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PSYC04H3 (1)
Chapter 14


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Zachariah Campbell

CHAPTER 14: THE PARIETAL LOBES ANATOMY OF THE PARIETAL LOBES Figure 14.1 shows the anatomy of parietal lobes SUBDIVISIONS OF PAREITAL CORTEX Inferior parietal lobe: supramarginal gyrus and angular gyrus 2 zones: anterior and posterior Anterior: includes postcentral gyrus (somatosensory cortex) and parietal operculum Posterior: inferior and superior parietal lobe Parietal separations: anterior-> central fissure ventral-> lateral fissure dorsal-> cingulate gyrus posterior-> parietaloccipital gyrus parietal lobes-> major expansion in evolution of humans specific pariatel lobe regions take part in dorsal visual processing intraparietal sulcus: contribute to control of saccades (and area LIP) A THEORY OF PERIETAL LOBE FUNCTION The anterior zone processes somatic sensations and perceptions; the posterior zone is specialized primarily for integrating sensory input from the somatic and visual regionsand, to a lesser extent from the other sensory regions, mostly for the control of movement. Some sort of internal representation of the location of diff objects around us seems obvious- a sort of map in the brain of where things are. furthermore, we assume that the map must be common to all of our senses, because we can move without apparent effort from visual to auditory to tactile information Parietal lobe plays central role in creation of this brain map Rather than a single map, there are a series of representations, diff representationds used for diff behavioural needs. Representations of space vary from simple to abstractones USES OF SPATIAL INFORMATION Recap difference beween egocentric and allocentric OBJECT RECOGNITION Milner suggests the brain oipperates on a need to know basis (selective attention) Temporal lobe- codes allocentric space between objects GUIDANCE OF MOVEMENT Posterior parietal-> egocentric-> viewer centered-> guiding movement-> space b/w me and object-> discovered via single cell recording study wit monkeys All posterior parietal neurons responsive to the movement of the eyes and location of the eye in its socket-> purpose is to signal the size of the saccade nessisary to move the visual stimulus into the fovea Posterior parietal: combining nessisary sensory input in order to construct commands for directing attention and guiding motor movement These cells may also play role in motivational characteristics of information ERPs can be used to study posterior parietal activity in humans-> large activity BEFORE an eyemovement occur-> suggests the planning of behaviour Evidence for dorsal stream-> spatial processing-> haxby found increase blood flow in posterior parietal cortex when subjects identified different spatial locations (but there is a complication in the interpretation of this finding cuz thisbloor flow could be in response to eye movements not spatial processing) We predict posterior parietal lesions result in impaired guidance of movement and perhaps detection of sensory events(because posterior parietal tells the eyes where to move in order to properly see a visual stimulus) Moving towards an object requires copies of afferent and efferent info SENSOYMOTOR TRANSFORMATION Posterior parietal region also produces sensorymotor transformations As we move, the location of our body parts changes, we must constantly be updated as to where our body parts are so that we can make future movements smoothly. Sensorymotor transofmation: refers to these neural calculations We can study planning of movement by implanting electrodes into PPR (posterior parietal region). This culd have implications for people who are paralyzed (we culd implant electrodes that read planning of movement, then the electrodes move a mechanical prosthetics.) or the electrodes could read what the person is trying to say, and a machine could read out the persons thought speech, thus bypassing letterboards and spelling progrms SPATIAL NAVIGATION Rout knowledge-> cognitive spatial map and mental list of directions-> allow us to travel subconsciously (you drive home without even thinking)-> MPR (medial parietal region) and PCC(posterior cingulate cortex) take part in this function-> dorsal visual stream neurons MPR neurons control body movements in a specific location Movement A and location B are necessary for MPR response MPR lesion-> you would be “lost” THE COMPLEXITY OF SPATIAL INFORMATION PRR lesion-> cant tell right from left-> impaired in mental manipulations -> mental manipulations are an elaboration of neural control of an actual physical manipulation, much as visualizing is an elaboration of actual perceotion of visual stimuli OTHER ASPECTS OF PARIETAL FUNCTION Alexander luria proposed that mathematics and arithmetic have a quasi-spatial nature analogus to the mental manipulation of concrete shapes but entailing abstract symbols. Acalculia: inability to do arithmetic (pariatel region damage) due to the spatial nature of arithmetic Language has many of the same demands as arithmetic- also quasi-spatial This abvility too, may depend on the polysensory region at the temporoparietal junction. In summary: PRR controls visuomotor guidance of movements in egocentric space. The polymodal region of the PPR also important for math, and reading , mental rotations and manipulation of visual images to sequencing movements. SOMATOSENSORY SYMPTOMES OF PARIETAL LOBE-LESIONS Postcentral gyrus lesion-> somatosensory thresholds become abnormaly high-> (means decreased sensitivity to somatosensory stimuli)-> impaired position sense-> impaired stereognosis (haptic perception)-> afferent paresis: is movements of the fingers are clumsy b/c person has lost feedback about the location of their fingers SOMATOPERCEPTUAL DISORDERS Astereogensis (greek for solid): inability to recognize the nature of an object by touch Simultaneour extinction: failure to report one stimulus is called extinction Figure 14.6 testing for simultaneous extinction When shown 2 of the same object, patient only sees the object in the right visual field When shows 2 different obvjects, the patient sees objects in both visual vields When shows 2 kinds of the same object, patient only sees object in right visual field Extinction- associated with damage to somatic secondary cortex BLIND TOUCH Tactile analogue to blind sight. Suggests that there are 2 specilized systems involved with haptic perceprion One for detectiction of stimuli and the other for localization Ex. Woman had lesions resulting in complete anesthesia of her right side, shecouldnt consciously feel anything with her right side but she could point with her left hand where she had been touched on her right side SOMATOSENSORY AGNOSIA 2 major types: astereognosis and asomatognosia Asomatognosia: the loss of knowledge or sense of ones own bod and bodily condition Varieties of asomatognosias include: Anosognosia (unawareness or denial of illness) Autopagnosia (inability to localize and name body parts) -> most common type is finger agnosia (unable to point to fingers or show them to examiner) Asymbolia for pain (absence of normal reactions to pain ie. Pain withdrawl reflex) Children who are unable to use their fingers to count (cuz they have a finger agnosia) have difficulty learning arithmetic SYMPTOMES OF POSTERIOR PARIETAL DAMAGE BALINT’S SYNDRO
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