The brains of vertebrates, including humans, have two hemispheres, and the left and right hemispheres are structurally symmetrical. Due to the fact that a large number of neural connections are mainly between neurons in the same hemisphere of the brain, research on the function of brain neural connections has long focused on connections within the same hemisphere, while neglecting the role of neural connections between two hemispheres. The reporter learned that Professor Liu Xing and Professor Ma Lan from Fudan University collaborated to study and found that the basal lateral amygdala (BLA) neurons in the mouse brain project to the nucleus accumbens (NAc) in the contralateral hemisphere through the anterior commissure connecting the left and right hemispheres. This cross hemisphere neural circuit has the opposite function to the ipsilateral neural circuit, mediating the generation of negative emotions such as fear, disgust, and avoidance behavior. Recently, this discovery was published in the journal Science under the title "The neural circuit encoding negative emotional valence from the amygdala to the contralateral hemisphere's nucleus accumbens". Liu Xing introduced that after cutting off the anterior commissure, mice showed impaired aversion and avoidance behavior. Through techniques such as brain transparency 3D imaging, neuronal transcriptome sequencing, anterograde and retrograde neural tracing fluorescence labeling, the research team observed the presence of two different groups of neurons in the BLA brain region, which receive neural innervation from different brain regions and project to the ipsilateral or contralateral hemisphere NAc, respectively. BLA is a critical brain area that controls emotional responses (fear, disgust, avoidance, etc.), learning and memory, social interaction, and other functions, while NAc plays a key role in reward, happiness, addiction, emotional regulation, and other aspects. By using methods such as implanting optical fibers into the mouse brain to record neuronal activity signals in real-time and using optogenetics for real-time specific intervention, the research team found that rewarding stimuli such as consuming sweet water and socializing with the opposite sex selectively activated the neural projection of BLA to the NAc in the ipsilateral hemisphere, while aversive stimuli such as consuming bitter water and facing danger selectively activated the neural projection of BLA to the NAc in the contralateral hemisphere. Further research has shown that the neural projections from BLA to the ipsilateral hemisphere NAc mainly innervate D1 type neurons, increasing dopamine release in NAc and promoting the formation of positive reward emotions; The neural projections from BLA to the contralateral hemisphere NAc mainly innervate D2 type neurons, reducing dopamine levels in NAc and leading to the formation of negative aversive emotions and related memories. This research achievement distinguishes the different roles of BLA projection to the ipsilateral and contralateral hemispheres in emotion and related memory formation, and discovers the key role of BLA projection to the contralateral NAc nerve in encoding negative emotions and triggering avoidance behavior, revealing an important function of neural connections across hemispheres. (New Society)