A recent study from UCL researchers has discovered that two conflicting memories can be triggered in a worm’s brain, even when only one memory influences the worm’s behavior.
Published in Current Biology, the study revealed that a worm’s sexual drive sometimes prevails over its hunger when deciding how to behave. This was examined in relation to a specific odor that has positive associations (like mating) and negative ones (such as hunger).
The researchers aimed to determine how a worm’s brain assesses whether an experience is positive or negative, and how that assessment informs the worm’s actions.
They discovered that training male worms to associate both positive and negative feelings with a certain odor results in both memories being activated when the worm detects the odor. However, only one of these memories will influence the worm’s actions.
The findings could lead to further studies on health issues where this memory process is dysfunctional, such as in post-traumatic stress disorder (PTSD), where suppressed memories continue to adversely affect behaviors and emotions.
Dr. Arantza Barrios, the lead author from UCL Cell & Developmental Biology, stated, “Our research focused on the male worm’s brain to comprehend the cellular and molecular mechanisms that dictate whether a memory influences behavior. A crucial aspect of learning is our ability to adjust to new experiences and to override prior associations.”
Co-first author Dr. Susana Colinas Fischer, also from UCL Cell & Developmental Biology, noted, “By examining what a tiny worm perceives, we can better understand the underlying processes that shape our own complex thought patterns.”
The study utilized male C. elegans roundworms, a 1mm-long species commonly used in scientific research. The worms were exposed to an odor that they naturally find appealing, similar to how a person might react to the smell of a tasty meal.
Through various experiments, the researchers altered the worms’ preference for this odor and observed their behavior and brain activity.
The worms’ natural inclination to seek out the odor was suppressed through aversive conditioning, during which the odor was paired with the negative experience of starvation. The researchers then attempted to replace this learned avoidance by introducing the same odor with a female mate and subsequent mating experiences, thereby helping the male worms regain a positive association with the odor.
The analysis uncovered a network of brain cells that encodes both positive and negative memories linked to previous encounters, focused on a specific neuropeptide (a brain chemical messenger) that retains memories of both the starvation and mating experiences associated with the odor.
The study concluded that, in worms trained to connect the odor with both starvation and mating, both memories were activated in their brains. However, only the mating memory influenced the worm’s decision to approach the odor.
This suggests that the motivation to mate could surpass the fear of starvation, even though the memory of starvation still existed in the brain’s activity. While the worms did not avoid the odor anymore, the negative association with starvation was still present in their brain function.
Dr. Laura Molina-GarcÃa, co-first author from UCL Cell & Developmental Biology, remarked, “Our research demonstrated that even in a simple organism like the roundworm, conflicting memories can be activated simultaneously—one influencing behavior while the other remains dormant.”
“This ability of an animal’s brain to represent something that is both positive and negative is crucial for learning and adapting to new experiences. By exploring how certain memories can override conflicting ones, we hope to contribute to research on addressing maladaptive memory processes, such as in PTSD.”
The research received support from the Royal Society, Wellcome, and the Leverhulme Trust.
