Dementia is a thief who chooses many pockets. In some ways, it takes away our memories. Other forms rob us of inhibition. Sometimes even happiness itself.
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 the loss of “hedonic hotspots” – regions of the brain associated with reward seeking.
An absence of pleasure is known as anhedonia and is a common symptom in mental health conditions such as depression and obsessive-compulsive disorder. Where most of us are rewarded with a sense of satisfaction, enthusiasm and happiness when we reach a goal or associate with loved ones, those who face anhedonia cannot.
Interestingly, early dementia is often confused with depression, and decreased motivation can be used as a criterion for diagnosis. So researchers at the University of Sydney and the University of New South Wales in Australia have decided to formally investigate this link between anhedonia and types of dementia 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 this ability for granted,” says neurologist Muireann Irish of the University of Sydney.
But consider 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 more likely to suffer from the clinical symptom of anedonia.
Of the group, 87 patients presented with 1 of 3 different types of frontotemporal dementia (FTD). FTD is an early-onset dementia with symptoms that usually begin between the ages of 40-65.
A variant of FTD affects the frontal lobe, tangling with the personality and emotional responses of the individual. A second variant hits the temporal lobe, reducing the person’s reading and understanding. The rarest of the three presents as a form of aphasia, reducing their ability to communicate through speech.
The team used several assessment tools to measure the prevalence of anhedonia 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 collected by similar evaluations performed on 34 Alzheimer’s volunteers and 51 healthier older participants.
They found that those with frontal and temporal forms of FTD – clinically called FTD-behavioral variant and semantic dementia – were much less likely to experience joy than they had before diagnosis, compared with those with the rarer aphasia variant or Alzheimer’s disease.
This finding was reflected in a mapping of patients’ tissue density throughout the brain, which repeatedly revealed a loss of cells in areas such as the orbitofrontal and prefrontal cortices, the insular cortex, and the putamen. These regions are related to the pleasure systems of the brain.
Importantly, atrophy associated with anhedonia was distinct from changes related to apathy or depression.
The regions surrounded by greenery are related to pleasure and the pursuit of 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, signaling potential treatments,” says Irish.
“Future studies will be essential to address the impact of anhedonia on daily activities and to inform the development of targeted interventions to improve the quality of life of patients and their families,” says Irish.
This research was published in Brain.