Chapter 14: The Parietal Lobes and Networks PSY341

Portrait: Varieties of Spatial Information

H.P.: 28-year-old accountant
Trouble doing simple subtraction problems
Trouble reaching for objects
Confused left and right
Difficulty reading (words appeared backward or upside down)
Tumor in the left parietal lobe
Died within a couple months

What does grasping while generating verbs produce?

Faster grasping speed

What did grasping lego while generating nouns produce?

Decreased speed and verbs did not interfere.

What are the subdivisions of the Parietal cortex responsible for?

Processing and integrating somatosensory and visual information.

What are the demarcation of anatomy of the parietal lobe?

Anterior border: Central Fissure
Ventral border: Lateral/Sylvian Fissure
Dorsal Border: Cingulate gyrus
Posterior Border: Parieto-occipital sulcus

What is the parietal lobe?

An area significantly expanded in the human brain consist of the polymodal parts of area PG and adjoining polymodal cortex in the superior temporal sulcus STS.

What are Polymodal cells?

cells that receive inputs from more than one sensory modality.

What does the area PG respond to?

to both somatosensory and visual inputs(larger on the RH than LH)

What does the STS respond to?

Various combinations of auditory, visual and somatosensory inputs

Which regions take part in the dosral stream of visual processing areas?

Intraparietal sulcus and Parietal Reach regions.

What do the regions in cIPS contribute to?

controlling saccadic eye movements
saccade: involuntary, abrupt, and rapid small movements made by the eyes when changing the fixation point

What does the PRR contribute to?

visually guided reaching movements.

What are the subdivisions of the Parietal Cortex?

Postcentral gryus, posterior partietal cortex, angular gyrus, precuneus, and supramarginal gyrus.

Who mapped these regions onto a cytoarchitecture map?

Brodmann and von Economo

Which stream projects to several parietal regions

Dorsal.

How is the precuneus divided?

Anterior: sensorimotor functions
Central: cognitive functions
Posterior: Visual functions.
There is a homonculus that runs through all three regions however most of what is known about this region is speculative.

Where do the somatosensory areas of the postcentral gyrus(primary somatosensory area) project to?

The secondary somatosensory areas in the parietal lobe as well as the motor planning and motor control areas in the front lobe.

Which area is known as the secondary somatosensory?

Area PE:- inputs from the primary somatosensory cortex
-outputs to primary motor cortex, supplementary motor cortex, premotor regions, and area PF
-guides movement by providing information about limb position.

The parietal love receives significant innervation from this cortex and sends porjections to the same regions of the paralimbic and temporal cortex as this cortex does.

Prefrontal cortex

Where does area PF receive heavy input from?

the somatosensory cortex (PE)
-also receives input from the motor and premotor cortex and a small visual input through area PG
-efferent connection similar to PE, projects to motor areas; elaborates similar info for the motor system.

Where does the Area PG have connections?

-receives more complex connections: visual auditory, somesthetic(skin sensations), proprioceptive(internal sensation), vestibular, oculomotor, and cingulate.

What is the Area PG described as?

Parieto-temporo-occipital corss rounds

What is the function of the Area PG?

correspsponds to this intermodal mixing.

Which Area is a part of the dorsal stream that controls spatially guided behavior with respect to visual and tactile information?

Area PG

Later studies proposed that the dorsal stream for the parietal lobe was the ____ pathway.

How

What are the three pathways that make up the dorsal stream?

Parieto-premotor pathway: primary "how" pathway for motor control
Parieto-prefrontal pathway: involved with working memory for visuospatial objects.
Parieto-medial-temporal pathway projects to the hippocampus and the parahippocampal region and is suggested to be imporant for spatial recognition and navigation.
All three invovled in guiding motor output, and ar enot ocmpletely distinct from each other.

What is the posterior parietal cortext important for?

Visuospatial behaviors and the more ventral regions are involved in perceptual functions.

Where is the close relation between posterior parietal connetions and the prefrontal cortex(PFC)?

In the connections between the posterior parietal cortex( PG and PF) and the dorsolateral prefrontal region.

How are the PPc and the PFC similar?

Project to the same areas of the paralimbic and temporal cortexes and to the hippocampus and the subcortical regions.
Play a rolein controlling spatially guided behavior.

What are the three Dorsal pathways that leave the posterior parietal regions?

Parieto-motor: how pathway
Parieto-prefrontal: visuospatial functions
Parieto-medial temporal: to hippocampus, parahippocampal regions, indirectly via posterior cingulate and retrosplenial cortex, role in spatial recognition and navigation.

How does the posterior parietal cortex contribute to the dorsal stream?

Participating in nonconscious visuospatial behavior: reaching, grasping, etc.

How does the posterior pariteal cortex contribute to the ventral stream?

contributes to the perceptual functions related to visuospatial behavior.

What does research suggest in connection with dorsal stream pathways?

