1. Functional Neuroanatomy: Occipital Lobes
Anatomical Features:
Where is it?
Most posterior portion.
Merges with temporal and parietal.
Most hidden from view.
Visual Pathways:
Retina:
Temporal retina:
Information from inner visual field.

2. Functional Neuroanatomy: Occipital Lobes

3. Functional Neuroanatomy: Occipital Lobes
Stays ipsilateral.
Nasal retina:
Information from outer visual field.
Crosses over at optic chiasm (decussation)
Optic Chiasm:
Comprised of fibers from rods and cones.
Lateral Geniculate Nuclei:
Subdivisions of thalamus.
Relay visual information to cortex.
On lateral aspect of thalamus.

4. Functional Neuroanatomy: Occipital Lobes
Composed of 6 layers:
Parvocellular
Top 4 layers, P layers.
Responsive to color, detail, stationary or slow moving objects.
Arise from cones.
Magnocellular
Bottom 2 layers, M layers.
Responsive to movement.
Also orientation.
Arise from rods.

5. Functional Neuroanatomy: Occipital Lobes
Optic Radiations:
The geniculocalcarine tract.
Courses deep in temporal lobes.
Carries info from LGN to cortex.
Visual Cortex:
Info from retina terminates here.
Processing of visual input begins.
Several different specialized areas.
“What” and “Where” visual streams begin here.

6. Functional Neuroanatomy: Occipital Lobes

7. Functional Neuroanatomy: Occipital Lobes
Functional Areas of Visual Cortex:
Area 17 (V1):
Primary projection for vision.
Retinotopic map.
Up is down, down is up.
Surrounds calcarine fissure.
Largely on medial aspect.
Aka striate cortex due to striped
appearance.
Surrounded by Area 18.

8. Functional Neuroanatomy: Occipital LobesV1 V2 V3
V3a V4
V5/MT V7 V8 VP LO

9. Functional Neuroanatomy: Occipital Lobes

10. Functional Neuroanatomy: Occipital Lobes
Area 18 (V2):
Secondary sensory area.
Elaboration and synthesis of visual info.
Many interhemispheric/commissural fibers.
Orientation, spatial frequency, color.
Surrounded by area 19.
Area 19 (V3):
Many connections with other regions of hemisphere.
Integration of visual info with info gathered from other senses.
Visual memory.

11. Functional Neuroanatomy: Occipital Lobes
Dynamic form, recognition of moving shapes.
No color.
Dorsal V3:
Part of dorsal stream to parietal lobe.
Processing global motion.
Ventral V3:
Strong connections with inferior temporal cortex.
V4:
Selective for color.
Some line orientation, also form.
Pattern recognition.

12. Functional Neuroanatomy: Occipital Lobes
Role in attention.
In the ventral stream.
Processes intermediate level of complexity.
Simple geometric shapes.
Not as with faces, more complex.
V5/MT:
In the occipitoparietal junction.
Cells respond to direction of motion.
Also to speed of motion.

13. Functional Neuroanatomy: Occipital Lobes
Effects of Lesions:
Visual Field Defects:
Arise from Area 17 lesions and it’s connections.
Additional deficits:
Achromatopsia
Damage to V4
Loss of ability to detect color, black and white world.
Akinetopsia
Damage to V5
Inability to detect objects in motion.

14. Functional Neuroanatomy: Occipital Lobes

15. Functional Neuroanatomy: Occipital Lobes
Macular Sparing:
Macula receives MUCH representation in cortex.
Often spared in homonymous hemianopia.
Cortical Blindness:
Bilateral occipital lobe damage.
Some recovery occurs.
Typical order of recovery:
Darkness punctuated with elementary visual sensations.
Visual fields become light, but no form perception.

16. Functional Neuroanatomy: Occipital Lobes
Appreciation of primitive movement.
Not direction or speed, just something moved.
Contours emerge.
Color last to return.
Blindsight:
Lesions to optic radiations = total loss of vision.
Riddoch (1917):
Some retain some visual function in blind area.
Especially for movement.
And color discrimination.

