As humans, we have the ability to alter out behavioral responses based on internal beliefs and external instructions. When tapping your foot in time to music, for example, your brain has to quickly process that incoming sound and then use its internal knowledge to remember how the song goes. 

In a recent study, a group of MIT neuroscientists successfully identified the strategy in which the brain employs to do this. The discovery was made by applying a dynamic systems analysis to learn the logic behind the evolution of activity within large populations of neurons. “The brain can combine internal and external cues to perform novel computations on the fly,” says Mehrdad Jazayeri, senior author of the study and the Robert A. Swanson Career Development Professor of Life Sciences. “What makes this remarkable is that we can make adjustments to our behavior at a much faster time scale that the brain’s hardware can change.” 


Previous studies conducted by Jazayeri and colleagues revealed that the brain initiates the movement by changing the speed at which neural activity patterns evolve. They also found that the speed in which this is adjusted to is controlled by two factors within the brain: external sensory inputs and adjustments of the internal states relating to the corresponding task.

Cognitive flexibility is the ability to quickly adapt to new pieces of information. Neuroscientists are under the impression that this cognitive flexibility occurs within the brain’s higher cortical regions, yet very little is known about how it’s done. In a similar way to how switches and dials are able to change certain outputs on electrical circuits, the MIT team figured that the brain also transforms beliefs and instructions into internal states and inputs that control the way in which neural circuits behave.

To test this theory, the researchers performed a flexible timing task called “ready, set, go”, while recording the neural activity in the frontal cortex. The test involved the animal seeing two visual flashes – a “ready” and a “set” flash. These are separated by intervals of varying time, and sometime after “set”, the animal initiates a “go” movement. The aim for the animal is to initiate the movement that’s the same time or 1.5 times the length of the “ready-set” interval. 


Completing the research enabled Jazayeri and his team to discover how the brain is able to adjust to various inputs and conditions experienced in the frontal cortex in order to flexibly control movement. Another success to come from the study was the development of new mathematical tools in which to analyze large amounts of data extracted from neuron readings. 

The next mission for the researchers is to try and find out which part of the brain is sending the information to the frontal cortex. They would also like to discover what happens in these neurons when they have to learn a particular task quickly. “We haven’t connected all the dots from behavioral flexibility to neurobiological details. But what we have done is to establish an algorithmic understanding based on the mathematics of dynamical systems that serve as a bridge between behavior and neurobiology,” says Jazayeri.


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