What Is Normal Brain Aging - and What Isn't

Aging Versus Inevitable Decline

Aging does not mean inevitable decline.

The brain is dynamic, adaptable and responsive throughout the lifespan. That is the principle of neuroplasticity. So too is the body that the brain serves. Both undergo normal age-related changes.

Of course, functions change as we grow older. However, there is an immense gray zone of what should change and what should not. Health, happiness, knowledge, wisdom, experience and relationships – these should all be retained. Provided the right forms of education, nurturing and cultivation occur throughout life and in our case, with the right strategic intensity later in life.

Normal age-related biological changes involve multiple systems. The metabolic system and digestive system slow down. There is less blood flow in the gastrointestinal system which results in slower digestion, reduced nutrient absorption and elimination. Kidney filtration and clearance ability slows down, increasing the likelihood of toxicity and UTIs. Circulatory system function involves reduced nutrient delivery and waste removal. Muscular tissue (sarcopenia) and bone loss (osteopenia) occur over time, leading to reduced physical resilience and confidence.

All together, these changes set the potential stage for age-related degenerative changes in neurological function and structure. Nonetheless, the healthy aging brain should remain healthy across a wide range of cognitive functions.

Only by knowing what healthy should look like can we better understand non normal changes in cognitive function- and appropriately work to rehabilitate them, the foundational purpose of our Empowered Brain Program.

How Cognition Is Organized

The first step in distinguishing normal brain aging from pathological change is to understand how cognition itself is organized.

Cognition can be broadly divided into two forms- crystalized cognition and fluid cognition.

Crystallized cognition refers to the skills, memories, learning, training and general knowledge that accumulate over the course of a lifetime. This includes things like reading comprehension, mathematics, historical information and vocabulary. Crystallized cognition is acquired knowledge, crystallized abilities.¹

Crystallized cognitive abilities not only remain stable, but often gradually improve through the sixth and seventh decades of life. This accumulated intelligence and life experience is one area in which older adults tend to outperform younger adults.²

Fluid cognitive abilities, in contrast, are related to in-the-moment processing and are largely independent of what one has previously learned. These abilities support problem solving and reasoning when dealing with new or unfamiliar information. They allow a person to take in and assess information, manipulate it, stay attentive to their environment and process it quickly in order to solve problems.^1,2

Multiple cross-sectional studies demonstrate improvement in crystallized abilities until the sixth decade approximately, which later plateau around age 80. Fluid cognitive abilities, on the other hand, especially psychomotor and processing speed steadily decline from age of 20 to age 80.^1,2

For most individuals, the formal academic learning process ends after high school or university. The ongoing exposure to structured information acquisition, processing, analysis and application fades into the background of everyday life. In other words, a muscle that was trained to work only in a specific environment is then left to weaken. These are basic principles of neuroplasticity - repeat it and reinforce it; and use it or lose it.

Core Cognitive Domains

Within the crystallized and fluid cognitive abilities, there are multiple core cognitive domains. These include processing speed, attention, memory, language, visuospatial abilities, and executive functioning and reasoning. Each domains has subdomains as well and, as you will see, some domains decline with age and while others do not.

Understanding how different domains and subdomains change over time provides a powerful strategic insight: whether an individual’s cognitive health is following a normal aging pattern or shifting toward a decline or dementia-related trajectory.

Quarterly testing of the following domains is built into the Empowered Brain Program’s curriculum for cognitive decline and dementia rehabilitation and serves as an important guide for the individualized therapies.

Processing Speed, Reaction Time and Motor Speed 

Processing speed refers to how efficiently an individual recognizes and processes information. It includes motor speed, fine motor coordination and visual-perceptual ability. In everyday life, this shows up in how well someone recognizes, responds and reacts to situations like driving, work tasks, identifying possible danger or maintaining accuracy and detail.

Reaction time refers to how quickly an individual can respond, in milliseconds, to both simple and complex stimuli and directions. Together these two domains form the foundation of psychomotor speed and motor speed as described below.

Motor speed refers to how quickly an individual can perform movements for action and purpose, such as reaching, maneuvering an object or stepping out of the way.

Psychomotor speed blends processing and motor speed, reflecting how well a person performs precise and intentional motor responses to incoming information. In everyday life, psychomotor speed supports skills such as manual dexterity, tool use, coordination between thinking and movement, driving a car, working in the kitchen or playing a musical instrument.

