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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