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

SSA serves as a fundamental mechanism for optimizing sensory processing by selectively reducing neural responses to prevalent stimuli. While well-characterized in mammals, its evolutionary conservation and functional impact in avian species, particularly on neural coding and decoding, remain largely unexplored. Here, we investigated visual SSA in the avian nucleus Imc by simultaneously analyzing LFP spectral power and single-unit spiking activity in pigeons. During exposure to constant-order moving dot stimuli, repeated presentations induced sustained suppression of both low-gamma-band (31-70 Hz) and high-gamma (71-120 Hz) LFP power, which recovered upon novel stimulus introduction. A similar adaptive pattern was observed in spike firing rates. Stimulus-specific indices revealed that over 80% of Imc neurons exhibited SSA in gamma-band LFP energy, compared to 65.6% based on spike rates. To quantify the functional consequence, we employed machine learning decoders to assess the discrimination of moving targets. Prior to adaptation, decoding based on the spike rate achieved up to 81.8% accuracy, outperforming LFP-based decoding. Critically, SSA may impair the encoding of directional information in sustained responses, reducing the decoding accuracy of classifiers using spike rates, LFP features, or their combinations to near-baseline levels. These findings indicate that gamma-band LFP energy in the Imc primarily reflects stimulus salience, whereas spike rates concurrently encode both identity and salience. This study elucidates the differential roles SSA and its effect on multiplexed neural codes, advancing the understanding of invariant visual representation in the avian brain.