Lecture 11: Visuospatial processing and disorders Flashcards
Posterior Parietal Lobe
Posterior Parietal Lobe = part of the parietal lobe that is posterior to the somatosensory cortex → Inferior and Superior parietal lobules (IPL and SPL) and IPS.
* Sense of space
* Parietal lobe is very well positioned in the middle of all the sensory areas of the brain. Very important for multisensory information: integrate somatosensory information from the postcentral gyrus and visual information from the occipital lobe.
* Close links with the occipital lobe and is involved in the dorsal stream of vision. It will use the spatial information to be able to guide us in more complex behaviours.
Extra info:
- Subdivided by the intraparietal sulcus into the: (1) superior, and (2) inferior parietal lobules
- Does NOT respond to tactile stimulation (neurons here are not activated by touch, they respond to very specific body movements)
- Codes for organization of body in space
- Allows us to interact with objects and tools in the environment/space
- Allows to produce movements and postures in space
Lesions:
- Patients lose a sense of where their body parts (e.g., a hand) are situated in space
- People may bump or run into objects because they cannot estimate where their body is in space and how far the objects are from their body or from each other
What is the posterior parietal lobe involved in?
- Involved in aspects of visuospatial perception and attention → involving occipital areas with parietal areas.
- Parietal lobe is important for allocating attention to the right part of the space.
- The representation and interactions with objects.
- Sensorimotor functions: forming of intentions and cognitive plans for specific types of movements. Guiding your movement to use objects or to move yourself in space.
- Allowing the production of the appropriate gesture and posture in space
- Representation of body schema (in right lobe - image of your body) and integration of information about the position of the body in space (where your body is in space in relation to external objects).
- Integration visual information with body schema
- Visual short term and visuospatial memory
- Visuospatial mental manipulations (ex: mental rotation). Mental operations that you can do that involve moving things in space.
- Navigation in space or topographical orientation. Navigation in your environment.
Main areas of parietal lobe
Somatosensory cortex: on post central gyrus
Inferior part: supramarginal and angular gyrus
Superior part: superior parietal lobule (SPL)
Intraparietal sulcus is important: sulcus is not just an empty space that seperates 2 regions, there is cortical areas within the sulcus. The IPS is a very large one, very deep and there’s a lot of cortex on each side of IPS.
Visuospatial disorders
- Affect ‘’spatial relationships between an observer and an object, between objects in extra corporal (outside the body) space or the orientation of external stimuli’’
(Newcombe and Ratcliff, 1989, p. 334) will affect the spatial relationship between you and an object, and also between two different objects or places outside of yourself. - Difficulty in remembering spatial information and/or using it to guide behavior and perform spatial operation mentally
- Normal low-level sensory processing (touch, visual, auditory processing…)
- Cognitive processing of visuospatial information is impaired
Common lesions: dorsal, occipito-parietal stream (posterior)
Disorder of sensory analysis
- Lesions in the posterior dorsal part of brain you can have deficits that affect either depth perception, localization in space or orientation.
- Impairments in more elementary perception: orientation, position, distance, depth…
- Damage to posterior brain areas
Different types of disorders
- Depth perception
- Localization
- Line orientation
Disorder of Depth perception
Lesions that involve more occipital parts of the brain → occipital parietal areas.
Depth perception requires monocular cues (color perception and shading) and binocular cues (stereopsis).
→ Binocular depth perception: the disparity between the views projected to each eye, Stereoscopic vision. Information from each eye is not exactly the same, so when you close one eye and then close the other eye, you do not see exactly the same thing. Your brain will overlap the two image/ input from each eye which helps a lot with depth perception.
→ In the occipital cortex the two images are fused together for a normal single three-dimensional
image
Disorder:
- Difficulty with depth perception, discriminating shade, color saturation…
- Makes object vision difficult
- Which object is near or far
Lesions in right dorsal occipito-parietal areas + occipito-temporal. Lesions in dorsal stream will affect depth perception.
