Dopamine decline underlies episodic memory decline in old age

December, 2012

Findings supporting dopamine’s role in long-term episodic memory point to a decline in dopamine levels as part of the reason for cognitive decline in old age, and perhaps in Alzheimer’s.

The neurotransmitter dopamine is found throughout the brain and has been implicated in a number of cognitive processes, including memory. It is well-known, of course, that Parkinson's disease is characterized by low levels of dopamine, and is treated by raising dopamine levels.

A new study of older adults has now demonstrated the effect of dopamine on episodic memory. In the study, participants (aged 65-75) were shown black and white photos of indoor scenes and landscapes. The subsequent recognition test presented them with these photos mixed in with new ones, and required them to note which photos they had seen before. Half of the participants were first given Levodopa (‘L-dopa’), and half a placebo.

Recognition tests were given two and six hours after being shown the photos. There was no difference between the groups at the two-hour test, but at the six-hour test, those given L-dopa recognized up to 20% more photos than controls.

The failure to find a difference at the two-hour test was expected, if dopamine’s role is to help strengthen the memory code for long-term storage, which occurs after 4-6 hours.

Individual differences indicated that the ratio between the amount of Levodopa taken and body weight is key for an optimally effective dose.

The findings therefore suggest that at least part of the reason for the decline in episodic memory typically seen in older adults is caused by declining levels of dopamine.

Given that episodic memory is one of the first and greatest types of memory hit by Alzheimer’s, this finding also has implications for Alzheimer’s treatment.

Caffeine improves recognition of positive words

Another recent study also demonstrates, rather more obliquely, the benefits of dopamine. In this study, 200 mg of caffeine (equivalent to 2-3 cups of coffee), taken 30 minutes earlier by healthy young adults, was found to improve recognition of positive words, but had no effect on the processing of emotionally neutral or negative words. Positive words are consistently processed faster and more accurately than negative and neutral words.

Because caffeine is linked to an increase in dopamine transmission (an indirect effect, stemming from caffeine’s inhibitory effect on adenosine receptors), the researchers suggest that this effect of caffeine on positive words demonstrates that the processing advantage enjoyed by positive words is driven by the involvement of the dopaminergic system.

Reference: 

Related News

A study involving 97 healthy older adults (65-89) has found that those with the “Alzheimer’s gene” (APOe4) who didn’t engage in much physical activity showed a decrease in hippocampal volume (3%) over 18 months.

An Indian study involving 648 dementia patients, of whom 391 were bilingual, has found that, overall, bilingual patients developed dementia 4.5 years later than the monolingual ones. There was no additional advantage to speaking more than two languages.

A study, involving 371 patients with mild cognitive impairment, has found that those with depressive symptoms had higher levels of amyloid-beta, particularly in the frontal cortex and the anterior and posterior

A study involving 206 spousal and adult children caregivers of dementia sufferers (mostly Alzheimer’s) has found that about 84% of caregivers reported a clinically significant burden. Three factors were significant contributors to the burden:

A study involving 254 people with dementia living at home has found that 99% of people with dementia and 97% of their caregivers had one or more unmet needs, 90% of which were safety-related.

A new U.S. study suggests that Alzheimer's disease and other dementias are markedly under-reported on death certificates and medical records. Death certificates tend to only provide an immediate cause, such as pneumonia, and don’t mention the underlying condition that provoked it.

It’s often argued that telling people that they carry genes increasing their risk of Alzheimer’s will simply upset them to no purpose. A new study challenges that idea.

11 new genetic susceptibility factors for Alzheimer’s identified

Understanding a protein's role in familial Alzheimer's disease

Analysis of data from 237 patients with mild cognitive impairment (mean age 79.9) has found that, compared to those carrying the ‘normal’ ApoE3 gene (the most common variant of the ApoE gene), the ApoE4 carriers showed markedly greater rates of shrinkage in 13 of 15 brain regions thought to be k

Pages

Subscribe to Latest newsSubscribe to Latest news