Cytoarchitectural characteristics associated with cognitive flexibility in raccoons

Abstract

With rates of psychiatric illnesses such as depression continuing to rise, additional preclinical models are needed to facilitate translational neuroscience research. In the current study, the raccoon (Procyon lotor) was investigated due to its similarities with primate brains, including comparable proportional neuronal densities, cortical magnification of the forepaw area, and cortical gyrification. Specifically, we report on the cytoarchitectural characteristics of raccoons profiled as high, intermediate, or low solvers in a multiaccess problem-solving task. Isotropic fractionation indicated that high-solvers had significantly more cells in the hippocampus (HC) than the other solving groups; further, a nonsignificant trend suggested that this increase in cell profile density was due to increased nonneuronal (e.g., glial) cells. Group differences were not observed in the cellular density of the somatosensory cortex. Thionin-based staining confirmed the presence of von Economo neurons (VENs) in the frontoinsular cortex, although no impact of solving ability on VEN cell profile density levels was observed. Elongated fusiform cells were quantified in the HC dentate gyrus where high-solvers were observed to have higher levels of this cell type than the other solving groups. In sum, the current findings suggest that varying cytoarchitectural phenotypes contribute to cognitive flexibility. Additional research is necessary to determine the translational value of cytoarchitectural distribution patterns on adaptive behavioral outcomes associated with cognitive performance and mental health.

The evolution of quantitative sensitivity

“…Our study is a rare demonstration of a relation between neuron number or neuron density and a particular cognitive ability. Previous within-species comparisons showed that neuron number in multiple brain regions did not predict performance on a battery of behavioural tasks in mice [135], and though raccoons who performed best on a puzzle box task had more cells in their hippocampus than lower performing individuals, this difference may have been driven by glial cells [136]. However, crossspecies comparisons in primates and birds suggest that neuron number has more behavioural explanatory power than cranial capacity, based on the correlation between cortical or pallial neuron number and performance on a self-control task [71].…”

Spindle-Shaped Neurons in the Human Posteromedial (Precuneus) Cortex

“…The emergence of VENs is not related to the relative brain size or encephalization of the studied species ( Allman et al, 2010 ). There is a possibility that VENs might be associated with the mechanical challenges associated with larger, gyrencephalic brains along with other evolutionary adaptations ( Jacob et al, 2021 ). Human VENs with sparse dendritic trees and symmetric ascending and descending main shafts were considered computationally simple compared to layer V pyramidal neurons, likely receiving few inputs within individual minicolumns for a rapid cortical radial signal transmission ( Watson et al, 2006 ).…”

“…Von Economo neurons (VENs) have a peculiar phylogenetic and ontogenetic development and are characterized by an elongated spindle-shaped or rod-shaped cell body mainly found in the cortical layer V of restricted brain areas of some species, including humans and other primates, but not in all mammals ( Nimchinsky et al, 1995 ; Allman et al, 2005 , 2010 ; Hakeem et al, 2009 ; Cauda et al, 2014 ; Raghanti et al, 2015 ; Hodge et al, 2020 ; Jacob et al, 2021 ). In humans, VENs have been reported mainly in the anterior cingulate cortex (ACC) and frontoinsular cortex (FI; Raghanti et al, 2015 ; Banovac et al, 2019 , 2021 ; Correa-Júnior et al, 2020 and references therein), but also in the dorsolateral prefrontal cortex (Brodmann area 9; Fajardo et al, 2008 ) and in the medial frontopolar prefrontal cortex (Brodmann area 10; González-Acosta et al, 2018 ).…”

Painful intelligence: What AI can tell us about human suffering

“…For coma patients who are incapable of saying anything or any motor responses whatsoever, measuring brain activity provides the last resort for assessing their consciousness. Surprisingly, it has been found that patients who were thought to be 11 (Critchley and Seth, 2012;Butti et al, 2013) 12 (Lamme and Roelfsema, 2000;Crick and Koch, 2003) 13 It is not very clear which animals have von Economo neurons and which don't; Jacob et al (2021) have recently claimed to find them even in raccoons.…”