Thinking 'drains the brain'

Glucose provides fuel for the brain

Scientists have come up with proof that too much thinking can be exhausting.

The impact of straining the grey matter is likely to be more pronounced in older people.

A team from the University of Virginia in the US carried out research on rats.

They found that increased memory load drains glucose from a key part of the brain in the animals.

This research implies that the contents and timing of meals may need to be co-ordinated to have the most beneficial effects that enhance learning

Professor Paul Gold

The effect was more dramatic in older rats, whose brains also took longer to recover.

Researcher Professor Paul Gold said the findings may have important implications for the way schools schedule classes and meals.

He believes they may also help scientists to develop a better understanding of age-related deficits in memory and learning.

Runs on glucose

Fellow researcher Dr Ewan McNay said: "The brain runs on glucose.

"Young rats can do a pretty good job of supplying all the glucose that a particular area of the brain needs until a task demanding that brain area becomes difficult.

"In older rats, even on tasks that cause no glucose drainage in young rats, we see big problems in supplying the brain with glucose. This correlates with a big deficit in performance. A lack of fuel affects the ability to think and remember."

Glucose, found in many foods and supplied from the bloodstream, is the main source of energy for brain.

It has long been thought that, unless a person is starving, the brain always receives an ample supply of glucose.

However, Professor Gold and Dr McNay measured glucose levels in the brains of rats as they negotiated their way through a maze.

They found that in a brain area concerned with memory for location the demand for glucose was so high that levels fell by 30%.

However, levels stayed constant in other brain areas that played no role in spatial memory.

In a follow up study, the researchers showed that in older rats glucose levels in the active brain areas dropped by 48% during the maze task.

They also found that in the older animals glucose supply did not return to normal until 30 minutes after the task was completed. In young rats recover was immediate.

Injections

The researchers found they could boost the performance of the rats by giving them glucose injections.

Professor Gold said: "Glucose enhances learning and memory not only in rats but also in many populations of humans.

"For schoolchildren, this research implies that the contents and timing of meals may need to be co-ordinated to have the most beneficial effects that enhance learning."

Dr Tonmoy Sharma, of the Institute of Psychiatry, told BBC News Online: "We all get exhausted by thinking, so it makes intuitive sense that glucose levels are depleted when we do.

"However, making cross-species generalisations has always been a problem."

Dr Sharma said there was also evidence that thinking became slower when blood sugar levels were down.

The research appeared in the Proceedings of the National Academy of Sciences and the journal Neurobiology of Learning and Memory.