The feel-good hormone dopamine improves long-term memory. This is the finding of a team lead by Emrah D-zel, neuroscientist at the German Center for Neurodegenerative Diseases and the University of Magdeburg. The researchers investigated test subjects ranging in age from 65 to 75 years, who were given a precursor of dopamine. Treated subjects performed better in a memory test than a comparison group, who had taken a placebo. The study provides new insights into the formation of long lasting memories and also has implications for understanding why memories fade more rapidly following the onset of Alzheimer's disease. The results appear in the "Journal of Neuroscience".
Dopamine is a multi-faced neurotransmitter. It provides communication between nerve cells as well as between nerve and muscle cells. If this signal transmission becomes disturbed, the consequences can be dramatic. This is illustrated by Parkinson's disease, whose symptoms - akinesia and other movement disorders - can be traced back to a lack of dopamine. On the other hand, when someone is pleased or motivated, a flood of dopamine is released in the brain, which is why the term "feel-good hormone" has become popular. There have already been indications of the special role of dopamine in forming long-lasting memories for some time. The signs came from various studies and also from the fact that rewarding incidents and other important events can usually be remembered for a long time. Researchers led by D-zel, who is also affiliated with University College London, have now been able to confirm this effect in older people.
"Our investigations for the first time prove that dopamine has an effect on episodic memory. This is the part of long-term memory, which allows us to recall actual events. Occurrences in which we were personally involved," D-zel says. The Site Speaker of the DZNE in Magdeburg and Director of the Institute of Cognitive Neurology and Dementia Research at the University of Magdeburg adds: "Episodic memory is that part of our capacity to remember, which is first affected in Alzheimer's dementia. This is why our results can contribute to a better understanding of the disease."
In particular animal studies have indicated that to store experiences permanently the brain has to release dopamine. D-zel and his colleagues examined whether this also applies to humans: the task of the test subjects ranging in age from 65 to 75 years was to recognise photos which they had been shown previously. Half of the test participants had first taken a placebo and the remainder had taken Levodopa. This substance, also known as L-DOPA, is able to reach the brain from the bloodstream, and there it is converted into dopamine. In this way the researchers could exercise a targeted influence over dopamine levels in the brains of the test subjects. "Neurons, which produce dopamine, decline with age," D-zel says. "Increasing dopamine levels in these elderly subjects, should show a clear effect." The neuroscientist mentions another reason for undertaking the study with older people: -In old age the episodic memory declines. This is why the topic we are investigating is particularly relevant for elderly people."
The participants were first shown black and white photos of indoor scenes and landscapes. They were to differentiate these images from others, which they had not seen before. When they first viewed the pictures brain activity of the participants was monitored using fMRT, a special form of magnetic resonance tomography. The photos which triggered hardly any activity in the memory centre were of particular interest to the neuroscientists. The reason: If this brain area is only slightly active, then it should cause little or no dopamine release. "In such cases the memory of these pictures should gradually fade. As they have been encoded only weakly," D-zel says, "we wanted to find out whether the memory of these pictures could nevertheless persist."
Effect after six hours
Two and six hours after the participants had memorized the photos, they were requested to recognise and distinguish them from new images.