Inferring learning rules from distribution of firing rates in cortical neurons

Information about external stimuli is thought to be stored in cortical circuits through experience-dependent modifications of synaptic connectivity. These modifications of network connectivity should lead to changes in neuronal activity, as a particular stimulus is repeatedly encountered. Here, we ask what plasticity rules are consistent with the differences in the statistics of the visual response to novel and familiar stimuli in inferior temporal cortex, an area underlying visual object recognition. We introduce a method that allows inferring the dependence of the ‘learning rule’ on post-synaptic firing rate, and show that the inferred learning rule exhibits depression for low post-synaptic rates and potentiation for high rates. The threshold separating depression from potentiation is strongly correlated with both mean and standard deviation of the firing rate distribution. Finally, we show that network models implementing a rule extracted from data show stable learning dynamics, and lead to sparser representations of stimuli.