Parahippocampal Gyrus (Areas 28, 34, 35, 36)

Jared A. Nielsen, PhD

Jeffrey S. Anderson, MD, PhD

Key Facts

Location and Boundaries

Areas 28, 34, 35, 36: Located on parahippocampal gyrus, extending lateral and posterior from hippocampus
- Entorhinal cortex (areas 28, 34): Comprises anteromedial parahippocampal gyrus
- Perirhinal cortex (area 35): Immediately lateral to entorhinal cortex
- Entorhinal cortex separated from perirhinal cortex by rhinal (collateral) sulcus
- Ectorhinal cortex (area 36): Posterolateral to perirhinal cortex

Function

Spatial navigation: Map of spatial location and trajectory in entorhinal cortex with grid cells encoding spatial location and path cells encoding direction
Olfaction: Primary olfactory cortex located at anterior margin of entorhinal cortex at level of anterior margin of amygdala
Encoding visual scenes: Parahippocampal place area (PPA) in posterior parahippocampal gyrus active during perception of scenes (e.g., buildings, houses, locations)
Memory: Bridge between hippocampus and neocortex for memory encoding and retrieval

Area 28-, 34-36-Associated Disorders

Alzheimer dementia: Entorhinal cortex shows greatest atrophy, site of earliest pathologic changes
Medial temporal sclerosis: Variable involvement of hippocampus, amygdala, and entorhinal/perirhinal cortex

(Left) Coactivation map of Brodmann areas 28, 34, 35, and 36 shows brain regions that reliably activate with the centroid of voxels lying within areas 28, 34, 35, and 36 in over 4,000 studies from the NeuroSynth database. Image is the average of left and right coactivation maps.

(Right) Coronal and axial slices from a cytoarchitectonic map of parahippocampal gyrus is shown. This quantitative probabilistic map was derived from postmortem human brains and is specific to cellular properties unique to areas 28, 34, 35, and 36 (data source: SPM Anatomy toolbox).

LOCATION AND BOUNDARIES

Location

Areas 28, 34, 35, and 36: Parahippocampal gyrus, extending lateral and posterior from hippocampus
- Area 28 (ventral entorhinal) and area 34 (dorsal entorhinal): Adjacent to hippocampal subiculum
- Area 35 (perirhinal cortex) and area 36 (ectorhinal, parahippocampal cortex): Occupy lateral parahippocampal and anterior fusiform gyri

Boundaries

Entorhinal cortex (areas 28, 34): Comprises anteromedial parahippocampal gyrus
- Separated from hippocampus by hippocampal fissure
- Boundary with subiculum at medial margin ventral to hippocampal fissure
- Separated from perirhinal cortex by collateral sulcus
- Areas 28 and 34 separated by tentorial notch
- Posteriorly contiguous with retrosplenial cingulate
Perirhinal cortex (area 35): Immediately lateral to entorhinal cortex
- Includes medial bank of collateral sulcus
- Bordered by temporal pole (area 38) rostrally
  - Anterior margin 2-3 mm anterior to limen insulae at anterior margin of collateral sulcus (˜ 24 mm caudal to temporal pole)
Ectorhinal cortex (area 36): Caudal to perirhinal cortex
- Overlapping terms: Ectorhinal, postrhinal, parahippocampal cortex
- Includes anterior medial fusiform gyrus
- Lateral margin at occipitotemporal sulcus, separating perirhinal from inferior temporal cortex (area 20)
- Bordered by fusiform gyrus (area 37) caudally