Visual Stimulus-Specific Adaptation in the Avian Imc and Its Effect on Target Decoding Performance

Abstract

Simple Summary Stimulus-specific adaptation (SSA) is a neural mechanism that selectively reduces responses to repeated, predictable stimuli while preserving sensitivity to novel, unexpected ones, thereby optimizing sensory processing. Although extensively studied in mammals, SSA in the avian visual system remains poorly understood. This study investigated visual SSA in the nucleus isthmi pars magnocellularis (Imc), a key inhibitory structure in the pigeon midbrain attention network. We simultaneously recorded spike firing rates and local field potentials (LFPs) while presenting moving dot stimuli in alternating directions. Our results suggest that Imc neurons exhibit SSA: responses to repeated stimuli progressively declined but recovered upon direction change, with gamma-band LFP energy showing stronger adaptation than spike firing rates. Using machine learning decoders, we found that before adaptation, spike rates effectively encoded motion direction. However, SSA may impair the encoding of directional information across all signal types, reducing decoding accuracy to near chance levels. These findings indicate that gamma-band LFP primarily reflects stimulus salience, while spikes encode both identity and salience. This study advances our understanding of how evolutionarily conserved adaptation mechanisms balance sensitivity to novelty and suppression of redundancy in the avian brain.