the lesioned brain Flashcards
what is neuropsychology
Studying brain damaged patients – by studying abnormal, it is possible to gain insight
into normal function
classical neuropsychology
What functions are disrupted by damage to region X?
Addresses questions of functional specialization, converging evidence to functional imaging
Tends to use group study methods
cognitive neuropsychology
Can a particular function be spared/impaired relative to other
cognitive functions?
Addresses questions of what the building blocks of cognition are (irrespective of where they are)
Tends to use single case methodology
types of brain damage
Cerebrovascular accident (CVA or stroke)
Neurosurgery (split brain)
Viral infections (HSE, HIV)
Tumour (glioma)
Head injury (traffic accidents, rugby)
Neurodegenerative disease (Dementias: Alzheimer type)
ischaemic stroke
lack of glucose and oxygen supply
occlusion
haemorrhage
bleeding into brain tissue
blood vessel rupture
test of semantic memory
pyramids and palm trees
visuospatial testing
figure of ray
what can we neuropsychologically test?>
Intelligence
Memory
Visuospatial
Executive functions
Sensation
single dissociation
If a patient is impaired on a particular task (Task A), but relatively spared on another task
(Task B)
classical single dissociation
If patient performs within the normal range on the Task B, this has been termed as
classical single dissociation
strong single dissociation
If patient is impaired on both tasks, but is significantly more impaired on one task,
this is referred to as a strong single dissociation
patient CF
ischemic stroke to the left parietal area
At the time of examination he was completely speechless, but could communicate through gestures.
Wrote with his left hand (right hemiplegia)
When writing words he systematically omitted vowel only
kay and Hanley (1994)
reported another patient who made spelling errors selectively on consonants (e.g. “record” is spelled as recorg)
logic behind single dissociations
that a difficulty in one domain, relative to an absence in difficulty in another domain can be used to infer the independence of these domains
This difference could be relative, neuropsychologist test for a whole range of stimuli in order to make conclusions about the exclusivity of function
double dissociation
al work aims at showing that 2 or more tasks have different cognitive and neural resources
Double dissociation is derived from 2 (or
more) single cases with complementary
profiles
issues with single case studies
Lesion needs to be assessed for each patient, and no guarantee that
same anatomical lesions have same cognitive effect in different
patients
Therefore the cognitive profile of each patient needs to be assessed separately from other patients
Argument is not against testing more than one patient, but this becomes a series of single case studies and not necessarily a group
study
-shouldn’t average
grouping in lesion studies
group by syndrome
group by behavioural symptom
group by lesion location
group by syndrome
useful for investigating neural correlates of a disease pathology (e.g. Alzheimer’s) but not for dissecting cognitive theory
measure lesion location
group by behavioural symptom
Can potentially identify multiple regions
that are implicated in a behaviour
measure lesion location
group by lesion location
Useful for testing predictions derived from
functional imaging
measure behavioural symptoms
forms of space in the brain
Locations on sensory surfaces (e.g. the retina; retinocentric space)
Location of objects relative to the body (egocentric space)
Location of objects relative to each other (allocentric space)
how do we locate things in space?
