Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease that primarily affects the nerve cells controlling voluntary muscles. It is traditionally understood as a condition of profound physical decline, causing muscle weakness, atrophy, and eventual paralysis. However, modern research shows that ALS is not solely a motor disorder, and a significant number of people with the disease also experience changes in thinking and behavior. These cognitive changes, which can include difficulties with memory, broaden the understanding of ALS as a multisystem disorder affecting both the body and the brain.
How ALS Affects Motor Function
ALS is defined by the progressive death of motor neurons, the specialized nerve cells that transmit signals from the brain to the muscles. The disease targets both upper motor neurons (originating in the brain) and lower motor neurons (extending from the brainstem and spinal cord). As these neurons degenerate, they can no longer send signals, causing the muscles to lose nourishment and waste away in a process called atrophy.
Upper motor neuron damage causes stiffness and spasticity, while lower motor neuron damage results in weakness and twitching. Early signs often include difficulty walking, tripping, or clumsiness in the hands and feet. As the disease progresses, it impairs the ability to perform basic actions like speaking, swallowing, and eventually breathing, leading to the need for supportive care.
The ALS-Cognitive Impairment Spectrum
Cognitive changes are a recognized feature of ALS, affecting between 30 and 50 percent of people with the condition. The impairment ranges from mild cognitive or behavioral changes to a severe form known as Frontotemporal Dementia (FTD). Because of this strong connection, ALS and FTD are often described together as the ALS-Frontotemporal Spectrum Disorder (ALS-FTSD).
Cognitive difficulties are rooted in brain pathology extending beyond the motor cortex, primarily impacting the frontal and temporal lobes. These areas manage functions like language, personality, and planning, which are the domains most commonly affected. Deficits in executive function are particularly common, leading to problems with planning, organizing, decision-making, and shifting attention.
Between 10 and 20 percent of people with ALS meet the criteria for FTD, involving a profound decline in frontal lobe functions. Unlike the memory loss typical of Alzheimer’s disease, ALS-FTD impairment is not primarily about losing access to stored memories or facts. Instead, memory issues relate to retrieval and working memory, functions managed by the frontal lobes.
Language difficulties are common, often involving problems with word-finding or forming sentences, which can be compounded by the physical difficulty of speaking. Significant cognitive or behavioral impairment can complicate disease management and is linked to a shorter survival time. Assessing the full spectrum of the disease is important for comprehensive care.
Understanding Memory Changes in ALS
The memory issues experienced by people with ALS tend to be specific and often relate to frontal lobe dysfunction. For instance, an individual may struggle with working memory—the ability to hold and manipulate information momentarily, such as remembering a complex instruction or following a multi-step conversation. They may also have trouble with memory retrieval, where information is stored but cannot be accessed efficiently.
These memory difficulties can manifest as trouble multitasking, following the plot of a television show, or managing finances. Because the motor symptoms of ALS are prominent, these subtle cognitive changes are sometimes overlooked or mistakenly attributed to the frustration and depression accompanying the diagnosis. However, the underlying cause is a distinct neurodegenerative process.
These ALS-related changes must be differentiated from general age-related memory decline. Normal aging involves occasional forgetfulness, but ALS impairs the higher-level cognitive processes necessary for planning and problem-solving. The memory storage function—allowing a person to remember personal events and recognize loved ones—is often preserved, distinguishing it from the profound storage memory loss seen in Alzheimer’s. Specialized cognitive screening is required to accurately identify these specific deficits, especially since physical limitations can make traditional testing difficult.