Researchers identify different brain patterns in planning/execution of movement
Our brains are wired to execute precise movements following a specific cue – such as halting movement upon a red light or warning sign. Researchers have recently discovered the neuronal network behind this action (cue-triggered movement) which is often plays out after a slight delay. The findings suggest that different mechanisms in the brain are responsible for self-initiated movement and cue-triggered movement, and may better explain the problem in motor disorders, such as Parkinson’s disease.
Research lead Dr. Hidehiko Inagaki from the Max Planck Florida Institute for Neuroscience (MPFI) likens the brain to an orchestra, “In a symphony, instruments play diverse tunes with different tempos and timbres. The collective of these sounds shapes a musical phrase. Similarly, neurons in the brain are active with diverse patterns and timing. The ensemble of neuronal activities mediates specific aspects of our behaviour.”
For example, activity patterns in the motor cortex of the brain are dramatically different between the phases of the actual movement. Yet, the brain areas controlling this transition were unknown.
“There must be brain areas acting as the conductor,” said Dr. Inagaki. “Such areas monitor environmental cues and orchestrate neuronal activities from one pattern to the other. The conductor ensures that plans are converted into action at the right time.”
Dr. Inagaki and colleagues studied trained mice to understand the relationship between environmental cues, behavioural control, and movement. They correlated complex neuronal activity patterns to relevant stages of a behavioural task. These patterns arose from a circuit of neurons in the midbrain, thalamus, and cortex, occurring immediately after the go cue and during the switch between motor planning and execution.
[The behavioural task involved mice trained to lick to the right if whiskers were touched or to the left if whiskers were not touched. The catch: the animals had to delay their movement until a tone, or “go cue,” was played. Only correct movements after the go cue would be rewarded.]
Further optogenetics (light-modulated) tests revealed how the mouse brains could execute or discard planned movements. Optogenetics enabled the researchers to activate or inactivate the neuronal circuit: activating this circuit during the planning phase of the behavioural task switched the mouse’s brain activity from motor planning to execution and caused the mouse to lick; on the other hand, turning off the circuit while playing the go cue suppressed the cued movement, so the mice remained in a motor planning stage as if they had not received the go cue.
“We have found a circuit that can change the activity of the motor cortex from motor planning to execution at the appropriate time. This gives us insight into how the brain orchestrates neuronal activity to produce complex behaviour. Future work will focus on understanding how this circuit and others reorganise[s] neuronal activity across many brain regions,” concluded Dr. Inagaki.
Read: Patterns of brain activity in newborns similar to adults within days of birth
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