Misalignment Between Backpropagation and the Hierarchy of Brain Responses to Images
arXiv:2605.28693 · 2026
Backpropagation is the core learning mechanism of deep networks, but whether the brain implements anything like it remains debated. Using fMRI and MEG recordings of humans viewing natural images, we extend standard encoding analyses from forward activations to backpropagated gradients. Across DINOv3 and eight other vision models, gradients reliably predict cortical activity in higher-level visual areas at later latencies — yet their spatial and temporal organisation diverges from a biologically plausible backpropagation. Brains and deep networks may share representations, but likely learn them through fundamentally different mechanisms.