Processing speed normally slows with aging, but accuracy and coordination should remain intact.

Attention

Attention involves the ability to concentrate and focus and is best understood as having several layers. There are two main forms: immediate attention and complex attention.

Immediate attention, which only shows slight natural decline with age, has two layers: Simple attention involves registering and holding information, such as remembering a string of numbers. Sustained attention involves maintaining focus over time.²

Complex attention, on the other hand, includes selective and divided attention. Selective attention reflects a person’s ability to apply a mental filter, such as focusing on a conversation in a noisy room or driving in busy environment. Divided attention allows a person to perform multiple tasks at the same time, such as preparing a meal while talking on the phone. Complex attention shows a more notable natural decline with age.²

Memory

Similar to attention, memory involves several layers. There are two main forms: declarative and non-declarative memory. Natural age-related changes in memory are influenced by slower processing speed, reduced complex attention (the mental filter for irrelevant information) and a reduced use of strategies to support learning and recall – in other words, we tend to exercise our learning and retention abilities less in later life we did in childhood.²

Declarative memory, also known as explicit memory, involves the conscious recollection of facts and events. It has two forms.

The first is semantic memory, an individual’s accumulated store of information, language use, and practical knowledge. For example, knowing the meaning of words.

The second form is episodic memory, also known as autobiographical memory, which involves the memories of personally experienced events including their specific place and time. Episodic memory is commonly measured through recall of stories, word lists, or figures.

Both semantic and episodic memory change with age but at different intervals. Episodic memory declines gradually across our lifespan whereas semantic memory declines late in life. ²

Non-declarative memory, also implicit memory operates below conscious awareness. An example is remembering how to sing a familiar song, such as “Happy Birthday.” Procedural memory is another form of non-declarative memory and involves ingrained motor and cognitive skills such as tying a shoe or riding a bicycle. Non-declarative memory remains unchanged throughout the lifespan.²

Acquisition refers to the ability to encode new information into memory. While the rate of acquisition naturally declines over the lifespan, cognitively healthy adults should retain information that has been successfully learned.²

New learning, also declines with age, in part because of slower retrieval of recently learned information.² Other limiting factors include the need for mental manipulation of material (working memory) and divided attention, or multitasking. Prospective memory – remembering to perform intended actions in the future, such as taking medication, also declines with age.¹

Language

Language involves both crystalized and fluid cognitive functions and generally remains intact with normal aging. Vocabulary remains stable and should improve over age. However, the ability to see a common object and name it tends to remain stable until about age 70 and then declines. Verbal fluency – the ability to search for and generate words within a certain category (such as animals, objects or letters) within a limited time also changes naturally with age.²

Visuospatial

Visuospatial cognitive abilities involve how we perceive and interpret the visual world together with spatial relationships. Many visuospatial abilities are retained with aging. These include object perception, the ability to recognize familiar objects such as household items or faces as well as spatial perception, the ability to understand the physical location of objects, either alone or in relation to other objects. On the other hand, visuospatial construction, involving the process of putting pieces and parts together to form a whole, naturally declines over time.²

Executive Function

Executive function refers to higher order cognitive abilities that govern how a person engages in independent, appropriate, purposeful, and self-directed behavior. These include self-monitoring, planning, organizing, reasoning, mental flexibility, critical thinking and problem-solving.

Research shows that concept formation, abstraction, and mental flexibility naturally decline with age, especially after age 70. This can appear as increased mental rigidity, such as difficulty considering other points of view or alternative possibilities. Response inhibition, the ability to apply a mental, verbal or motor filter, also changes with age and is closely related to processing speed.

Other natural changes involve inductive reasoning, which is measured by verbal and mathematical reasoning tasks, as well as reasoning with unfamiliar material. However, several aspects of executive function are retained throughout life including the ability to appreciate similarities, describing the meaning of proverbs (stories and life lessons) and reasoning about familiar material. ²

What Normally Happens To Brains With Age

Normal age-related changes involve slower processing speed and reaction time, mild changes in attention and recall and reduced metabolic efficiency. This is aging, not disease.

