isocortex (neocortex)

Introduction

The larger part of the mammalian cerebral cortex, distinguished from the allocortex by a larger number of cells, roughly arranged in 6 layers. The human neocortex is about 3 times as large as would be expected for a non-human primate of the same size.

The isocortex may be further categorized:

• homotypical isocortex (6 distinct layers)
  • unimodal association cortex
  • heteromodal association cortex
• heterotypical (idiotypic) isocortex
  • 6 layer architecture is obscured by structural variations
  • primary visual, auditory, somatosensory & motor cortex

The 6 layers of the neocortex:

• molecular layer (plexiform or tangential layer)
• corpuscular layer (dysfibrous or extragranular layer)
• pyramidal layer (suprastriate of external pyramidal layer)
• granular layer (internal granular layer of external band of Baillarger)
• ganglionic layer (internal pyramidal or interstriate layer, or internal band of Baillarger)
• spindle layer (multiform, infrastriate of fusiform layer)

Cortical columns:

The basic unit of the mature neocortex is the minicolumn, a narrow chain of 80-100 neurons that extends from layers 2-6. Columns are formed through the binding together of minicolumns by dense, short-range connections. Each column is a complex processing & distributing unit.

Column size: 300-500 um in diameter

More general terms

• cerebral cortex

More specific terms

• heterotypical (idiotypic) isocortex
• homotypical isocortex

Additional terms

• allocortex
• cortical column
• layers of the neocortex
• mesocortex