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.

Functional Neuroanatomy: Occipital Lobes

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.

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.

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.

Functional Neuroanatomy: Occipital Lobes

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.

Functional Neuroanatomy: Occipital Lobes V1 V2 V3 V3a V4 V5/MT V7 V8 VP LO

Functional Neuroanatomy: Occipital Lobes

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.

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.

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.

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.

Functional Neuroanatomy: Occipital Lobes

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.

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.

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.

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.

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.

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.”

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.

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.

Functional Neuroanatomy: Occipital Lobes

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.

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?

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).

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.

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.

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.

Functional Neuroanatomy: Occipital Lobes

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.