DIFFERENTIAL CODING OF ABSOLUTE AND RELATIVE AVERSIVE VALUE IN THE DROSOPHILA BRAIN
A new study from Emmanuel Perisse’s team at the IGF reveals new mechanisms of value coding in the fly brain.
Value-based decisions require animals to make choices between several options based on a prediction of their relative subjective value learned through prior experience. Associative learning provides a means to assign absolute (good or bad) values to experience that can be used to guide future approach or avoidance behaviors. During learning, animals can also compare the value of their current experience with that of prior knowledge and assign a relative value (better or worse) between these experiences to promote more accurate economic-based choices. Notwithstanding that a substantial body of research has investigated mechanisms for relative reward-value coding, we know less about how relative aversive value is computed during learning to guide appropriate value-based decisions.
To address this question, Emmanuel Perisse’s team at IGF, in collaboration with the University of Oxford, UK and the FMI, Basel Switzerland, used state-of-the-art combination of genetics, behavioral and in vivo calcium imaging approaches in Drosophila to investigate the neural mechanisms of absolute and relative aversive value coding. Their results revealed a crucial role of specific dopaminergic neurons relaying punishment in assigning absolute aversive value (intensity of aversiveness) to odors during learning. They also showed that other dopaminergic neurons involved in reward processing compare neuronal plasticity related to different aversive experiences to signal a relative aversive “better than” aversive value during learning. Flies then use these absolute and relative aversive value information during decision-making to choose the best option.
This work highlights a new mechanic understanding of the valuation system altered in many neurological pathologies such as addiction and Parkinson’s disease.
Top. In the fly learning and memory center, the Mushroom body (MB), distinct dopaminergic (DA) neurons relaying punishment respond differently to specific punishment (i.e. electric shock intensities). Learning-dependent plasticity (following odor-shock association) measured in the MB output neurons is scaled to the intensity of the punishment and specific to MB compartments. Bottom. Comparing learning-dependent plasticity of different aversive experiences (odor A + high shock vs odor B + low shock) in the MB output circuits (g2a´1) activates specific DA neurons relaying reward (b´2ag5n) to signal a relative “better than” aversive value.
