Chapter 14: The Parietal Lobes

Lesions of the post central gyrus produce...

- Abnormally high sensory thresholds - Impaired position sense - Deficits in stereognosis

Varieties of asomatognosia include:

- Anosognosia - Anosodiaphoria - Autotopagnosia - Asymbolia for Pain

Patients with lesions of the post central gyrus (TESTS)

- 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) - Localizing points of touch on the skin on the side of the body contralateral to the lesion

The principal regions of the parietal lobe include:

- Postcentral Gyrus (Brodmann's area 1-3) - Superior Parietal Lobule (area 5 &7) - Parietal Operculum (Are 43) - Surpramarginal gyrus (Area 40) - Angular Gyrus (Area 39) ASSPP

Area PG (part of area 7 and visual areas)

- Receives more complex connections including visual, somesthetic (skin sensations), proprioceptive (internal stimuli), auditory, vestibular (balance), oculomotor (eye movement), and cingulate (motivational)

Case Study Contralateral Neglect: Mr. P.

- Suffered a right parietal stroke Neglected the left side of his body and of the world - Lifting arm: failed to lift his left arm BUT could do so if one took his arm and asked him to lift it - Crowded numbers to right side of clock - Compound words: only read right portion of compound word - Did not put on L-side of clothing - Shaved only R-side of face - Unaware that anything was wrong with him (anosognosia))

Contralateral Neglect: Recovery - Passes through two stages:

1) Allesthesia 2) Simultaneous Extinction

Why does contralateral neglect arise? (2 reasons)

1) Defective sensation/perception 2) Defective attention/orientation

Three parietal-lobe systems do not fit obviously into the simple view of a visuomotor control centre:

1) Difficulties with arithmetic 2) Aspects of language 3) Movement sequences

Symptoms characteristic of L-parietal lesions (5):

1) Disturbed language function 2) Apraxia 3) Dyscalculia 4) Right-left discrimination 5) Right hemianopia

Two basic types of form recognition

1) Object Recognition 2) Guiding Movement to Objects

2 Theories of Parietal-Lobe Function for Complexity of Spatial Information

1) Recognizing objects and guiding movement 2) Complexity

Symptoms that accompany finger agnosia (3):

1) Right-left confusion 2) Agraphia (inability to write) 3) Acalculia (inability to perform simple arithmetic calculations)

Responses of posterior parietal neutrons have two important characteristics in common:

1) They receive combinations of sensory, motivational and related motor inputs 2) Their discharge is enhanced when an animal attends to a target or moves towards it

Symptoms of Baliant Syndrome

1) can move eyes but not fixate on specific visual stimuli 2) Simultagnosia 3) Optic Ataxia

Finger Agnosia

A condition in which a person is unable either to point to the various fingers or to show them to an examiner

PPR is active when...

A participant is preparing and executing a limb movement

Simultaenous Extinction

A person confronts an environment i which many sensory stimuli impinge simultaneous, yet the person can distinguish and perceive each individual sensory impression

Posterior Parietal Corext includes:

A posterior zone that includes the remaining areas: Areas 5,7,39,40

Saccade:

A series of involuntary, abrupt and rapid small movements or jerks made by both eyes simultaneously in changing the point of fixation

Constructional Apraxia

A visuomotor disorder, spatial organization is disturbed

Asymbolia for Pain:

Absence of typical reactions to pain, such as reflexive withdrawal from a painful stimulus

Somatosensory cortex includes:

Area 3-1-2 and 43

If we use this system, Area PF is equivalent to (three areas), Area PE is equivalent to ( ) and the remainder of ( ). Area PG is roughly equivalent to ( )and ( ).

Area PF: Brodmann's areas 43, 40 and part of area 7 Area PE: Area 5 and remainder of area 7 Area PG: Broadmann's area 39 and 40

The polymodal region of the posterior parietal cortex is also important in various aspects of mental space, including:

Arithmetic Reading Mental rotation Manipulation of visual images Sequencing movement

Sensorimotor Transformation

As we move, the locations of body parts change and perceptions of our body must constantly be updated so that we can make future movements smoothly

Gertsmann Syndrome aka Finger Agnosia

Asomatogonia - Inability to name or recognize the fingers on either hand

The increased size of area PH and the STS is especially interesting because this region is anatomically

Asymmetrical

Numb Touch

Blindsight: visually impaired patients can identify the location of a visual stimulus even though they deny 'seeing' it

