Visual resolution and sensitivity of single cells in the primary visual cortex (V1) of a nocturnal primate (bush baby): correlations with cortical layers and cytochrome oxidase patterns

Abstract

1. This study describes the response properties of V1 cortical cells in a nocturnal primate and examines the receptive field organization of these cells in relationship to anatomically defined layers and cytochrome oxidase (CO) rich blobs and CO poor interblob compartments. Visual resolution and contrast sensitivity are consistent with other physiological and behavioral measures in this species. Comparisons are made with response properties of the same zones in macaque monkey, as well as of area 17 of a distantly related species (cat) that also occupies a nocturnal niche. 2. The responses of single cells to drifting sinusoidal gratings were recorded in V1 (striate cortex) of anesthetized, paralyzed bush babies (Galago crassicaudatus). Cells tended to be grouped with respect to ocular dominance, orientation preference, and direction selectivity. There was a high proportion of monocularly driven cells as in macaque monkey. Only 6% of the cells were nonoriented. These were poorly tuned complex cells and bore no resemblance to nonoriented lateral geniculate nucleus (LGN)-like cells reported in layer IV of macaque monkeys. Unidirectional cells were most frequently encountered in cortical layers that receive input from the magnocellular layers of the LGN. 3. Cells were classified as simple (31%) or complex (69%) according to standard criteria. Simple cells were significantly more narrowly tuned than complex cells for both orientation and spatial frequency. Complex cells had significantly higher average optimal spatial frequencies and spatial frequency cutoffs than simple cells. Contrast sensitivity of simple and complex cells averaged 38 and 34, respectively. Spatial resolution and sensitivity of these cells matches behavioral measures in bush baby. The spatial and temporal resolution of bush baby cells are similar to those of cats, which is likely related to the nocturnal niche of both species. 4. Cells in supragranular (I-III) and infragranular (V, VI) layers differed significantly in their response characteristics. The cells in the supragranular layers had significantly higher contrast sensitivity than did the cells in the infragranular layers. Cells in the supragranular layers likewise had higher temporal frequency cutoffs, significantly lower optimal spatial frequencies, lower spatial frequency cutoffs, and tighter orientation tuning than did cells in the infragranular layers. 5. Properties of cells in individual layers and CO blob and interblob compartments also showed differentiation. Layer III had the narrowest orientation and spatial frequency tuning with the tightest tuning in layer IIIC (IVB).(ABSTRACT TRUNCATED AT 400 WORDS)