How Animals Find Their Way in the Dark

Scientists have revealed the brain activity in animals that helps them find food and other vital resources in unfamiliar environments where there are no cues, such as lights and sounds, to guide them.

Animals that are placed in such environments display spontaneous, seemingly random behaviors when foraging. These behaviors have been observed in many organisms, although the brain activity behind them has remained elusive due to difficulties in knowing where to look for neural signals in large vertebrate brains.

Now, in a study to be published in the journal eLife, researchers have used whole-brain imaging in larval zebrafish to discover how their brain activity translates into spontaneous behaviors. They found that the animals’ behavior in plain surroundings is not random at all, but is characterized by alternating left and right turn “states” in the brain, where the animals are more likely to perform repeated left and right turning maneuvers, respectively.

“We noted that a turn made by the zebrafish was likely to follow in the same direction as the preceding turn, creating alternating “chains” of turns biased to one side and generating conspicuous, slaloming swim trajectories,” says first author Timothy Dunn, a postdoctoral researcher at Harvard University.

“Freely swimming fish spontaneously chained together turns in the same direction for approximately five to 10 seconds on average, and sometimes for much longer periods. This significantly deviates from a random walk, where movements follow no discernible pattern or trend.”

By analyzing the relationship between spontaneous brain activity and spontaneous behavior in the larval zebrafish, the researchers generated whole-brain activity maps of neuronal structures that correlated with the patterns in the animals’ movements.

Image shows neurons in a zebrafish brain.
Mapping neurons that control spontaneous swimming behavior across the zebrafish brain. Gray and cyan are anatomical markers, with cyan showing neurons that project to the spinal cord. The green, red, and blue cells result from functional mapping, where green cells control leftward turning, the red cells control rightward turning, and the blue cells are tuned to forward swimming. These populations of neurons guide spontaneous zebrafish behavior when external environmental cues are lacking. Credit: Dunn, Yu, Narayan, Randlett, Naumann, Yang, Schier, Freeman, Engert, and Ahrens.

They discovered a nucleus in the zebrafish hindbrain, which participates in a simple but potentially vital behavioral algorithm that may optimize foraging when there is little information about the environment available to the animal.

As such behavioral strategies must exist in other animals that explore environments much larger than themselves, the team expects that the neural systems observed in the zebrafish must also exist in other organisms.

“Overall, our whole-brain analysis, neural activity experiments, and anatomical characterization of zebrafish revealed a circuit contributing to the patterning of a spontaneous, self-generated behavior,” explains co-first author Yu Mu, a postdoctoral researcher at Janelia Research Campus.

“As our study makes very specific predictions about this circuit, future experiments will be required to validate its critical components. It will also be interesting to see if different environmental contexts and the motivational state of zebrafish influence their spontaneous swim patterns.”

About this neuroscience research

Funding: This research was funded by the Howard Hughes Medical Institute (HHMI), National Institutes of Health (NIH), Marie Curie Fellowship, National Science Foundation (NSF).

Source: Emily Packer – eLife
Image Source: The image is credited to Dunn, Yu, Narayan, Randlett, Naumann, Yang, Schier, Freeman, Engert, and Ahrens.
Original Research: Abstract for “Brain-wide mapping of neural activity controlling zebrafish exploratory locomotion” by Timothy W Dunn, Yu Mu, Sujatha Narayan, Owen Randlett, Eva A Naumann, Chao-Tsung Yang, Alexander F Schier, Jeremy Freeman, Florian Engert, and Misha B Ahrens in eLife. Published online March 22 2016 doi:10.7554/eLife.12741


Brain-wide mapping of neural activity controlling zebrafish exploratory locomotionm

In the absence of salient sensory cues to guide behavior, animals must still execute sequences of motor actions in order to forage and explore. How such successive motor actions are coordinated to form global locomotion trajectories is unknown. We mapped the structure of larval zebrafish swim trajectories in homogeneous environments and found that trajectories were characterized by alternating sequences of repeated turns to the left and to the right. Using whole-brain light-sheet imaging, we identified activity relating to the behavior in specific neural populations that we termed the anterior rhombencephalic turning region (ARTR). ARTR perturbations biased swim direction and reduced the dependence of turn direction on turn history, indicating that the ARTR is part of a network generating the temporal correlations in turn direction. We also find suggestive evidence for ARTR mutual inhibition and ARTR projections to premotor neurons. Finally, simulations suggest the observed turn sequences may underlie efficient exploration of local environments.

“Brain-wide mapping of neural activity controlling zebrafish exploratory locomotion” by Timothy W Dunn, Yu Mu, Sujatha Narayan, Owen Randlett, Eva A Naumann, Chao-Tsung Yang, Alexander F Schier, Jeremy Freeman, Florian Engert, and Misha B Ahrens in eLife. Published online March 22 2016 doi:10.7554/eLife.12741

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