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PSY318H5 (12)
Chapter 14-17

Chapter 14-17 Notes

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Ayesha Khan

CHAPTER 14 PARIETAL LOBES Parietal cortex processes and integrates somatosensory and visual information, with regard to control of movement ANATOMY lies between the frontal and occipital lobes roughly demarcated anteriorly by the central fissure, ventrally by the lateral fissure, dorsally by the cingulate gyrus, and posteriorly by the parietal-occipital sulcus. Inferior parietal lobe: supramarginal gyrus and angular gyrus Parietal lobe can be divided into 2 functional zones o Anterior zone: somatosensory cortex o Posterior zone: posterior parietal cortex PG (parietal area G) has visual function and is larger in humans (especially in the RH). PE has tactile recognition function Specific parietal-lobe regions take part in DORSAL STREAM of visual processing: o cIPS = intraparietal sucus control in saccadic eye movements (area LIP) and visual control of object-directed grasping (AIP) o PRR = parietal reach regions Role in visually guided grasping movements Saccade is a series of involuntary, abrupt and rapid small movements or jerks made by both eyes simultaneously changing the point of fixation Anterior parietal cortex has connections from the primary somatosensory cortex to the PE, as well as motor areas (including primary motor cortex and supplementary motor and premotor regions) Motor connections must be important for providing sensory info about limb position in control of movement Area PE is a somatosensory area, receiving most of its connections from primary somatosensory cortex. o Cortical outputs are to the primary motor cortex and to supplementary motor (SMA) and premotor regions, as well as to PF o Plays role in guiding movement by providing info about limb position Area PF has heavy input from primary somatosensory cortex, through area PE. o Receives inputs from motor and premotor cortex and small visual input through area PG www.notesolution.com o Provide elaboration on similar info for the motor systems as PE Are PG receives more-complex connections including visual, somesthetic (skin responses) proprioceptive (internal stimuli), auditory, vestibular (balance), oculomotor (eye movement) and cingulate (motivational) o A part of the dorsal stream o Role in controlling spatially guided behaviour with respect to visual and tactile info Close relations between posterior parietal connections and the prefrontal cortex o Therefore, connections between posterior parietal cortex and dorsolateral prefrontal regions o Important role in control of spatially guided behaviour. THEORY OF PARIETAL-LOBE FUNCTION Anterior zone processes somatic sensations and perceptions Posterior zone is specialized primarily for integrating sensory input from somatic and visual regions and to other sensory regions, for control of movement USE OF SPATIAL INFORMATION spatial information about the location of objects in the world is needed both to direct action sat those objects and to assign meaning and significance to them spatial information is coded in more than one way Two types of form recognition 1) Object Recognition: spatial information needed to determine the relations between objects, independent of what the subjects behaviour might be, is very different form the spatial information needed to guide eye, head or limb movements to object. visuomotor control must be viewer-centered location, orientation and motion must be relative to the viewer object characteristics, like colour, are irrelevant to visuomotor guidance, not needed to guide hand action brain operates on a need to know basis too much information can be counter productive However! Object-centered system must be concerned with properties such as size, shape and colour and relative location so object can be recognized in different visual contexts or vantage points Details in O-C system are important 2) Guidance of Movement: www.notesolution.com posterior parietal cortex has role in viewer-centered system prefrontal region have a role in short-term memory of location of events in space most neurons in posterior parietal region are active both during sensory input and during movement neurons are sensitive to the features of an object that determine the posture of the hand during manipulation neuron responsiveness to movements of the eyes and location of the eye in its socket cells detect visual information and then move the eye to get fine vision of the fovea to examine it cells are affected by the motivational characteristic of information such as cue signaling the availability of a reward Responses of posterior parietal neurons have 2 characteristics in common They receive combination of sensory, motivational and related motor inputs Discharge is enhanced when an animal attends to a target or makes a movement toward it These neurons are therefore well suited to transforming the necessary sensory info into commands for directing attention and guiding motor outputs Blood flow increases preferentially in the posterior parietal region when subjects direct their attention to visual targets in the studied spot of the visual field Posterior parietal region plays a significant role in directing movements in space and in detecting stimuli in space Superior parietal cortex plays a role in the control of eye movements, which has significant implications for PET studies of o Blood flow to posterior parietal cortex when identifying different spatial locations is evidence that the DORSAL stream of processing deals with spatial processing SENSORIMOTOR TRANSFORMATION: when we move towards an object, we must integrate the movements of different body parts with sensory feedback of what movements are actually being made (efference copy) and plans to make the movements. As we move, locations of our body parts change and must constantly be updated. Neural calculations are called sensorimotor transformation. cells in the posterior parietal cortex produce both the movement- related and the sensory-related signals to make these also important in movement planning www.notesolution.com o Pareital Reac Region (PRR) is active when subject is preparing and executing a movement o PRR is coding for the desired goal of the movement (not limbs required) Monkeys were first trained to make a series of reaches to touch different locations on a computer cell activity was analyzed to determine which activity was associated with movement to each location monkeys then instructed with a briefly flashed cue to plan to execute a reach to different locations but without making a movement thinking about reaching a target were observed in their brain activity SPATIAL NATIVATION Cognitive Spatial Map: needed when we travel and we take the correct turns at choice points until we reach our destination. Hypothetical map that allows us to visualize our spatial location Route Knowledge: mental list of what we do at each spatial location. o Unlikely to be in only one part of the brain o Medial parietal region (MPR) which includes parietal region ventral to the PRR as well as cingulate cortex. o Neurons in dorsal visual stream could be expected to participate in route knowledge must make specific visually guided movements at specific locations in our journey of the cells in MPR showed responses with specific movement at a specific location o same movement in different location did not activate cells MPR control only body movements to specific locations, and PRR control the planning of limb movements to locations o Inactivation of MPR, monkeys lost and failed to navigate correctly COMPLEXITY OF SPATIAL INFORMATION use of spatial info for object recognition and for guiding Concept of left and right are viewer-centered and complex but need not require movement Visualize objects and manipulate these mental images spatially bt posterior parietal lesions impare it OTHER ASPECTS OF PARIETAL FUNCTION 3 parietal lobe symptoms do not fit simple view of lobe as visuomotor control center: 1) Arithmetic: have quasi-spatial nature analogous to mental manipulation of concrete shapes, but entailing abstract symbols. www.notesolution.com
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