Expansion of cortical layers 2 and 3 in human left temporal cortex associates with verbal intelligence

Abstract

The expansion of supragranular cortical layers is thought to have enabled evolutionary development of human cognition and language. However, whether increased volume of supragranular cortical layers can actually support greater cognitive and language abilities in humans has not been demonstrated. Here, we find that subjects with higher general and verbal intelligence test (VIQ) scores have selectively expanded layers 2 and 3 only in the left temporal cortex, an area associated with language and IQ-test performance. This expansion is accompanied by lower neuron densities and larger cell-body size. Furthermore, individuals with higher VIQ scores had neurons with larger dendritic trees in left temporal cortex, potentially impacting their function. Indeed, neurons of subjects with higher VIQ scores had faster action potential upstroke kinetics, which improves information processing. These data show that expansion of supragranular layer volume, cortical and cellular micro-architecture and function are associated with improved verbal mental ability in human subjects.

Upper cortical layer–driven network impairment in schizophrenia

“…Throughout our analysis, we observed a prevailing impairment of neuronal subtypes residing in the upper layers of the cortex, which involves subtypes of GABAergic neurons from all four families—PVALB, SST, VIP, and ID2—and L2_3_CUX2 subtypes of principal neurons; additionally, several subtypes of L4_6_FEZF2 principal neurons (most of them—L4_5_FEZF2_LRRK1) showed significant compositional and transcriptomic changes. It is known that upper layers receive information from other cortical and subcortical areas ( 70 ) and are critical for human cognition ( 71 ), while lower layer principal neurons are known to transmit information projecting to other regions of the brain. Overall, schizophrenia-associated brain circuits might include a large assembly of neuronal circuitry that sends information into the cortex, where it is received, transformed, and forwarded to other cortical and subcortical regions.…”

Human voltage-gated Na+and K+channel properties underlie sustained fast AP signaling

“…Although there is strong supporting evidence that both AP stability and phase-locking are associated with human cognitive performance (18)(19)(20), it is currently not known how exactly these cellular features contribute to improved network function. However, a recent study found that AP speed and dendritic size of human neurons are related to individual differences in functional network integration (35).…”

“…We recently showed that human neurons are indeed able to maintain fast and stable AP kinetics during sustained firing and this is relevant for cognitive function (18,19). Neurons from subjects with higher IQ are able to maintain fast APs, while in subjects with lower IQ the AP rising speed slows down during repeated firing.…”

“…We recently showed that human neurons are indeed able to maintain fast and stable AP kinetics during sustained firing and this correlates with cognitive function (17,18). Furthermore, the encoding ability of single neurons in awake humans has been linked to cognitive task performance (19,20).…”

How Can Laminar Microelectrodes Contribute to Human Neurophysiology?

“…On the network level, human cortex is much more recurrent than rodent cortex [12][13][14][15]. These interspecies differences are particularly pronounced in supragranular layers, which disproportionately expanded in humans [16,17], are more cellularly heterogeneous than in rodents [5], and may be critical for human specific cognitive abilities [18][19][20]. Therefore, the use of animal models for laminar physiology must be validated directly in humans.…”