Assigning valence, appeal or aversion, to gustatory stimuli and relaying it to higher-order brain regions to guide flexible behaviors is crucial to survival. Yet the neural circuit that transforms gustatory input into motivationally relevant signals remains poorly defined in any model system. In Drosophila melanogaster, substantial progress has been made in mapping the sensorimotor pathway for feeding and the architecture of the dopaminergic reinforcement system. However, where and how valence is first assigned to a taste has long been a mystery. Here, we identified a pair of subesophageal zone interneurons in Drosophila, termed Fox, that impart positive valence to sweet taste and convey this signal to the mushroom body, the fly's associative learning center. We show that Fox neuron activity is necessary and sufficient to drive appetitive behaviors and can override a tastant's intrinsic valence without impairing taste quality discrimination. Furthermore, Fox neurons transmit the positive valence to specific dopaminergic neurons that mediate appetitive memory formation. Our findings reveal a circuit mechanism that transforms sweet sensation into a reinforcing signal to support learned sugar responses. The Fox neurons exhibit a convergent-divergent "hourglass" circuit motif, acting as a bottleneck for valence assignment and distributing motivational signals to higher-order centers. This architecture confers both robustness and flexibility in reward processing: an organizational principle that may generalize across species. ### Competing Interest Statement The authors have declared no competing interest. National Institute of General Medical Sciences, https://ror.org/04q48ey07, R35GM147504, GM104941, GM103446
📣 Now published:
"Auditory-motor adaptation and de-adaptation for speech depend more on time in the new environment than on the amount of practice"
https://www.nature.com/articles/s44271-025-00304-8
#MotorLearning #Adaptation #Speech #Sensorimotor #MotorControl
Speech auditory-motor adaptation to a formant-shift perturbation and de-adaptation after the perturbation is removed both depend more on total amount of time spent in the corresponding environment than on the number of practice trials.
Actin-based cell motility drives many neurodevelopmental events including guided axonal growth. Fascin is a major family of F-actin bundling proteins, but its role in axon development and brain wiring is unknown. Here, we report that fascin is required for axon development, brain wiring and function. We show that fascin is enriched in the motile filopodia of axonal growth cones and its inhibition impairs axonal extension and branching of hippocampal neurons in culture. We next provide evidence that fascin is essential for axon development and brain wiring using Drosophila melanogaster as an in vivo model. Drosophila express a single ortholog of mammalian fascin called Singed (SN), which is highly expressed in the mushroom body (MB) of the central nervous system. We observe that loss of SN results in drastic MB disruption, highlighted by α- and β-lobe defects that are consistent with altered axonal guidance. SN-null flies also exhibit defective sensorimotor behaviors as assessed by the negative geotaxis assay. MB-specific expression of SN in SN-null flies rescues MB structure and sensorimotor deficits, indicating that SN functions autonomously in MB neurons. Together, our data from primary neuronal culture and in vivo models highlight a critical role for fascin in brain development and function. Significance statement ### Competing Interest Statement The authors have declared no competing interest.
What are the neural correlates of the multiple competing processes that occur simultaneously during sensorimotor learning? This study reveals three distinct neural connectivity patterns with the motor cortex that are associated with implicit learning, explicit learning, and the tracking of performance.
flypapers
Max Lab UW Seattle
PLOS Biology