Chapter 14 - Parietal Lobes

what were the symptoms of a growing tumour in left parietal lobe?

* simple math errors
* trouble reaching for obj
* confuse left and right
* some words appeared backward or upside down

what does the parietal cortex process and integrates?

* somatosensory and visual info
* esp w/ regard to controlling movement

what demarks the parietal lobe as as anterior?

central fissure

what demarks the parietal lobe as ventral?

lateral (Sylvian) fissure

what demarks the parietal lobe as dorsal?

cingulate gyrus

what demarks the parietal lobe as posterior?

parietal-occipital sulcus

what are the principle regions of parietal lobe?

* postcentral gyrus (Brodmann’s areas 3-1-2)
* superior parietal lobule (area 5 & 7)
* parietal operculum (area 43)
* supramarginal gyrus (area 40)
* angular gyrus (39)

what are the supramarginal gyrus and angular gyrus often referred to as?

inferior parietal lobe

what includes the anterior zone?

* areas 3-1-2
* 43

what includes the posterior zone?

remaining areas

what is the anterior zone?

* somatosensory cortex

what is the posterior zone called?

posterior parietal cortex

what part of parietal lobe has undergone a major expansion?

inferior region mostly

have we found areas 39 and 40 in monkey brain?

no

how many posterior parietal areas are there in Von Economo’s map found in both monkeys and human brain?

* 3
* PE, PF, PG

what other areas in human brain has sig expanded?

* consists of the polymodal parts of area PG and adjoining polymodal cortex in the superior temporal sulcus (STS)

where do polymodal cells receive inputs from?

more than one sensory modality

what do cells in PG respond to?

both somatosensory and visual inputs

what do cells in STS respond to?

various combos of auditory, visual, and somatosensory inputs

what can the asymmetry of PG and STS be because of?

much larger area PG (possibly STS too) on the right than on the left

what can we expect if PG area gets lesion?

* unique visual symptoms

what specific parts of parietal regions that part in dorsal stream of visual processing?

* intraparietal sulcus (cIPS)
* parietal reach regions (PRR)

how were human and monkey map mapped?

* human → fMRI
* monkey → single-neuron recording techniques

what do regions in the intraparietal sulcus contribute to controlling?

* saccadic eye movement (area LIP) and
* visual control of obj-directed grasping (AIP)

what does PRR have role in?

visual guided grasping movements

what is a saccade?

series of invulun, abrupt, and rapid small movements or jerks made by both eyes simultaneously in changing the pnt of fixation

how many pathways were identified leaving the posterior parietal regions?

* 3
* travels to either, premotor, prefrontal, and medial temporal regions

what is the parieto-premotor pathway proposed to be?

principle of “how” pathway

what is the parieto-frontal pathway proposed to be?

to have visuospatial funcs, esp related to visuospatial working memo

what odes the parieto-medial temporal pathway do?

proposed to have a role in spatial navigation

where does the parieto-medial temporal pathway flow to?

* directly to the hippocampus and parahippocampal regions
* indirectly via posterior cingulate and retrosplenial cortex

would does posterior parietal cortex contribute to and how?

* to the dorsal stream
* by participating in nonconscious visuospatial behv
* reaching for and grasping objs

what have parietal lobe injuries demonstrated?

the parietal lobe plays a central role in creating a brain map

is there evidence for a map in the brain?

* not rlly
* it is actually more likely that there is a series of neural representations of space that vary in 2 ways


1. diff representations serve diff behv needs
2. spatial representations vary, from simple ones applicable to controlling simple movements to abstract ones that may represent info such a topographic knowledge

what is spatial info another property of?

visual info

what must visuomotor control must be for spatial info needed to guide eye, head, or limb movements to obj?

viewer-centered → obj location and its local orientation and motion must be determined relative to the viewer

what details are irrelevant for visuomotor guidance?

object characteristics such as colour

what does the brain operate on?

a “need-to-know” basis

what does obj centrered sys be concerned with?

characteristics such a obj size, shape, colour and relative locations so that the objs are recog when they are encountered in diff visual contexts or form diff vantage pnts

what does the temporal lobe codes?

* obj’s relational properties
* prob occurs in polymodal regions of of STS and hippocampal formations

what does accommodating many differing viewer-centered movement requires?

* separate control sys
* e.g., eye control based on optical axis of eye, whereas limb control is based on positions of the shoulders and hips

what do results of single-cell studies in posterior parietal lobes of monkeys confirm?

* the posterior parietal’s role in visuomotor guidance
* the activity of these neurons depends on the concurrent behv of an animal w/ respect to visual stimulations

when are most neurons in posterior parietal region active?

* both during sensory input and during movement
* e.g., some cells show only weak responses to stationary visual stimuli, but if the animal makes an active eye or arm movement toward the stimulus or even if it just shifts its attention to the obj, the discharge of these cells is strongly enhanced

what happens with lesions in posterior parietal lobe?

impairs movement guidance and may detecting sensory events

what are cells in monkey responding to when they manipulate obj?

