Cortical representation of the horizon in V1 and peripheral scaling in mammals with lateral eyes.

Abstract

In the present investigation we mapped the primary visual area of the South American diurnal rodent, Dasyprocta aguti, by standardized electrophysiological mapping techniques. In particular, we performed a series of mapping experiments of the visual streak in the primary visual cortex. We found that the representation of the visual streak in V1 is greatly expanded, the nasal 10 degrees of the visual streak representation occupies ten times more cortical area than equivalent areas in the central or temporal representation. Comparison of these data with those on the density of ganglion cells in the retina at corresponding locations in the visual field reveal a significant mismatch between these two variables. The nasal representation is greatly expanded along the horizontal meridian in V1 as compared to the central and temporal regions whereas the density of ganglion cells decreases with progression along the visual streak from central region towards the nasal or temporal visual field. A review of the available data reveals that all lateral-eyed mammals exhibit a similar mismatch between the retinal and cortical representation of the visual field, and this mismatches is greater in those species with well defined visual streaks such as rabbit and agouti.

Origins of Functional Organization in the Visual Cortex

“…The agouti clearly has quite lateral eyes but no specific optical measure has been conducted, so we show it as a span of eye divergence angles (horizontal gray line). However, its binocular overlap has been measured as 20 • (Picanço-Diniz et al, 2011). The wallaby is a particularly interesting species to study as its eye divergence is almost exactly 45 • , placing it between the two extremes.…”

Topography and architecture of visual and somatosensory areas of the agouti

“…On the other hand, architectonic distinction between the binocular and monocular fields representations in the agouti's area 17 is not as conspicuous as in both the gray and ground squirrels, with the amount of cortex dedicated to representation of the binocular field being larger than in the agouti (Picanço Diniz et al, 1989;. Since the gray squirrel has a binocular field wider than both the agouti and the ground squirrel, it is not surprising to find that the amount of cortex devoted to represent the binocular field in the former is proportionally larger than in the latter species (Picanço Diniz, 1987;Picanço-Diniz et al, 2011). It is interesting to note that the analysis of myelin and SMI-32 staining patterns revealed that V1 was not homogeneously stained along its anterior to posterior extent.…”

Dendritic structure varies as a function of eccentricity in V1: A quantitative study of NADPH diaphorase neurons in the diurnal South American rodent agouti, Dasyprocta prymnolopha

“…Tissue was obtained from captive-bred animals used in other electrophysiological experiments (Picanc¸o-Diniz et al, 2011). Data for the present study were obtained from five adult male agoutis (Dasyprocta primnolopha), weighing between 2.6 and 3.2 kg (…”

“…A composite map of V1 topography was constructed from electrophysiological data obtained in the previous mapping studies, to assist in the present study, see Fig. 2 of Picanc¸o-Diniz et al (2011). A digitizing table was then used to measure the lateral position of each penetration in relation to the fundus of the lateral sulcus by generating a flat map reconstruction of the visual recording sites; see Figs.…”