Task 8 Lesion studies

Question 1

Lesion methods (def)

Answer 1

study of the effect of damage to a particular area

Question 2

Classical neuropsychology

Answer 2

• infer function of a brain region by taking patients with lesions to that region and examine pattern of impaired/spaired abilities
• favours group studies

Question 3

Cognitive neuropsychology

Answer 3

• pattern of spared/impaired abilities used to infer building blocks of cognition (irrespective of location)
• favours single cast studies

Question 4

Limits to interpretation: Modularity

Answer 4

assumption that discrete anatomical modules deal with different cognitive functions (homunculus)
–> brain functions are carried out in distributed manner: most brain damage is not limited by boundaries of underlying functional modules

Question 5

Limits to interpretation: Universality

Answer 5

assumption that functional modules are in the same locations in different individuals
–> brain shows great anatomical differences & plasticity

Question 6

Limits to interpretation: Differential vulnerability

Answer 6

• locations of brain damage are not randomly distributed –> difficulties in interpreting lesion overlap plots

Question 7

Limits to interpretation: Functional compensation

Answer 7

• brain regions can be disabled but intact

Question 8

Limits to interpretation: Temporal resolution

Answer 8

• not possible to assess time course of information processing
• testing patient in accute stage of illness: can’t accurately identify all impaired brain areas
• waiting for initial problems (e.g., swelling) to resolve: brain plasticity

Question 9

Single case study

Answer 9

data from different patients are not combined

Question 10

Assumptions of Single case studies

Answer 10

1. Fractionation assumption: damage to brain produces selective lesions (unlikely due to functional distribution)
2. Transparency assumption: lesions affect components within preexisting cognitive system but don’t result in new system being created : needed because we study abnormal brain to understand normal brain
3. Universality assumption: generalizability of all cognitive systems

Question 11

Strong arguments for single-case study

Answer 11

• in non-brain damaged population: okay to average observations of group because the only existing difference between participants is noise
• in brain-damaged population: each patient has different lesion –> difference in performance may be due to lesion rather than noise

Question 12

Group studies

Answer 12

performance of different patients is combined to yield group average

Question 13

Basic concept

Answer 13

• to localize which region is critical for performing a given task –> in fMRI: activity does not imply critical involvement!
• lesions are rarely restricted to the area of interest –> several patients need to be considered

Question 14

Grouping in group studies

Answer 14

1. Grouping by syndrome: patients are assigned based on cluster of different symptoms (schizophrenia)
2. Grouping by cognitive symptom: assigned based on one particular symptom
3. Grouping by anatomical lesion: based on having lesion to particular anatomical region

Question 15

Disadvantages of group studies

Answer 15

• indivdiual brains differ –> standardization required

Question 16

Localization of function: single dissociation

Answer 16

• if patient is impaired on task A but not on task B:
  1. Tasks rely on different cognitive processes
  2. Tasks rely on same cognitive process but Task A requires more neural resources than B
  3. Hierarchical relationship: functions are separate but one function is necessary for the other

Question 17

Localization of function: double dissociation

Answer 17

• two single dissociations in two individuals with complementary profile of abilities:
  –> provides stronger evidence for functional specialization and that two functions are independent (speech and comprehension)

Possible artifacts:
1. Task-resource artifact: brain damage depletes important resource that leads to impairment of task
2. Task-demand artfifact: patient performs one of the tasks sub-optimally

Question 18

Advantages of double dissociation

Answer 18

• tells which areas are involved in particular function
• lesion is not due to nonspecific brain dysfunction
• tells which areas are not involved (unimpaired task B)

Question 19

Limitations of double dissociations

Answer 19

• dissociations don’t tell us where the function is localized, only necessary areas
• lesion may exert disruptive effects on neighbouring tissue (diaschisis)

Question 20

Association

Answer 20

• consistent co-occurrence of 2+ impairments suggests one underlying process
• can be due to proximity of regions
• disruption of single underlying process is responsible for both impairments

Question 21

Application lesion method (Broca’s area)

Answer 21

Claim: third convolution of inferior frontal gyrus is involved with speech production

Support:
- patient who was only able to produce one syllable –> studied correlation between behavioural disorder & location of brain injury

Question 22

Hemineglect

Answer 22

• unilateral damage to parietal, temporal, and frontal cortices
• Consequence: difficulties in attending to and processing information from one side of body or environment

Question 23

Neglect as disorder of attention

Answer 23

• neglect patients show activation of visual cortex
• able to detect objects if cued or externally motivated (salient items, emotionally charged)

Question 24

Line cancellation task

Answer 24

• patients are asked to bisect lines in middle –> only bisect unaffected side

Question 25

Vision vs. visual imagery: single case study

Answer 25

Patient C.K.:
- car accident and suffered head injury: damaged ventral stream of visual processing pathway –> cannot recognize objects anymore but has intact imagery
Study:
- 2 opposing single dissociations form double dissociation
- previous study: perception intact, imagery impaired

Question 26

Patient C.K.: Experiments

Answer 26

Experiment 1: to find out whether there is impairment:
- impaired object recognition but semantic unimpaired –> appropriate semantic information cannot be accessed for items presented in visual modality

Experiment 2: What is C.K. able to recognize?
- able to identify letters and objects when presented by touch or auditory input

Experiment 3: Perceptual processing: Is C.K. impairment bsed on interference with other visula impairments?
-> funcitonal deficits concern intermediate stages of visula processing because
- not for all types of input
- not for all types of objects (letters but not faces)
- not for based visual input

Experiment 4: Imagery of objects, size, colour, form
–> C.K. retained knowledge about phyiscal characteristics of objects & could use it for imagery

–> proof of single dissociation between imagery (intact) and perception (impaired)