Optic Ataxia Flashcards
What is Optic Ataxia
the inability to accurately point to or reach for objects under visual guidance with intact ability when directed by sound or touch despite strength
Therefore, a patient who can see an object may be unable to reach for it accurately until they physically contact it
Optic ataxia: lesions
Optic ataxia has lesions in the:
- superior parietal lobe
- around the intraparietal sulcus.
Lesions in BA (Brodmann’s areas, 5, 7,19, 39, 37)
Motor and visual functions
Primary motor cortex
- BA4
- Receives projections from Primary motor cortex
- Projects to spinal cord
- Delivers most of the commands through the spinal cord to the muscles
- BA 6&8 – receives projections from PFC and PPC, M1
- Projects mainly to M1 and spinal cord
Visual cortex
- Includes BA17 (v1), BA 18 (v2), BA19 (other secondary visual areas)
- Also, subcortical areas such as tegmentum, superior colliculus etc
- Cortical visual areas project largely to the temporal and parietal lobes
- Middle and inferior temporal cortex are also visual
- Responsible for visual recognition process e.g., faces, objects, patterns, etc
- Projections to parietal lobe as well
Spatial processing
Visuo-spatial processing is the ability to tell where objects are in space
- including your own body parts
- it also involves being able to tell how far objects are from you and from each other
- Object recognition
Objects must be recognisable from various viewpoints - Navigation
Medial parietal region seems involved in route navigation
Visuomotor processing
Where vision meets somatosensorial is a good candidate for the control of visually guided movements
Somatosensory symptoms of parietal lobe lesions
Mainly associated with damage to primary areas (1-3) and secondary (area 5) somatosensory cortex
May also cause astereognosis – the inability to recognise objects by touch.
Posterior Parietal Cortex (PPC)
- Involved in the control of saccades as well as visual spatial attention.
- The PPC is active during a variety of visuospatial and cognitive tasks including eye movements and spatial memory.
The posterior parietal cortex, along with the temporal lobe and prefrontal cortex, is one of the three major regions in the brain.
- It is located between the visual cortex and the somatosensory cortex just behind the central sulcus.
Damage to PPC:
Language deficits
- Includes but is not limited to Wernicke’s aphasia
- Can also include problems with reading and writing
Left IPL (inferior parietal lobe)
Left-right discrimination: A complex neuropsychologic process that calls upon several higher functions, including visuospatial processing, memory, language, and integration of sensory information
-The ability to discriminate between left and right is essential in everyday life
-Lesions to IPL- Memory for left vs right is disturbed following lesions of left IPL (inferior parietal lobe)
Dyscalculia: Difficulty in performing arithmetical calculations resulting from damage to the brain
-Inability to do calculations mentally
-The patient may be unable to do simple maths such as 10 + 10
-During developmental dyscalculia, an overactivation of left IPL is observed
Right inferior parietal lobe
Right PL lesion- spatial cognition
-Can have difficulty telling which object is nearer or whether one object is higher than the other
Unilateral neglect
- Following damage to right inferior parietal lobe
- Involves inattention to or neglect of the left side of space
- Patients may simply ignore half the world
Object recognition (Warrington & Taylor, 1973)
-Showed that patients with right PL damage could recognise an object viewed canonically but not when presented non-canonically
-Supports the idea that the right PL is involved in spatial manipulations of images e.g., mental rotation
Balint’s Syndrome (Balint, 1909)
Reported a patient with a bilateral PPC lesion
Intact visual fields and could recognise, use, and name objects normally, but had three main problems:
- Neglect
When presented with an array of objects, his gaze would automatically shift to those on his right - Simultagnosia
When his attention was directed towards an object, he did not notice other objects without prompting from the examiner - Optic Ataxia
A severe deficit in reading under visual guidance
Balint’s patient – the syndrome included optic ataxia
-The patient was inaccurate in reaching with one hand in one visual field only
-Could not be a simple visuoperceptual or attentional problem (would affect both hands)
-Could not be a simple motor problem (would affect both visual fields)
-Therefore, it must have been a problem with the visuomotor system
Deficits in optic ataxia
-Pointing to targets in the periphery (fixate central location, point to a peripheral target)
-Posting hand in slot (slot in various orientations, also in visual periphery)
-Grasping (time course of grip aperture is affected)
-Manual tracking (target moves about at random, must track target with finger)
