Unable to make quick decisions when they are actually needed? Then blame your brain.

Scientists say the ability to act fast depends on whether your brain wirings are the neural equivalent of broadband or dial-up Internet connection.

An international team which examined the brain mechanisms underpinning decision-making flexibility found that structural features of the brain affect a person's ability to take fast decisions.

Quick decisions tend to be error-prone while relative slower contemplation tends to produce more accuracy, said Scott Brown of the University of Newcastle's Cognition Laboratory.

This trade-off between speed and accuracy means people need to be able to switch between the fast risky and slower cautious modes of decision-making, as required.

But, little is known about the neurology underpinning this flexibility, said Brown, who led the research.

In their study, Brown and researchers from the UK, Germany and The Netherlands, found that decision-making flexibility is determined by the "purely physical measurement" of the thickness of the connections between the brain's cortex and the striatum of the basal ganglia.

According to Brown, the results are the equivalent of brain communication being reliant on a broadband connection or still using dial-up.

"The underlying finding that a purely physical measurement could predict behaviour is very surprising," he was quoted as saying by the Discovery News.

Though his team could not determine what causes one person's connections to be thicker than another's, Brown said it could be the "use it or lose it" phenomena.

In the research paper, appeared in the Proceedings of the National Academy of Sciences, Brown said they found that the fast decision making ability thins as people age.

"As you get older the bandwidth gets slower and slower," he said.

For the study, the researchers placed participants in an MRI scanner and measured the thickness of "fibbers" that carry inputs from the cortex to the basal ganglia.

These measurements were done when the participants were not making decisions. They were also required to undertake a series of tasks that required them to make decisions either quickly or slowly.