These results may help explain how the brain of people with Schizophrenia, ADHD, and depression learns and rehearses on its own, without the need for external triggers.
Historically, the scientific community believed that tangible rewards, such as food or monetary gains, stimulate learning through the release of dopamine, a hormone associated with pleasure. This release was thought to be instrumental in solidifying new information in our brains. However, recent research reveals that learning can also happen without such instant rewards.
The study, led by experts from the NYU Grossman School of Medicine, delved deep into the interplay between dopamine and acetylcholine, another neurotransmitter linked to memory and learning.
Previous studies suggested that these two hormones inversely affected each other: an increase in one would cause a drop in the other. It was believed that tangible rewards instigated this fluctuation, laying the groundwork for memory formation—a phenomenon attributed to the brain’s adaptability, called neuroplasticity.
However, the new research challenges the exclusivity of external rewards as the only catalyst for this learning process. They aimed to discern when dopamine levels surge while acetylcholine levels drop.
Intriguingly, they observed that this combination happens often, even without any rewards present. The dynamic relationship between these hormones, ebb and flow in the brain, prepares the ground for ongoing learning.
Anne Krok, PhD, the study’s primary author, remarked, “Our findings challenge the current understanding of when and how dopamine and acetylcholine work together in the brain.
“Rather than creating unique conditions for learning, rewards take advantage of a mechanism that is already in place and is constantly at work,” added Krok, who is also a medical student at NYU Grossman School of Medicine.
Krok is concurrently pursuing her medical studies at the NYU Grossman School of Medicine.
For this research, published today in the journal Nature, the team provided several mice with a wheel and occasionally gave them water. They then assessed the mice’s brain activities and the subsequent hormonal releases. While rewards did initiate the expected dopamine and acetylcholine patterns, these cycles were naturally present even before any reward was given. The findings reveal that these hormones interact in a rhythmic manner, independent of the mice’s activity. Similar neural rhythms have been observed in humans during reflective or restful states.
Senior author and neuroscientist, Nicolas Tritsch, PhD, commented, “These results may help explain how the brain learns and rehearses on its own, without the need for external incentives.
“Perhaps this pulsing circuit triggers the brain to reflect on past events and to learn from them.”
However, Tritsch, an affiliate of the Department of Neuroscience and Physiology at NYU Langone Health, emphasized that this study doesn’t definitively confirm that human brains mirror mouse brains in this spontaneous learning process.
Tritsch further hypothesized that the study could provide fresh perspectives on neurological conditions linked to dopamine imbalances, such as schizophrenia, ADHD, and depression.
For instance, in schizophrenia, patients often grapple with false beliefs. If the continuous interaction of dopamine and acetylcholine fortifies neural pathways, any malfunction in this system might lead to the reinforcement of false memories.
Similarly, the intrinsic motivation system’s potential disruption could explain the debilitating lack of drive seen in depression, affecting daily activities like rising from bed or attending work.
Tritsch mentioned that the team’s next objective is to investigate how these hormonal interactions behave in animal models with these mental health conditions, as well as during sleep—a crucial phase for memory solidification.
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