The Parahippocampal Gyrus
The parahippocampal gyrus is connected to numerous areas of the cortex. It acts as a gateway for all signals that are to reach the hippocampus. This makes damage to this area all the more serious, for example, through Alzheimer's disease.
Scientific support: Prof. Dr. Horst-Werner Korf
Published: 28.11.2025
Difficulty: serious
The parahippocampal gyrus is the interface through which the hippocampus connects to the isocortex. Damage to this area leads to serious memory disorders.
In a 2009 study published in the Journal of Neuroscience, Taylor Schmitz from the University of Toronto investigated the relationship between mood and perception. To do this, he first showed his test subjects images that triggered either pleasant or unpleasant emotions. The researchers then presented images with faces in the center and houses in the background. The subjects were asked to indicate the gender of the face – a task that was emotionally neutral. Meanwhile, imaging techniques were used to record brain activity in an area of the parahippocampal gyrus known as the parahippocampal place area, or PPA for short.
Those who had seen unpleasant images and were therefore in a gloomy mood had a comparatively silent PPA. However, those who had seen images of small children and puppies, and were therefore in a positive mood, had a very active PPA. Schmitz and colleagues see this as confirmation of an everyday experience: when you are in a good mood, your field of vision expands – you perceive more details and are more open to new information. A bad mood, on the other hand, causes tunnel vision.
The parahippocampal gyrus also has very specific functions, as shown by imaging studies. Its anterior region is active when it comes to places and houses, spatial arrangement, and background. This area is therefore referred to as the parahippocampal place area (PPA).
The temporal lobe has a convolution on its inner surface that is named after its immediate neighborhood: The parahippocampal gyrus is located right next to (para) the hippocampus. However, this gyrus is not only located next to it, but merges seamlessly into the hippocampus, or more precisely, into its subiculum. The cortical layer that covers the parahippocampal gyrus is called the entorhinal cortex, and both terms are often used synonymously. Entorhinal cortex literally means “right in the middle of smelling” cortex. In fact, in many animals, this area is dominated by fibers from the bulbi olfactori, i.e., the olfactory bulbs, hence the name. However, this is not the case in humans.
Structure and appearance
The entorhinal cortex belongs to the so-called allocortices, meaning it does not have the typical six-layer structure of the isocortex, which covers most of the hemispheres. It is by no means simpler, but rather more complex in its layering than the isocortex; some authors describe more than 10 layers. It is characterized by cell clouds – or cell islands – located just below the surface.
Connections and functions
The entorhinal cortex is reciprocally connected to all association centers of the isocortex and also to the olfactory areas of the temporal lobe and the amygdala. For its part, it sends a massive bundle of fibers – the perforant tract – into the neighboring hippocampal formation. One could therefore say that the entorhinal cortex is to the hippocampus what the thalamus is to the isocortex: the gateway or bottleneck through which everything that is supposed to reach the hippocampus must pass. If this bottleneck becomes too narrow, the gateway closed, and the hippocampus is, so to speak, cut off from the neocortex – with serious consequences.
In the well-known Alzheimer's disease, which begins in the entorhinal cortex but then spreads to almost the entire brain, this is exactly what happens initially: the neurons of the entorhinal cortex that form the perforant pathway are the first to die. This results in amnestic syndromes: new memories can no longer be formed, and existing ones can no longer be retrieved.
First published on August 23, 2011
Updated on November 28, 2025
