In a recent study published in Npj AgingThe researchers reviewed current knowledge about age-related cognitive decline and brain changes based on studies from rat models and humans, covering a wide range of cognitive tests. from pen and paper tests to behavioral paradigms based on virtual reality.
Study: Assessing cognitive decline in the aging brain: lessons from rodent and human studies. Image Credit: Carlos_Pascual/Shutterstock.com
While modern medicine and major improvements in the quality of life increase longevity, the aging population also brings with it a variety of health problems associated with age decline.
Age is also associated with an increased incidence of cardiovascular disease, arthritis, cancer, and neurodegenerative diseases. Age-related cognitive decline is one of the main reasons for the increased prevalence of neurological diseases.
Additionally, while age is a known risk factor for Alzheimer’s disease, neurobiological changes resulting in cognitive deficits occur as a natural part of aging. They are very different from those observed in Alzheimer’s disease.
Studies report that mild cognitive impairment and dementia are present in about 16% and 14%, respectively, of adults over 70 years of age.
Research from human and animal models also reports that age-related cognitive decline is largely characterized by synaptic loss, while Alzheimer’s disease also involves neuron loss.
In the current study, researchers analyzed human and animal model studies to understand the biological changes associated with cognitive decline that occur with age and have no associations with specific diseases.
The review does not examine changes related to synaptic and molecular plasticity and instead discusses the major types of memory and the changes in various brain regions associated with altered cognitive function in age They also discuss the methods used to conduct age-related clinical trials.
Research over the past few decades has shown that age-related cognitive dysfunction is similar in various animal models, such as rodents and primates, and given the various logistical and ethical challenges of designing and completing long-term aging. studies in humans, these animal models provide an appropriate system to study age-related cognitive decline over time.
As in humans, age-related decline in cognitive function in animal models such as canines, rodents, and non-human primates is seen predominantly in the hippocampal region, which is associated with memory impairments but not with loss. of neurons.
Therefore, age-related cognitive changes in animal models are translatable to humans, providing a good alternative for conducting longitudinal studies of aging and cognitive changes.
The review examined the major types of memory affected during aging and found that intelligence was classified into two major categories – crystallized and fluid intelligence.
Crystalline intelligence, which includes vocabulary knowledge/acquisition and procedural memories, does not decline over time and generally increases with age.
Fluid intelligence, which includes reasoning and problem-solving abilities and the processing of new information, peaks during early adulthood and then declines with age.
Furthermore, while autobiographical memories from the past remain unaffected, the ability to form new memories declines with age. Studies in human and rat models have also found that aging is associated with altered brain activity in the hippocampus, cortex, cerebellum, and motor-related brain regions.
Several cognitive tests have been used to study cognitive decline with age in humans and animal models. The simplest of these include questionnaire-based methods such as the Mini-Mental State Examination and the Montreal Cognitive Assessment to assess cognitive impairment and dementia.
However, these methods are often subject to bias based on gender and education level and are less sensitive to milder cognitive impairments.
Behavioral paradigms based on factors such as Pavlovian conditioning and spatial navigation are widely used in animal models to understand age-related cognitive decline.
Studies of Pavlovian conditioning include contextual and cue-based fear-conditioning and conditioning based on aversive stimuli. In contrast, spatial navigation assessments use designs such as Morris water and Barnes mazes.
Recent studies have also used virtual-reality-based methods to assess the cognitive abilities of humans and mice.
The authors also discuss some shortcomings and potential strategies for improvement regarding cognitive tests used for screening older adults for clinical trials investigating cognitive decline. which is related to age.
To summarize, the review presents a comprehensive assessment of findings from human and animal model-based studies of aging-related cognitive decline.
The findings cover major changes in the brain associated with aging and cognitive impairments and discuss the various assessments used in these studies to assess cognitive function.