The parahippocampal gyrus (or hippocampal gyrus') is a
grey matter cortical region of the
brain
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...
that surrounds the
hippocampus and is part of the
limbic system. The region plays an important role in
memory encoding
In communications and information processing, code is a system of rules to convert information—such as a letter (alphabet), letter, word, sound, image, or gesture—into another form, sometimes data compression, shortened or secrecy, secret ...
and
retrieval
Retrieval could refer to:
Computer science
* RETRIEVE, Tymshare database that inspired dBASE and others
* Data retrieval
* Document retrieval
* Image retrieval
* Information retrieval
* Knowledge retrieval
* Medical retrieval
* Music informati ...
. It has been involved in some cases of
hippocampal sclerosis.
Asymmetry has been observed in
schizophrenia.
Structure
The anterior part of the gyrus includes the
perirhinal
The perirhinal cortex is a cortical region in the medial temporal lobe that is made up of Brodmann areas 35 and 36. It receives highly processed sensory information from all sensory regions, and is generally accepted to be an important region f ...
and
entorhinal cortices.
The term parahippocampal cortex is used to refer to an area that encompasses both the
posterior parahippocampal gyrus and the medial portion of the
fusiform gyrus.
Function
Scene recognition
The parahippocampal place area (PPA) is a sub-region of the parahippocampal cortex that lies medially in the inferior temporo-occipital cortex. PPA plays an important role in the encoding and
recognition of environmental scenes (rather than faces).
fMRI studies indicate that this region of the brain becomes highly active when human subjects view topographical scene stimuli such as images of landscapes, cityscapes, or rooms (i.e. images of "places"). Furthermore, according to work by
Pierre Mégevand et al. in 2014, stimulation of the region via intracranial electrodes yields intense topographical visual hallucinations of places and situations.
The region was first described by
Russell Epstein and
Nancy Kanwisher in 1998 at MIT,
see also other similar reports by
Geoffrey Aguirre and
Alumit Ishai.
Damage to the PPA (for example, due to stroke) often leads to a syndrome in which patients cannot visually recognize scenes even though they can recognize the individual objects in the scenes (such as people, furniture, etc.). The PPA is often considered the complement of the
fusiform face area (FFA), a nearby cortical region that responds strongly whenever faces are viewed, and that is believed to be important for face recognition.
Social context
Additional research has suggested that the right parahippocampal gyrus in particular has functions beyond the contextualizing of visual background. Tests by a California-based group led by Katherine P. Rankin indicate that the lobe may play a crucial role in identifying social context as well, including paralinguistic elements of verbal communication.
For example, Rankin's research suggests that the right parahippocampal gyrus enables people to detect sarcasm.
Additional images
File:Parahippocampal gyrus animation.gif, Animation. Parahippocampal gyrus shown red.
File:Gray727 parahippocampal gyrus.png, Medial surface of left cerebral hemisphere. Parahippocampal gyrus shown in orange.
File:Human brain inferior-medial view description.JPG, Human brain inferior-medial view. Parahippocampal gyrus labelled as #5
File:Gehirn Frontalschnitt hippocampus.png, Coronal section. Parahippocampal gyrus labelled at bottom center.
File:Hippocampus (brain).jpg, Coronal section of hippocampus. Parahippocampal gyrus labelled at bottom.
File:Gehirn, basal - beschriftet lat.svg, Basal view of a human brain.
File:Parahippocampal gyrus.jpg, Basal view of a human brain. Parahippocampal gyrus shown in yellow.
File:Slide4MIR.JPG, Close up of parahippocampal gyrus.
Parahippocampal - DK ATLAS.png, Parahippocampal gyrus, shown in right cerebral hemisphere.
File:Parahippocampal gyrus coronal sections.gif, Parahippocampal gyrus highlighted in green on coronal T1 MRI images
File:Parahippocampal gyrus sagittal sections.gif, Parahippocampal gyrus highlighted in green on sagittal T1 MRI images
File:Parahippocampal gyrus transversal sections.gif, Parahippocampal gyrus highlighted in green on transversal T1 MRI images
References
External links
*
* https://web.archive.org/web/20090505072544/http://www2.umdnj.edu/~neuro/studyaid/Practical2000/Q35.htm
Temporal-lobe.com An interactive diagram of the rat parahippocampal-hippocampal region
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Hippocampus (brain)
Gyri