* structural features, such as size and orientation → sensitive to the features that determine the hand’s posture during obj manipulation

what are the things that the responses of posterior parietal neurons have in common?

1. they receive combo of sensory, motivational, and related motor inputs
2. their discharge is enhance when an animal attends to a target or moves toward it

* these neurons r well suited to transforming requisite sensory info into commands for directing attention and guiding motor output
* allows to predic that posterior pariet

when we move toward obj, we must integrate movements of various body part with what?

sensory feedback of what movements are actually being made → efferent copy and the plans to make the movements

when we move, the locations of our body parts change, and perceptions of our body must constantly be updated so that we can make future movements smoothy, what is this called?

sensorimotor transformation

what do cells in the posterior parietal cortex produce in terms of sensorimotor transformation?

* movement related and
* sensory related signal to make em

when is area PRR active?

* when participant is preparing and executing a limb movement

what is PRR coding?

* the desired goal of the movement NOT the limb variables required to make the movement
* e.g., goal of grasping cup rather than detail of movement towards cup

Andersen’s group studied what?

* decoded from parietal neural activity the animals’ intentions to reach to position a cursor on scree
* monkeys first were trained to make a series of reaches to touch different locations on a computer screen.
* Their cell activity was analyzed to determine which activity was associated with movement to each location.
* The monkeys then were instructed with a briefly flashed cue to plan to execute a reach to another location but without making a movement.
* Their cellular activity was compared with activity associated with actual movements to the requested target.
* If it was the same as in an actual movement, the monkeys were rewarded with a drop of juice in the mouth and visual feedback showing the correct location.

why is the monkey experiment important?

* study is foundational to dev neuroprosthetic devices that enable paralyzed people and amputees to use mental activity to move prosthetics and even to feel what they are touching
* For example, an array of electrodes can be implanted over the PRR and the recorded activity used to move the mechanical devices. The implications of such advances could go well beyond limb movements. Implants over speech areas might allow a verbal readout of thoughts, thus bypassing cumbersome letter boards and spelling programs. Similarly, one could ask patients questions and have them move a cursor mentally to identify the correct answers, thus gaining access to a wide variety of their thoughts and even emotions

what has been a key to neuroprosthetic applications?

technological dev enabling use of multiple recording channels that confer redundancy of control and hence reliability

can behaviourally meaningful info be transferred between brains of 2 rats?

* yes
* in experiment, an “encoder” rat performed a tactile discrimination task while samples of neural activity were recorded from the parietal cortex
* This activity was transmitted through microstimulation electrodes in another rat that learned to make behavioral selections solely via the information provided the encoder rat’s brain.
* Clearly, transforming sensorimotor activity into action using a brain-to-brain interface for realtime sharing is in its infancy and poised to grow

what is route knowledge?

* internal lists of what we do at each spatial location in cog spatial map

where is route knowledge located in brain?

* dispersed in:
* medial parietal region (MPR) → parietal region ventral to PRR and adjacent posterior congulate cortex
* part of the parieto-mediotemporal pathway in dorsal stream

what do three-quarter of the cells in the MPR show response to?

* specific movement at a specific location
* same movement in a diff location did not activate the cells
* can conclude that cells in MPR control only body movements to specific locations

what would happen if researches inactivate the MPR pharmacologically in monkeys?

they become lost and failed to navigate correctly → act like human patients with medial parietal lesions

what is the first aspect of theory parietal lobe func?

considers the users spatial info for recog obj and guiding movement

what is the second aspect of spatial representation?

* complexity
* e.g., viewer-centered representations, mental roation are complex

can peep w/ posterior pareital lesions do mental manipulations?

no

what are mathematics and arithmetic related problems related to?

quasi-spatial nature analogous to mentally manipulating concrete shapes but entailing the manipulation of abstract symbols correct solutions.

what is acalculia?

* inability to perform mathematical operations bc of the task’s spatial nature

what area may arithmetic operations depend on?

* polysensory tissue
* found at the temoroparietal junction → where temporal and parietal lobes meet at the end of sylvian fissure

can lang also be seen as quasi-spatial?

* yes
* patients with damage may understand individual ele clearly, but they cannot understand the whole when the syntax becomes important

language may rely on what?

polysensory tissue found at the temoroparietal junction as well

can people with parietal-lobe injuries copy movements?

have difficulties

also relate to polysensory tissue found at the temoroparietal junction

snapshot - Spatial Cognition and White Matter Organization

* Studies of lesion patients and noninvasive imaging reveal that the posterior parietal cortex carries out mental transformations such as object rotation
* sex diff favours males in mental obj transformation
* neuroanatomy and cog strategies influence this
* white matter differences was tested for in male participants
* recorded a tight relation between mental spatial rotation proficiency and white-matter organization near the anterior part of the intraparietal sulcus.
* includes a variety of factors such as myelinization, axon diameter and density, and fiber crossing.
* note: this was done on males ONLY
* some say no sex-related difference appears in the vol of posterior parietal cortex area, but interperson variability in the size of diff regions was sig larger in males

what is damage to the postcentral gyrus typically associated with?

marked changes in somatosensory thresholds

what did focal cortical surgery help with?

relieving epilepsy

what do lesions of the postcentral gyrus produce?

