TOOL USE RELATED NEURONAL ACTIVITY IN THE CROW NIDOPALLIUM CAUDOLATERALE

Flexible tool use requires the skill to sequentially handle and use a tool accurately, while also being able to adapt as needed, but how the brain achieves this balance between stability and flexibility remains unknown. Here, we trained carrion crows (Corvus corone) to use a beak-held stick-tool to retrieve food pellets from beneath a Plexiglas plate in a controlled laboratory setting. We found that their complex, tool use related action sequences are modular and composed of 15 discrete “action syllables”, which we identified with a custom, napari-based graphical user interface. These annotated data were subsequently used as a training data set for an action segmentation transformer model (ASFormer), which leverages video and kinematic features to automatically identify action syllable boundaries. Equipped with this method, we asked if and how action syllables are represented in the crow nidopallium caudolaterale (NCL)—a highly integrative, multimodal premotor structure in the crow telencephalon. Using 64-channel silicon probes, we recorded the activity of NCL neurons in tool-using crows and found that approximately 20% of single units were reliably modulated by the occurrence of at least one action syllable. Some low firing rate neurons were almost exclusively active during a single syllable, whereas most high firing rate neurons were sharply modulated at the boundaries of multiple action syllables. These findings are consistent with the idea that NCL functions as a high-level premotor structure within the avian general motor system and provide novel neuronal correlates of complex non-vocal action sequencing in a songbird.