A recent brain scanning study has been widely reported as suggesting that Alzheimer’s disease is linked to the brain functions of daydreaming. The actual study is both complex and interesting, although not as clear cut as the headlines make out.
Th research project, led by neuroscientist Randy Buckner, conducted brain scans on 10 people with Alzheimer’s disease and 8 older people without, and also used data from previous studies on young people.
The newly conducted scans looked at how amyloid plaques, damaging accumulations of proteins linked to Alzheimer’s disease, were distributed across the brain. Further scans looked for other types of structural changes in the brain, such as shrinkage.
This distribution was matched with activity from the scans of young people. In contrast to the structural scans, these functional scans looked at how active the brain was.
Normally, functional scans involve participants being asked to do a particular task. In Buckner’s study, however, the activity was from participants who were just ‘resting’ and were not asked to do any specific mental activity – something the researchers called ‘default activity’.
The researchers noted that ‘default activity’ showed a similar pattern in the brain to the distribution of amyloid plaques in Alzheimer’s disease (shown in the image on the right), and have suggested there might be a link.
There are several unanswered questions though, which the researchers themselves acknowledge.
One is simply that ‘resting’ or ‘default’ brain activity is a mystery, no one is quite sure what the brain is doing in this state. ‘Daydreaming’ is just an everyday term that is used, because we assume that’s what we do when we’re not doing much.
In reality, the brain areas highlighted by the study are involved in a range of diverse of contrasting mental activities.
A further difficulty is that the correlation between ‘default activity’ and amyloid plaque distribution was found between two sets of people. More convincing would be if these distributions were found to correlate in the same people.
With these issues in mind, the final difficulty is with interpreting the results. The researchers suggest that mental activity in younger adults could be related to the later development of Alzheimer’s, but there is no clear understanding of how this happens.
My guess is that ‘daydreaming’ is unlikely to be a significant part of this explanation, although as the scientific paper only mentions it in passing, I suspect the researchers don’t think so either.