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Dodging dots helps explain brain circuitry

July 7, 2014
Brown University
Neuroscientists looked cell by cell at the brain circuitry that tadpoles, and possibly other animals, use to avoid collisions. The study produced a model of how individual inhibitory and excitatory neurons can work together to control a simple behavior. The basic circuitry involved is present in a wide variety of animals, including people, which is no surprise given how fundamental collision avoidance is across animal behavior.




"Imagine yourself walking in a forest while keeping a conversation with your friend," said Arseny Khakhalin, neuroscience postdoctoral scholar at Brown and lead author of the study in the European Journal of Neuroscience. "You can totally keep the conversation going, and at the same time avoid tree trunks and shrubs without even thinking about them consciously. That's because you have a whole region in your brain that is dedicated, among other things, to this task."

Turning tail

To learn how collision avoidance works, Khakhalin studied the task using tadpoles as a model organism, because as senior author and neuroscience professor Carlos Aizenman put it, they are "sufficiently complex to produce interesting behavior, but have nervous systems sufficiently simple to address in an integrated experimental approach."


The researchers then sought to determine how the tadpoles process different stimuli. To do that they held the tadpoles in place while presenting a variety of simple animations via a fiber optic cable held next to an eye. The animations included a flashed circle, an apparently approaching circle (it became larger and larger), and a couple of "in between" animations, such as a circle that was faded in, rather than simply flashed into being.

While the tadpoles watched the animations, the researchers tracked their tail movements with a high-speed camera (to determine if the tadpoles were executing a fleeing maneuver) and recorded electrical signals along the visual processing circuitry: at the optic nerve leading from the retina to the brain's optic tectum region, at "excitatory" and "inhibitory" synaptic inputs of neurons in the optic tectum, and at the outputs of the tectal neurons.



"The tectum is the first place that responded to approaching stimuli not just differently, but stronger," Khakhalin said.

Inhibition moderates the conversation






Khakhalin's hypothesis of how it works is that inhibitory/excitatory balance allows the tectum to build up a necessary degree of excitement about the stimulus of interest (e.g. something has been getting bigger) while still allowing enough "calm" to consider the next moment wave of input (it just got bigger again).



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Journal Reference:

  1. Arseny S. Khakhalin, David Koren, Jenny Gu, Heng Xu, Carlos D. Aizenman. Excitation and inhibition in recurrent networks mediate collision avoidance inXenopustadpoles. European Journal of Neuroscience, 2014; DOI: 10.1111/ejn.12664

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Brown University. "Dodging dots helps explain brain circuitry." ScienceDaily. ScienceDaily, 7 July 2014. <>.
Brown University. (2014, July 7). Dodging dots helps explain brain circuitry. ScienceDaily. Retrieved May 27, 2015 from
Brown University. "Dodging dots helps explain brain circuitry." ScienceDaily. (accessed May 27, 2015).

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