Intrinsic lattice connections of macaque monkey visual cortical area V4

Abstract

We made focal iontophoretic as well as larger pressure injections (n = 30; 19 used for most analyses) of the tracer biocytin in visual area V4 of six macaque monkeys. The resulting transported label enabled mapping of intrinsic inter- and intralaminar connections within the region. We found that pyramidal neurons of layers 2 and 3 make extensive lateral projections within area V4, with oval or circular patches of terminals in layers 1-3. Any small patch of tissue (approximately 250 microns wide) injected in the superficial layers appeared to connect reciprocally to patches scattered up to 3 mm around the injection. The patches of terminal label measure 250-450 microns across, spaced roughly 600 microns (range, 450-1300 microns) center to center, and where most densely packed they occupy 33% of the cortical area with approximately 3-4 patches/mm2. Small injections in layers 4 and 6 did not produce contributions to these patchlike lattice connections, while injections in layer 5 gave very weak rising contributions to the superficial layer patch system. Large pressure injections of biocytin gave wider spread and more densely labeled patches, but their size and spacing appeared much the same as with small injections. The V4 pattern of label was compared to the patterns seen in areas V1 and V2 after similar-sized injections of biocytin; patches in V1 and V2 were slightly smaller (roughly 250-300 microns across) and more closely spaced (425-450 microns center to center), consistent with earlier measures in these areas using HRP. The peak areal occupancy of patches was approximately the same, 27-33% in each region. We interpret these findings as indicating a functional repeat distance of 450-600 microns in area V4 (fixed tissue measures) with a patchy, discontinuous layout. Given the dimensions of the V4 intrinsic connectional system demonstrated here, it seems unlikely that it relates directly to the topography of specific afferent terminations or efferent neuron groups, which appear from other studies to have a larger scale of repeat (2-3 mm). However, patches in V4 tend to aggregate, forming clusters extended in the mediolateral direction, suggesting a possible relation to coarser connection zones.

Effects of the anesthetic agent propofol on neural populations

“…For instance, in layer 2 and 3 in rat visual cortex (Hellwig 2000), the average size of axonal branches is *18 mm and the probabiflity of axonal connections between a pyramidal neuron and a dendritic tree falls off to its half at a distance of about 200 lm. Moreover, in the monkey visual cortex area V4 (Yoshioka et al 1992), layer 3 shows axonal extensions up to 1 mm. These examples show the diversity of axonal spatial ranges and it is clear that a spatial range in a model may take values of the same order.…”

Stereotypical Bouton Clustering of Individual Neurons in Cat Primary Visual Cortex

“…The predictable order in cluster properties suggests that there is a fundamental rule governing axonal growth and its associated Luhmann et al, 1986;Burkhalter, 1989;Kaas et al, 1989;Blasdel, 1992;Kisvárday and Eysel, 1992;Yoshioka et al, 1992;Amir et al, 1993;Lund et al, 1993;Levitt et al, 1994;Fujita and Fujita, 1996;Kisvárday et al, 1997;Malach et al, 1997;Fitzpatrick et al, 1998). bouton formation.…”

Cortical Orofacial Motor Representation in Old World Monkeys, Great Apes, and Humans

“…Thus, pyramidal neurons in area 4 have complex horizontal interconnections across large spans of cortex to coordinate the movements of synergistic muscles [Huntley and Jones, 1991]. In macaques, these transcolumnar connections have been shown to form an orderly lattice-like array of patches of pyramidal neurons concentrated in the superficial layers [Juliano et al, 1990;Huntley and Jones, 1991;Yoshioka et al, 1992;. Large basket cells are hypothesized to play an important role in the development of the inhibitory surround that creates this horizontal lattice-like organization because the lateral spread of the basket cell axonal field corresponds closely to the size of the inter-patch territory .…”