Memory loss is monkey business

Monkeys, like humans, become more forgetful as they grow older. Now, a new study has captured the decline in the performance of brain memory circuits as a monkey ages.

Associate Professor Sharon Naismith, of the Brain and Mind Research Institute at the University of Sydney, looks for interventions that can improve cognitive function in the elderly.

She says the study conducted on monkeys is valuable because it identifies changes in the ‘delay neurons’.

“As people age they just can’t hold as much in their working memory, and taking in conversations and things they see on the news becomes difficult; but of course, we have to understand normal ageing first before we can really target diseases like Alzheimer’s,” Professor Naismith says.

The study, reported in this week’s journal Nature, sheds light on the normal processes of ageing in monkeys and offers hope for improvement.

Professor Amy Arnsten and colleagues at Yale University looked at the brain region of Rhesus macaque monkeys; associated with spatial working memory which holds information for only a short time, but is the key to effective everyday functioning.

“It’s the memory you use when you ask yourself, ‘Now where did I leave my car keys this time?’” Professor Arnsten says.

The monkeys were required to remember where a flashing light had most recently appeared on a computer screen. The light could appear in one of eight different positions, assigned randomly. If, after a brief delay, the monkeys remembered the most recent position of the flashing light correctly, they earned a reward of their favourite juice.

During this trial electrical recordings were being made from about 50 neurons in the prefrontal cortex (the brain region holding spatial working memory) of each monkey.

The study found there were age-dependent differences in the response of a particular group of neurons in the monkeys – called ‘delay’ neurons, which hold the memory ‘in mind’ by continuing to fire even though there is no outside stimulation. The researchers’ aim was to form an ‘excitatory’ network, keeping other neurons firing through connections known as dendritic spines. If the delay neurons stop firing, the memory is allegedly lost.

While completing the task, the middle-aged and elderly monkeys showed much lower firing rates in their delay neurons than the young monkeys.

Professor Arnsten says this mimics what we see in middle-aged and elderly people. “It is harder to shift attention and harder to hold things in mind especially in the presence of distractions,” she says.

Researchers found by applying ‘minute’ quantities of drugs that block the potassium channels, the delay neurons in the older monkeys would fire at rates similar to those seen in the young animals; one of these drugs is guanfacine, which is used to treat high blood pressure.

A separate group of researchers at Yale University are conducting clinical trials to see whether guanfacine is helpful in improving the working memory in people aged over 75 years.