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A Speed Limit on Thought?

DW Staff (dc)March 15, 2004

A group of German neuro-physicists say they've discovered an upper limit on how fast human beings can think. It all depends on how closely connected the brain's nerve cells are.

The brain's neural network imposes a natural speed limit on thought.Image: Max-Planck-Institut für Strömungsforschung

If you've ever been envious of people who seem able to think faster or be more coordinated, take heart. There is a limit, it seems, even for them.

Three theoretical neuro-physicists from the Max Planck Institute for Flow Research in Göttingen used models of neural networks in the brain to discover an upper limit to the speed of thought.

Complex neural networks

The brain's neural networks are made up of nerve cells that exchange pulses via synaptic connections. Unlike atoms in a crystal, which are arranged on a regular, cubic lattice, nerve cells grow synaptic connections in a highly specific but irregular fashion. The team of researchers -- Theo Geisel, Marc Timme, and Fred Wolf --came up with a mathematical model which can precisely determine how fast neurons can coordinate their activity.

As could be expected, they found that the more highly connected the neural networks are, the faster the neurons can synchonize. But what was surprising was that this speed has an upper limit. Even in areas of the brain with the most dense neural networks, thought coordination can only happen so fast.

This "speed limit" on thought comes about because of the complicated switching structure of the neural networks. Only if every single neuron in the brain were connected with every other single neuron would the speed limit not apply.

Connectivity equals speed

If the researchers' model correctly describes how the brain functions, it means that the way we think and behave -- how fast we can coordinate our thoughts -- depends on the density and connectivity of the neural networks in our brains. "If you're missing connections, it can influence your processing," researcher team member Timme, told DW-WORLD.

Though it's still to be proved, Timme believes that it is possible to change and rearrange the brain's connectivity. Using the example of learning a new language, Timme said that the difference in reading and writing levels of a complete beginner to that of a more advanced student can be understood as a change in the brain's connectivity.

But, unfortunately for anyone cramming for a chemistry exam or for those hoping to learn French quickly, scientists don't yet know how to externally manipulate connectivity to speed up thought processes in less densely networked parts of the brain.