Human brain seen from below. Parahippocampal gyrus shown in blue
Medial view of left cerebral hemisphere. Parahippocampal gyrus shown in orange.
The parahippocampal gyrus (Syn. hippocampal gyrus) is a grey matter cortical region of the brain that surrounds the hippocampus and is part of the limbic system. This region plays an important role in memory encoding and retrieval. It has been involved in some cases of hippocampal sclerosis. Asymmetry has been observed in schizophrenia.
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.
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.
Coronal section of hippocampus. Parahippocampal gyrus labelled at bottom.
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- Ferreira NF, de Oliveira V, Amaral L, Mendonça R, Lima SS (September 2003). "Analysis of parahippocampal gyrus in 115 patients with hippocampal sclerosis". Arq Neuropsiquiatr. 61 (3B): 707–11. doi:10.1590/s0004-282x2003000500001. PMID 14595469.
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- Mégevand P, Groppe DM, Goldfinger MS, et al. (2014). "Seeing Scenes: Topographic Visual Hallucinations Evoked by Direct Electrical Stimulation of the Parahippocampal Place Area". Journal of Neuroscience. 34 (16): 5399–5405. doi:10.1523/jneurosci.5202-13.2014.
- Epstein R (1998). "A cortical representation of the local visual environment". Nature. 392 (6676): 598–601. doi:10.1038/33402. Retrieved 2009-11-03.
- Aguirre; et al. "The Parahippocampus Subserves Topographical Learning in Man". Cerebral Cortex. 6 (6): 823. doi:10.1093/cercor/6.6.823. Retrieved 2009-11-03.
- "Neuron - An Area within Human Ventral Cortex Sensitive to "Building" Stimuli". Retrieved 2009-11-03.[permanent dead link]
- Ishai A (1999). "Distributed representation of objects in the human ventral visual pathway — PNAS". Proceedings of the National Academy of Sciences. 96 (16): 9379–9384. doi:10.1073/pnas.96.16.9379. PMC 17791. Retrieved 2009-11-03.
- Hurley, Dan (2008-06-03). "Katherine P. Rankin, a Neuropsychologist, Studies Sarcasm - NYTimes.com". The New York Times. Retrieved 2009-11-03.
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