Neural Basis of Motivation and Learning (NEUR0014)
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The Egocentric Representation of Space in the Parietal Cortex
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Neural Basis of Motivation and Learning (NEUR0014)
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University College London (UCL)
The Egocentric Representation of Space in the Parietal Cortex (Lecture 8 of 16 in NEUR0014: Neural Basis of Motivation and Learning)
Thorough review of the parietal cortex as it relates to its egocentric encoding of space, as opposed the allocentric encoding in the hippocampus (see Lecture 5 of ...
Neural Basis of Motivation and Learning (NEUR0014)
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Lecture 8: The Egocentric Representation of
Space in the Parietal Cortex
How the brain creates a representation of space, so as to remember the places of goals and
navigate to them
Also, perform actions and understand and spatially organise stimuli coming from the outside world
Egocentric Space
The egocentric representation of space in the parietal cortex
• Body-centred sensation of space
• Outside the limbic system Commented [IM157]: Not talking about motivation, learning or
memory directly in this lecture
Spatial Hemineglect Syndrome But as hippocampus has a role in spatial memory and as a spatial
cognition device, its important to contrast that with another sense
Human patients, through brain damage, lose part of their egocentric representation of space of space that the brain has (Egocentric, parietal)
• Good example of a brain injury showing up a cognitive function in the brain, where it’s not AND understandhow these two systems work together
clear this function is there when looking at the whole individual, but when it breaks it
The egocentric and allocentric space systems are not two opposing
produces a striking set of cognitive deficiencies systems – they help us understand hwree we are in space and
navigate and act in the world together
Egocentric neglects (spatial hemineglect) is the result of damage to the inferior parietal
lobule (neocortex)
Relatively common syndrome - common outcome following stroke of middle cerebral artery (Mort
et al. 2003)
Middle cerebral artery runs through inferior parietal lobule
The inferior parietal lobule is thought to support an egocentric representation of space
Symptoms of spatial neglect:
There is a strong unilateral bias in how hemispatial neglect presents:
Neglect almost always involves right cerebral hemisphere damage, with the left-hand side of
egocentric space being neglected (i.e. patients unaware of stimuli (inc. objects) on currently left-
hand side of their body)
• Ignore people standing on their left-hand side, even if speaking
• Only eat food on the right-hand side of their plates
• Only dress, or make-up, their right-hand sides
• Get lost by always taking right-hand turns (i.e. neglect also applies to larger-scale space)
A neglect of ALL stimuli currently on the left-hand side
This is an egocentric problem, if you turn around (move your own body in space), the stimuli
previously neglected you will be aware of and previously aware stimuli will be neglected
, This is a problem of awareness, as opposed to lack of ability to sense left-hand sensory stimuli (i.e.
NOT a problem with visual or auditory system); the symptoms are modulated by mechanisms
involving attention
• The deficits in this syndrome (what you are not aware of) are modulated by attention, not
just a simple sensory deficit
Patient PP (Halligan & Marshall, 1998) Commented [IM158]: Hemineglect case study
• ‘I think concentrating is a better word than neglect’ ‘If it’s not there how can you neglect it?’
• Handwriting of a hemineglect person will drift towards the right-hand side of the paper, until
they realise that they are not writing on all the paper
Neglect modulated by attention/awareness
The line bisection task
Patients are presented with a horizontal line and asked to bisect it with a vertical line
Because they are suffering from hemineglect, the line that the patient draws is always to the right of
true centre
• If you ask the patient to mark the left-hand end of the line, unexpectedly, they can do it, due
to experimenters directing their retention to the left-hand end of the line
o Following that, their bisecting line is closer to true
• Neglect patients will also ignore the left-most of a row of objects: adding another object on
the left will allow perception of a previously unattended object
The neglect of stimuli in this syndrome is modulated by attention Commented [IM159]: Systemic/ quantitative data to reflect
that neglect is modulated by attention
As well as anecdotal evidence in Patient PP
Related to all of these symptoms, comes the debate of the true nature of this neglect: is it
egocentric or object-centred?
‘Object-centred’ neglect
Are the patients neglecting everything on the left-hand side of their body or the left of the objects
they perceive (object-centred neglect)?
Demonstrating object-centred (egocentric) neglect
• Neglect patients will often draw the right-hand side of multiple objects, regardless of their
relative positions
o Patients produce a sketch of the right-hand side of each object in the image, as
opposed to a detailed drawing of the right-hand side of the image
§ A demonstration that the neglect is not based on their own body
necessarily, but on the objects they are perceiving
• It’s still egocentric in a sense, as what is important is what is on the patient’s left and right
o If you turned image around, they would perceive the absolute right of the object
The neglect is always egocentric with respect to the patient's body
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