Having a bigger brain does not mean you have a better memory, according to scientists.
Researchers scanned the brains of more than 330 adults and got them to take learning and memory tests.
They found that those with a larger hippocampus, a section of the brain which serves as the memory centre, did not necessarily perform better on the tests.
Past research has shown that the hippocampus shrinks with age and may be linked to memory loss in pensioners and people with Alzheimer’s disease.
But this study found that, more specifically, it was the quantity of a specific type of white matter – called limbic white matter – which dictated how good someone’s memory was.
This was demonstrated by people with larger hippocampuses but less intact white matter having worse memories than those with the opposite.
A 2004 study showed that the size of the hippocampus is not always related to memory performance in older adults.
But this is the first study to shed light on why, the researchers said.
Michigan State University’s Dr Andrew Bender, who authored the new study, said the findings showed the need to look at the connection between the hippocampus and the rest of the brain when looking at memory decline in older adults.
He and his colleagues, who included researchers from Hungary and Germany, looked at different types of MRI scans on the brains of participants.
One scan was to reveal the size of the hippocampus, while the second examined white matter.
White matter is flesh in the centre of the brain which is crammed full with nerves relaying messages all over the organ in the form of electrical signals.
It differs from grey matter which is composed of other types of cells such as blood vessels and ones which transport nutrients into the brain tissue.
People in the study then did brainpower test, one of which included them needing to listen to 15 words and write down as many as they could remember afterwards.
They re-did the test five times so the scientists could see how good they were at learning through repetition.
Dr Bender and his colleagues then tried to find a link between how quickly people learned the words and the size of their hippocampus and white matter.
They found that only those with both a larger hippocampus and also more white matter circuits connecting it to the rest of the brain learned faster than the others.
Dr Bender added: ‘Our findings reinforce a growing perspective that studying age-related changes in learning and memory from a systems perspective appears far more informative in understanding different patterns of brain and cognitive declines than focusing on any single brain region.’
Next, the research team want to use more data from the same people to see if they can see a change in their brain structures which is linked to learning or memory declines.
The findings could help doctors make more accurate early diagnoses of age-related conditions such as Alzheimer’s.
Alzheimer’s, the most common form of dementia, is a progressive disease which destroys memory and thinking skills and ultimately the ability to carry out even simple tasks.
The condition affects around 500,000 people in the UK, with more than 850,000 suffering from dementia more generally.
There are around 5.7million dementia sufferers in the US, with 4million of them suffering from Alzheimer’s.
The research was published in the medical journal Cerebral Cortex.