task 8 - lesion studies

Question 1

Lesion method assumptions (also limitations)

Answer 1

fractionation assumption: damage to the brain can produce selective cognitive lesions

Transparency assumption: lesions affect one or more components within the preexisting cognitive system, but they do not result in a completely new cognitive system

Universality assumption: lesions affect one or more components within the preexisting cognitive system, but they do not result in a completely new cognitive system

Question 2

Lesion method limitations

Answer 2

• Identifying the site of a lesion caused by a tumor is particularly problematic: certain tumors may infiltrate surrounding tissue and so have no clear boundary
• diaschisis: very discrete brain lesion can disrupt the functioning of distant brain regions that are structurally intact
• challenge of differential vulnerability: some areas of the cortex are particularly likely to be damaged by stroke > then locations of brain damage are not randomly distributed in the brain
• to understand how different regions function, we need to have a good idea of the temporal sequence of information processing > lesion method does not allow this

Question 3

Single dissociation

Answer 3

-patient is impaired on a particular task (task A) but relatively spared on another task (task B)

Classical: patient performs entirely normally on task B compared with a control group

Strong: patient performs entirely normally on task B compared with a control group

Question 4

Single dissociation interpretation

Answer 4

• two functions are separate to some degree but one of them is necessary for the other
• This suggests a kind of hierarchical relationship between the two

-leaves open the possibility that the critical lesion produced its effect, not because the area it disrupted is specifically involved in the particular function in question, but because that region of the brain is simply more important in some gen¬eral sense

Question 5

Double dissociation

Answer 5

-Two single dissociations that have a complementary profile of abilities
-task A doesn’t function, task B does
And
-task B doesn’t function, task A does

Question 6

Double dissociation interpretation

Answer 6

-provide evidence that 2 functions are relatively separate / independent

Question 7

Task – resource artifact

Answer 7

If two tasks share the same neural/cognitive resource but one task uses it more, then damage to this resource will affect one task more than the other.

Question 8

Task-demand artifact

Answer 8

One task is performed worse than another because the task is performed sub-optimally (but not because some aspect of the task is compromised).

Question 9

Syndromes

Answer 9

-cluster of different symptoms that are believed to be related in some meaningful way.

Question 10

Single case studies principles

Answer 10

-In cognitive neuropsychology, the data from different patients are not combined.

Question 11

Single case studies disadvantages

Answer 11

• one cannot create a theory based on observations from only a single case (counterargument: nobody is trying to construct whole new theories of cognition)
• not possible to generalize

Question 12

Single case studies advantages

Answer 12

-helpful for establishing how cognitive processes might be subdivided.

Question 13

Group case studies

Answer 13

-In neuropsychology, the performance of different patients is combined to yield a group average.

Question 14

Ways of grouping studies

Answer 14

by syndromes: Patients are assigned to a particular group on the basis of possessing a cluster of different symptoms
> appropriate for understanding the neural correlates of a given disease pathology rather than developing theories concerning the neural basis of cognition
by cognitive symptom: possessing one particular symptom
> advantage of working forward from a symptom to a lesion location: potentially reveals more than one region
as being critically involved

Question 15

Group case studies advantages

Answer 15

• more appropriate for establishing lesion-deficit associations
• lesions of patients typically large, rarely restricted to the region of interest
• > to localize which region is critical for a given task, several patients may need to be considered

Question 16

Group case studies disadvantages

Answer 16

• each patient may have a different lesion to the cognitive system (L1 to Ln) and so difference in observed performance may be attributable to differences in lesion rather than between-patient noise and, as such, averaging across patients is not possible.
• As individual brains differ in brain shape, size and structure, brains from different individuals need to be transformed to a standard stereotaxic space to make group comparisons

Question 17

Interpretation of data from lesion method:

necessity

Answer 17

tells us only that the lesioned area is necessary for the function in question and that the other lesioned area, which did not produce the impairment, is not.

Question 18

Interpretation of data from lesion method:

localization

Answer 18

-dissociation does not tell us that the impaired function is localized in the area of the lesion

Question 19

Interpretation of data from fMRI

Answer 19

• can show every part of a neural network that is involved in a task or a behavior
• evidence that a particular task correlates with activation in a particular brain region
• BUT: not clear whether this region is necessary to perform this task
• We cannot conclude that an area that does not show changes in bloodflow during a task is not involved with that task

Question 20

Control patients in lesion studies

Answer 20

-simple overlay plots for patients who have a disorder can be misleading
> regions that they highlight might reflect increased vulnerability of certain regions to injury rather than any direct involvement with the disorder of interest

Question 21

Example control patients lesion studies - speech

Answer 21

Example:

• compare patients who show impaired speech production with those who do not. These control patients should have brain lesions in the same hemisphere
• regions of the brain that are simply vulnerable to brain damage should be commonly damaged in both groups
• regions that are specifically involved with speech production should be selectively damaged in those patients who have problems in generating speech

Question 22

Example lesion method – spatial neglect

Answer 22

-brain’s attention network is damaged in one hemisphere

-typically occurs from a stroke
-reduced arousal and
processing speeds, as well as an attention bias in the direction of their lesion (ipsilesional)

• One way to observe this phenomenon is to look at the patterns of eye movements in patients with neglect
• eye movements are compared to those of patients with right hemisphere strokes who showed no signs of neglect
• neglect can also affect the imagination and memory

Question 23

Extinction

Answer 23

• visual field testing can show that neglect patients detect stimuli normally when those stimuli are salient and presented in isolation
• patient does not have a primary visual deficit
• presence of the competing stimulus in the ipsilateral hemifield prevents the patient from detecting the contralesional stimulus

Question 24

Balint’s syndrome

Answer 24

three main deficits:
Simultanagnosia: difficulty perceiving the visual field as a whole scene

ocular apraxia: deficit in making eye movements (saccades) to scan the visual field, resulting in the inability to guide eye movements voluntarily

optic ataxia: problem in making visually guided hand movements

Question 25

Comparing neglect and Balint’s syndrome

Answer 25

Dissociation:

• neglect can be based on spatial coordinates either with respect to the patient (egocentric reference frame) or with respect to an object in space (allocentric reference frame)
• the brain mechanisms involved with attending objects can be affected even when no spatial biases are seen
• Bálint’s syndrome: relatively normal visual fields but cannot attend to more than one or a few objects at a time, even when the objects overlap in space

Question 26

Sodium amobarbital test

Answer 26

-creates a transient and reversible inactivation of one cerebral hemisphere

-sodium amobarbital test
thus serves the critical role of providing the surgeon with information about whether the intended removal is in the language hemisphere in patient