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LM Neuropsyc
Disorders of the visual system Lecture Four
| Question | Answer |
|---|---|
| Read the first slide "The Eye" | .... |
| The light passes through the pupil. The iris expands depending on? | Light conditions |
| What is the sclera? | The white of the eye that surrounds the iris |
| What is the cornea? | Translucent part of eye that light passes through to get to the retina |
| Where do you have receptors in the eye? | The retina |
| What is at the centre of the retina? | The macula and at the very centre of the macula is the fovea |
| Why is the centre portion of the retina important? | It has highest resolution - most accurate vision |
| What is this? "the opening that allows light to enter the eye and reach the retina" | Pupil |
| What is this? "The internal lining of the rear two-thirds of the eye; it converts images into electrical impulses, which are sent to the brain. | Retina |
| What is this? "The centre area of the retina that is specialized for central vision (less distortion)" | Macula |
| What is this? "The portion where the visual image is the least distorted; marks the centre of the retina and the centre of the macula | Fovea |
| What is this? "Made up of the axons of retinal ganglion cells; carries impulses for vision from the retina toward the brain" | Optic nerve |
| There are three pairs of eye muscles. What is the overall name for them and what test can be used to test eye movement control? | Extraocular muscles and bedside assessment for eye movement |
| What do the extraocular muscles enable? | the eye to move within its orbit |
| The visual system begins with the eye. At the back of the eye is the retina, which contains photoreceptor cells that convert _______ energy into _______ activity. What is the flow of visual information in the retina? | light, neural, 1. photoreceptors 2. Bipolar cells 3. Ganglion cells |
| So where does the conversion of light energy into neural signals occur in the eye? | In the millions of photoreceptors (rods and cones) at the back of the retina |
| What are the two types of photoreceptors and what are each good for? | Rods (specialized for low light levels) and Cones (specialized for higher light levels and colour vision |
| Describe the anatomy of rods and cones: | At one end they have photopigment with cell body in the middle and then at other end they have synaptic terminal. |
| Describe how info passes through photoreceptors (rods and cones) | The light is drawn to the photopigment end of the rod or cone and passes through and exits at the synaptic terminal |
| The light passes through the photoreceptors first and then through what? | The bipolar cells and ganglion cells |
| After light has passed through the photoreceptors, bipolar cells and ganglion cells what happens to get info to brain? | The retinal ganglion cells form the optic nerve to project out of the eye into the brain |
| What photoreceptors do you have higher concentration of at central vision and at peripheral vision? | More cones at central and more rods at periphery. |
| How can you see dim stars while stargazing at night? | By putting the star into periphery so that rod pick up on it as rods are better when seeing in dim lights and are more in the periphery |
| The visual field is the total amount of space that can be viewed by the _________ | retina |
| images are __________ onto the retina - images from the left side are going to project onto the _________ hemiretina | inverted, right |
| The visual fields for each eye are not the same - left eye cant see all the way to the _______ and the _______ eye cant see all the way to the left | right, right |
| Within the left eye: the left half of the retina of the left eye receives info from the _______ visual field whereas the right half of the retina of the left eye is receiving info from the _______ visual field. Look and read this on slide | RIGHT, LEFT |
| In the left eye for example what retinal ganglion cells cross at the midline and which don't? And where is the midline? | Ganglion cells located in the temporal hemi-retina of the left eye do not cross, they stay on the left side. Ganglion cells located in the nasal hemi-retina cross at the midline via the optic chiasm. |
| Why do some ganglion cells cross and others do not? | So that we end up with ganglion cells responsive to visual stimuli from each hemifield projecting to the opposite optic tract/side of brain. |
| The ganglion cells in both retinas that are responsive to visual stimuli in the right hemifield project axons via the left or right? optic tract to the left or right? half of the brain? | left, left |
| If the left optic nerve is cut prior to optic nerve, vision via the left eye will be lost completely resulting in what? | loss of far left peripheral vision |
| If the left optic nerve is cut prior to optic nerve you can test what vision you would lose by doing what? | Closing left eye |
| What do you lose if you cut the optic chaism? | Vision of the far periphery will be lost bilaterally/on both sides |
| What happens if you cut your left optic tract after the optic chiasm? | You lose you right vision completely also referred to as right hemianopia |
| After the optic chiasm info is crosses so any damage will be____________ (always damage to the opposite side of the cut) | contralateral |
| What causes right hemianopia? | When your left optic nerve is transected after the optic chiasm |
| What is optic glioma? | Tumour based on glial cells in the optic nerve. |
| What does the patient with optic glioma experience? | Decreased visual acuity |
| In this patient the optic glioma grew along the optic nerve and involved the optic chiasm and optic tracts | ... |
| The name of the tracts change prior and after the optic chiasm. What are they? | The optic nerve and then after the optic chiasm the optic tract |
| So the axons of the ganglion cells are called the optic ________ before they cross at the optic chiasm | nerve |
| The axons of the ganglion cells are called the optic ________ after they cross at the optic chiasm | tract |
