Abstract
In reversal learning, subjects first learn to respond to a reinforced stimulus A and not to a non-reinforced stimulus B (A+ vs. B−) and then have to learn the opposite when stimulus contingencies are reversed (A− vs. B+). This change in stimulus valence generates a transitory ambiguity at the level of stimulus outcome that needs to be overcome to solve the second discrimination. Honey bees (Apis mellifera) efficiently master reversal learning in the olfactory domain. The mushroom bodies (MBs), higher-order structures of the insect brain, are required to solve this task. Here we aimed at uncovering the neural circuits facilitating reversal learning in honey bees. We trained bees using the olfactory conditioning of the proboscis extension reflex (PER) coupled with localized pharmacological inhibition of Gamma-AminoButyric Acid (GABA)ergic signaling in the MBs. We show that inhibition of ionotropic but not metabotropic GABAergic signaling into the MB calyces impairs reversal learning, but leaves intact the capacity to perform two consecutive elemental olfactory discriminations with ambiguity of stimulus valence. On the contrary, inhibition of ionotropic GABAergic signaling into the MB lobes had no effect on reversal learning. Our results are thus consistent with a specific requirement of the feedback neurons (FNs) providing ionotropic GABAergic signaling from the MB lobes to the calyces for counteracting ambiguity of stimulus valence in reversal learning.
Highlights
Associative learning may be divided in two main categories: (i) elemental learning, in which linear and unambiguous links are established between events (Rescorla and Wagner, 1972); and (ii) non-elemental learning, in which the links established between events are ambiguous and non-linear (Rudy and Sutherland, 1989; Sutherland and Rudy, 1989)
A comparison between the phosphate buffer saline solution (PBS) and the PTX groups at this stage showed no significant difference in their acquisition performances confirming that the learning of the first-phase discrimination was identical between groups prior to drug injection
CGP54626 was not used in this experiment given its failure to block reversal learning
Summary
Associative learning may be divided in two main categories: (i) elemental learning, in which linear and unambiguous links are established between events (Rescorla and Wagner, 1972); and (ii) non-elemental learning, in which the links established between events are ambiguous and non-linear (Rudy and Sutherland, 1989; Sutherland and Rudy, 1989). In Pavlovian learning, for instance, two levels of stimulus ambiguity are represented by differential and reversal conditioning. Two conditioned stimuli (CS) A and B are unambiguously associated. Reversal learning in honey bees with an unconditioned stimulus (US) and with the absence of US, respectively (A+ vs B−). A first differential conditioning phase (A+ vs B−) is followed by a second phase, in which stimulus contingencies are reversed (A− vs B+). The addition of the second phase generates a transient ambiguity of stimulus outcome (A+ → A− and B− → B+) that needs to be overcome
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
