Can Dementia Make People Forget Familiar Faces
One of the most heartbreaking symptoms that families face when a loved one develops dementia is the moment when that person no longer recognizes them. A parent forgets their child’s face. A spouse becomes a stranger. A lifelong friend is met with confusion instead of warmth. This painful experience is not just an emotional burden – it is a real neurological change happening in the brain, and recent research has finally begun to explain why this happens and what might be done to prevent it.
The answer to whether dementia can make people forget familiar faces is a clear yes. But understanding how and why this happens requires us to look deep into the brain’s structure and the specific mechanisms that allow us to recognize the people we love.
What Makes Face Recognition Special
Our ability to recognize familiar faces is not the same as our ability to remember other things. When you see your mother’s face, your brain does not just retrieve a file like a computer would. Instead, it activates a complex network of memories, emotions, and associations that are tied to that specific person. You remember not just what they look like, but who they are to you – the relationship you share, the experiences you have had together, and the feelings you have for them.
This type of memory is called social recognition memory, and it is fundamentally different from other types of memory. You might forget where you put your keys or struggle to remember a phone number, but social recognition memory is about remembering people and your relationships with them. It involves remembering faces, names, and the emotional significance of those relationships.
The reason this type of memory is so special is that it relies on a very specific part of the brain. Researchers have identified a region in the hippocampus called CA2 as being crucial for this function. The hippocampus is the part of the brain most commonly associated with memory formation and storage, but within this region, CA2 appears to have a specialized role in social recognition.
The Discovery About Perineuronal Nets
For a long time, scientists knew that people with Alzheimer’s disease and other forms of dementia gradually lost the ability to recognize familiar faces, but they did not fully understand the mechanism behind this loss. Recent research has provided a breakthrough explanation.
Researchers at the University of Virginia and Virginia Tech conducted a study that was published in the journal Alzheimer’s and Dementia. They discovered that the loss of social recognition memory in Alzheimer’s disease is linked to the breakdown of protective structures around neurons in the CA2 region of the hippocampus. These protective structures are called perineuronal nets, or PNNs.[1]
Perineuronal nets are mesh-like structures that surround and stabilize nerve connections. Think of them as protective coatings around the neurons that help keep them functioning properly. These nets are made up of proteins and other molecules that form a lattice-like structure around brain cells. They serve an important function in maintaining the stability of neural connections and supporting the proper functioning of neurons.
In healthy brains, these perineuronal nets remain intact and continue to protect the neurons in the CA2 region. But in brains affected by Alzheimer’s disease, these protective structures begin to break down. The researchers found that this breakdown happens relatively early in the disease process – in their mouse models of Alzheimer’s, the perineuronal nets began to deteriorate by six months of age, which is when the mice also lost their ability to recognize other mice they had previously met.[1]
What makes this finding particularly important is that the breakdown of perineuronal nets appears to happen independently of the classic hallmarks of Alzheimer’s disease. Alzheimer’s disease is typically characterized by the buildup of amyloid plaques and tau tangles in the brain. However, the CA2 region showed few amyloid plaques, suggesting that the loss of social recognition memory occurs through a different mechanism than the one that causes other cognitive problems in Alzheimer’s disease.[1]
The Role of Enzymes in Breaking Down Protective Structures
The researchers did not stop at simply identifying that perineuronal nets break down in Alzheimer’s disease. They went further to understand why this breakdown occurs. Through gene sequencing of hippocampal tissue, they discovered that enzymes called matrix metalloproteinases, or MMPs, were more active in the brains of mice with Alzheimer’s disease. These enzymes are responsible for breaking down the proteins that make up the perineuronal nets.[1]
In a healthy brain, there is a balance between the creation and destruction of the extracellular matrix – the material that surrounds and supports brain cells. But in Alzheimer’s disease, this balance is disrupted. The MMPs become overactive, leading to excessive breakdown of the perineuronal nets. This molecular imbalance is what appears to be driving the loss of social recognition memory.
The researchers tested whether blocking these enzymes could prevent the loss of social recognition memory. They treated mice with a drug called GM6001, which blocks the activity of MMPs. The results were striking. When the MMPs were blocked, the perineuronal nets were preserved, and the loss of social recognition ability was delayed.[1]
This finding suggests a potential new approach to treating the loss of social recognition in Alzheimer’s disease. Rather than trying to address the amyloid plaques and tau tangles that are the focus of many current Alzheimer’s treatments, a new therapeutic approach could focus on protecting or rebuilding the perineuronal nets in the CA2 region.
Experimental Evidence from Mouse Studies
The researchers conducted several experiments to test their hypothesis about the role of perineuronal nets in social recognition memory. These experiments provided compelling evidence that the breakdown of these structures is directly responsible for the loss of the ability to recognize familiar faces.
In one set of experiments, the researchers used genetic techniques to artificially remove perineuronal nets from the CA2 region in healthy mice whose brains were otherwise completely normal. These mice had no Alzheimer’s disease and no other brain pathology. Yet when the perineuronal nets were removed, the mice lost their ability to recognize other mice they had previously met. This was a crucial finding because it showed that the loss of social recognition memory is directly caused by the loss of perineuronal nets, not by other aspects of Alzheimer’s disease.[2]
In another set of experiments, the researchers tested whether the loss of social recognition memory could be reversed if the perineuronal nets were allowed to regrow. They used an enzyme that temporarily dissolved the perineuronal nets in healthy mice. Within five days, the mice had lost their social memory – they could no longer recognize mice they had previously met. But then something remarkable happened. The perineuronal nets regrew naturally over the course of two weeks, and as they regrew, the mice’s ability to recognize other mice returned.[2]
This reversibility experiment was particularly important
