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Developmental biology - Brain|
To Flee or Not to Flee: How the Brain Decides
"This result is very important. It is the first showing how the behavioral state of an animal can influence its choice of defensive strategy," Vasconcelos points out. These observations opened the door to identifying the actual neurons that determined whether the fly would flee or freeze. Using state-of-the-art genetic tools, the team found a single pair of neurons important for the flies' defensive behaviors.
Vasconcelos: "It was quite incredible. There are hundreds of thousands of neurons in the brain of the fly, and among all of those, we found that freezing was controlled by two identical neurons, one on each side of the brain."
When the team turned the neurons off, flies didn't freeze anymore, they escaped from the threat. But, when they turned the neurons on without the presence of a threat — flies would freeze in a manner dependent on their walking speed.
Zacarias: "If we turned the neurons on when the fly was walking slowly, it would freeze. But, not if it was walking quickly. This result places these neurons directly at the gateway of the circuit of choice!"
Moita: "This is exactly what we were looking for: how the brain decides between competing strategies. And moreover, these neurons are of the type that sends motor commands from the brain to the 'spinal cord' of the fly. This means that they may be involved not only in the choice, but also in the execution."
"We can now study directly how the brain makes choices between very different defensive behaviors. And because defensive behaviors are common to all animals, our discoveries provide a good starting point towards identifying the 'rules of the game' that define how all animals choose to defend themselves."
The most fundamental choice an animal has to make when it detects a threat is whether to freeze, reducing its chances of being noticed, or to flee to safety. Here we show that Drosophila melanogaster exposed to looming stimuli in a confined arena either freeze or flee. The probability of freezing versus fleeing is modulated by the fly’s walking speed at the time of threat, demonstrating that freeze/flee decisions depend on behavioral state. We describe a pair of descending neurons crucially implicated in freezing. Genetic silencing of DNp09 descending neurons disrupts freezing yet does not prevent fleeing. Optogenetic activation of both DNp09 neurons induces running and freezing in a state-dependent manner. Our findings establish walking speed as a key factor in defensive response choices and reveal a pair of descending neurons as a critical component in the circuitry mediating selection and execution of freezing or fleeing behaviors.
Ricardo Zacarias, Shigehiro Namiki, Gwyneth M. Card, Maria Luisa Vasconcelos and Marta A. Moita.
The authors declare no competing interests.
Champalimaud Research, Champalimaud Centre for the Unknown, 1400-038, Lisbon, Portugal
Ricardo Zacarias, Maria Luisa Vasconcelos and Marta A. Moita.
Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
Shigehiro Namiki and Gwyneth M. Card.
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How the brain decides what to do in the face of danger? Image credit: Gil Costa.