Face Repetition Probability Does Not Affect Repetition Suppression in Macaque Inferotemporal Cortex.

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Primate Vision

Background:

• Repetition suppression, reduced neural activity for repeated stimuli, is often explained by bottom-up adaptation or top-down predictive coding.
• Human fMRI studies suggest repetition suppression magnitude is influenced by repetition probability, supporting the perceptual expectation hypothesis.
• Previous macaque studies found no repetition probability effect in inferior temporal (IT) cortex, but used unfamiliar stimuli and lacked attention demands.

Purpose of the Study:

• To investigate if repetition probability modulates neural responses in the macaque IT cortex for familiar stimuli (faces) under attention.
• To test the perceptual expectation account of repetition suppression in a controlled primate model.
• To reconcile conflicting findings between human fMRI and macaque electrophysiology regarding repetition suppression.

Main Methods:

• Simultaneous recording of spiking activity and local field potentials (LFPs) in face-responsive regions (ML) of two macaques (one male, one female).
• Presentation of face stimuli with varying repetition probabilities.
• Monkeys were trained to attend to stimulus content, and behavioral decisions were recorded.

Main Results:

• Significant repetition suppression was observed in both spiking activity and high gamma-band LFPs for faces.
• No effect of repetition probability on neural responses was found, even when repetitions were task-relevant and influenced behavior.
• Neural responses in the macaque IT cortex did not show the repetition probability effect seen in human fMRI studies.

Conclusions:

• Repetition suppression in the macaque IT cortex for faces is not modulated by repetition probability, even under attentive conditions.
• These findings challenge the generalizability of the perceptual expectation account of repetition suppression.
• The study suggests that mechanisms other than fulfilled perceptual expectations may underlie repetition suppression in this brain region.