Lesions in ventral occipito-temporal areas:
- The ‘what’ pathway is involved in depth perception
- Color vision abnormalities
Ventral stream is also involved in depth perception (ventral stream is responsible for the identification of the colour, if you lose color perception, you also lose depth perception - colour, contrast, shading is needed).
Disorder of Localization
Dorsal stream is important for localization of objects - lesion in dorsal stream
Perceptual matching tasks
- Ask the patients to compare pairs of visual stimuli with each other and make same/different judgements. Are the objects placed at the same location on the piece of paper. Estimating the location of objects or a different spatial aspect that they see.
- Right parietal lesions most impaired (74 patients: Warrington et al 1970)
- Difficulties in estimating location of objects in peri corporal space (near the body, within an arm reaching distance)
Disorder of line orientation
Test for dorsal stream of vision.
Judgment of line Orientation (JLO) (Benton 1978):
- Show a line at a certain angle and match the line to the template.
- Difficulties associated with RIGHT posterior parietal or occipitoparietal regions → dorsal stream
- Assesses more complex visual reasoning and visual construction
- It is something that gets more difficult in degenerative disorders
Parietal lesions
- Right posterior parietal lesions mostly causes Hemineglect because the right parietal lobe is specialized for allocating attention in the visual space (lesion in left does not cause hemineglect).
- Optic ataxia (one of the symptoms of Balint-Holmes’ syndrome): parietal lobe lesion
together with deficits of visual attention, of estimating distances and depth, and with apraxia of gaze = Balint-Holmes’ syndrome → typically associated with bilateral posterior parietal and occipital damage. - Cause disorders of body image (body schema)
Optic Ataxia
(opposite of apperceptive agnosia)
Difficulty reaching and grasping under visual guidance→ they can perceive objects, decribe orientation but they can’t reach correctly. Guiding from the parietal lobe to the motor areas.
* Lack of coordination between visual input and motor output
* Not only have difficulty reaching in the correct direction, but they also show deficits in their ability to adjust the orientation of their hand when reaching toward an object
* No difficulty in verbally describing the orientation of the object
* Unable to adapt their grasp
* No elementary visuo-motor impairments
* No deficits when reaching is aided by non-visual cues (proprioceptive or auditory) (ex: the object makes a noise)
* Reaching which is not under visual guidance is normal. If they don’t normaly need visual guidance to do a specific task then they don’t have any deficits (ex: bring food to mouth to eat).
→ Lesions in SPL, parieto-occipital and IP sulcus
Disorder of body image
Disorders of body image associated with left parietal areas.
Information about your own body = associated with left parietal lesions.
Autotopagnosia
* Inability to localize (ex: point or describe location of your foot) body parts on oneself. Lost spatial sense of body)
* Preserved abilities to name the body parts
→ left parietal lesions
Finger agnosia
* Involves individuating the fingers: as if the patient’s fingers become collectively fused and undifferentiated (difficult to look at fingers and deferentiate which one is which).
* Hypothesis: evolutionary mechanism separating the representation of the digits? Fingers evolutionarly have a very important role so it makes sense that there is a part of them brain associated to them.
→ left angular lesions
* If Tetrad of symptoms (left-right disorientation, acalculia (difficulty with mathematical calculations), finger agnosia, and agraphia) termed Gerstmann’s syndrome
Left hemisphere - spatial processing of your body
Right hemisphere - spatial processing of the environment
Disorders of Spatial Cognition
Parietal is important for there
* Mental rotation
* Memory for location and
spatial memory
* Maze learning
Mental rotation
Mental rotation is something very complex, used for IQ test. Higher order cognitive function.
Mental rotation: the ability to imagine movements,
transformations, or other changes in visual objects
(Newcombe and Ratcliff, 1989)
Task: same or different
The more mental manipulation is required, the harder it is. If there is only a slight rotation, it is easier to do.