| Where do the axons of the ganglion cell (optic tract) then project to after the optic chiasm? | The superior colliculus (only about 10%) and the Thalamus (lateral geniculate nucleus) |
| There are two types of visual pathways. What are they called? | Retinotectal Pathway and Retinogeniculostriate Pathway |
| Which visual pathway goes to the PVC | The Retinogeniculostriate Pathway |
| Describe the flow of info in the Retinotectal pathway | The retina --> Superior colliculus |
| Describe the flow of info in the Retinogeniculostriate pathway | The retina --> Thalamus (lateral geniculate nucleus) --> PVC |
| In the name retinotectal what does retino mean and what toes tectal mean? | retino=retina and rectal = colliculus |
| What percentage of the ganglion cells in the retina project to the part of the midbrain called the superior colliculus? | 10% |
| The SC is not just involved in processing visual input but also have ________ functions | motor |
| A patient has damaged right SC while left is relatively intact. What would you expect the result to be of an experiment measuring visually guided eye movements | Their eye movements to the contralesional targets (left stimuli) will be slower than ipsilesional targets. They can still make eye movements but are just delayed - doesn't prevent visual perception of contralesional target |
| Where is the Lateral Geniculate Nucleus (LGN)? | Thalamus |
| The left and right LGN located in the thalamus are the major targets of the two _____ _____ (i.e retinal ganglion cells synapse on LGN neurons) | optic tracts |
| If you damage the right LGN you would expect to see deficit on what side? | The left side |
| So the retinal ganglion cells in the optic tract (in the rectinogeniculostriate pathway) synapse onto neurons in where? | The lateral geniculate nucleus within the thalamus |
| From the lateral geniculate nucleus the info continues via optic radiation to the ? | Primary visual cortex/striate |
| Both the ______ and the ________ __________ _________ have retinotopic maps | retina and lateral geniculate nucleus (LGN) |
| The right LGN receives info about the right or left? visual field | left |
| Most neurons in the LGN project their axons to which cortex? | PVC |
| The PVC receives visual input (relayed through the _____________) | thalamus |
| What is the first region of cortex to process visual information? | PVC/V1 |
| Because the projections are orderly, striate cortex contains a complete neural map of the _________ | retina |
| Where is the PVC located? | located primarily in the medial part of the occipital lobe and buried within the calcarine fissure |
| What are other three names that the PVC is called? | V1, Striate cortex and area 17 |
| Describe the study where we see a retinotopic map in the PCV | Used monkey and injected radioactive agent which then travelled to and was absorbed in the PVC revealing a retinotopic map of what the monkey was fixated on. |
| So just like with anything else after the optic chiasm, if you wipe out the V1 in the right hemipshere what will the patient experience? | Left sided hemianopia - not able to detect any visual stimuli in his left visual field. |
| What two types of tests can you use to test for hemianopia? | Bedside test where wiggle finger at different positions within the visual field or Perimetry Testing |
| What does Perimetry testing involve? | presenting a small spot of light at random locations across the visual field while the patient fixates on a central stimulus. The patient reports if they detect light. Read slide for rest of it... |
| In order to test whether humans have residual vision in the absenCe of V1, researchers used a task that, unlike perimetry testing, does not require explicit report but rather taps into patient's ______ knowledge of their hemianopic field. | implicit |
| Describe the experiment that Rafal (1990) used to test whether humans have residual vision without PVC. | Used patients with unilateral heminopia and measured how fast they could look at stimulus presented in their intact hemifield with and without distractors appearing in their cortically blind hemifield. |
| What were the results of the study that tested whether humans have residual vision without PVC? | The latency with which patient initiated eye movements toward the spot of light in the intact hemifield was slower when distractor appeared in the cortically blind hemifield compared to when there was no distractor.So the distractor activated retinotectal |
| The residual vision which occurred in the absence of being aware of distractors in the cortically blind hemifield was termed what name? | Blindsight. |
| Read the conclusion for the blindsight study | ..... |
| Where is the extrastriate cortex? | occipital, temporal and parietal lobes |
| There are two main projection routes from the PVC (V1) to the association visual cortex (extrastriate cortex). What are they called? | The ventral pathway and the dorsal pathway |
| What part of the association cortex does the ventral pathway project to? And what does this area process? | The occipito-temporal association cortex. Processes detailed stimulus features and object identity |
| What part of the association cortex does the dorsal pathway project to? And what does this area process? | The occipito-parietal association cortex. Processes motion, location and spatial relationships |
| So beyond the striate cortex is the extra striate cortex/areas which are __________order visual areas that also contain representations of the ________ | higher, retina |
| The extra striate cortical areas are all the V-areas after V_. They do not project in a sequential order. For example there is a direct projection from V1 to V5. Beyond V1 are extrastriate areas which contain specific aspects of vision and maps.... | such as colour processing and motion processing |
| So each visual area has a ________________ representation of the contralesional hemifield. | topographic |
| The numbering scheme should not be taken to mean that the synapses proceed sequentially from one area to the next. The interconnectivity of the different areas of visual cortex is complex but not ____________ | random |
