The neocortical circuit: themes and variations

Abstract

Similarities in neocortical circuit organization across areas and species suggest a common strategy to process diverse types of information, including sensation from diverse modalities, motor control, and higher cognitive processes. Cortical neurons belong to a small number of major classes. The properties of these classes are remarkably similar between areas, including their local and long-range connectivity, developmental history, gene expression, intrinsic physiology, and in vivo activity patterns. Each class contains multiple subclasses; for a rapidly growing number of these, conserved patterns of input and output connections are also becoming evident. The ensemble of circuit connections constitutes a basic circuit pattern that appears to be repeated across neocortical areas, with area- and species-specific modifications. Such “serially homologous” organization may adapt individual neocortical regions to the type of information each must process.

Jointly reduced inhibition and excitation underlies circuit-wide changes in cortical processing in Rett syndrome

“…Our in vivo functional measurements of inhibitory conductances in adult MeCP2 gKO mice, along with targeted cell-specific recordings of PV + neurons, consistently reveal reduced inhibition or reduced inhibitory neuronal responses in adult cortical circuits. Furthermore, our measurements of reduced visually driven excitatory conductances demonstrate that reduced visual responses of V1 pyramidal neurons or reduced propagated activity in slices in MeCP2 mutant mice (70,71) are likely due not to increased inhibition but to reduced feedforward and recurrent excitatory drive, both of which are crucial elements of cortical circuits (82,83). PV + neuron-specific MeCP2 deletion leads to cell-autonomous effects, including immature membrane and synaptic properties in PV + cells (81).…”

Astrocytic neuroligins control astrocyte morphogenesis and synaptogenesis

“…10f). L5 neurons possess large dendritic trees that project to all cortical layers and receive extensive excitatory and inhibitory synaptic inputs 32 . The frequency and amplitude of mEPSCs were significantly reduced in NL2 cKO neurons compared to cHETs (Fig.…”

Cortical computation in mammals and birds

“…This finding suggests that, as mammals evolved, a common "canonical cortical microcircuit" has been repurposed to implement the different types of information processing required by different species, including, in our case, language and abstract reasoning (2,3). In PNAS, Calabrese and Woolley (4) present data that suggest that computations akin to those performed by the mammalian cortex occur also in birds.…”

“…The cortex contains a great variety of excitatory and inhibitory neuronal classes (3). Whereas most of these cannot be distinguished in electrophysiological recordings, one class of cells-the fast-spiking interneurons-can be putatively distinguished by their narrow action potential waveforms (13).…”