Normal age-related cognitive changes are most notable on tasks that require quick processing or transformation of information, including working memory and the flexibility and inhibitory control aspects of executive function. Importantly, cumulative knowledge and experiential skills remain well preserved into advanced age.¹

Normal Age-related Structural Changes In The Brain

The Big Picture

The size of the brain naturally decreases over time.

Just as it is essential to understand natural age-related changes in cognition, it is equally important to appreciate normal age-related changes in brain structure. Together, this vital information forms the backbone for understanding non-normal brain aging and for responding to those changes appropriately.

The structure of the brain can be understood in terms of gray matter and white matter, based on its appearance. Gray matter refers to the cerebral and cerebellar cortex and subcortical nuclei – regions that predominantly contain nerve cell bodies and dendrites. White matter, on the other hand, refers to regions composed of primarily of myelinated nerve fibers that connect gray matter structures.¹

Gray Matter Aging Patterns

Gray matter volume begins to decrease after approximately age of 20. Volume loss occurs predominantly in the dorsolateral prefrontal cortex and the temporal lobes, which contain the hippocampus. Importantly, the entorhinal cortex, a region that serves as a relay center between the hippocampus and association areas, shows early volumetric loss in Alzheimer's disease, but not in normal aging.^1,2

White Matter Aging Patterns

White matter volume loss occurs predominantly in the frontal lobes and major white tracts such as the corpus callosum³, as well as the cerebellum and substantia nigra.¹

MRI diffusion tensor imaging further demonstrates age-related volumetric loss in white matter tract integrity with age, reflecting reduced efficiency of communication between brain regions with aging.⁴

Neuronal and Synaptic Structural Change

Age-related changes in brain volume are primarily due to structural changes within the neurons, rather than widespread loss of neurons themselves. In other words, it is the connections between neurons that change most with aging. These changes include:

• A decrease in the number and length of dendrites
• Loss of dendritic spines
• Reduction in the number of axons
• Segmental demyelination along axons
• Significant loss of synapses

In fact, synaptic loss is one of the most important structural markers of aging in the nervous system.¹

Plasticity, Dendritic Spines, and Cognitive Change

Dendrites are branch-like extensions of neurons that receive synaptic signals from other nerve cells and transmit this information toward the cell body, where it can be integrated and processed. Dendritic spines are extensions of the dendrites themselves that receive excitatory impulses from other nerves. They play a crucial role in learning, memory and synaptic plasticity.

Studies have demonstrated approximately a 46% loss of thin dendritic spines — a highly plastic subtype of cortical neuron spine — in the dorsolateral prefrontal cortex.  Thin spines are the most plastic form of spines- their loss results in reduced dynamic plasticity in neural circuits responsible for cognitive flexibility, working memory and executive functioning. Their loss therefore directly contributes to the normal, age-related decline in fluid cognitive abilities described in the previous section.

Notably, crystallized cognitive abilities are supported by a second, more stable type of dendritic spine, the mushroom spine, which shows relative preservation in the same dorsolateral prefrontal cortex. This structural distinction helps explain why experience-based knowledge and reasoning remain intact despite declines in speed and flexibility.⁵

Amyloid In Normal Aging

Beta-amyloid plaques can be detected in the cortex of approximately 20–30% of cognitively normal adults. Although beta-amyloid was once thought to inevitably signal future Alzheimer’s disease, the research shows a more nuanced picture. One study found that higher amyloid levels in cognitively normal individuals were associated with reduced hippocampal volume and poorer episodic memory. This suggests that amyloid may function as an early biological stressor, but that it is the downstream structural and network effects, particularly cortical volume loss, that more directly contribute to the emergence of clinical symptoms.²

Network-level Effects and Cognition

In Alzheimer’s disease and other neurodegenerative conditions, the structural changes seen in normal aging become accelerated and exaggerated. This is especially evident in the brain’s Default Mode Network (DMN), a large-scale network spanning the prefrontal cortex, parietal and temporal lobes, posterior cingulate cortex and precuneus.¹ The DMN plays a central role in connecting a range of functions including self-reflection and social cognition, memory processing, self-awareness, integration of internal and external information and both memory retrieval and formation. Disruption within this network therefore has widespread cognitive and functional consequences.

