Visual cortex
The region at the back of the brain that processes vision. In aphantasia it is structurally normal but less strongly recruited when a person tries to form a mental image.
The visual cortex sits in the occipital lobe and is organised hierarchically — the primary layer (V1) receives input from the eyes; higher areas (V2, V4, inferotemporal cortex) extract colour, motion, shape, and object identity. The same hardware is re-used when we imagine things: mental imagery recruits much of the same cortex as actual seeing.
In aphantasia the visual cortex itself appears structurally normal. What differs is how strongly it is called upon during voluntary imagery. The Liu and Bartolomeo 2025 framework argues that the frontal-parietal control networks in aphantasic brains are not recruiting the visual cortex top-down in the way typical imagers do — the hardware is present but the lines of communication into it are quieter. This is why people with aphantasia can see the world perfectly well but cannot picture it with their eyes closed.