| Which stream dorsal or ventral is important for location? | Dorsal |
| Which stream is important for motion? | Dorsal |
| Which stream is important for detailed stimulus features? | Ventral |
| Which stream is important for spatial relationships? | Dorsal |
| Which stream is important for object identity/what objects look like? | Ventral |
| The ventral pathway is the what or the where pathway? | What (object identity, stimulus detail) |
| The dorsal pathway is the what or the where pathway? | Where (location, motion, spatial relationships) |
| What is agnosia? | normal perception stripped of its meaning. this would be "pure" agnosia where complete absence of perceptual deficits (V1 is working so can see fine and perception is fine but problem with understanding what they are seeing. |
| What is the difference between pure agnosia and apperceptive agnosia (perceptual agnosia)? | Pure agnosia normal perception stripped of its meaning while apperceptive agnosia (perceptual agnosia) is impairment of perceptual impairments as well so can contribute to difficulties in recognition |
| A patient cannot recognise the item based on sight, however his ability to recognize the item based on tactile information is in tact. He also has a field cut. Does he have pure agnosia or apperceptive agnosia? | Apperceptive agnosia |
| What is the vascular territory of the WHAT pathway? (might need to check this with someone) | posterior cerebral artery |
| What are the names of the three syndromes of the inferior occipitotemporal cortex? And pathway is damaged (what or where)? | 1. Achromatopsia, 2. Object agnosia, 3. Prosopagnosia. WHAT pathway |
| What is achromatopsia? | the inability to recognize colours due to a disruption in processing colours |
| What are the three symptoms of achromatopsia? | Cannot name, point to, or match colours. But they can name the colour if its describe to them verbally, but not through vision |
| What causes achromatopsia? | Damage to the inferior occipitotemporal cortex |
| Achromatopsia is cortical colour blindness as opposed to what? | colour blindness caused by cone abnormality seen in males |
| What is the difference between achromatopsia and colour agnosia? | In colour agnosia colour perception is intact but stripped of meaning (because its agnosia) and can't name colours or point but can match colours because still have colour perception whereas achromatopsia you dont have colour perception |
| What is colour agnosia? | When patients are impaired in naming and pointing to colours presented visually but perception of colours is preserved enabling them to be able to match colours presented visually. Can name colour described verbally as well so just visual system deficit. |
| If patient has damage to unilateral ventral occipital temporal junction and perception of luminance, orientation or motion are not effected but hue perception, form vision & visual attention is damaged in contralesional visual field, what pathway is it? | WHAT pathway |
| What are the three main V areas in the WHAT pathway? | V1 --> V2 --> V4 |
| What are the two main V areas in the WHERE pathway? | V1 --> V5 (MT) |
| Describe object agnosia: | The patient has difficulty reporting the name of objects based on visual information but can do so based on tactile or somatosensory information. So memory is working fine |
| How can we tell that patient with object agnosia's impairment is specific to visual input? (two things) | Cos when doctor tells patient what objects are & then asks her to point to them as he says their names,the patient remembers and knowledge of the object is retained. And that patients can name gestures fine based on visual info so very specific to object |
| What is prosopagnosia? and what are the symptoms? | Inability to recognize faces. Symptoms are that people are unable to recognize people by looking at their faces |
| What is the usual lesion location for prosopagnosia? | Bilateral inferior occipitotemporal cortex. Usually right hemisphere on its own even though important for face processing is not enough for prosopagnosia (have to have both sides damaged) |
| What is the vascular territory of the WHERE pathway? (check this with someone) | Posterior cerebral artery and middle cerebral artery |
| The WHERE pathway is in what extrastriate cortex? | Occipitalparietal cortex |
| What are the two syndromes from damage to the occipitoparietal cortex? Are theres bilateral or unilateral parietal lesions? | Simultaneous agnosia and impaired depth perception. Have to be bilateral to occur |
| Lesions in the occipitoparietal cortex can cause deficits in visual processing related to spatial localization and __________ | motion |
| So bilateral occipitoparietal damage affects mostly what lobe? | Parietal lobe |
| Describe a patient with simultaneous agnosia | The patient shows impaired ability to become aware of multiple parts of a visual scene; reports only one object, even if two objects are spatially overlapping. |
| Simultaneous agnosia reflects a limitation of visual attention, NOT '__________' vision | tunnel |
| A patient is presented with a circle with an X inside it and has difficulty becoming aware of the X. What syndrome do they have and what pathway and cortex is effected? | Simultaneous agnosia, WHERE pathway in the occipitoparietal cortex |
| What is an example of how patients can be tested for simultaneous agnosia? | With computer experiment where both green and red dots are presented randomly but patient with simultaneous agnosia are only aware of the red nots and cannot access information about the green dots. |
| Describe man with Impaired Depth Perception syndrome. What pathway and cortex is damaged to cause this? | Man is not good at saying whether the doctor is moving spoon towards or away from him even when there is a huge movement towards him he still says away. Caused by damage to the WHERE pathway in the Occipitoparietal lobe |
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