Fig. 3: Stereotypy does not require learning.

a, b Comparison of PRED stereotypy with correlation stereotypy in the responses of the readout neuron in the simulations of the untrained (a) or trained (b) piriform network using code provided by Schaffer et al.²⁴. c, d Stereotypy in the simulations of the untrained piriform network, with and without the weight normalization step calculated using both correlation (c) and PRED (d) metrics. The three different colors represent simulations with different levels of overlap among the olfactory bulb responses to odors as described by Schaffer et al.: 70% overlap (green), 30% overlap (blue) and 0% overlap (gray). a–d have 18 data points each (6 iterations × 3 sets of odors). e Stereotypy in MBON response reduces with the learning rate, as seen in simulations with 100 odors and 2 individuals. Learning of an odor resulted in either increasing or decreasing the number of synapses between the MBON and the KCs activated by that odor. Half of the odors, selected randomly for each individual, were learnt sequentially, and each learning event resulted in increase or decrease in synapses with equal probability. When the synapses were increased, of all the KCs that were activated by the learned odor and were not connected to the MBON, a certain fraction (indicated by the learning rate) were connected to the MBON. When the synapses were reduced, of all the KCs that were activated by the learned odor and were connected to the MBON, the same fraction were disconnected from the MBON. The MBON responses for both individuals were recalculated after modifying the synapses, n = 100 iterations. Error bars represent s.e.m. f Analytical model proved the existence of stereotypy in absence of learning. Plot of stereotypy versus the number of KCs suggested a dependence of stereotypy on the size of the network, as later seen in the simulations (compare to Fig. 6d). Each value is calculated using the formulae derived in the analytical model (see Supplementary equations). Arrow indicates the default value (matching the Drosophila system).