The area is roughly demarcated: - Anteriorly by the ___________ fissure - Ventrally by the __________ fissure - Dorsally by the _________ gyrus - Posteriorly by the ________-_________ sulcus

Central fissure lateral (Sylvian) fissure Cingulate gyrus parieto-occiptal gyrus

Allesthesia

Characterized by a person's beginning to respond to stimuli on the neglect said as if the stimuli were on the unlesioned side

Posterior Parietal Cortex

Contributes to the dorsal stream by participating in non conscious visuospatial behaviour, that is reaching and grasping objects

The regions in the intraparietal sulcus (cIPS) contribute to: (2 functions)

Controlling saccadic eye movements (area LIP) Visual control of object-directed grasping (area AIP)

Patients with posterior parietal lesions are impaired at...

Distinguishing left from right Mental rotations

Specific parietal regions take part in the ______ stream of visual processing, in particular the intraparietal sulcus (cIPS) and the parietal reach regions (PRR)

Dorsal (WHERE pathway)

Failure to report one stimulus is usually called...

Extinction

Most common autotopagnosia

Finger agnosia

Parieto-medial temporal pathway

Flows directly to the hippocampus and the parahippocampal regions is proposed to have a role in spatial navigation

The parietal region of the cerebral cortex lies between the:

Frontal and occipital lobes, underlying the parietal bone at the roof of the skull

The deficits in eye gaze and visually guided reaching are most likely to result from lesions

In the superior parietal region (area PE)

Autotopagnosia:

Inability to localize and name body parts

Acalculia

Inability to perform mathematical operations, in this case because of the task's spatial nature

Anosodiaphoria:

Indifference to illness

Ideomotor Apraxia: L-parietal lesion vs. R-parietal lesion

L-parietal: Grossly impaired in copying a series of arm movements R-parietal: Perform normally

The motor connections must be important for providing sensory information about _____ position in ____________ control.

LIMB position MOVEMENT control

Lesion location for Gerstmann syndrome:

Left parietal lobe, roughly corresponding to the angular gyrus (area PG)

Asomatognosia is most common on the

Left side

Afferent paresis (clumsy finger movements)

Loss of kinaesthetic feedback that results from lesions to the post central gyrus (areas 3-1-2)

Asomatognosia

Loss of knowledge or sense of one's own body and bodily condition

Damages to the post central gyrus is typically associated with...

Marked changes in the somatosensory threshold

Regions involved in route knowledge:

Medial parietal region (MPR) - This includes the parietal region ventral to the PRR - Posterior cingulate cortex - Part of the parieto-mediotemporal pathway in the dorsal stream

The posterior parietal cortex also plays a significant role in

Mental imagery - Especially related to both object rotation and navigation in space

Apraxia

Movement disorder in which the loss of skilled movement in which the individual has difficulty with the motor planning to perform tasks o movements when asked

Contralateral Neglect

Neglecting a certain side of the body and of the world

The DORSAL stream from the ( ) cortex to the ( ) ( ) regions was conceived as the where pathway

Occipital cortex Posterior parietal regions

Constatin von Economo: His maps consist of parietal regions called:

PA, PB and three posterior parietal areas (PE, PF, PG)

Connections of the Parietal Cortex: Projections from the primary somatosensory cortex (area 3-1-2) extend to secondary somatosensory area ___, which has tactile recognition function as well as to motor areas including ________ (area 4) and the supplementary and premotor area in the frontal lobes.

PE (Area 5) Primary motor cortex

This asymmetry may be due to a much larger area __ (and possibly ___) on the _____ hemisphere.

PG, STS Right hemisphere

Difference between PRR and MPR

PRR: Control the PLANNING of limb movements MPR: Control ONLY body movement to SPECIFIC LOCATIONS

Three Functional pathways leaving the posterior parietal region:

Parieto-Prefrontal pathway Parieto-Medial Temporal pathway Posterior Parietal Cortex

Ideomotor Apraxia

Patients are unable to copy movements or to make gestures

Tests for astereoignosis:

Placing a pattern on blindfolded subject's palm for 5 secs and then placed within an array; - Must match the original shape based solely on tactile information

Cells responsible for sensorimotor transformations are found in the

Posterior parietal cortex

Location of damage: Constructional Apraxia

Posterior parietal lesion

PE's cortical outputs are to the (4 areas):

Primary motor cortex (area 4) Supplementary motor (SMA) Premotor (area 6 and 8) Area PF

Anterior Zone of Parietal-Lobe Function:

Processes somatic sensation and perceptions

Apraxic or aphasic left-hemisphere patients performed poorly in (drawing)...