Connections with V5 and the superior temporal sulcus(regions involved in motion and form processing)

What is the goal of all dorsal-stream pathways?

Pathways are not entirely divergent
-guide visuospatial behavior through motor ouput.
-parieto-premotor is the most direct, but the other two still indirectly ifnluence motor output.

What are anterior zones in the parietal lobe?

zones that process somatic sensations and perceptions

What are posterior zones in the parietal lobe?

zones that integrate information from the somatic and visual regions and to a lesser extent from otehr sensory regions for controllign movement, eye movements, reaching and grasping, and whole-body movement in space.

Why is the posterior parietal cortex significant?

has a role in mental imagery, related to object rotation and navigation through space.

T or F: Spatial information about objects is important to direct actions to those objects and to understand their significance

True

T or F:In some ways, location is a property of the object, like form, color, motion, and so on

True

T or F: Like form information, spatial information can be used for object recognition or to guide movements

True

What are the two types of form recognition?

One for recognizing objects and the other for guiding movements to objects.

What kind of information does the brain extract for object recognition?

Information about object size, shape, color, location relative to other objects.
temporal lobe seems to encode information about how objects relate to each other.

What is true for movement guidance?

the representation needs to be centered on the viewer. brain operates on a need to know so it does not need extra information.

What properties of the object-centered system concerned with?

Object size, shape, colors, and relative locations so that the objects are recognized when they are encountered in different visual contexts or from different vantage points.

What regions are important for the object-centered system?

The polymodal regions of the STS and other areas in hippocampal formation are important.

T or F: Viewer-centered movements (eye, head, limbs, and body in combo and separate) likely have different control systems

True

What are eye movements based on?

Position of the eye

What is limb control based on?

Position of the joints

How does the posterior parietal cortex play a role in guiding visuomotor behaviors?

It has projections from posterior parietal cortex(PPC) to motor frontal lobe for the eyes
- connections to the PFC have a role in short-term memory for the location of events in space.

What does the activity of neurons in posterior parietal cortext depend on?

Visual stimulaiton and the ongoing behaviors of the individual.
-som eneurons are only active when the individual makes an eye or arm movement toward an object.
-Other neurons are active when the individual interacts with or manipulates the object.
- these neruons are sentitive to the feautres that determine the hands posutre during object manipulation

What do neurons in the posterior parietal cortex do?

Integrate sensory information, motivations, and motor control information.
- more active when the individual shifts attention toward o rmakes a movement toward the target.

Summarize Posterior Parietal Function

First receive combinations of sensory, motivational, and related motor inputs
Second, their discharge is enhanced when an animal attends to a target or moves towards it
-Neurons are well suited to transforming requisite sensory information into commands for directing attention and guiding motor output. We can predict, therefore, that posterior parietal lesions impair movement guidance and perhaps, detection of snsory events.

What is sensorimotor transformation?

the integration of movement intention with sensory feedback about how the intended movement compares with the actual movement ot perform smooth movements towards the target.

Which area is active when prearing and executing limb movement, not the actual movement, but the desired goal.

Area PRR

How can PRR recording be used to control a prosthetic device?

Rat tactile discrimination, patterns of electrical activity in the parietal cortex were recorded and a second rat was stimulated in the parietal corext using the activity patterns from the first rat and the second one knew how to do the task without being trained.

How would designing prosthetics to be used by electrical stimulation operate?

Implant electrode in area PRR and record activity to move the mechanical devices.
-implants over speech areas might allow verbal read-out thoughts
-BCI paralyzed arm to move robotic arms to make fine, controlled movements.
-technological developments enabling use of multiple recording channels that confer redundancy of control and hence reliability.

What do we need to navigate our world successfully?

An internal map of the world and a list of what to do at each decision point in the route knowledge.
-we take the route subconsciously
- information is likely to be delocalized

What does research suggest about the medial parietal region?

It is important for route knowledge
- 3/4 cells are active when a specific movement is made at a particular location.
- cells control body movements specific to locations
- if this region is inactivated in a monkey, the animal gets lost and cannot navigate correctly(humans too_

What is defining left and right dependent on?

The frame of reference(viewer centered)

When we manipulate mental images what can it be considered as?

An application or extension of manipulating objects with the hands.

What does posterior parietal damage do?

Impairs the ability to tell left from right as well as the mental manipulation of objects.

What is acalculia?

patients with parietal-lobe dysfunction are unable to perform calculations, but can do simple non-borrowing subtraction, cannot do subtractions involving borrowing.
-math can be interpreted as having a spatial component.

Summarize posterior parietal lobe

-controls visuomotor movement
-movement control is obvious in grasping and reaching, as well as in the eye movements needed to grasp or manipulate objects.

Why are eye movements important?

They are important to the visual system because they allow the visual system to attend to particular sensory cues in the environment.

Why is the polymodal region of the posterior parietal cortext important?

