According to scientists from the University of Cambridge, people with dementia find it difficult to adapt to changes in their environment due to damage to areas of the brain known as “multiple demand networks”, areas highly evolved brain functions that support general intelligence.
There are many types of dementia, such as Alzheimer’s disease and frontotemporal dementia (FTD), which are characterized by the accumulation of different toxic proteins in different parts of the brain. This means that the symptoms of dementia vary and can include problems with memory, speech, behavior or vision. But a symptom seen in every type of dementia is difficulty reacting to unexpected situations.
Dr Thomas Cope from the MRC Cognition and Brain Science Unit and Department of Clinical Neurosciences at the University of Cambridge said: “At the heart of all dementias is a central symptom, which is that when things change or unfold unexpectedly, people find it very difficult. If people are in their own surroundings and everything goes as planned, then they are fine. But as soon as the kettle is broken or they go to a new place, they may find it very difficult to deal with.”
To understand why this happens, Dr. Cope and his colleagues analyzed data from 75 patients, all of whom are affected by one of four types of dementia that affect different areas of the brain. The patients, along with 48 healthy controls, listened to changing sounds while their brain activity was recorded by a magnetoencephalography machine, which measures tiny magnetic fields produced by electrical currents in the brain. Unlike traditional MRI scanners, these devices allow very precise timing of what is happening in the brain and when. The results of their experiment are published today in the Journal of Neuroscience.
During the analysis, the volunteers watched a silent film – that of David Attenborough Earth, but without its soundtrack – while listening to a series of beeps. The beeps happened at a regular rate, but sometimes a beep sounded different, such as a higher pitch or different volume.
The team found that the unusual beep triggered two responses in the brain: an immediate response followed by a second response about 200 milliseconds — a fifth of a second — a little later.
The initial response came from the basic auditory system, recognizing that it had heard a beep. This response was the same in patients and healthy volunteers.
The second response, however, acknowledged that the beep was unusual. This response was much weaker in people with dementia than in healthy volunteers. In other words, in healthy controls, the brain was better able to recognize that something had changed.
The researchers looked at which areas of the brain were activated during the task and how they were connected, and combined their data with data from MRI scans, which show the structure of the brain. They showed that damage to areas of the brain known as ‘multiple demand networks’ was associated with reduced subsequent response.
Multiple demand networks, which are found in both the front and back of the brain, are areas of the brain that do not have a specific task, but are instead involved in general intelligence – for example problem solving. They are highly evolved and are only found in humans, primates and smarter animals. It is these networks that allow us to be flexible in our environment.
In healthy volunteers, sound is picked up by the auditory system, which relays the information to the multi-demand network for processing and interpretation. The network then “reports” to the auditory system, telling it whether to continue or deal with the sound.
“There’s a lot of controversy about exactly what multiple demand networks do and how they affect our fundamental perception of the world,” Dr Cope said. “It was assumed that these intelligence networks operate ‘on top’ of everything else, doing their own thing and just gathering information. But what we’ve shown is no, they’re fundamental to how we perceive the world.
“That’s why we can look at an image and immediately select faces and immediately select relevant information, whereas someone with dementia will look at that scene a bit more randomly and not immediately select what’s important.”
While the research doesn’t point to any treatment that might alleviate symptoms, it does reinforce the advice given to dementia patients and their families, Dr Cope said.
“The advice I give in my clinics is that you can help people with dementia by taking a lot more time to report changes, by letting them know that you’re going to start talking about something different or that you’re going to do something And then repeat yourself more when there is a change, and understand why it is important to be patient while the brain recognizes the new situation.
Although their study only involved patients with dementia, the findings may explain similar phenomena experienced by people living with conditions such as schizophrenia, where brain networks may be disrupted.
The research was funded by the Medical Research Council and the National Institute for Health Research, with additional support from Wellcome, the Biotechnology and Biological Sciences Research Council and the James S McDonnell Foundation.
Dr Cope is a Fellow of Murray Edwards College, Cambridge.