Cortex

The workhorse of human intelligence; it first came into being in early vertebrates hallmarked by the development of pyramidal cells. Many other cell types work alongside these in highly specific cortical microcircuits in modern vertebrate brains.

The cortex is highly stereotypical and structured. Fish have a 3-layer cortex, whereas mammals have a 6-layer neocortex. The cortex -> neocortex transformation included:

• ventral cortex -> associative amygdala (pattern recognition, especially attuned to valence)
• auto-associative smell-pattern detectors in lateral cortex -> olfactory cortex
• spatial-map learning medial cortex -> hippocampus
• the new neocortex (small fraction of the brain in early mammals but 70% of brain volume in humans)