Modelled Mushroom Body Output Neuron Predicts Appetitive Behavior
(A) Three experimental protocols differing for CS/US inter stimulus interval (ISI) were used for training the model (B-D) and for behavioural measurements of the proboscis extension reflex conditioning (E,F). Trained simulated MBONs, as well as conditioned honey bees were tested against the CS (blue) and a novel odorant (NOd, green).
(B) Time course of action potential (AP) probability of a trained MBON upon stimulation with the CS (blue) or with the novel odorant (NOd, green). Olfactory learning was modelled according to backward (top), early (middle) and delay (bottom) CS/US contingencies. Glomerular responses for 8 bees to 1-hexanol and peppermint oil were used alternatively as CS and NOd. Data for responses to CS and NOd were pooled together (n = 16 traces for each condition. Blue traces, CS; green traces, NOd). The thick trace shows the average AP probability profile; dotted vertical lines delimit the stimulation interval; grey bar delimits the simulated learning window.
(C) Distribution of the mean values of traces in (B) during CS and NOd stimulation. Because appetitive learning produces a decrease in MBON firing rate, the complementary value of the probability fraction is used as a proxy for a learned appetitive response (pbackward = 0.06; pearly = 1.41*10-6; pdelay = 1.04*10-5; Kruskal-Wallis statistical test; n = 16).
(D) Latency of 90% of minimal MBON activity in response to the CS+ for early and delay conditioning protocols (Kruskal-Wallis test for difference in distribution across protocols, p = 0.002; Barlett’s test for variance difference across protocols, p = 0.0109).
(E) Memory retention test of honey bees 1 h after absolute conditioning. Bars indicate the percentage of individuals showing proboscis extension reflex (PER) when presented with the conditioned or the novel odorant. Error bars indicate 95% confidence intervals. (Responses to the CS/NOd were compared with a McNemar test for binomial distribution; pearly = 0.003, pdelay = 0.004)
(F) Latency of the PER to the conditioned stimulus at the 1 h memory retention test (Kruskal-Wallis test for difference in distribution across protocols, p = 0.036; Barlett’s test for variance difference across protocols, p = 5*10-6; nearly = 26; ndelay = 20).