Predicting visual acuity from the structure of visual cortex

Abstract

Three decades ago, Rockel et al. proposed that neuronal surface densities (number of neurons under a square millimeter of surface) of primary visual cortices (V1s) in primates is 2.5 times higher than the neuronal density of V1s in nonprimates or many other cortical regions in primates and nonprimates. This claim has remained controversial and much debated. We replicated the study of Rockel et al. with attention to modern stereological precepts and show that indeed primate V1 is 2.5 times denser (number of neurons per square millimeter) than many other cortical regions and nonprimate V1s; we also show that V2 is 1.7 times as dense. As primate V1s are denser, they have more neurons and thus more pinwheels than similar-sized nonprimate V1s, which explains why primates have better visual acuity., in an influential and controversial article entitled "The basic uniformity in structure of the neocortex," reported that the number of neurons underneath a square millimeter of neocortical surface is constant for six cortical areas and five species with one exception: primate primary visual cortex (V1) has a surface density of about 250,000 neurons/mm 2 , around two and a half times the usual density for other areas studied.The Rockel et al. paper has, for a third of a century, continued to generate controversy for two reasons. One reason stems from its implications for an equally energetic debate among neuroscientist "lumpers" and "splitters." Cortical uniformity supports a theory of neocortical processing wherein different cortical areas are subserved by the same canonical circuit, a view favored by lumpers. Splitters, however, believe each cortical area to be different and doubt the paper's claims (2). The second reason is that studies from various laboratories using different measurement methods over the last three decades have alternately agreed and disagreed with Rockel et al.'s results (2).Notably, however, Rockel et al's studies have never been directly replicated. We set out to repeat the observations for the same areas and species Rockel et al. used. We used Rockel et al.'s counting techniques but with attention to the precepts of modern stereology (2). Our goal was to simply determine if Rockel et al.'s observations are repeatable rather than address the larger question of numerical uniformity of neocortex across species and areas. In an earlier publication (2), we confirmed Rockel et al.'s conclusions for nonvisual areas. Here we focus on the primary V1 for the same species used in the original report of Rockel et al.V1 is part of the visual circuit from the retina to the cortex, which is retinotopically organized, and the 2D image of the world that is mapped onto the retina is recreated in V1 (3). Cells within the retina capture visual information for each image location or pixel such as color and light intensity and convey it to structures in V1 (4, 5), which perform computations that contribute to visual abilities. An especially well-studied V1 structure is a pinwheel, which comprises orientation columns tha...

Evolution of Osteocrin as an activity-regulated factor in the primate brain

“…Our findings indicate that MEF2, by regulating OSTN expression, restricts the dendritic growth of layer IVC neurons and thus may play an important role in the organization of dense primate neocortical networks 31–33 . However, the potential contribution of OSTN function to primate cognitive processing and what drove OSTN repurposing specifically in primates during evolution are still unknown.…”

Quantification of neuronal density across cortical depth using automated 3D analysis of confocal image stacks

“…It has previously been described that overall neuronal density in primate V1 is higher than in other cortical areas (Rockel et al 1980; Collins et al 2010a; Srinivasan et al 2015). In the current study, neuronal density across layers 1 through 6 was 1.8 times higher in V1 than in V2.…”

Cortical cell and neuron density estimates in one chimpanzee hemisphere

“…Thus, V1 has densely packed small neurons (granular cells) in layer 4 that are activated by just a few neurons in the dorsal lateral geniculate nucleus, and they activate other neurons in V1 that are, with few exceptions, small pyramidal neurons with small apical arbors contacted by relatively few inputs (46,48). The high neuron densities for V1 of primates have been postulated as a mechanism for preserving the high visual acuity of primates (49). Motor cortex is known for its large pyramidal cells and lack of small layer 4 granular cells, which promotes integration from more sources of information.…”