Cortical Structure and Function

OCCIPITAL LOBE

Connections of the Visual Cortex

• Connections– Primary Visual Cortex (V1)

• Input from LGN• Output to all other levels

– Secondary Visual Cortex (V2)• Output to all other levels

– After V2• Output to the parietal lobe -

Dorsal Stream • Output to the inferior

temporal lobe - Ventral Stream

• Output to the superior temporal sulcus (STS) - STS Stream

• Dorsal Stream– Visual Guidance of Movements

• Ventral Stream– Object Perception

• STS – Visuospatial functions (bio movement)

Disorders of Visual Pathways• 2. Monocular Blindness

– Loss of sight in one eye– Results from destruction of the retina or optic

nerve• 3. Bitemporal Hemianopia

– Loss of vision from both temporal fields– Results from a lesion to the optic chiasm

• 4. Nasal Hemianopia– Loss of vision of one nasal field– Results from a lesion of the lateral chiasm

• 5. Homonymous Hemianopia– Blindness of one entire visual field– Results from a complete cut of the optic tract,

LGN or V1• 7. Macular sparing

– Sparing of the central or macular region of the visual field

– Results from a lesion to the occipital lobe• 6. Quadrantoanopia or Hemianopia

– Complete loss of vision in one-quarter of the fovea or in one-half of the fovea

– Results from a lesion to the occipital lobe

Disorders of Visual Pathways• Field Defects

– Scotomas - small blind spots

– Results from small lesions to the occipital lobe

Visual Agnosia

• Object Agnosia– Apperceptive Agnosia

• Deficit in the ability to develop a percept of the structure of an object or objects (still see color, motion, acuity)

• Simultagnosia– Unable to perceive more than one object at a time

• Results from bilateral damage to the lateral parts of the occipital lobes

– Associative Agnosia• Can perceive objects, but cannot identify them• Results from lesions to the anterior temporal lobes

Visual Agnosia• Other Agnosias

– Prosopagnosia• Cannot recognize faces • Can recognize facial features, facial expressions,

and tell human from nonhuman faces

– Alexia• Inability to read• Form of object agnosia - inability to construct

perceptual wholes from parts or • Form of associative agnosia - word memory is

damaged or inaccessible• Results from damage to the left fusiform and

lingual areas

Neuropsychological Tasks seemingly linked to Occipital

lobe• Benton task of Facial Recognition– Fusiform gyrus (temporal lobe)

• Hooper Visual Organization Test (VOT)– Dorsal stream (parietal lobe)

• Visual Motor Integration (VMI)– Dorsal stream (parietal lobe)

• Test of Visual-Perceptual Skills (TVPS)– Not sure what region it tests and poor normative data

• Visual Neglect (Bells Test)– Simultagnosia (occipital) or contralateral neglect (parietal)?

• Wide Range Assessment of Visual Motor Abilities (WRAVMA)– No links to brain structures

• Embedded Figures Task (EFT)– No links to brain structures

Benton Face Recognition• History: “facial agnosia”/ prosopagnosia • Purpose: Measures visualoperceptual discrimination of unfamiliar

faces (not recognition/memory) • Associated with right hemisphere: parietal, occipitoparietal and

occipitotemporal• 3 parts:

– Match identical front view– Match front view with ¾ view– Match front view with various lighting conditions

Hooper Visual Organization Test (VOT)

• Test of the ability to conceptually rearrange disarranged pictures

• Posterior parietal lobe (dorsal visual stream)• 30 items, total # correct

Answers at end of Occipital Lobe section

Visual Motor Integration (VMI)

• 3 parts: VMI, Visual Perception, Motor Coordination.• VMI: Copy a developmental sequence of geometric

forms• Visual Perception: ID the exact match for as many of the

27 stimuli as possible in 3 minutes. • Motor: Trace the stimulus forms with a pencil without

going outside double-lined paths in 5 min.

Test of Visual-Perceptual Skills (TVPS)Using 7 subtests, in theory, assesses visual processing of form, but limited data

Visual discrimination

Visual form constancy

Visual figure ground

Visual-spatial relationships

Visual closure

Visual memory(response page)

Visual sequential memory(stimulus page)

Visual Neglect (Bells Test)

Visual Neglect (Bells Test)

Visual field defects and hemianopia impact performance minimally. This is about right parietal lesions not the occipital lobe.

