Polymodal+Receiving+Area

AREA 7 & THE SUPERIOR-POSTERIOR PARIETAL LOBULE

Connections From
-Primary Somesthetic Area -> Association Somesthetic Area -> Area 7 -Visual receiving areas of occipital and middle temporal lobe -Motor and non-motor areas of lateral convexity -Inferior parietal and temporal lobe (including parahippocampal gyrus)

Also has auditory receptive capacities (determining sound location) Cells in area 7 process both body-referenced and world-referenced signals, which provide information for the control of gaze and navigation and movement in space.

Polymodal Information Processing
Concerned with the highest levels of somesthetic integration. Heavily involved in the analysis and integration of higher order visual, auditory and somesthetic information, and single neurons often have quite divergent capabilities.

Three-Dimensional Analysis Of Body-Spatial Interaction
A single area 7 neuron can monitor activities occuring in many different body parts simultaneously Via the reception of auditory, somesthetic, and visual input, area 7 is thus also able to create a three-dimensional image of the body in space. Cells in this area also receive information about the interaction of the body with external objects and events in visual space. Many become highly active when the hand is moved toward or while reaching for and/or manipulating objects. They also act to coordinate and guide gaze and whole body-positional movement through visual and auditory space.

"Generates an internal neural construction of the immediately surrounding space, of the location and movements of objects within it in relation to body position, and of the position and movements of the body in relation to that immediately surrounding space. The region appears in general to be concerned with continually updating information regarding the relation between internal and external coordinant systems"

Visual-Spatial Properties
The parietal lobe, in part, evolved from the hippocampus, and maintains rich interconnections with this nucleus via the parahippocampal gyrus. Given that the hippocampus is concerned with the body-in-space, and with the position of various objects and stimuli in visual space, not surprisingly, the parietal lobe performs similar functions.

Like some hippocampal neurons, single parietal neurons are also involved in the representation of space as well as the body in space including topographic learning. Area 7 neurons also have quite large visual receptive fields, sometimes occupying a whole quadrant, hemifield, or the entire visual field. However, the receptive visual fields of these neurons do not usually include the fovea and are more sensitive to objects in the periphery and lower visual fields; i.e. where the hands, feet, and ground are more likely to be viewed.Many of these cells are not concerned with the identification of form but rather place, position, and reaching distance as well as depth perception and the coordination of the body as it moves through space. This requires that this area of the brain also participate in memory and place this information in short-term memory so that comparison can be made and information retained. Because many of the neurons in area 7 receive highly processed visual (as well as limbic) input, including information regarding ocular movement and direction of gaze, they are also responsive to and can determine a variety of visual-object qualities and interrelationships: -Motivational significance -Direction of movement -Distance -Spatial location -Figure-ground relationships -Depth - including discrimination and determination of an objects 3-dimensional position in space

Cells are largely insensitive to velocity or speed of movement. Many cells respond most to stimuli which are within grasping distance, whereas others respond most to stimuli which are just beyond arms reach.

Neurons are able to accomplish this by responding to somesthetic positional information provided by area 5, visual input from areas 18,19, and the inferior and middle temporal lobe and hippocampus, as well as from extraretinal signals regarding convergence and accomodation of the eyes, and the position and movement of the eyes while tracking.

By integrating these signals these cells are able to monitor and mediate eye movement and visual fixation, map out the three-dimensional positions of various objects in visual space, and determine the relation of these objects to the body and to other objects. Thus the visual analysis performed by many of these cells is largely concerned with visual spatial functions. This area also has extensive interconnections with the frontal eye fields and superior colliculus as well as visual areas 18 and 19.

-Elicits lateral eye movements -Also convergence, accomodation, and pupil dilation
 * Electrical stimulation**

-Impaired Depth perception -Impaired Figure-ground analysis -Inability to tract objects or to correctly manipulate objects in space (e.g. constructional and manipulospatial skills)
 * Damage**

Visual Attention
Many neurons act to -Increase or decrease visual fixation -Direct attention to objects of motivational significance -Promote the maintenance of visual grasp such that a moving object continues to be visually scanned and followed.

-Disrupted attentional functioning: extreme cases- neglect Neglect is most common with right cerebral lesions but in some instances may be seen initially following massive left cerebral destruction.
 * Damage/Lesions**

Circumscribed parietal lesions involving area 7, neglect is more pronounced for the lower visual fields. The lower visual fields, in turn are a predominant sensory domain of the parietal lobes, for this is the area of visual space in which the hands and feet are most likely to view -therefore making movement of the body in space more efficient. The lower visual field is also the area in which objects are most likely to be physically explored by the hand, which in turn are guided by the parietal lobe.

Motivational & Grasping Functions
Cells have been described as exerting "Command" functions - especially those located along the inferior lateral convexity. These are -Motivationally responsive -Can direct visual attention -Become excited when certain objects are within grasping distance -Can motivate and guide hand movements including the grasping and manipulation of specific objects

Most of these cease to fire when the object fixated upon is actually grasped, suggesting that they may be exerting some type of driving force or at least an alerting function so that objects of desire or of general (vs. specific) interest will be attended to.

Has been argued many neurons in area 7 execute a matching function between the internal drive state of the subject and the object which is being attended. i.e. responding to signals transmitted from the limbic system (cingulate gyrus) as well as the middle and inferior temporal lobe, these cells in turn direct visual attention to objects of potential interest, and when detected, act so as to maintain visual grasp. Although not concerned with form recognition, these cells will guide as well as monitor eye movement so that the object of interest is fixated upon. These cells then exert motor command functions so that the hand is guided toward the object until it is grasped.