17. Functional Neuroanatomy: Occipital Lobes
Some patients can detect and localize stimuli in blind field.
Many don’t recognize or deny existence of deficit.
Visual system disconnected from rest of brain.
May result from residual retinal connections with brain stem – superior colliculus.
Superior colliculus projects to pulvinar of thalamus and visual association areas.
These include hemianopia, quadrantanopia, and scotoma.
Scotoma is a blind spot.

18. Functional Neuroanatomy: Occipital Lobes
Adaptation:
Patient’s adapt well.
May behave normally.
As if vision was normal.
Completion:
Information in affected area gets filled in.
Similar process as with memory.
There was a picture on the wall, but not in your memory.
There is no black hole in your memory of the room.

19. Functional Neuroanatomy: Occipital Lobes
The test for completion:
Patient shown a figure.
½ in good visual field, ½ in defective field
They report “seeing” the whole object.
Also, may “see” your entire face, even if ½ is covered.
As result, may not be aware they have a deficit.
Lesion often parietal or occipitoparietal.

20. Functional Neuroanatomy: Occipital Lobes
Visual Agnosia:
What is it?
Failure to recognize objects.
Not due to sensory impairment.
Or impairment in attention or language.
Can occur in any sensory modality.
Here we’ll talk about vision.
Literally “lack of knowledge.”

21. Functional Neuroanatomy: Occipital Lobes
Two Forms (Lissauer, 1890):
Apperceptive:
Inability to recognize due to problems perceiving the object.
Cannot generate a unified percept, a gestalt.
Cannot put together the individual elements.
But can describe the individual elements.
Particular problems when viewing from unconventional angles.
Or with distracting stimuli, shadows, or embellishments.

22. Functional Neuroanatomy: Occipital Lobes
Difficulty copying objects.
Because they only see the pieces.
Lesions can be L or R hemisphere.
Most common site is R parieto-occipital.

23. Functional Neuroanatomy: Occipital Lobes

24. Functional Neuroanatomy: Occipital Lobes
Associative Agnosia:
Problems associating objects with meaning.
Can perceive objects as a whole, can synthesize, get gestalt.
Percept is intact.
Thus, they can copy the object.
They can describe what they see.
Good quote is “I can tell you how to use it, but I have no idea what it is used for.”
Lesion in L parieto-occipital.

25. Functional Neuroanatomy: Occipital Lobes
Additional Forms:
Simultanagosia:
Inability to appreciate more than one aspect of an object at a time.
No global attention.
Don’t play poker – can see value of each card, but a royal flush has no significance.
Luria’s patient when shown a picture of glasses: “There is a circle…and another circle…and a stick…and a cross bar…why, it must be a bicycle.”
R occipital lesion?

26. Functional Neuroanatomy: Occipital Lobes
Prosopagnosia:
Inability to recognize familiar faces.
May identify individual elements of a face.
But not the entire face, even their own.
Can involve other perceptual categories, such as chairs (Faust, 1955), cars (Glonning et al., 1966), and even farm animals (Assal, 1969; Bornstein, 1969).
Many studies say requires bilateral lesion to fusiform gyri.
Others say right hemisphere lesion is sufficient (Benton, 1990).

27. Functional Neuroanatomy: Occipital Lobes
Some may have inability to recognize familiar faces but be okay with unfamiliar faces (Benton & Van Allen, 1972).
This is for faces specifically.
Can recognize based on other cues, such as clothes or voice.
Color Agnosia:
Problems identifying colors.
Color discrimination is intact.
Different from achromatopsia – there is no color.
Left hemisphere lesion implicated.

28. Functional Neuroanatomy: Occipital Lobes
Alexia without Agraphia:
What is it?
Cannot recognize words.
No aphasia.
But, they can write.
Spontaneously or to dictation.
Some difficulty with copying written material.
Cannot read their own written material.
A disconnection syndrome:
Lesion affects left occipital lobe.

29. Functional Neuroanatomy: Occipital Lobes
Together with the splenium of corpus callosum.
Info to right
occipital cannot
reach language
centers of left
hemisphere.
Right
homonymous
hemianopia
typically
present.

30. Functional Neuroanatomy: Occipital Lobes

31. Functional Neuroanatomy: Occipital Lobes
Different from alexia with agraphia.
Here there is inability to read and inability to write.
This is an angular gyrus lesion.