* high sensory thresholds,
* impaired position sense
* deficits in stereognosis
* afferent paresis

what is stereognosis?

* tactile perception
* e.g., patients performed poorly at detecting a light touch to the skin (pressure sensitivity), determining whether they were touched by one or two sharp points (two-point sensitivity), and localizing points of touch on the skin on the side of the body contralateral to the lesion. If blindfolded, these patients also had difficulty reporting whether the fingers of the contralateral hand were passively moved.

what is afferent paresis?

* loss of kinesthetic feedback that results from lesions to the postcentral gyrus (areas 3-1-2)
* finger movements are clumsy bc the person has lost the necessary feedback abt their exact positions

what is astereognosis?

* inability to recog the nature of an obj by touch

what kind of tests done for astereognosis?

Objects are placed on the palms of blindfolded subjects, or the subjects are told to handle shapes. The task is to match the original shape or object to one of several alternatives solely on the basis of tactile information.

what is simultaneous extinction?

can only report one obj when presented with two of the same

what is a test for simultaneous extinction?

tests for simultaneous extinction present two tactile stimuli simultaneously to the same or different body parts. The objective is to uncover those situations in which both stimuli would be reported if applied singly but only one would be reported if both were applied tgt

what is it called when cant report one stimulus in simultaneous extinction test?

extinction

what is extinction associated with (damage to what area)?

* secondary somatic cortex (areas PE + PF), esp in the right parietal lobe

what is is called when patient can point with her left hand to locations on her right hand where she had been touched even tho she failed to report feeling the touch?

* numb touch
* tactile equivalent of blindsight

what is numb touch associated with (what lesions?)?

areas PE, PF and some of PG

what does tactile analog of blindsight suggests?

existence of 2 tactile sys - one specialized for detection and the other for localization

how many major somatosensory agnosias are there?

* 2
* astereognosis and asomatognosia

what is asomatognosia?

loss of knowledge or sense of one’s own body and bodily condition

what are the varieties of asomatognosia?

* anosognosia → unawareness or denial of illness
* anosodiaphoria → indifference to illness
* autopagnosia → inability to localize and name body parts
* asymbolia for pain → absence of typical reactions to pain, such as reflexive withdrawal from a painful stimulus

what side of body can asomatognosias affect?

* both sides
* most common on left side as a result of right-hemis lesions

what is the most common autopagnosia?

finger agnosia → condition in which a person is unable either to pnt to the various fingers of either hand or to show them to an examiner

what relation exists between finger agnosia and dyscalculia (difficulty in performing arithmetic operations)?

* if unable to use fingers to counts, will have difficulty learning arithmetic during childhood since use fingers to count

in what condition is finger agnosia present in?

spina bifida

what were the 3 peculiar symptoms in patient with bilateral parietal lesion in Balint’s syndrome?

1. could move his eyes but could not fixate on specific visual stimuli
2. simultagnosia → field of attention was limited to one object at a time
3. optic ataxia → severe deficit in reaching under visual guidance

when can optic ataxia develop?

* unilateral and bilateral lesions in posterior parietal lesions


* specifically, lesions in superior parietal region (area PE)

symptoms of contralateral neglect?

* neglected left side of body
* crowded all num on one side of clock when ask to draw it
* would read right side of word in compound word
* e.g., only “cream” in ice-cream

what is the disorder where one is impaired at combining blocks to form designs?

constructional apraxia

part of contralateral neglect

topographic disability symptoms?

* being unable to draw maps of well known regions from memory. He attempted to draw a map of his neighborhood, but it was badly distorted with respect to directions, spatial arrangement of landmarks, and distances.
* knew where he was and what day it was, and he could recognize his family’s faces. He also had good language functions: he could talk, read, and write normally.

what are the stages of recovery for contralateral neglect?

1. allesthesia → person beginning to respond to stimuli on the neglected side as if the stimuli were on the unlesioned side. Person responds and orients to visual, tactile, or auditory stimuli on the left side of the body as if they were on the right
2. simultaneous extinct → The person responds to stimuli on the hitherto neglected side unless both sides are stimulated simultaneously, in which case he or she notices only the stimulation on the side ipsilateral to the lesion.

where is damage in contralateral neglect?

both the right intraparietal sulcus and right angular gyrus

what is contralateral neglect occasionally observe in subsequent lesions where?

frontal lobe and cingulate cortex and subcortical structs including the superior colliculus and lateral hypothalamus

why does neglect arise?

caused by either


1. defective sensation or perception (stronger argument)
2. defective attention or orientation

integration and disruption terms in contralateral neglect?

morphosynthesis and amorphosynthesis