In normal aging, correlated structural changes occur without widespread neuronal death. The synaptic loss and altered connectivity lead to gradual reorganization of neural networks. Neurodegenerative conditions, follow the same loss pattern, but at a faster pace, destabilizing and breaking down these networks, overwhelming the brain’s compensatory capacity.¹

Given the structural changes seen in normal and non-normal aging, obtaining a baseline volumetric brain MRI early in the course of evaluation can be invaluable. At the Empowered Brain Program, we recommend this not as a diagnostic label, but to establish a clear baseline, assess structural patterns and regional vulnerability, and track trajectory over time to inform appropriate and timely intervention.

Non-normative Aging Features

What Creates Non-Normative Brain Aging?

One of the most important reasons non-normative brain aging is so often misunderstood is that significant brain pathology can exist in individuals who appear cognitively normal.

A landmark 2013 clinical–pathological study combining data from the Rush Memory and Aging Project and the Religious Orders Study examined older adults without dementia and revealed striking findings.⁷ Among individuals without clinical dementia:

• 100% had neurofibrillary tangles
• 82% had amyloid plaques
• 29% had macroscopic infarcts
• 25% microscopic infarcts
• 6% had neocortical Lewy bodies

How Alzheimer’s Pathology Develops Before Symptoms

Studies in individuals with genetic forms of Alzheimer’s disease show that cortical amyloid deposition is the earliest detectable marker of the disease, with amyloid plaques identifiable up to 15 years before clinical symptoms appear. Additional markers of early neurodegeneration include hippocampal volume changes on MRI and alterations in cerebrospinal fluid tau levels. Importantly, these biological changes can be detected before even very mild cognitive symptoms are measurable.¹

The hippocampus, a structure critical for memory and multiple cognitive functions, naturally undergoes some volume loss with aging. However, accelerated hippocampal atrophy is strongly associated with Alzheimer’s disease and with progression from amnestic Mild Cognitive Impairment to clinically diagnosed Alzheimer’s disease. ¹

How Non-normative Decline Presents

In individuals who develop Alzheimer’s disease, cognitive change typically begins with a subtle decline in memory and new learning, followed by early changes in executive function, and later involvement of language and visuospatial processing. While also seen with normal aging, in Alzheimer’s disease these changes are earlier, faster, and more severe. ¹

Age-related disease processes accelerate neuronal dysfunction, synaptic loss, and cognitive decline, often progressing to impairments that interfere with everyday functioning. ¹

Certain changes should never be dismissed as normal aging, including:

• Executive dysfunction
• Personality or behavioral change
• Loss of navigation, sequencing, or word-finding
• Decline in self-care or judgment
• Rapid cognitive shifts following illness, stress, or surgery

These reflect network failures, not the passage of time.

When Dementia Emerges

Symptomatic dementia is thought to occur when approximately 40% of neocortical synapses are lost compared with healthy adults.¹ At this stage, non-normative aging is characterized by:

• Progressive memory loss affecting daily function
• Repetition, disorientation, and behavioral or personality change
• Loss of insight, judgment, and problem-solving ability

These features mark a transition beyond normal aging and help explain why dementia is not simply aging, but rather the result of crossing critical biological thresholds.

It Does Not Start With Dementia - What Are The Risk Factors

Cognitive decline and dementia do not start in the brain alone. Rather, they are downstream outcomes of a multiplicity of health and lifestyle factors, all of which affect the integrated brain-body-mind system.

The 2024 Lancet study commission on dementia outlines the currently established risk factors and mechanisms for dementia. These include lower educational attainment (reduced cognitive reserve), hearing loss, hypertension, smoking, obesity, depression, diabetes, physical inactivity, alcohol consumption, traumatic brain injury (TBI), air pollution, social isolation, vision loss and elevated LDL cholesterol levels.⁸

The central takeaway is that the potential for dementia prevention is substantial. The Commission estimates that up to half of dementias could be prevented by addressing these modifiable risk factors. Of even greater significance, the study further emphasizes that dementia remains modifiable irrespective of APOE genetic status.⁸

While changes in cognitive function and brain structure are age-normalized, many of these changes are strongly shaped by lifestyle context, including nutrition, physical activity, learning and environmental exposure – rather than by age alone. This distinction is foundational to research-based integrative approaches to cognitive rehabilitation.

Disclaimer: The information presented in this article is intended to share concepts derived from evidence-based research. It is not intended to diagnose, treat, or replace individualized medical care. Decisions regarding evaluation or treatment should be made in consultation with a qualified healthcare professional.