Producing fewer recognizable drawings and fewer lines

Parieto-Prefrontal Pathway

Proposed to have visuospatial functions, especially related to visuospatial working memory

Mathematics and arithmetic have:

Quasi-spatial nature analogous to mentally manipulating concrete shapes

Area PF (part of area 7)

Receives heavy input from the somatosensory cortex (3-1-2) through area PE

Temporoparietal Junction

Region where the temporal and parietal lobes meet at the end of the Sylvian fissure

Neglect: Damage - Two locations

Right intraparietal sulcus (roughly dividing PE and PF) and the right angular gyrus

Damage in the ( ) is believed to have the greatest influence on drawing ability

Right parietal

Most common on the right side as a result of

Right-hemisphere lesions

Extinction is most commonly associated with damage to the

Secondary somatic cortex (area PE and PF), especially in the right parietal lobe

Optic Ataxia

Severe deficit in reaching under visual guidance; can make accurate movement directed towards the body, presumably by using tactile info but cannot make visually guided movements

Cells in area PG responds to both

Somatosensory and visual inputs

The parietal lobe can be divided into two function zones:

Somatosensory cortex Posterior parietal cortex

Area PE: Brodmann's area 5 plus part of area 7

Somatosensory receiving most its connections from the primary somatosensory cortex (area 3-1-2)

The parietal cortex processes and integrates _______________ and ____________ information, especially with regard to controlling ____________.

Somatosensory, visual, movement

Area PG is part of the dorsal stream that control __________ guided behaviour with respect to ( ) and ( ) information

Spatially visual tactile

Posterior Zone of Parietal-Lobe Function:

Specializes primarily in integrating sensory input from the somatic and visual regions and to a lesser extent from other sensory regions, mostly for controlling movements

The Inferior parietal lobe consists of:

Supramargnial guris and angular gyrus

Stereognosis

Tactile perception

Apraxic or aphasic right-hemisphere patients

Tended to omit details from the L-side of their drawings and to rotate the drawings on the page.

Astereignosis

The inability to recognize an object by touch

Simultaenous Extinction

The person responds to stimuli on the hitherto neglected side unless both sides are stimulated simultaneously, in which case they notice only the stimulation on the side ipsilateral to the lesion

Somatosensory symptoms are associated with damage to

The post central gyrus (areas 3-1-2) Adjacent cortex (areas PE and PF)

Deficits in using topographic information are more likely associated with damage to: - Right or left hemisphere

The right hemisphere

The goal for all the dorsal stream pathways is:

To guide visuospatial behaviour through motor output

Asomatognosias may affect one or both sides of the body.

True

T or F: The PG is also larger on the left and in humans than in monkeys

True

T/F: Language has many demands similar to those of arithmetic

True

T/F: The brain works on a "need-to-know" basis

True: having too much information may be counterproductive for any given system

Anosognosia:

Unawareness or denial of illness

Exception: Autotopagnosia

Usually results from lesions of the left parietal cortex.

... Whereas cells in the STS respond to

Various combinations of auditory, visual and somatosensory input

The PRR has a role in:

Visually guided grasping movements

Simultagnosia

When attention was towards an object, no noticing of other stimuli

Cognitive Spatial Map

When we travel the world, we can take the correct route subconsciously, making the correct turns at choice points until we reach our destination

Area PG is part of the: a) Dorsal stream b) Ventral stream

a) Dorsal

The temporal lobe code's objects: a) Spatial properties b) Relational properties c) Size properties

b) Relational properties

Together, the supra marginal gyrus and angular gyrus are often referred to as the: a) Maximal parietal lobe b) Superior parietal lobe c) Inferior parietal lobe d) Minimal parietal lobe

c) Inferior parietal lobe

PG areas are primarily: a) Auditory b) Verbal c) Visual d) Somatosenory

c) Visual

The fact that humans parietal lobes have evolved to a much ___________ size than those of monkeys implies that humans may show some symptoms not seen in monkeys.

larger

Arthimetic operations may depend on the _________________ tissue at the left temporoparietal junction

polysensory