PSYCH 2NF3 Chapter Notes - Chapter 14: Posterior Parietal Cortex, Postcentral Gyrus, Supramarginal Gyrus

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25 Aug 2016
The parietal region of the cerebral cortex lies between the frontal and occipital lobes, underlying the parietal bone at the roof of the skull
This area is roughly demarcated anteriorly by the central fissure, ventrally by the lateral (Sylvian) fissure, dorsally by the cingulate gyrus, and posteriorly parieto-
occipital sulcus
The principle regions of the parietal lobe include the postcentral gyrus (Brodmann's areas 3-1-2), superior parietal lobule (areas 5 and 7), parietal operculum (area
43), supramarginal gyrus (area 40), and angular gyrus (area 39)
Supramarginal gyrus and angular gyrus = INFERIOR PARIETAL LOBE
Anterior zone including areas 3-1-2 and 43=43 somatasensory cortex
Posterior zone includes area 5,7,40, and 39= posterior parietal cortex
Through human evolution, the parietal lobes have undergone major expansion, specifically in inferior region
Three posterior parietal areas = PE, PF, and PG
PG=areas 43 and 40 plus part of 7
PE=areas 5 and remainder of 7
PG= ~39 and 40 (primarily visual)
Von Economo's map= described in humans and monkeys
Areas significantly expanded in the human brain are the polymodal parts of area PG and adjoining polymodal cortex in the STS
Polymodal cells receive inputs from more than one sensory modality
Those in PG response to both somatosensory and visual inputs
STS respond to auditory, visual, and somatasensory inputs
PG and STS are asymmetrical - may be due to a much larger area PG (and maybe STS) on the right than on the left.
If PG has a visual function and is larger in humans, especially in the right hemisphere, then we might expect unique visual symptoms after right parietal lesions
PG is larger on the left in the human than in the monkey
Subdivisions of the parietal cortex
Anterior parietal cortex makes straightforward connections
Motor connections are important for providing sensory info about limb position in movement control
Projections from the primary somatosensory cortex (area 3-1-2) extend to secondary somatosensory area PE (area 5), which has a tactile recognition function, we
well as to motor areas including the primary motor cortex (area 4) and the supplementary motor and premotor regions (area 6) in the frontal lobes
Cortical outputs are to the primary motor cortex (area 4) and to the supplementary motor (SMA) and premotor (6 &8) and PF
Plays some role in guiding movement by providing information about limb position
Area PE (area 5 & part of 7)=somatosensory, receiving most of its connections from the primary somatosensory cortex (area 3-1-2)
PF's efferent connections are similar to PE, and these connections presumably elaborate similar info for the motor systems
Area PF (part of 7) has input from the primary somatosensory cortex (area 3-1-2) through area PE. Also receives inputs from the motor and premotor cortex and a
small visual input through area PG
"parieto-temporo-occipital crossroads"
Intermodal mixing
Part of the dorsal stream that controls spatially guided behavior with respect to visual and tactile information
Area PG (part of 7 and visual areas) receives more-complex connections including visual, somesthetic (skin sensations), proprioceptive (internal stimuli), auditory,
vestibular (balance), oculomotor (eye movement), and cingulate (motivational?)
Connections of the parietal cortex
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Part of the dorsal stream that controls spatially guided behavior with respect to visual and tactile information
Prefrontal and posterior parietal regions project to the same areas of the paralimbic cortex and temporal cortex as well as t o the hippocampus and various
subcortical regions
These connections emphasize a close functional relation between the prefrontal and parietal cortices - important role in controlling spatially guided
Close relation between the posterior parietal connections and the pre-frontal cortex (especially area 46) are apparent in the connections between posterior
parietal cortex (PG and PF) and the dorsolateral prefrontal region
PARIETO-PREMOTOR- principal "how" pathway
PARIETO- PREFRONTAL- visuospatial functions (especially related to working memory)
PARIETO-MEDIAL- flows directly to hippocampus and parahippocampal regions as well as indirectly via the posterior cingulate and retrosplenial cortex, is
proposed to have a role in spatial navigation
Three functional pathways leaving the posterior parietal region and travel to the premotor, prefrontal, and medial temporal regions
Posterior parietal cortex would contribute to the dorsal stream by participating in nonconscious visuospatial behavior - ex. Reaching for and grasping objects
Anatomy of the dorsal stream
Anterior parietal zone (somatosensory): somatic sensations and perceptions
Play a significant role in mental imagery - object rotation and navigation through space
Posterior parietal zone (spatial): integrating sensory input from the somatic and visual regions and to a lesser extent from other sensory regions, mostly for controlling
movements- reaching and grasping as well as whole-body movements in space
We need spatial information about the location of objects in the world, both to direct actions at those objects and to assign meaning and significance to them -
spatial information is simple another property of visual information
Object's location and its local orientation and motion must be determined relative to the viewer
Brain operates on a "need-to-know" basis. Having too much info may be counterproductive for any system
With the viewer- centered system, the object-centered system must be concerned with such properties as the object's size, shape, color, and relative
location so that the objects are recognized when they are encountered in different visual contexts or from different vantage points
Temporal lobe codes objects' relational properties. Part of this coding probably occurs in the polymodal region of the superi or temporal sulcus and another
part in the hippocampal formation
Object recognition
Connections to the prefrontal region have a role in short-term memory for the location of events in space
They receive combinations of sensory, motivational, and related motor inputs
Their discharge is enhanced when an animal attends to a target or moves toward it
Posterior parietal neurons have two important characteristics:
These neurons are well suited to transforming requisite sensory information into commands for directing attention and guiding motor output
Posterior parietal lesions impair movement guidance and detection of sensory events
Movement guidance
As we move, the locations of our body parts change, and perceptions of our body must constantly be updated so that we can mak e future movements
smoothly - neural calculations = SENSORIMOTOR TRANSFORMATION. Cells in the posterior parietal cortex produce both the movement - related and the
sensory related signals to make them
PRR is coding not the limb variables required to make the movement but the desired goal of the movement (ex. Goal of grasping a cup, rather than
the details of the movements toward the cup)
Area PRR is active when participant is preparing and executing a limb movement
Sensorimotor transformation
Route knowledge is found in medial parietal region (MPR), which includes the parietal region ventral to the PRR as well as th e adjacent posterior cingulate
cortex, part of the parieto-mediotemporal pathway in the dorsal stream
Neurons in dorsal visual stream = participate in route knowledge, we must make specific visually guided movements at specific locations in our journey
Like the cells in PRR, which control the planning of limb movements to locations, the cells in MPR control only body movement s to specific locations
Spatial navigation: we have a "cognitive spatial map" in our brains as well as a mental list of what we do at each spatial location (route knowledge)
Behavioral uses of spatial information
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