It is well known that aging can involve the long-term memory decline—even if a person isn’t developing dementia. What is less known is the reason why some seniors don’t seem to experience memory problems yet others continue to do so.
Some new findings suggest that part of this answer may be rooted in the brain’s dopamine receptors, specifically one type of receptor that until now didn’t have a clearly identified role.
The neurotransmitter dopamine is associated with a host of important psychological factors such as pleasure, addiction, and memory. Among the various neurotransmitter receptors in the brain are the D1 and D2 dopamine receptor systems. While the D1 system has been linked to various frontal lobe functions for some time, the D2 system has not been known to have any specific role. The researchers wanted to know if the D2 receptor system had any connection to human memory.
For the study, 181 healthy individuals were used, all between ages 64 and 68. Participants went through a performance test of long-term episodic memory, working memory, and memory processing speed along with MRI scans. The researchers noticed that D2 system function was positively correlated to episodic memory, meaning that the more the system was active, the better the test results. No connection was found to processing speed or working memory.
When PET scan data was incorporated into the findings, the researchers also noted that the D2 system was tied to the hippocampus, the part of the brain that governs long-term memory. This suggests that the D2 receptor system is involved in long-term, episodic memory, and it has this involvement through connections within the hippocampus.
If confirmed, these findings do have certain useful implications. Impairment of the dopamine systems could be considered when trying to evaluate dementia or age-related memory loss and examination of those systems may lead to further knowledge about age-related cognitive decline.
Nyberg, L., et. al., “Dopamine D2 receptor availability is linked to hippocampal-caudate functional connectivity and episodic memory,” PNAS, 2016; 10.1073/pnas.1606309113.