Split second decisions, how does our brain decide?

We make countless decisions every minute of every hour of every day. Some we make easily, some we may ponder on for longer such as which colour socks to buy for Uncle George. But some decisions have to be made extremely fast in milliseconds, as that split second decision that could mean the difference between life and death. How do you choose to respond when coming up to traffic lights and they've just turned from green to amber? Do you shoot across at high speed, or slam on the brakes to stop?

How does the brain choose which action to take?

Researchers in Freiburg have come up with a proposal for how this brain mechanism works and it comes down to the level of individual neurons.

Using a computerised model, the researchers set up an experiment where one set of brain cells in a network were sending an “excitatory” signal and another an “inhibitory” signal. A further brain cell network was set up as gatekeepers, where the cells could control ie 'decide" whether the excitatory signal or the inhibitory signal was sent through. A bit like changing railway signals determining which track a train will run on. What they showed was that the crucial determining factor is the time gap between the excitatory signal and inhibitory signal arriving shortly after.

A very small time gap meant the gatekeeper neurons were unable to send on the message because the activity of the cells at the gate was quenched too quickly. If the time gap was longer the gatekeeper neurons were able to open to pass on the signal.

Maybe this also explains why some of us are more likely to be “impulse buyers” dependent on the time gaps of our excitatory and inhibitory networks.

J. Kremkow, A. Aertsen, A. Kumar. Gating of Signal Propagation in Spiking Neural Networks by Balanced and Correlated Excitation and Inhibition. Journal of Neuroscience, 2010; 30 (47): 15760 DOI: 10.1523/JNEUROSCI.3874-10.2010