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Abstract
Understanding how single neurons and small circuits integrate information is essential for uncovering the neural basis of cognition. The retinal direction‑selective circuit, centered on direction‑selective ganglion cells (DSGCs), provides a powerful model for studying these computations, yet key mechanisms have remained unresolved. Using in‑vitro patch‑clamp recordings and two‑photon calcium imaging, we demonstrate that DSGCs rely on orthograde dendritic spikes to locally integrate excitatory and inhibitory inputs and enhance direction selectivity—the first evidence of a defined computational role for dendritic spiking in these cells. We also show that starburst amacrine cells (SBACs), the source of directional inhibition, receive directionally biased inputs that are amplified by tetrodotoxin‑resistant sodium channels. These findings indicate that direction selectivity arises presynaptically within SBACs and is boosted by non‑typical sodium conductances, revealing new mechanisms underlying directional computation in the retina.