cross modal
egocentric space
Location of objects relative to the body
allocentric space
Location of objects relative to each other
attention
Attention is the process by which certain information is selected for further processing
and other information is discarded
Limited capacity to process all received information, so selection based on relevance or importance to current goals
Attention tends to be directed to locations in space (space is a common dimension of different sensory systems
and our motor system) – spotlight metaphor
Attention may be needed to bind together different aspects of conscious perception (e.g. shape and colour,
sound and vision)
spotlight metaphor as attention
Spotlight may move from one location to another (e.g. in visual search)
It may zoom in or out (narrow or wide “beam”), e.g. if attending to words or
attending to central letter in a word
Limited capacity: not everything is illuminated
location of attention and eye fixation
Location of attention not necessarily same as eye fixation (“looking out corner of
one’s eyes”) – however, there is a natural tendency for attention and eye-fixations
to go together
control of attention
exogenous
inhibition of return
exogenous control
externally guided by a stimulus
inhibition of return
slowing of speed of processing when going back to previously attended location
Visual search
scanning the environment to find something you are looking for
feature integration theory (FIT)
Perceptual features (e.g. colour, line orientations) are encoded in parallel and prior to attention
If an object has a unique perceptual feature then it may be detected without the need for attention – “pop-out” (left array)
If an object shares features with other objects (right array) then it cannot be detected from a single perceptual feature and attention is needed to search all candidates serially
“Pop-out” is not affected by number of
items to be searched
space and attention neural correlates
Parietal lobes (ventral) specialized for spatial processing and have been called the “where” route
(Ungerleider & Mishkin)
Parietal lobes (dorsal) also bring together different types of spatial representation that are needed for action (e.g. integrating visual space with body space) so also called the “how” route
two main attention related networks
- a dorso-dorsal network (blue) involving lateral intraparietal area (LIP) and Frontal eye fields (FEF).
- ventro-dorsal stream (right tempo-parietal junction and ventral frontal cortex)
that interrupts any cognitive task in order to divert attention away from processing
dorso-dorsal network
FEF
LIP
vernto-dorsal attention stream
right tempo-parietal junction
ventral frontal cortex
right parietal lobe and space
Right parietal lobe contains richer representation of space (left space and
some right space)
left parietal lobe and space
Left parietal lobe contains an impoverished representation of space
(predominantly of right side only)
pseudoneglect
The greater spatial specialization of right parietal lobe means that we all have
a tendency to attend to left side of space (pseudoneglect)
synonyms neglect
unilateral neglect, spatial neglect, or hemispatial neglect
what is neglect?
Patients fail to attend to stimuli on the opposite side of space to their lesion
(a right sided lesion would affect the left side of the space)
what is neglect caused by?
Neglect is most prominent following stroke to the right hemisphere of the human brain
Neglect could arise from different mechanisms:
* loss of neurons dedicated for representation of that space
* a failure to shift attention to that side
* some combination of the two
neuroanatomy of neglect
The lesion is in parietal association cortex – integration of multiple sensory signals and extensive connections with frontal areas
what does lesion site of neglect overlap with?
right angular gyrus
clinical picture of neglect
Individuals with neglect do not suffer from any primary disorder of perception,
sensation or movement
Most commonly observed in the visual modality – visual neglect
Multimodal neglect reported: auditory and somatosensory (tactile)
Left parietal lesions can result in neglect – less severe and faster recovery
clinical tests of neglect
line bisection
cancellation tasks (albert’s lines, star cancellation)
copy a drawing
draw from memory
different types of neglect
perceptual vs representational neglect
neglect for near vs far space
personal vis peripersonal spcae
within object vs between object
spatial vs object based
representational vs perceptual neglect
Neglect can affect memories of scenes
The brain contains different references for spatial and imagined events in external space.
Perception and imagery can dissociate at higher levels of visual processing
in both cases the information on the left side is compromised (RH damage)
Piazza del duomo experiment
Two patients (IG, 86 and N.V., 72 with large right parietal lesions) were asked to
describe a familiar place, the Piazza del Duomo in Milan, according to different perspectives.
First (a), they were asked to imagine themselves
looking at the front of the cathedral from the opposite side of the square; then
the reverse perspective.
