Cortical fields participating in spatial frequency and orientation discrimination: Functinal anatomy by positron emission tomography

With the purpose of localising those anatomical structures participating in the discrimination of spatial frequencies and orientations of gratings, we measured regional cerebral blood flow (rCBF) changes with positron emission tomography (PET) and 15 O‐butanol as tracer in ten healthy young male volunteers. The subjects performed two‐alterative forced‐choice discriminations of pairs of squarewave gratings regarding their spatial frequencies or orientations (spatial frequency and orientation tasks) or pairs of a grating and a two‐dimensional random noise pattern regarding the presence or absence of grating pattern (reference task). In both the spatial frequency and orientation discrimination tasks a widely distributed network of functional fields is activated in the occipital, temporal, parietal, and frontal cortices and in the cerebellum. Spatial frequency discrimination required the activation of more cortical fields than orientation discrimination, and whereas the total volume of activated fields in temporal and frontal lobes were similar in the two tasks, the volumes of activated fields in the occipital lobes as well as in the parietal lobes were about two and a half times larger in spatial frequency discrimination than in orientation discrimination. The two networks of cortical fields were partially overlapping in the two tasks. The findings indicate that the discrimination of spatial frequency and orientation signals engages functional networks of cortical fields widely distributed in the human brain. Whereas both the occipito‐temporal and occipito‐parietal visual pathways are involved in both tasks, the processing and analysis of spatial frequency information activates occipital and parietal lobe regions more extensively than those of orientation information. © 1995 Wiley‐Liss, Inc.