A groundbreaking study conducted by researchers at ICVS, U.Minho, has shed light on how D1 and D2 neurons in the nucleus accumbens (NAc) process positive and negative stimuli. Contrary to earlier assumptions that these neurons function as opposites, the research reveals a more nuanced relationship where they complement each other during associative learning. This discovery holds significant implications for understanding mental health disorders such as post-traumatic stress and depression.

In an effort to better understand how the brain distinguishes between pleasurable and aversive stimuli, scientists led by Ana João Rodrigues and Carina Soares-Cunha employed advanced imaging techniques to monitor hundreds of neurons in mice exposed to various stimuli. Their findings, published in Nature Communications, demonstrate that both D1 and D2 neurons respond simultaneously to both types of stimuli, albeit through distinct mechanisms. The study highlights the role of these neurons in shaping learning processes and memory reclassification based on past experiences.

The researchers observed that during associative learning—when a stimulus is linked with either reward or punishment—both neuron populations are activated. However, their roles differ significantly. For instance, when adapting to changes in stimulus consequences, such as eliminating the unpleasant effects of a previously aversive event, D2 neurons play a crucial part in extinguishing negative associations. This insight could pave the way for innovative treatments targeting anxiety-related conditions.

Furthermore, the study underscores the brain's remarkable ability to reinterpret external signals depending on individual contexts and memories. As explained by Carina Soares-Cunha, while certain sounds may evoke joy for some, they can trigger distressing flashbacks for others, emphasizing the complexity of neuronal circuits involved in this adaptive process.

This collaborative work, involving institutions like Columbia University and the Allen Institute, was supported by organizations including the BIAL Foundation and the European Research Council. By unraveling the intricate interplay of D1 and D2 neurons, the research not only advances neuroscience but also offers hope for addressing mental health challenges more effectively.