Published on: May 22, 2012
by Carolyn Herbert for ABC Science:
Our ability to imagine our future depends on a part of the brain used to store general knowledge, which is affected by some forms of dementia, an Australian-led study has found.
Semantic dementia affects the part of the brain that stores and remembers general knowledge. As a result, people with the condition may lose the ability to name simple objects or recognise a popular tune.
“Our results highlight that when these memory systems are affected, the ability to imagine yourself at a time point in the future is also severely impaired,” says Dr Muireann Irish, cognitive neuroscientist at Neuroscience Research Australia and lead author of the study published in the journal Brain.
In previous research, scientists discovered that Alzheimer’s patients, who cannot recall past memories, were also unable to think about the future. However, Irish says that nobody had investigated whether this was also the case in people with semantic dementia.
In this study, scientists compared MRI brain images of patients with Alzheimer’s disease and those with semantic dementia.
In patients with semantic dementia, the scans revealed atrophy in the anterior temporal lobes, where the brain stores general and conceptual knowledge. People with Alzheimer’s had changes in the medial temporal lobes, which are used to lay down memories and retrieve personal events.
Researchers then asked the patients to remember past incidents and then imagine and describe plausible future events. Unlike Alzheimer’s patients, people with semantic dementia showed well-preserved memories of the recent past; however, they found it difficult to imagine the future.
Irish says this suggests our ability to see into the future relies on both the anterior and medial temporal lobes.
Impacts on the patient
“This can have quite serious implications for the patient,” says Irish.
She says in social situations patients may not understand the consequences of an inappropriate comment or the effect of their actions on other people. Also, they may not be able to look forward to an upcoming event, leading to feelings of apathy and lack of motivation.
Irish says people with semantic dementia may also be unable to comprehend the long-term effects of financial decisions. “They can’t project forward and conceive what a decision may mean for them in a month or a year,” she says.
According to Irish these results suggest general knowledge is necessary to form a framework for visualising the future.
She says further research into the disease may help to reveal more precisely how semantic memory (remembering general knowledge) contributes to future-oriented thinking.
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