DISTRIBUTION OF NEURONS PROJECTING TO THE SUPERIOR COLLICULUS CORRELATES WITH THICK CYTOCHROME-OXIDASE STRIPES IN MACAQUE VISUAL AREA V2

In visual area V2 of macaque monkeys, cytochrome oxidase (CO) histoche mistry reveals a pattern of alternating densely labeled thick and thin stripe compartments and lightly labeled interstripe compartments. Thi s modular organization has been associated with functionally separate pathways in the visual system. We examined this idea further by compar ing the pattern of CO stripes with the distribution of neurons in V2 t hat project to the superior colliculus. Visually evoked activity in th e superior colliculus is known to be greatly reduced by blocking magno cellular but not parvocellular layers of the lateral geniculate nucleu s (LGN). From previous evidence that V2 thick stripes are closely asso ciated with the magnocellular LGN pathway, we predicted that a signifi cant proportion of V2 neurons projecting to the superior colliculus wo uld reside in the thick stripes. To test this prediction, the tangenti al distribution of retrogradely labeled corticotectal cells in V2 was compared with the pattern of CO stripes. We found that neurons project ing to the superior colliculus accumulated preferentially into band-li ke clusters that were in alignment with alternate CO dense stripes. Th ese stripes were identified as thick stripes on the basis of their phy sical appearance and/or by their affinity to the monoclonal antibody C at-301. A significantly smaller proportion of labeled cells was observ ed in thin and interstripe compartments. These data provide further ev idence that the spatial distribution of subcortically projecting neuro ns can correlate with the internal modular organization of visual area s. Moreover, they support the notion that CO compartments in V2 are as sociated with functionally different pathways. (C) 1997 Wiley-Liss, In c.