Synaptic configurations play a key role in how the nervous system processes sensory information to generate behavioral responses. While chemical synapses are well understood in this context, less is known about how electrical synaptic configurations influence sensory processing and context-dependent behaviors.
Scientists at Yale and the University of Connecticut have made a significant breakthrough in understanding how animal brains make decisions. Their research highlights the key role of electrical synapses in “filtering” sensory information. It shows how a particular configuration of electrical synapses helps animals make context-appropriate choices, even when exposed to similar sensory inputs.
Animal brains are constantly inundated with sensory information, requiring a sophisticated filtering system to prioritize relevant details and enable appropriate actions. This system, known as “action selection,” doesn’t just block out irrelevant stimuli but actively focuses on pertinent information based on the situation.
The Yale-led study investigated *C. elegans*, a worm that serves as an effective model for understanding action selection. When exposed to a temperature gradient, the worm can learn to prefer specific temperatures and uses a simple yet efficient strategy to navigate toward its preferred temperature.
Worms first move toward their preferred temperature across a gradient, and once they find a favorable temperature, they track it to stay within their preferred range. They can also adjust their behavior depending on the context, using gradient migration when far from their preferred temperature and isothermal tracking when closer to it. The question arises: how do they perform the correct behavior in the right context?
In their new study, researchers focused on electrical synapses, a connection between neuronal cells that differs from the more commonly studied chemical synapses. They discovered that these electrical synapses, mediated by the protein INX-1, link a specific pair of neurons (AIY neurons) responsible for controlling locomotion decisions in *C. elegans*.
Daniel Colón-Ramos, the Dorys McConnell Duberg Professor of Neuroscience and Cell Biology at Yale School of Medicine and the study’s corresponding author, said, “Altering this electrical conduit in a single pair of cells can change what the animal chooses to do.”
The researchers found that these electrical synapses do more than transmit signals—they also act as a “filter.” In worms with normal INX-1 function, the electrical connection dampens signals from thermosensory neurons, allowing the worm to ignore minor temperature variations and focus on significant changes in the temperature gradient.
This filtering mechanism ensures the worms move efficiently toward their preferred temperature without being distracted by irrelevant signals, such as those from isothermal tracks that occur throughout the gradient but aren’t at the preferred temperature.
In worms lacking INX-1, the AIY neurons become hypersensitive and respond more strongly to minor temperature fluctuations. This heightened sensitivity causes the worms to react to small signals, leading them to get trapped in isotherms that are not at their preferred temperature. As a result, the worms struggle to move efficiently across the temperature gradient, impairing their ability to reach their preferred temperature due to abnormal tracking of isotherms in the wrong context.
Colón-Ramos said, “It would be like watching a confused bird flying with its legs extended. Birds normally extend their legs before landing, but if a bird extends and extends its legs in the incorrect context, it would be detrimental to its normal behavior and goals.”
Since electrical synapses are present in the nervous systems of many animals, from worms to humans, these findings have broader implications. They suggest that the mechanisms discovered in *C. elegans* could offer insights into how electrical synapses influence behavior and sensory processing in other species, potentially including humans.
Colón-Ramos said, “Scientists can use this information to examine how relationships in single neurons can change how an animal perceives and responds to its environment. While the specific details of action selection will likely vary, the underlying principle of the role of electrical synapses in coupling neurons to alter responses to sensory information could be widespread.”
“For example, in our retina, a group of neurons called ‘amacrine cells’ uses a similar configuration of electrical synapses to regulate visual sensitivity when our eyes adapt to light changes.”
Synaptic configurations are key to how animals process sensory information and respond. The new study suggests that the arrangement of electrical synapses plays a critical role in modulating how nervous systems process context-specific sensory information, ultimately guiding animal perception and behavior.
Journal Reference:
- Agustin Almoril-Porras, Ana C. Calvo et al. Configuration of electrical synapses filters sensory information to drive behavioral choices. Cell. DOI: 10.1016/j.cell.2024.11.037