@article {68008, title = {Hierarchical architecture of dopaminergic circuits enables second-order conditioning in Drosophila}, journal = {eLife}, year = {2023}, month = {2023 Jan 24}, abstract = {

Dopaminergic neurons with distinct projection patterns and physiological properties compose memory subsystems in a brain. However, it is poorly understood whether or how they interact during complex learning. Here, we identify a feedforward circuit formed between dopamine subsystems and show that it is essential for second-order conditioning, an ethologically important form of higher-order associative learning. The\ Drosophila\ mushroom body comprises a series of dopaminergic compartments, each of which exhibits distinct memory dynamics. We find that a slow and stable memory compartment can serve as an effective {\textquotedblleft}teacher{\textquotedblright} by instructing other faster and transient memory compartments via a single key interneuron, which we identify by connectome analysis and neurotransmitter prediction. This excitatory interneuron acquires enhanced response to reward-predicting odor after first-order conditioning and, upon activation, evokes dopamine release in the {\textquotedblleft}student{\textquotedblright} compartments. These hierarchical connections between dopamine subsystems explain distinct properties of first- and second-order memory long known by behavioral psychologists.

}, doi = {10.7554/eLife.79042}, url = {https://doi.org/10.7554/eLife.79042}, author = {Daichi Yamada and Daniel Bushey and Li Feng and Karen Hibbard and Megan Sammons and Jan Funke and Ashok Litwin-Kumar and Toshihide Hige and Yoshinori Aso} } @article {68571, title = {Neural circuit mechanisms for transforming learned olfactory valences into wind-oriented movement}, journal = {eLife}, year = {2023}, month = {2023 Sep 18}, abstract = {

How memories are used by the brain to guide future action is poorly understood. In olfactory associative learning in Drosophila, multiple compartments of the mushroom body act in parallel to assign valence to a stimulus. Here, we show that appetitive memories stored in different compartments induce different levels of upwind locomotion. Using a photoactivation screen of a new collection of split-GAL4 drivers and EM connectomics, we identified a cluster of neurons postsynaptic to the mushroom body output neurons (MBONs) that can trigger robust upwind steering. These UpWind Neurons (UpWiNs) integrate inhibitory and excitatory synaptic inputs from MBONs of appetitive and aversive memory compartments, respectively. After training, disinhibition from the appetitive-memory MBONs enhances the response of UpWiNs to reward-predicting odors. Blocking UpWiNs impaired appetitive memory and reduced upwind locomotion during retrieval. Photoactivation of UpWiNs also increased the chance of returning to a location where activation was initiated, suggesting an additional role in olfactory navigation. Thus, our results provide insight into how learned abstract valences are gradually transformed into concrete memory-driven actions through divergent and convergent networks, a neuronal architecture that is commonly found in the vertebrate and invertebrate brains.

}, doi = {10.7554/eLife.85756}, url = {https://doi.org/10.7554/eLife.85756}, author = {Yoshinori Aso and Daichi Yamada and Daniel Bushey and Karen Hibbard and Megan Sammons and Hideo Otsuna and Yichun Shuai and Toshihide Hige} }