Cortical Evolution: Judge the Brain by Its Cover

Abstract

To understand the emergence of human higher cognition, we must understand its biological substrate—the cerebral cortex, which considers itself the crowning achievement of evolution. Here, we describe how advances in developmental neurobiology, coupled with those in genetics, including adaptive protein evolution via gene duplications and the emergence of novel regulatory elements, can provide insights into the evolutionary mechanisms culminating in the human cerebrum. Given that the massive expansion of the cortical surface and elaboration of its connections in humans originates from developmental events, understanding the genetic regulation of cell number, neuronal migration to proper layers, columns, and regions, and ultimately their differentiation into specific phenotypes, is critical. The pre- and postnatal environment also interacts with the cellular substrate to yield a basic network that is refined via selection and elimination of synaptic connections, a process that is prolonged in humans. This knowledge provides essential insight into the pathogenesis of human-specific neuropsychiatric disorders.

The Crossed Projection to the Striatum in Two Species of Monkey and in Humans: Behavioral and Evolutionary Significance

“…It is appealing to speculate that this projection might be unique to humans because specifically involved in language. Differences between the human and nonhuman primates can be expected considering that there are additional human-specific traits (Clowry et al 2010) and many molecular and cellular differences even between close relatives such as chimpanzees and humans (Geschwind and Rakic 2013). In particular, other connectional differences between the human and the monkey brains are beginning to emerge.…”

Components of the Language-Ready Brain

“…Summarizing these findings, it appears that the developed interneurons and dendritic spinal strength proposed by Geschwind and Rakic (2013) fortified long-distance assembly connections and, in turn, the mechanisms of ephaptic coupling, CFC and other neuronal processes (operating within the confines of the CTC hypothesis) necessary for the rhythmic interactions claimed above to be the source of computations like labeling and cyclic transfer. The targeting of the perisomatic region of pyramidal neurons by inhibitory interneurons in particular leads to the formation of γ rhythms and their concomitant properties of conceptual assimilation.…”

“…Hominid-unique features which may have led to the higher mental faculties of humans include novel neuronal cell types and the duplication of developmental proteins such as SRGAP2, leading to unique dendritic spine density and form (Geschwind and Rakic, 2013). Synaptic and dendritic maturation also occurs in humans for a considerably longer time than in non-humans (Bianchi et al, 2013).…”

Dynamics of the association of heat shock protein HSPA6 (Hsp70B’) and HSPA1A (Hsp70–1) with stress-sensitive cytoplasmic and nuclear structures in differentiated human neuronal cells

“…The presence of HSPA6 in the human genome could provide human neuronal cells with a highly dynamic mechanism for transcriptional recovery after stressful stimuli. This is particularly critical for the human brain that requires rapid recovery of neurons involved in higher cognitive function in the greatly expanded human neocortex compared to instinctive neural functions that are operative in mouse and rat (Lui et al 2011;Geschwind and Rakic 2013;Taverna et al 2014;Florio et al 2015). …”