Abstract:Metric features and modular and laminar distributions of intrinsic projections of area 17 were studied in Cebus apella. Anterogradely and retrogradely labeled cell appendages were obtained using both saturated pellets and iontophoretic injections of biocytin into the operculum. Laminar and modular distributions of the labeled processes were analyzed using Nissl counterstaining, and/or cytochrome oxidase and/or NADPH-diaphorase histochemistry. We distinguished three labeled cell types: pyramidal, star pyramidal… Show more
“…This result corroborates our working hypothesis that long-range collinear interactions in V1 constitute the anatomical substrate for the completion phenomena we observe. V1 horizontal connections, for example, give rise to specialized circuits, which shape the direction and orientation tuning of the neurons by linking columns with similar response properties ( Amorim and Picanco-Diniz 1997 , Bosking et al 1997 ; Buzas et al 1998 , 2001 ; Crook et al 1996 , 1997 , 1998 ; de Amorim and Picanco-Diniz 1996 , Kisvarday et al 1997 , 2000 ; Sincich and Blasdel 2001 ). In this way, neurons inside the BSR would receive long-distance input (up to ∼8 mm, see Calford et al 2003 ; Chino et al 1995 ; Gilbert et al 1996 ) from neurons with similar response properties located outside the BSR, explaining the relevance of collinear flanks to the active completion process.…”
The optic disk is a region of the retina consisting mainly of ganglion cell axons and blood vessels, which generates a visual scotoma known as the blind spot (BS). Information present in the surroundings of the BS can be used to complete the missing information. However, the neuronal mechanisms underlying these perceptual phenomena are poorly understood. We investigate the topography of the BS representation (BSR) in cortical area V1 of the capuchin monkey, using single and multiple electrodes. Receptive fields (RFs) of neurons inside the BSR were investigated using two distinct automatic bias-free mapping methods. The first method (local mapping) consisted of randomly flashing small white squares. For the second mapping method (global mapping), we used a single long bar that moved in one of eight directions. The latter stimulus was capable of eliciting neuronal activity inside the BSR, possibly attributable to long-range surround activity taking place outside the borders of the BSR. Importantly, we found that the neuronal activity inside the BSR is organized topographically in a manner similar to that found in other portions of V1. On average, the RFs inside the BS were larger than those outside. However, no differences in orientation or direction tuning were found between the two regions. We propose that area V1 exhibits a continuous functional topographic map, which is not interrupted in the BSR, as expected by the distribution of photoreceptors in the retina. Thus V1 topography is better described as “visuotopic” rather than as a discontinuous “retinotopic” map.
“…This result corroborates our working hypothesis that long-range collinear interactions in V1 constitute the anatomical substrate for the completion phenomena we observe. V1 horizontal connections, for example, give rise to specialized circuits, which shape the direction and orientation tuning of the neurons by linking columns with similar response properties ( Amorim and Picanco-Diniz 1997 , Bosking et al 1997 ; Buzas et al 1998 , 2001 ; Crook et al 1996 , 1997 , 1998 ; de Amorim and Picanco-Diniz 1996 , Kisvarday et al 1997 , 2000 ; Sincich and Blasdel 2001 ). In this way, neurons inside the BSR would receive long-distance input (up to ∼8 mm, see Calford et al 2003 ; Chino et al 1995 ; Gilbert et al 1996 ) from neurons with similar response properties located outside the BSR, explaining the relevance of collinear flanks to the active completion process.…”
The optic disk is a region of the retina consisting mainly of ganglion cell axons and blood vessels, which generates a visual scotoma known as the blind spot (BS). Information present in the surroundings of the BS can be used to complete the missing information. However, the neuronal mechanisms underlying these perceptual phenomena are poorly understood. We investigate the topography of the BS representation (BSR) in cortical area V1 of the capuchin monkey, using single and multiple electrodes. Receptive fields (RFs) of neurons inside the BSR were investigated using two distinct automatic bias-free mapping methods. The first method (local mapping) consisted of randomly flashing small white squares. For the second mapping method (global mapping), we used a single long bar that moved in one of eight directions. The latter stimulus was capable of eliciting neuronal activity inside the BSR, possibly attributable to long-range surround activity taking place outside the borders of the BSR. Importantly, we found that the neuronal activity inside the BSR is organized topographically in a manner similar to that found in other portions of V1. On average, the RFs inside the BS were larger than those outside. However, no differences in orientation or direction tuning were found between the two regions. We propose that area V1 exhibits a continuous functional topographic map, which is not interrupted in the BSR, as expected by the distribution of photoreceptors in the retina. Thus V1 topography is better described as “visuotopic” rather than as a discontinuous “retinotopic” map.
“…This implies in incomplete reconstructions from which only metric features that do not depend on the order of the segments are suitable for analysis. As previously recommended elsewhere (Amorim and Picanco-Diniz, 1997;Gomes-Leal et al, 2002;Rocha et al, 2007) we have done similar choice in the present morphometric analysis, providing consistent quantitative data through density values in [ ( ) T D $ F I G ] , and field area (E) of axon trees of the S1 to S2 somatosensory ipsilateral projections in the agouti. Significant distinctions between axon fragments Types I and II (left column) and between hind and forelimb (right column) are indicated by asterisk (two-tailed Student's t-test, p < 0.05).…”
“…V2 is a belt of cortex located in the opercular region of the occipital pole in front of V1. It is limited posteriorly by V1, except in the most anterior region of the calcarine sulcus, which borders the area of prostriata of Sanides ( 14 , 21 ). V2 is limited anteriorly by V3 except at the representation of the fovea region at the lateral surface between the lunate sulcus and the inferior occipital sulcus, where V2 borders V4 21 ).…”
Section: Methodsmentioning
confidence: 99%
“…We studied the receptive field properties of V2 neurons before and after the inactivation of a small portion of area V2 in the capuchin monkey ( Cebus apella ). Several aspects of the visual system of this New World monkey, including the thalamic organization ( 16 - 18 ), intrinsic circuitry of V1 ( 19 - 21 ), and topographical characteristics of areas V1, V2, MT, and V4 ( 14 , 22 - 25 ) have been studied for almost two decades, making this monkey a suitable experimental model for this study. In addition, we recently studied the effect of GABA inactivation of visual area MT ( 26 ), visual area V4 ( 27 ), and previously (2004) the pulvinar ( 28 ) on the direction and orientation selectivity of V2 neurons.…”
We investigated the GABA-induced inactivation of V2 neurons and terminals on the
receptive field properties of this area in an anesthetized and paralyzed
Cebus apella monkey. Extracellular single-unit activity was
recorded using tungsten microelectrodes in a monkey before and after
pressure-injection of a 0.25 or 0.5 M GABA solution. The visual stimulus
consisted of a bar moving in 8 possible directions. In total, 24 V2 neurons were
studied before and after blocker injections in 4 experimental sessions following
GABA injection into area V2. A group of 10 neurons were studied over a short
period. An additional 6 neurons were investigated over a long period after the
GABA injection. A third group of 8 neurons were studied over a very long period.
Overall, these 24 neurons displayed an early (1-20 min) significant general
decrease in excitability with concomitant changes in orientation or direction
selectivity. GABA inactivation in area V2 produced robust inhibition in 80% and
a significant change in directional selectivity in 60% of the neurons examined.
These GABA projections are capable of modulating not only levels of spontaneous
and driven activity of V2 neurons but also receptive field properties such as
direction selectivity.
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