FUNCTIONAL-ORGANIZATION OF OWL MONKEY LATERAL GENICULATE-NUCLEUS AND VISUAL-CORTEX

The nocturnal, New World owl monkey (Aotus trivirgatus) has a rod-domi nated retina containing only a single cone type, supporting only the m ost rudimentary color vision. However, it does have well-developed mag nocellular (M) and parvocellular (P) retinostriate pathways and stria te cortical architecture [as defined by the pattern of staining for th e activity-dependent marker cytochrome oxidase (CO)I similar to that s een in diurnal primates. We recorded from single neu rons in anestheti zed, paralyzed owl monkeys using drifting, luminance-modulated sinusoi dal gratings, comparing receptive field properties of M and P neurons in the lateral geniculate nucleus and in V1 neurons assigned to CO ''b lob,'' ''edge,'' and ''interblob'' regions and across layers. Tested w ith achromatic stimuli, the receptive field propel-ties of M and P neu rons resembled those reported for other primates. The contrast sensiti vity of P cells in the owl monkey was similar to that of P cells in th e macaque, but the contrast sensitivities of M cells in the owl monkey were markedly lower than those in the macaque. We found no difference s in eye dominance, orientation, or spatial frequency tuning, temporal frequency tuning, or contrast response for V1 neurons assigned to dif ferent CO compartments; we did find fewer direction-selective cells in blobs than in other compartments. We noticed laminar differences in s ome receptive field properties. Cells in the supragranular layers pref erred higher spatial and lower temporal frequencies and had lower cont rast sensitivity than did cells in the granular and infragranular laye rs. Our data suggest that the receptive field properties across functi onal compartments in V1 are quite homogeneous, inconsistent with the n otion that CO blobs anatomically segregate signals from different func tional ''streams.''