposable architecture of the brain or a computer. I will first discuss the fundamental challenges in current consciousness models and then propose a new model based on the fractality principle: "the whole is in each of its parts". This new model copes with the atomism paradox by implementing an iterative mapping of information from higher order brain structures to smaller scales on the cellular and molecular level, which I will refer to as "fractalization". This information fractalization gives rise to a new form of matter that is conscious ("bright matter"). Bright matter is composed of conscious particles or units named "sentyons". The internal fractality of these sentyons will close a loop (the "psychic loop") in a recurrent fractal neural network (RFNN) that allows for continuous and complete information transformation and sharing between higher order brain structures and the endpoint substrate of consciousness at the molecular level.

Influence of aging and neurodegeneration on dendritic spine morphology

In neuronal circuits, excitatory synaptic transmission predominantly occurs at postsynaptic protrusions called dendritic spines. Spines are highly plastic structures capable of formation, enlargement, shrinkage, and elimination over time. Individual spine morphology is widely variable, and evidence suggests these differences in morphology are relevant to spine function. Recent reports provide evidence that spine structural plasticity underlies functional synaptic changes, including those seen in animal models of learning and memory plasticity. Conversely, impairments in cognitive functions, such as those commonly seen in aging, have recently been linked to and correlated with alterations in spine density and morphology. In addition, dendritic spine density and morphology also appear to be altered in various transgenic animal models of neurodegenerative diseases. Ultimately, an understanding of the synaptic basis of age- and disease-related cognitive impairments may lead to the development of drug treatments that can restore or protect synaptic profiles in neural circuits that mediate cognition.

Use it or lose it: environmental enrichment as a means to promote successful cognitive aging

Environmental enrichment has become increasingly utilized in rodent models of aging and neurodegenerative disease in order to prevent or reverse cognitive decline and neuronal dysfunction. However, the potential application of this body of work to human cognitive aging has rarely been discussed. The present article provides an overview of the rodent research that has tested the effects of environmental enrichment on hippocampal and neocortical function, and the types of memories mediated by these brain regions. Although data from models of neurodegenerative disease are presented, primary emphasis is given to studies of aging rodents and to methodological issues (e.g., age, treatment duration, treatment type) central to the mnemonic effectiveness of enrichment treatment. The implications of this work for human cognitive aging are discussed.