Functional organization of spatial frequency tuning in macaque V1 revealed with two-photon calcium imaging


Guan S., Ju N., Tao L., Tang S., Yu C.

PROGRESS IN NEUROBIOLOGY, vol.205, 2021 (Peer-Reviewed Journal) identifier identifier identifier

  • Publication Type: Article / Review
  • Volume: 205
  • Publication Date: 2021
  • Doi Number: 10.1016/j.pneurobio.2021.102120
  • Journal Name: PROGRESS IN NEUROBIOLOGY
  • Journal Indexes: Science Citation Index Expanded, Scopus, Academic Search Premier, Animal Behavior Abstracts, EMBASE, MEDLINE
  • Keywords: Primary visual cortex, Spatial frequency, Functional map, Two-photon imaging, Macaque, PRIMARY VISUAL-CORTEX, CONTRAST SENSITIVITY, MICRO-ORGANIZATION, RECEPTIVE-FIELDS, NEURONS, ORIENTATION, MAPS, ARCHITECTURE, SELECTIVITY, ANATOMY

Abstract

V1 neurons are functionally organized in orientation columns in primates. Whether spatial frequency (SF) columns also exist is less clear because mixed results have been reported. A definitive solution would be SF functional maps at single-neuron resolution. Here we used two-photon calcium imaging to construct first cellular SF maps in V1 superficial layers of five awake fixating macaques, and studied SF functional organization properties and neuronal tuning characteristics. The SF maps (850 x 850 mu m2) showed weak horizontal SF clustering (median clustering index = 1.43 vs. unity baseline), about one sixth as strong as orientation clustering in the same sets of neurons, which argues against a meaningful orthogonal relationship between orientation and SF functional maps. These maps also displayed nearly absent vertical SF clustering between two cortical depths (150 & 300 mu m), indicating a lack of SF columnar structures within the superficial layers. The underlying causes might be that most neurons were tuned to a narrow two-octave range of medium frequencies, and many neurons with different SF preferences were often spatially mixed, which disallowed finer grouping of SF tuning. In addition, individual SF tuning functions were often asymmetric, having wider lower frequency branches, which may help encode low SF information for later decoding.