How Does Dementia Affect Brain Communication Pathways
The human brain is like a vast city with billions of residents constantly sending messages to each other. These messages travel along pathways, much like roads and highways connecting different neighborhoods. When someone develops dementia, these communication pathways begin to break down, and the messages get scrambled, delayed, or lost entirely. Understanding how dementia disrupts these critical brain communication systems helps us grasp why people with dementia experience the symptoms they do.
The Brain’s Communication Network
To understand how dementia damages brain communication, we first need to know how the brain normally works. The brain contains roughly 86 billion neurons, which are specialized cells that communicate with each other through electrical and chemical signals. These neurons connect to one another through structures called synapses, creating an intricate web of connections. When you think, remember, speak, or move, millions of these connections are firing simultaneously, sending signals across different brain regions.[1]
The brain is organized into functional networks, which are groups of brain regions that work together to accomplish specific tasks. Some networks handle memory, others manage attention, and still others control language or movement. These networks don’t work in isolation. Instead, they constantly communicate with each other, sharing information and coordinating their activities. This coordination is what allows us to perform complex tasks like having a conversation, remembering a name, or recognizing a face.
How Dementia Disrupts These Pathways
Dementia is not a single disease but rather a group of conditions that cause progressive damage to brain cells. The most common form is Alzheimer’s disease, followed by frontotemporal dementia and other types. Each type of dementia damages different parts of the brain, but they all share one thing in common: they disrupt the normal communication between brain regions.[1]
In Alzheimer’s disease, the damage tends to start in the posterior regions of the brain and spreads outward. This leads to reduced functional connectivity in the default mode network, which is a set of brain regions that are active when we’re not focused on the outside world.[1] People with Alzheimer’s also show weaker communication in primary sensory networks, which are the brain regions responsible for processing basic sensory information like sight, sound, and touch. At the same time, other networks become overactive, particularly subcortical and association networks.[1]
Frontotemporal dementia follows a different pattern. This type of dementia primarily damages the frontal and temporal lobes, which are located at the front and sides of the brain. This leads to reduced connectivity in the salience network, which helps the brain determine what information is important and what should be ignored.[1] Because these regions are so critical for language and social behavior, people with frontotemporal dementia often experience severe language problems and personality changes early in the disease.
The Breakdown of Brain Structure
One of the key ways dementia disrupts communication is through the physical breakdown of brain tissue. When brain cells die, the connections between them are lost. Researchers have discovered that changes in brain shape can actually reveal early signs of Alzheimer’s disease and dementia. When the brain’s shape changes, the communication pathways become less efficient.[6] This is not just a minor problem. The backbone of brain communication, which consists of fiber density and the shortest pathways between regions, accounts for 81 to 92 percent of all brain communication.[8] When this backbone is damaged, the entire communication system suffers.
The damage to brain tissue also affects something called functional gradients. These are like organizational principles that help the brain maintain order and efficiency in its communication patterns. Research has shown that atrophy, or shrinkage of brain tissue, is associated with reductions in gradient amplitude and changes in how different gradients work together.[1] In simpler terms, as brain tissue dies, the organizational structure that keeps communication running smoothly begins to fall apart.
Neural Flexibility and Network Instability
One surprising finding from recent research is that the brains of people with Alzheimer’s disease show increased neural flexibility compared to healthy brains. This might sound like a good thing, but it’s actually a sign of trouble. Neural flexibility refers to how much the communication patterns within the brain change from moment to moment. In healthy brains, these patterns are relatively stable. In Alzheimer’s brains, they’re constantly shifting and changing.[4]
This increased neural flexibility appears to be a sign that the brain’s network organization is breaking down. As core cognitive networks begin to degrade, other systems like the visual network may need to reorganize more frequently just to maintain basic function.[4] Think of it like a city where the main highways are damaged. The traffic system has to constantly reroute and reorganize to keep things moving, but it’s never as efficient as it was before.
Interestingly, this increased neural flexibility in the visual network at the beginning of the disease can actually predict which people will develop dementia in the future. Researchers followed over 600 people for more than 11 years and found that those with higher neural flexibility in their visual networks at the start of the study were more likely to develop Alzheimer’s-related dementia later on.[4] This suggests that the brain’s attempt to compensate for early damage may be one of the first warning signs of the disease.
Language and Communication Problems
One of the most noticeable ways that disrupted brain communication affects people with dementia is through language problems. Difficulty with speech and language, also called aphasia, is a common effect of dementia.[2] The brain regions responsible for language are primarily located in the frontal and temporal lobes, particularly in an area called Broca’s area in the left hemisphere.[2] When dementia damages these regions, people struggle to find the right words, follow conversations, or understand what others are saying.
The symptoms of language problems in dementia can be quite varied. Some people talk very slowly and need others to speak slowly as well. Others say words in the wrong order or mix up tenses. Many people have difficulty understanding what others say because they can only grasp individual words rather than understanding the sentence as a whole.[2] These communication difficulties often lead to emotional distress and frustration because the person cannot express their needs, discomfort, or feelings effectively.[5]
The damage to communication pathways doesn’t just affect language production. It also affects the ability to process and understand language. When neural pathways that send messages between different brain areas are damaged or blocked, the brain cannot efficiently process the information it receives.[2] It’s as if the message arrives at the brain, but the brain cannot decode it or make sense of it.
Emotional and Behavioral Changes
The disruption of brain communication pathways also explains many of the emotional and behavioral changes seen in dementia. The prefrontal cortex, which is the region at the very front of the brain, is responsible for logic, judgment, and impulse control. When dementia damages this region and disrupts its communication with other parts of the brain, people