Fronto-parietal network is important for mental rotation.
fMRI studies show the importance of the intraparietal sulcus (cortical areas that are within the intraparietal sulcus) for mental rotation.
brain activation is very bilateral for for mental rotation.
Bilateral?
- People are trying to figure out if the brain activation is bilateral or more right lateralized?
Hypothesis:
* Bilateral activations are not due to mental rotation processes per se but to processes subserving task performance- the processes in the background (like controlling eye movements…) (Jordan et al. 2011)
* When more difficult: more bilateral (mental rotation is very complex. Maybe right parietal lobe is the primary lobe but recruits left lobe for help when it is very complex)
* Right parietal: more for non-bodily stimuli (abstract stimuli) (left lobe for body parts that you need to rotate)
- Manipulating type of task
- Cona and Scarpazza (2018): Right hemisphere dominance for Mental rotation and Spatial imagery and navigation but attentional or working memory aspects more bilateral. Since you still need attentional and working memory aspects to keep the information in your mind when you do the rotation, those aspects make the brain activation more bilateral.
What did lesion studies teach us about the parietal lobe and mental rotation?
Original study that associated mental rotation with the right parietal lobe: Newcombe and Ratcliff, 1989
* Task: say which hand is marked, left or right?
* Damage to the posterior brain areas, most often right
parietal
* Made more errors in the inverted condition
* Difficulties with mental rotation
* Normal sensory perception and memory
Maze learning (Task)
Test of spatial orientation
* Stylus maze task (Milner 1965)→ Find the correct path from the start to finish. Learn a path (trial and error task: try one peg if it is incorrect buzzing sound).
- Lateral temporal lesions left or right: not affected
- Parietal lesions only: not affected
- Right parieto-temporo-occipital: very affected
- (Hippocampal lesions: very affected also)
Test for spatial relations
Locomotor map test → Patients with parietal lesions are impaired
* Large paper on the floor with 9 dots (North is identified)
* Give a starting point, a destination and a specific trajectory (on a map they hold in their hand,
not allowed to turn this map). You need to mentally rotate the map.
* Map drawing of familiar and more novel environment
Another test that you can use:
- ask a participant to draw a map of something (ex: can you draw a map of the path you took in the hospital from the main lobby to this room)
- Patients with parietal lessions will struggle with this
What is the part of the brain that they call the inner GPS?
How does the brain create a map of the space surrounding us and how can we navigate our
way through a complex environment?
We have specific cells that encode spatial information about our environment to create a mental map.
Research with rodents:
* Nerve cells in the hippocampus region of the brain that are always activated when a rat was
at a certain location → ‘’Place cells’’
* Certain cells only fired when the rat was at a specific location in the maze.
* Other nerve cells that permit coordination and positioning, in entorhinal cortex → grid cells
* When the rat passed multiple locations → Each cell activated in unique spatial patterns.
Types of Spatial Firing Recorded from Neurons in the Hippocampal Formation of Freely Moving Rats
1) Place cells, in the hippocampus proper, typically fire in a restricted portion of the environment.
2) Grid cells, in medial entorhinal cortex, typically fire in a regular triangular array of locations.
3) Boundary cells, in entorhinal cortex, typically fire at a specific distance from an environmental boundary along a specific direction. Only fire along a specific boundary of the environment.
London Taxi Driver study
- Maguire et al. 2000. Navigation-related structural
change in the hippocampi of taxi drivers - MRI study of how the brain can be modified even in adults when you learn something or when you do something more often.
- London taxi drivers, were analyzed and compared with those of control subjects who did not drive taxis.
- The posterior hippocampi of taxi drivers were significantly larger relative to those of control subjects. Bigger on both sides but even bigger on right side.
- Posterior hippocampus stores a spatial representation of the environment
- Where ‘place cells’ are located
- Size of hippocampus or volume of grey mater in hippocampus directly impacted by number of years as a taxi driver.
Navigation in the brain summary
parietal cortex = egocentric disorrientation
lesions in middle temporal libe = anterograde disorientation
