Parcellations and Connectivity Patterns in Human and Macaque Cerebral Cortex

Abstract

To decipher brain function, it is vital to know how the brain is wired. This entails elucidation of brain circuits at multiple scales, including microscopic, mesoscopic, and macroscopic levels. Here, we review recent progress in mapping the macroscopic brain circuits and functional organization of the cerebral cortex in primates-humans and macaque monkeys, in particular. There are many similarities across species in terms of overall patterns of cortical gray matter myelination as well as functional areas that are presumed to be homologous. However, there are also many important species differences, including cortical convolutions that are much more complex and more variable in humans than in monkeys. Our ability to analyze structure and function has benefited from improved methods for intersubject registration that cope with this individual variability. To characterize long-distance connectivity, powerful but indirect methods are now available, including resting-state functional connectivity and diffusion imaging coupled with probabilistic tractography. We illustrate how connectivity inferred from diffusion imaging and tractography can be evaluated in relation to 'ground truth' based on anatomical tracers in the macaque. Interspecies registration between human and macaque cortex based on presumed interspecies homologies demonstrates an impressive degree of areal expansion in regions associated with higher cognitive function.

Shared and distinct transcriptomic cell types across neocortical areas

“…connectional and functional studies, up to 180 distinct cortical areas have been identified in humans 32 (Glasser et al, 2016) and dozens in rodents (Kolb, 1990;Ng et al, 2009). Cortical areas are often 33 categorized as sensory, motor or associational, based on their connections with other brain areas.…”

“…Most sensory areas contain L4, and they are termed 35 'granular', whereas motor and associational areas usually do not have L4, and are hence 'agranular'. In 36 vertebrate evolution, cortex underwent disproportionally greater expansion in terms of the number of cells, 37 layers and functional areas compared to the rest of the brain, coinciding with the acquisition of increasingly 38 sophisticated cognitive functions (Jerison, 2009;Kaas, 2009; Man et al, 2013;Van Essen et al, 2016). 39…”

Developmental changes in connectivity between the amygdala subnuclei and occipitotemporal cortex

“…Line drawing summarizing the organization of projections between the amygdala and ventral stream visual cortical areas in adult macaques (reproduced from Freese & Amaral, 2005, pending approval) Do these connections show a similar pattern in human development? We know that macaque cortex is oriented differently than human cortex, and although homologies exist, the connectivity pattern in macaques may not necessarily perfectly map to humans (Passingham, 2009;Van Essen et al, 2016). Moreover, in humans, it is more challenging to study amygdalar connections, especially with respect to the basal vs. lateral nucleus and their connections to visual cortex.…”

Delineating the Macroscale Areal Organization of the Macaque Cortex In Vivo

“…The availability of histological atlases for various NHP species provides an alternative means of guiding intracranial measurements and interventions. However, such atlases are inherently limited in their ability to account for differences in brain areal organization among animals, which can negatively impact experimentation when not properly considered (Cerliani et al, 2017; Gordon et al, 2017a, 2017b; Van Essen et al, 2016). …”