It is important in aspects of mental space, arithmetic and reading to mental rotation and manipulation of visual images to sequencing movements.

What is the parietal lobes involvement in language?

Spatial organization of letters in a word and words in a sentence matters.
tap vs pat
my sons wife vs my wifes son

Why do patients with posterior parietal damage have difficulties with language?

The spatial components of the organization of words is needed to successfully interpret and speak a sentence.

A patient has difficulty copying observed movements is a result of

Posterior parietal damage

What does damage to the postcentral gyrus and the adjacent posterior parietal cortex(Anterior parietal) result in?

Somatosensory symptoms

What does damage to the post central gyrus elicit?

High sensory thresholds
-impaired ability to sense position
-impaired stereognosis

Define stereognosis

the ability to identify an object by touch

With afferent paresis what do lesions in the postcentral gyrus result in?

Loss of feedback about the positions of the limbs, resulting in clumsy movements.
-loss of kineshetic feedback that results from lesions to the postcentral gyrus.

Define Astereognosis

the loss of the ability to identify an object by touch.

Simultaneous extinction

the inability to detect a sensory event when it is paired with an identical one on the opposite side of the body or visual space.

When simultaneous extinction is performed what occurs.

A subject is presented with two objects at the same time, but patients with damage to the second somatosensory cortex(PE and PF) notice and report only one of the objects. Favors the right parietal lobe.

What is numbtouch?

Somatosensory equivalent of blind sight
-patient reports loss of sensation from a region but can accurately report when they were touched within that region.

Patient with numbtouch

PE PF some PG damage
-can point with her left hand to locations on her right where she had been touched even though she failed to report feeling the touch.

What are the two tactile sytems?

One specialized for detection
One for localization

Define Asomatognosia

a condition where the patient loses knowledge about or sense of their own body or condition.
- may affect one or both sides of the body, but most commonly right hemisphere lesions affecting left side of the body

Anosognosia

unawareness or denial of illness

Anosodiaphoria

Indifference to illness

Asymbolia for pain

lack of typical avoidance reactions to pain such as reflective withdrawal from a painful stimulus.

Autopagnosia

inability to locate and name body parts.
-Finger agnosia
-person is unable either to point to various fingers of either hadn or to show them to an examiner.
-finger agnosia and dycalculia(performing arithmetic difficulties) are related.

Children with congenial spina bifida

have finger agnosia and are terrible at arithmetic

Balint

bilateral parietal lesions
-normal vision and can recognize and use objects, pictures, and colors
- can move their eyes but not fixate ona target.(30-40 degrees to the right)
-simultagnosia: attention directed to an object a time. reading is difficult
-Patient with optic ataxia: unable to reach a specified target with visual guidance

A pateint with optic ataxia can experience

-unable to reach a specified target with visual guidance
-severe deficits in reaching under visual guidance
-most common symptom of bilateral and unilateral lesions in the posterior parietal regions(PE)
-Movements not requiring visual guidance were OK

Deficits in eye gaze and visually guided movements are results of

Lesions in the superior parietal region(PE). Optic Ataxia does not accompany lesions in the inferior parietal regions.

What is contralateral neglect in association with right parietal stroke?

Patients tend to neglect the left side of their own body and the world
-only copy the right side of a picture, only dress the right side of the body,
only reading the right half of the word, ignoring tactile stimulation to the left side of the body.
-impairment in drawing and cutting.

What is constructional Apraxia?

impaired in combining blocks to form designs.

Topographic disability

in contralateral neglect, cannot draw maps from memory

What agnosia do patients with right parietal stroke have?

Anosagnosia

T or F: Patients can recover by starting to respond to stimuli on the neglected side of the body as if they were on the intact side, and recovery can continue to simultaneous neglect

True

Damage to which area is needed for contralateral neglect?

The right IPS which divide the PE and PF and the right angular gyrus.

How can contralateral neglect be induced in healthy individuals?

Applying TMS to the right IPS and angular gyrus.

What is neglect caused by?

impaired sensation and perception or impaired attention.

What difficulties do patients with right posterior parietal damage experience with object recognition?

-recognizing objects in unfamiliar views or orientations
- mentally rotating the image to match the more traditional depiction.

What is Gertsmann syndrome?

-damage to the left parietal lobe around area PG(angular gyrus)
-patient experienced finger agnosia, left-right confusion, agraphia, disturbed language function and acalculia.

What are some symptoms associated with left parietal lesions?

-Difficulties with writing, reading, and grammar
Apraxia
Dyscalculia
Decreased digit span in verbal working memory
Difficulty with left-right discrimination

Apraxia

Movement disorder in which the loss of movement is not caused by weakness, inability to move, abnormal muscle tone, intellectual deterioration, poor comprehension, or other disorders of movement

Ideomotor Apraxia

patients are unable to copy movements made by other people or make gesutres(left parietal lobe lesions)