Cellular precision of orientation and spatial frequency maps in macaque V1

Abstract

Functional organization of neuronal response properties along the surface of the neocortex is a fundamental guiding principle of neural computation in the brain. Despite this importance, the cellular precision of functional maps is still largely unknown. We address the challenge by using two-photon calcium imaging to measure cell-specific orientation and spatial frequency (SF) responses across fields of macaque V1 superficial layers. The cellular orientation maps confirm iso-orientation domains, but rarely show pinwheels. Pinwheels obtained through conventional Gaussian smoothing and vector summation of orientation responses mostly overlap with blood vessel regions, suggesting false singularities. Cellular SF maps clarify existing controversies by showing weak iso-frequency clusters, which also suggests a weak geometric relationship between orientation and SF maps. Most neurons are tuned to medium frequencies, but the tuning functions are often asymmetric with a wider low- or high-frequency branch, which may help encode low or high SF information for later decoding.