Extrastriate cortex
| Extrastriate Cortex | |
|---|---|
 Extrastriate cortex is shown in yellow on this picture of a brain (Brodmann area 19) and orange (Brodmann area 18). Striate cortex (Brodmann area 17) is shown in red. | |
| Details | |
| Identifiers | |
| Latin | Area extrastriata |
| NeuroLex ID | nlx_anat_200905010 |
| Anatomical terms of neuroanatomy | |
The extrastriate cortex is the region of the occipital cortex of the mammalian brain located next to the primary visual cortex, which is also named striate cortex because of its appeareance in the microscope. The extrastriate cortex encompasses multiple functional areas, including V3, V4, V5/MT.[1] The extrastriate body area (EBA) is used in the perception of human bodies.[2]
Anatomy
In terms of Brodmann areas, the extrastriate cortex comprises Brodmann area 18 and Brodmann area 19, while the striate cortex comprises Brodmann area 17.[3]
In primates, the extrastriate cortex includes visual area V3, visual area V4, visual area MT (sometimes called V5),[3] and visual area DP, while V1 corresponds to the striate cortex, and V2 to the prestriate cortex.
Function
The extrastriate cortex is a category-selective region for the visual processing of static and moving images of the human body and parts of it. It is also modulated even in the absence of visual feedback from the limb movement. It is insensitive to faces and stimulus categories unrelated to the human body. The extrastriate cortex responds not only during the perception of other people’s body parts but also during goal-directed movement of the participant's body parts.[2] The extrastriate cortex represents the human body in a more integrative and dynamic manner, being able to detect an incongruence of internal body or action representations and external visual signals. In this way, the EBA might be able to support the disentangling of one's own behavior from another's.[4]
Experiments and Research
As published in the article, “A Cortical Area Selective for Visual Processing of the Human Body,”[5] researcher, Paul E. Downing, Yuhong Jiang, Miles Shuman and Nancy Kanwishe, first discovered the EBA in 2001. The experiment originally intended to find out what area of the brain dealt with the human form and recognition of body parts, as the face had been mapped to a specific area of the brain (Fusiform Face Area, FFA)by Nancy Kanwisher in 1997. What the experiment found was a specific area of the lateral occipitotemporal cortex that responds selectively to visual images of human bodies and body parts, with the exception of faces.
The experiment had subjects view images of different objects, including faces (as a control group), body parts, animals, parts of the face and intimate objects. While viewing the images, the subjects were scanned via an fMRI to see what area of the brain was activated. Through the trials and compilation of the fMRI’s, a specific region was determined to have increased activity when shown visual stimuli of body parts and even more activity when viewing whole bodies.
There have been no studies involving brain damage to the EBA. Thus far, only scans of brain activity, as well as transcranial magnetic stimulation, have been used to study the EBA. To find the specific functions of the EBA, Comimo Urgesi, Giovanni Berlucchi and Salvatore M. Aglioti used repetitive transcranial magnetic stimulation (rTMS) to disrupt part of the brain, making the brain less responsive in the target area. The study used event-related rTMS to disrupt the EBA, resulting in inactivation of cortical areas. This inactivation caused a slower response time in discriminating body parts. The study used facial features and motorcycle parts as non human parts for control groups. The facial features and motorcycle body parts did not display any change in response time. The neural activity data shows the EBA handles some of the visual processing of human body and parts but is not related to the processing of the face or other objects.
The actual experiment had people make a “two-choice matching-to-sample task. Fourteen right handed participants were required to decide which of two similar upper-limb images matched a single sample previously seen during a tachistoscopic exposure. Photos of face parts and motorcycle parts served as control stimuli in two-matching-to-sample tasks that were comparable to the former task.”[6] rTMS was then applied 150 ms after each sample exposure. The section of the graph, Body Parts, shows the response time while using rTMS. The SHAM category refers to measuring the EBA without rTMS while viewing the images. The Visual Cortex category measures the response of the FFA to be used as the control of the experiment. This measurment of response time, occuring while rTMS was effecting the EBA, further shows that the two areas process visual data of the human form, yet respond to different stimuli. While the magnetic stimulation was temporarily disabling the extrastraite body area, reaction time decreased by about 100 ms. The data from the Sham and Visual Cortex categories on the graph show what was the expected normal results from the experiment. This evidence reveals that applying rTMS to the EBA slowed the response of recognizing images of body parts.[6]
See also
References
- ^ Guy A. Orban. Higher Order Visual Processing in Macaque Extrastriate Cortex. Physiol Rev January 1, 2008 88:(1) 59-89; doi:10.1152/physrev.00008.2007
- ^ a b "Extrastriate body area in human occipital cortex responds to the performance of motor actions"
- ^ a b
R.F. Schmidt and G. Thews (eds.), ed. (1983). Human Physiology (second, completely revised edition). Berlin, Heidelberg, New York: Springer-Verlag. p. 725. ISBN 0-387-11669-9.
{{cite book}}:|editor=has generic name (help); Cite has empty unknown parameter:|coauthors=(help) - ^ "The Extrastriate Cortex Distinguishes between the Consequences of one’s Own and Other’s Behavior"
- ^ "A Cortical Area Selective for Visual Processing of the Human Body"
- ^ a b Urgesi, Cosimo (14). "Magnetic Stimulation of Extrastriate Body Area Impairs Visual Processing of Nonfacial Body Parts". Current Biology. 14: 2130–2134. Retrieved Nov. 7, 2011.
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