Long-Range Clustered Connections within Extrastriate Visual Area V5/MT of the Rhesus Macaque

Abstract

Visual area V5/MT in the rhesus macaque has a distinct functional organization, where neurons with specific preferences for direction of motion and binocular disparity are co-organized in columns or clusters. Here, we analyze the pattern of intrinsic connectivity within cortical area V5/MT in both parasagittal sections of the intact brain and tangential sections from flatmounted cortex using small injections of the retrograde tracer cholera toxin subunit b. Labeled cells were predominantly found in cortical layers 2, 3, and 6. Going along the cortical layers, labeled cells were concentrated in regularly spaced clusters. The clusters nearest to the injection site were approximately 2 mm from its center. In flatmounted cortex, along the dorsoventral axis of V5/MT, we identified further clusters of labeled cells up to 10 mm from the injection site. Quantitative analysis of parasagittal sections estimated average cluster spacing at 2.2 mm; in cortical flatmounts, spacing was 2.3 mm measured radially from the injection site. The results suggest a regular pattern of intrinsic connectivity within V5/MT, which is consistent with connectivity between sites with a common preference for both direction of motion and binocular depth. The long-range connections can potentially account for the large suppressive surrounds of V5/MT neurons.

Neural plasticity and concepts ontogeny

“…9-10). These distributions are consistent with the increase of integration in upper visual areas, and in visual area V5 of rhesus monkeys horizontal connections up to 10 mm have been found (Ahmed et al 2011). As we will see, these longer lateral connections seem to undergo intra-map plasticity as well.…”

Plasticity in the Structure of Visual Space

“…The separations between testing locations were 0, 0.4, or 0.8 degrees larger than the separations between training locations. These visual field separations correspond to a cortical separation of 10–14 mm in human V1 (Schira et al, 2007) and overlap with the reported extent of lateral connections in primate visual cortex (Ringo, 1991; Burkhalter et al, 1993; Kaas, 2000; Levitt and Lund, 2002; Voges, et al, 2010; Ahmed et al, 2012; Lyon et al, 2014). Moreover, at an eccentricity of 6 degrees, the number of neurons activated by a point stimulus (cortical point image) should be minimal (Van Essen et al, 1984; Harvey and Dumoulin, 2011), thereby favoring the activation of distinct groups of neurons.…”

“…The contraction was maximal at a training separation of 4.4 degrees, which corresponds to a cortical separation of 12 mm in human V1 (Schira et al, 2007) and falls within the extent of V1 lateral connections (Ringo, 1991; Burkhalter et al, 1993; Kaas, 2000; Levitt and Lund, 2002; Voges, et al, 2010; Ahmed et al, 2012; Lyon et al, 2014). Because of the mirror-symmetry of human retinotopic organization, V1 is the only early visual cortical region whose ventral part (representation of upper visual field) and dorsal part (representation of lower visual field) are contiguous, whereas the ventral and dorsal parts of other early visual cortical regions (e.g., V2, V3) are segregated by V1 (Sereno et al, 1995; Brewer and Barton, 2012; Wang et al, 2014).…”

Dynamics of the functional link between area MT LFPs and motion detection

“…Horizontal connections can transmit spiking activity to cortex within a radius of several millimeters (Nauhaus et al , 2012; but see Ray and Maunsell 2011b)-while MT has clusters of connected neurons that are several millimeters apart on average, which was the approximate separation between our recording electrodes (Ahmed et al 2012). Therefore, if one recording location in MT responded to a motion pulse in its RF, then horizontal connections could have passed that response to the other recording location.…”