Dissociable neural networks for processing fearful bodily expressions at different spatial frequencies

The human brain processes visual input across various spatial frequency (SF) ranges to extract emotional cues. Prior studies have extensively explored SF processing in facial expressions, yielding partly conflicting results. However, bodily expressions, which provide complementary emotional and survival-relevant cues, remain unexplored. We investigated the neural mechanisms underlying the processing of low (LSF), high (HSF), and broad spatial frequency (BSF) components in fearful versus neutral bodily postures. Using functional Magnetic Resonance Imaging, we examined brain activity in 20 participants viewing SF-filtered images of bodily expressions in a semi-passive task. A multivariate "searchlight" analysis based on Multi-Voxel Pattern Analysis was employed to decode the non-linear activation patterns associated with each SF band. Our findings reveal that SF processing engages distinct neural networks in response to fearful bodily expressions. BSF stimuli activated a widespread network, including the amygdala, pulvinar, frontal, and temporal cortices. These findings suggest a general threat-detection system integrating information across all SFs. HSF stimuli engaged cortical regions associated with detailed emotional evaluation and motor planning, such as the orbitofrontal cortex, anterior cingulate cortex, and premotor areas, suggesting that processing fine-grained fear cues involves computationally demanding networks related to emotional resonance and action preparation. In contrast, LSF stimuli primarily activated motor-preparatory regions linked to rapid, action-oriented responses, highlighting the brain prioritization of quick readiness to low-detail threats. Notably, the amygdala showed no SF selectivity, supporting its role as a generalized "relevance detector" in emotional processing. The present study demonstrates that the brain flexibly adapts its SF processing strategy based on the visual details available in fearful bodily expressions, underscoring the complexity and adaptability of emotional processing from bodily signals.