Modality-invariant audio-visual association coding in crow endbrain neurons

Single neuron activity in the corvid nidopallium caudolaterale (NCL), the supposed avian functional analog of the prefrontal cortex, represents associations of auditory with visual stimuli. This is of high adaptive value for songbirds that need to rely on audio-visual associations to communicate, find a mate or escape predators. However, it remains unclear whether NCL neurons can represent cross-modal associations in a modality invariant, abstract fashion. To dissociate between modality-dependent and modality-invariant NCL activity, we trained two crows to match auditory sample cues with visual test stimuli, and vice versa, across a temporal memory delay. During sample presentation, NCL activity selectively encoded associations in a modality invariant fashion. During the delay, we observed subject specific, population-level coding biases in NCL activity. Despite of these biases, task relevant information could be decoded equally well from either subject's neuronal delay activity. Decoding success was facilitated by many mixed selectivity neurons, which mediated high dimensional representations of task variables on the NCL population level. These results parallel findings from the mammalian PFC, suggesting common mechanisms responsible for the adaptability of multimodal association areas across taxa.