Scientists have made significant progress in unraveling the decision-making processes of animal brains, highlighting the vital role of electrical synapses in “filtering” sensory information. This recent study showcases how a particular arrangement of electrical synapses allows animals to make appropriate decisions based on context, even amid similar sensory input.
Researchers from Yale and the University of Connecticut have made a significant advancement in understanding how animal brains make choices, highlighting the key role of electrical synapses in “filtering” sensory information.
According to findings published in the journal Cell, a specific configuration of electrical synapses empowers animals to select behaviors that suit their context, regardless of encountering similar sensory cues.
Animal brains are continuously exposed to a myriad of sensory inputs such as sights, sounds, and smells. Scientists argue that deciphering this information necessitates an advanced filtering mechanism, which enhances vital details and enables appropriate action. This filtering system doesn’t merely eliminate irrelevant noise—it actively prioritizes information relative to the circumstances. The process of concentrating on certain sensory information to develop context-sensitive behavior is known as “action selection.”
The study, led by Yale, focused on the worm C. elegans, which surprisingly serves as an effective model for understanding the neural mechanisms underlying action selection. These worms can be trained to favor particular temperatures, utilizing a straightforward yet efficient strategy to navigate towards their preferred temperature in a gradient.
Initially, worms move through the temperature gradient toward their desired temperature—a behavior referred to as “gradient migration.” Once they identify a temperature they prefer, they engage in “isothermal tracking,” which allows them to remain within that favorable temperature range. They can also adapt their behaviors according to context, using gradient migration when distanced from their ideal temperature and resorting to isothermal tracking when nearby.
But what enables them to perform the appropriate action in the right context?
The researchers explored a unique type of connection between neurons known as electrical synapses, which differ from the more prevalent chemical synapses. They discovered that these electrical synapses, mediated by a protein called INX-1, connect specific neurons (AIY neurons) responsible for directing locomotion decisions in the worm.
“Modifying this electrical connection in just one pair of neurons can alter the animal’s behavior,” stated Daniel Colón-Ramos, the Dorys McConnell Duberg Professor of Neuroscience and Cell Biology at Yale School of Medicine, and the study’s corresponding author.
The findings revealed that these electrical synapses not only relay signals but also function as a “filter.” In worms with normal INX-1 functionality, the electrical connection effectively dampens signals from thermosensory neurons, allowing the worm to disregard minor temperature changes and concentrate on more significant variations in the gradient. This way, the worms can efficiently traverse the gradient towards their preferred temperature without being distracted by irrelevant signals from isothermal tracks present in the gradient.
In contrast, worms lacking INX-1 show hypersensitivity in their AIY neurons, reacting excessively to small temperature shifts. This heightened sensitivity can lead to the worms responding to these minor cues, causing them to get trapped in isotherms that do not align with their preferred temperature. This flawed behavior impacts their ability to navigate towards their choice temperature within the gradient.
“It’s akin to seeing a disoriented bird attempting to land with its legs extended,” Colón-Ramos said. “Birds typically extend their legs before landing, but if they do so inappropriately, it could hinder their natural behavior and objectives.”
Given that electrical synapses are present in the nervous systems of various animals, from worms to humans, these findings have broad implications extending beyond just worm behavior.
“This research will enable scientists to investigate how relationships within individual neurons can influence an animal’s perception of its surroundings and how it reacts,” Colón-Ramos noted. “Though the specifics of action selection may differ, the fundamental concept of how electrical synapses influence neuron interaction to shape sensory responses could be widely applicable.”
“For instance, in our retinas, a type of neuron called ‘amacrine cells’ employs a similar arrangement of electrical synapses to adjust visual sensitivity when our eyes adapt to lighting changes.”
Synaptic configurations are essential for the way animals interpret sensory information and respond, and the new study’s results indicate that electrical synapse configurations are critical in modulating how nervous systems process context-relevant sensory data to steer perception and actions in animals.
Colón-Ramos also serves as the associate director of Yale’s Wu Tsai Institute, dedicated to cognitive studies.
The study’s co-lead authors include Agustin Almoril-Porras and Ana Calvo from Yale, with contributions from Jonathan Beagan, Malcom DÃaz Garcia, Josh Hawk, Ahmad Aljobeh, Elias Wisdom, and Ivy Ren, all from Yale, as well as Longgang Niu and Zhao-Wen Wang from the University of Connecticut.
This research was supported by the National Institutes of Health, the National Science Foundation, and a Howard Hughes Medical Institute Scholar Award.
