Allocortical

Allocortical is an anatomical term used to describe regions of the cerebral cortex that do not belong to the six-layered neocortex. The allocortex comprises the archicortex and the paleocortex, which have fewer cortical layers and distinct cellular organization compared with the isocortex.

The archicortex includes structures such as the hippocampus and the dentate gyrus. The paleocortex includes olfactory-related regions, notably the piriform cortex, as well as surrounding olfactory and entorhinal areas. In contrast to the six-layered neocortex, the laminar structure of allocortical tissue is simpler, commonly consisting of three to five layers depending on the region.

Functionally, allocortical regions are involved in memory formation, spatial navigation, and olfactory processing, as well as broader limbic system interactions. A key example is the hippocampal formation, which participates in declarative memory consolidation and episodic recall. The hippocampus communicates with the entorhinal and other cortical areas through pathways that support the tri-synaptic circuit and associated memory processes.

In clinical and research contexts, allocortical structures are of interest because they are among the earliest-affected regions in certain neurodegenerative and epileptic conditions. Evolutionarily, allocortex is considered older than the neocortex, reflecting its foundational roles in memory and basic sensory processing.