The brain sometimes interprets harmless things as threats during decline because its ability to correctly assess and filter information weakens. Normally, the brain evaluates sensory signals—like sights, sounds, or smells—and decides if they are safe or dangerous based on past experience and context. But when the brain ages or undergoes decline due to disease or stress, this filtering system becomes less precise.
One reason is that certain brain regions involved in processing emotions and fear responses become more sensitive or overactive. For example, the amygdala—a key area for detecting threats—can start reacting strongly even to neutral stimuli because it forms indirect associations between harmless cues and negative experiences. This means that if a harmless smell was once linked indirectly to something unpleasant, the brain might treat that smell as a threat later on.
Additionally, aging brains often show changes at the cellular level such as mitochondrial dysfunction and oxidative damage which impair how neurons communicate. These changes can disrupt circuits responsible for distinguishing real danger from false alarms. As a result, signals that should be ignored may trigger fear responses instead.
Emotional states also play a role: negative feelings tend to bias perception toward threat detection by engaging avoidance-related motivational systems in the brain more than positive emotions do. This heightened vigilance can cause people with declining brains to misinterpret benign stimuli as harmful simply because their emotional processing is altered.
In summary, during brain decline there is a combination of increased sensitivity in fear-related areas, impaired neural filtering due to cellular aging processes, and shifts in emotional processing—all contributing to why harmless things may be seen as threats when they are not.