Wide Range Assessment of Visual Motor Abilities (WRAVMA)

• Measure of visual motor, visual spatial and fine motor skills

• 3 parts– Drawing Test: Visual Motor Ability – Matching Test: Visual Spatial ability – Pegboard Test: Fine motor ability

Embedded Figures Task (EFT)

• Cognitive “style” measure• Task= Find simple target shape within complex design•Scoring: Average time in seconds

•Higher score= greater difficulty analyzing a parts separate from whole/tendency to perceive complete patterns instead of separate parts

Answers to Hooper Visual Organization Test (VOT)

PARIETAL LOBE

The Parietal Lobes

• Postcentral Gyrus – Brodmann’s areas 1,2, and

3

• Superior Parietal Lobule– Brodmann’s areas 5 and 7

• Parietal Operculum– Brodmann’s area 43

• Supramarginal Gyrus– Brodmann’s area 40

• Angular Gyrus – Brodmann’s area 39

Inferior Parietal Lobule

Use of Spatial Information

• Spatial information can be used :– Object recognition

• Viewer centered object identification– Determines the location, location orientation and motion of an

object

• Posterior parietal cortex

– Guidance of Movement• Sensitive to eye movements• Posterior parietal cortex

– Sensorimotor Transformation• Neural calculations of the relative position of the body with

respect to sensory feedback from movements being made and planned

Use of Spatial Information

• Spatial Navigation– Cognitive spatial map

• Route knowledge, unconscious knowledge of how to reach a destination

• Mental transformations are carried out by the posterior parietal cortex

• Other functions of parietal lobes: – Aspects of math– Aspects of language– Movement sequencing

Somatosensory Symptoms of Parietal-Lobe Lesions

• Lesions to the postcentral gyrus produce:– Abnormally high sensory thresholds– Impaired position sense– Deficits in stereognosis, or tactile perception– Afferent paresis

• Clumsy finger movements due to lack of feedback about finger position

Somatoperceptual Disorders

• Astereognosis– Inability to recognize an object by touch

• Simultaneous Extinction– Two stimuli are applied simultaneously to opposite

sides of the body – A failure to report a stimulus on one side is referred to

as extinction

• Blind Touch – Cannot feel stimuli, but can report their location

Somatoperceptual Disorders

• Agnosias– Asomatognosia

• Loss of knowledge or sense of one’s own body

– Anosognosia• Unawareness or denial of illness

– Anosodiaphoria• Indifference to illness

– Asymbolia for pain• Absence of normal reactions to pain

– Finger Agnosia• Unable to point to the fingers or show them to the examiner

Symptoms of Posterior Parietal Lobe Damage

• Contralateral Neglect– Neglect for visual, auditory, and

somesthetic stimulation on one side of the body or space

– Lesion most often in the right inferior parietal lobe

• Right intraparietal sulcus and the right angular gyrus

– Defective sensation or perception

– Defective attention or orientation

Left Parietal Symptoms

• Disturbed Language Function• 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

• Dyscalculia– Difficulties with arithmetic

• Poor recall• Inability to discriminate left from right• Right hemianopia

Apraxia and the Parietal Lobe

• Ideomotor Apraxia– Cannot copy serial movements– More likely to be associated with left parietal

lesions

• Constructional Apraxia– Cannot copy pictures, build puzzles, or copy a

series of facial movements– Associated with right and left parietal lesions

Symptoms of Posterior Parietal Lobe Damage

• Deficits in drawing appear after damage to the right parietal lobe

• Spatial Attention– Function of the parietal lobe to selectively

attend to different stimuli– Disengagement

• Shifting attention from one stimulus to the next

Disorders of Spatial Cognition

• Mental rotation requires:– Mental imaging of the stimulus– Manipulation of the image

• Left hemisphere deficit associated with the inability to generate the image

• Right hemisphere deficit associated with the inability to manipulate the image

• Inability to use topographic information is associated with right hemisphere damage

Major Symptoms

Neuropsychological Tasks linked to Parietal lobe

• Two Point Discrimination• Seguin-Goddard Form Board/Tactual

Performance Test• Line bisection• Incomplete Figures• Mooney Closure• Right-left differentiation

Two point discrimination

• Sharp, two point calipers

• 2.85 cm, 2.7, 2.54….

• At each distance, touch either 1 or 2 points

• 2 1 1 2 1 1 1 2 2 2, 1 2 1 1 1 1 2 2 2 2, etc

• Examinee indicates one or 2 touches.

• Linked to contralateral postcentral gyrus (BA1, 2, & 3).

Seguin-Goddard Form Board/Tactual Performance

Test• Formboard, pieces, blindfold• Repeat for left, right, and both hands• Total time to place pieces in formboard for

each trial.• Remove formboard, provide paper• Examinee draws formboard and places the

shape in the outline of the formboard.• Contralateral parietal lesions (PE, PF) for

tactile and PG for drawing part

Line bisection

• Mark the middle of each line.

• Contralateral neglect• With right parietal

lesion, the lines to the left side of the page would be left blank.

Incomplete Figures/Mooney Closure

• Label the object• Right parietotemporal

junction (ventral stream)

Right-left differentiation

• Left parietal lesions

Answers to Incomplete Figures Test

Answers to Incomplete Figures Test