Ta. Nealey et Jhr. Maunsell, MAGNOCELLULAR AND PARVOCELLULAR CONTRIBUTIONS TO THE RESPONSES OF NEURONS IN MACAQUE STRIATE CORTEX, The Journal of neuroscience, 14(4), 1994, pp. 2069-2079
Anatomical and physiological studies of the primate visual system have
suggested that the signals relayed by the magnocellular and parvocell
ular subdivisions of the LGN remain segregated in visual cortex. It ha
s been suggested that this segregation may account for the known diffe
rences in visual function between the parietal and temporal cortical p
rocessing streams in extrastriate visual cortex. To test directly the
hypothesis that the temporal stream of processing receives predominant
ly parvocellular signals, we recorded visual responses from the superf
icial layers of V1 (striate cortex), which give rise to the temporal s
tream, while selectively inactivating either the magnocellular or parv
ocellular subdivisions of the LGN. Inactivation of the parvocellular s
ubdivision reduced neuronal responses in the superficial layers of V1,
but the effects of magnocellular blocks were generally as pronounced
or slightly stronger. Individual neurons were found to receive contrib
utions from both pathways. We furthermore found no evidence that magno
cellular contributions were restricted to either the cytochrome oxidas
e blobs or interblobs in V1. Instead, magnocellular signals made subst
antial contributions to responses throughout the superficial layers. T
hus, the regions within V1 that constitute the early stages of the tem
poral processing stream do not appear to contain isolated parvocellula
r signals. These results argue against a direct mapping of the subcort
ical magnocellular and parvocellular pathways onto the parietal and te
mporal streams of processing in cortex.