Fundamentals of Human Neuropsychology,Sixth Edition

Chapter 13 Lecture PPT

Prepared by Gina Mollet, Adams State College

Bryan Kolb & Ian Q. Whishaw’s

Cha

pter

13

The Occipital Lobes

Portrait: An Injured Soldier’s Visual World

• P.M. – Struck by a bullet in the back of his brain– Lost sight in the right visual field– Could accurately guess about the presence or

absence of light– Difficulty reading and recognizing faces

Anatomy of the Occipital Lobes

• No clear division on lateral surface of brain• Medial Surface

– Parieto-occipital surface– Calcarine Sulcus

• Contains much of primary visual cortex• Separates upper and lower visual fields

• Ventral Surface– Lingual gyrus

• V2 and VP

– Fusiform gyrus• V4

Subdivisions of the Occipital Cortex

• Map based on monkey occipital cortex

Subdivisions of the Occipital Cortex

• Roger Tootell– Map of human cortex

Subdivisions of the Occipital Cortex

• Area V1– Laminar organization most distinct of all

cortical areas– Heterogenous

• Has more than one distinct function• Preserved in V2

• Striate cortex– Another name for visual cortex due to its

striped appearance

Subdivisions of the Occipital Cortex

• Color Vision– Primary job of V4, but distributed throughout

occipital cortex– Plays a role in detection of movement, depth,

and position

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

Visual Pathways

• Dorsal Stream– Visual Guidance of Movements

• Ventral Stream– Object Perception

• STS – Visuospatial functions

A Theory of Occipital Lobe Function

• Vision begins in V1 (primary visual cortex), that is heterogeneous, and then travels to more specialized cortical zones

• Selective lesions up the hierarchy produce specific visual deficits

• Lesions to V1 are not aware of seeing

Visual Functions Beyond the Occipital Lobe

• Vision-related areas in the brain make up about 55% of the total cortex

• Multiple visual regions in the temporal, parietal, and frontal lobes

• Vision – Not unitary, composed of many quite specific

forms of processing– Five categories for vision

Five Categories of Vision

• Vision for Action– Parietal Visual Areas in the Dorsal Stream– Reaching– Ducking– Catching

• Action for Vision– Visual Scanning– Eye Movements and Selective Attention

Categories of Vision

• Visual Recognition– Temporal Lobes– Object Recognition

• Visual Space– Parietal and Temporal Lobes– Spatial location

• Location of an object relative to person (egocentric space)

• Location of an object relative to another (allocentric space)

Categories of Vision

• Visual Attention– Selective attention for specific visual input– Parietal lobes guide movements and temporal

lobes help in object recognition

Visual Pathways Beyond the Occipital Lobe

• Milner and Goodale – The dorsal stream is a set of systems for on-

line visual control of action– Evidence:

• Visual neurons in the parietal cortex are active only when the brain acts on visual information

• 3 pathways run from V1 to the parietal cortex, must be functionally dissociable

• Visual impairments after parietal lesions can be characterized as visuomotor or orientational

Visual Pathways Beyond the Occipital Lobe

• STS stream– Characterized by polysensory neurons

• Neurons are responsive to both auditory and visual input or both visual and somatosensory input

– Originates from structures in the parietal and temporal cortex

Imaging Studies of Dorsal and Ventral Streams

• Haxby and colleagues – PET study – Found activation for facial stimuli in the

temporal region and activation during a location task in the posterior parietal region and frontal lobes

– Detection of motion activated V5, while detection of shape activated the STS

– Color perception activated area V4

Disorders of Visual Pathways

• Monocular Blindness– Loss of sight in one eye– Results from destruction of the retina or optic nerve

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

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

Disorders of Visual Pathways

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

LGN or V1

• Macular sparing– Sparing of the central or macular region of the

visual field – Results from a lesion to the occipital lobe

Disorders of Visual Pathways

• 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

• Field Defects– Scotomas - small blind spots– Results from small lesions to the occipital lobe

Disorders of Cortical Function

• B.K.: V1 Damage and a Scotoma– Right infarct (dead tissue) in the occipital lobe– Experienced blindsight - could perceive

location without perceiving content– Lost one-quarter of the fovea, poor vision in

the upper left quadrant– Slow facial recognition

Disorders of Cortical Function

• Case D.B.: V1 Damage and Blindsight– Had an angioma in the right calcarine fissure– Has a hemianopia– Cortical Blindness - blindsight in which he

reports no conscious awareness of seeing but can report movement and location of objects

Disorders of Cortical Function

• Case J.I.: V4 Damage and Loss of Color Vision – Sustained a concussion and suddenly lost

color vision– Specific damage in the occipital cortex – Improved acuity at twilight or at night– Years later, no longer remembered color

Disorders of Cortical Function

• Case P.B.: Conscious Color Perception in a Blind Patient– Suffered an ischemia that destroyed large

area of the posterior cortex– Can only detect presence or absence of light

and has intact color vision

Disorders of Cortical Function

• Case L.M.: V5 (MT) Damage and the Perception of Movement– Vascular abnormality that produced bilateral

posterior damage – Loss of movement vision– Unable to intercept moving objects by using

her hand

Disorders of Cortical Function

• Case D.F.: Occipital Damage and Visual Agnosia– Bilateral damage to the LO region and tissue

between the parietal and occipital lobes– Visual form agnosia - inability to recognize

line drawings of objects– Can use visual information to guide

movements, but not to recognize objects

Disorders of Cortical Function

• Case V.K.: Parietal Damage and Visuomotor Guidance– Bilateral hemorrhages in the occipitoparietal

regions – Optic Ataxia - Deficit in visually guided hand

movements

Disorders of Cortical Function

• Cases D. and T.: Higher-Level Visual Processes– D

• Right occipitotemporal lesion• Prosopagnosia - Facial recognition deficit• Could read lips

– T• Left occipitotemporal lesion • Alexia - Inability to read• Impaired lip reading

Conclusions from Case Studies

• Distinct syndromes of visual disturbance

• Some provide evidence for a fundamental dissociation between the dorsal and ventral streams

• Visual experience is not unified

• Asymmetry in functions of occipital lobes

Visual Agnosia

• Object Agnosia– Apperceptive Agnosia

• Deficit in the ability to develop a percept of the structure of an object or objects

• 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

Visual Imagery

• Neural structures mediating perception and visualization are not completely independent

• Right hemisphere superiority in mental rotation

• Evidence that the left temporal-occipital region is responsible for image generation

Snapshot: Generating Mental Images

• Mark D’Esposito and colleagues– What is the neural basis for visual imagery? – fMRI study – Found that visualization of concrete words

increases activation in the left posterior temporal-occipital region

– Findings consistent with other imaging studies and case studies