Dementia is a thief who takes out a lot of pockets. In some ways, it takes us by surprise. Other forms rob us of inhibition. Sometimes happiness is even taken away.
A new study has shown for the first time how some forms of early-onset dementia are associated with a profound loss of pleasure related to a waste of “hedonic hotspots”: brain regions associated with the pursuit of rewards.
Absence of pleasure is known as anhedonia and is a common symptom in mental health conditions such as depression and obsessive-compulsive disorder. When most of us are rewarded with a sense of satisfaction, excitement, and happiness when we reach a goal or relate to loved ones, those who experience anedonia cannot.
Interestingly, early dementia is often confused with depression and decreased motivation may be used as a criterion for diagnosis. So researchers at the University of Sydney and the University of New South Wales, Australia, decided to formally investigate this link between anedonia and dementia types for what they believe is the first time.
“Much of the human experience is motivated by a desire to experience pleasure, but we often take that ability for granted,” says neuroscientist Muireann Irish of the University of Sydney.
“But keep in mind what it might be like to lose the ability to enjoy the simple pleasures of life; this has strong implications for the well-being of people affected by these neurodegenerative disorders.”
In the study, researchers evaluated 121 patients diagnosed with various forms of dementia to determine who was most likely to suffer from the clinical symptom of anedonia.
Of the group, 87 patients had 1 of 3 different types of frontotemporal dementia (FTD). FTD is an early onset dementia, with symptoms that usually begin between the ages of 40 and 65.
A variant of FTD affects the frontal lobe, wrapping itself around people’s personality and emotional responses. A second variant strikes the temporal lobe, reducing the person’s reading and comprehension. The rarest of the three presents itself as a form of aphasia, reducing their ability to communicate through speech.
The team used several assessment tools to measure the prevalence of anedonia in each subset of FTD both as a solitary symptom and as a feature of depression and a general lack of motivation.
The results were compared with those obtained through similar evaluations performed on 34 Alzheimer’s volunteers and 51 healthy older participants.
They found that those with frontal and temporal forms of FTD (clinically known as FTD variant of behavior and semantic dementia) were much less likely to experience joy than before diagnosis, compared with those with the rarer variant of aphasia or Alzheimer’s disease.
This finding was reflected in a mapping of patients ’tissue density throughout the brain, which repeatedly revealed cell loss in areas such as the orbitofrontal and prefrontal cortex, the insular cortex, and the putamen. These regions are related to the pleasure systems of the brain.
It is important to note that atrophy associated with anedonia was different from changes related to apathy or depression.
Regions surrounded by green are related to the pursuit of pleasures and rewards. (University of Sydney)
The discovery may seem bleak, but it could help doctors better diagnose and ultimately treat the disease.
“Our findings also reflect the functioning of a complex network of brain regions, which indicate possible treatments,” says Irish.
“Future studies will be essential to address the impact of anhedonia on daily activities and to report on the development of specific interventions to improve the quality of life of patients and their families,” says Irish.
This research was published in Brain.