Double dissociation between perceptual (line bisection) and representational neglect suggests different spatial reference frames for external versus imagined (mind’s eye) space. Also – spatial knowledge not lost, but unavailable to report
neglect for near vs far space
Double dissociation between near space: line bisection using pen and paper – IMPAIRED
(Halligan and Marshal, 1991) and far space = SPARED when tested with a light pointer
(Vuilleumier et al., 1998)
personal vs peripersonal space
Double dissociation between personal (bodily) space and near space
Body neglect = failure to groom left of body, notice position of limbs, or feel pain in the left limbs
vs
Near space neglect = visual search of
array of external objects
within objects vs between objects
Some neglect patients attend to objects on the left side of space but omit to attend to one
half of the object itself (object-based neglect) - STG
Forms a double dissociation with space-based neglect - AG
spatial vs object based neglect
Axis-based neglect Driver and Halligan (1991) – patient with object neglect cannot detect differences on left side of an object even when falling into right side of space
Neglect as a Disorder of Attention and Not
Low-Level Perception
Neglect patients still activate visual regions in occipital lobes for the information that they claim not to be aware of
They are often able to detect objects on the left if cued there
Affects auditory and tactile judgments as well as vision (e.g. sounds on left are mislocalized but still heard)
Phenomenon of visual extinction suggests different perceptual representations are competing for attention (and visual awareness)
neglect and extinction
When two stimuli (targets) presented simultaneously to the left and right of the
patient’s midline – left target typically extinguished
what happens to neglected information?
neglected information implicitly coded
rehabilitation of neglect: adaption
involves patients wearing prism lens glasses that shift their view to the right
When asked to point at objects, they make errors by missing to the right. However, visual
feedback allows them to compensate for the errors and correct towards the left
the deviation to the left persists
after the prism lenses are removed and this can produce a relatively long lasting
improvement in symptoms
video games, shaping attention and learning
Studied the effects of video games on perceptual and motor skills
Perceptual learning tends to be specific with a trained task
Action video game playing is capable of altering a range of visual skills
brain game
when searching for a particular objects in a sea of shapes, people who played video games regularly showed less activation of the brain regions linked to attention
brains performing the tasks more efficiently
The tests of variable association (TOVA)
TOVA assesses impulsivity and sustained attention. In this test, participants are required to
press a key as fast as possible in response to a target and to withhold responding to non-target stimuli
In one condition, the targets are rare and the nontargets appear frequently. The extent
to which participants are able to stay on task and respond quickly to rare targets is a
measure of sustained attention.
In a different set of trials, targets appeared frequently, whereas nontargets were rare.
The extent to which participants are able to withhold responding to nontargets is a
measure of impulsivity.
TOVA to assess impulsivity and sustained attention in young adults who
were either non-video game players (NVGP) of habitual video game players (VGP)
Their results show that VGPs were overall faster than NVGPs in both the sustained attention and
the impulsivity condition. This increased speed did not come at the expense of accuracy as both
groups did not differ on this measure, indicating overall enhanced attentional control in VGPs
cognitive control
set of neural processes that allow us to
interact with our complex environment in a goal-direct manner
multitasking
attempt to accomplish simultaneous goals
EEG and multi-tasking training
After NeuroRacer training EEG pattern resembled those of 20-year-olds. The key change was in prefrontal cortex – suggesting improvement in
executive functions
Measures of coherence were much better
– how well different brain areas
communicate with each other
TDCS and Multitasking
The dorsolateral prefrontal cortex (DLPFC) has been proposed to play an important
role in neural processes that underlie multitasking performance
Anodal tDCS or sham tDCS at 1.0 mA was applied over left DLPFC in healthy young adults
immediately before they engaged in a 3-D video game designed to
assess multitasking performance
The anodal group showed enhanced multitasking performance and decreased
multitasking cost during the second session , suggesting delayed cognitive benefits of tDCS.
Performance benefits were
observed only for multitasking
and not on a single-task version
of the game
First evidence of how custom designed
video games can be used to assess and
enhance cognitive abilities across the
lifespan.
TDCS and Multitasking
The dorsolateral prefrontal cortex (DLPFC) has been proposed to play an important
role in neural processes that underlie multitasking performance
Anodal tDCS or sham tDCS at 1.0 mA was applied over left DLPFC in healthy young adults
immediately before they engaged in a 3-D video game designed to
assess multitasking performance
The anodal group showed enhanced multitasking performance and decreased
multitasking cost during the second session , suggesting delayed cognitive benefits of tDCS.
Performance benefits were
observed only for multitasking
and not on a single-task version
of the game
