Neuropsychology: Research Methods III & IV

1. Neuropsychology: Research Methods III & IV Ref: Banich, pp. 62-99 (skim through sections on brain imaging)

2. Four Main Methods • A. Lesion (or subtraction) method • B. Experiments with intact humans • C. Functional imaging studies • D. Electrical recording techniques

3. Lesion (or Subtraction) Method Some ways of using: • Observe function after damage to a structure • Examine damage after impairment to a function • Look for associations & dissociations between impairments • Examine in detail a known functional impairment

4. a. Observe function after damage to a structure animals: ablation studies humans: observe after illness/injury Phineas Gage: * Known damage to frontal lobes * Inability to plan, socially inappropriate behaviour, moodiness, capriciousness. * Conclusion: damaged region involved in goal setting, modulation and inhibition of behaviour and emotion.

5. b. Examine damage after impairment to a function • Broca's patient "Tan": • Understood speech, but said only one word, "Tan” • Post-mortem -> damage to Broca's area Conclusion: speech production relies on Broca's area

6. b. Examine damage after impairment (cont’d) • More recent studies: • use modern localisation techniques such as CAT, MRI.

7. c. Look for associations & dissociations between impairments • Example of Dissociation: • Patient HM: Can’t form new long-term memories • BUT Normal at this task: Repeat the following sequence of numbers 3 7 9 1 8 4

8. c. Associations & dissociations (cont’d) Compare to JK: • Mr. K suffered a mild stroke which affected a small region in the left parietal lobe. He made a good physical recovery, and some months later, was able to return to his previous, demanding position as a private secretary in a large corporation. He had little difficulty resuming his former duties: he was able to remember which tasks/clients he had worked with just before his illness, and had no problem learning new tasks and remembering new clients. However, he noticed a sudden difficulty with numbers. He found himself unable to accurately record numerical information given to him verbally. Also, when dialing phone numbers, he could still deal with familiar numbers, but would repeatedly make mistakes when dialing a new number for the first time. • JK underwent further neuropsychological tests which revealed that he had a digit span of only one

9. c. Associations & dissociations (cont’d) • HM & JK show opposing patterns for 2 abilities Impaired Intact Intact Impaired

10. c. Associations & dissociations (cont’d) • -> "Double Dissociation" • Must have: • i. at least two individuals • ii. at least two tasks/abilities • iii. opposite performance on each

11. c. Associations & dissociations (cont’d) • Association: When function X is impaired, what other functions are affected ? e.g.Mr. JK: Does he have problems understanding language? If so -> STM important in language comprehension.

12. d. Examine in detail a known functional impairment Left Hemineglect: A few days after suffering a mild stroke, Mrs. K began to realise things were not quite right. When she had visitors in hospital, she would often lose track of where they were in the room. She would inquire about someone's absence, only to be told that the person had not left the room, but was in fact right by her side, sitting to her left. Also, although Mrs. K normally took great care in her appearance, the nurses would often tell her that she had forgotten to brush the left side of her hair, or to apply lipstick on the left of her mouth. And finally, perhaps most troubling, she had great difficulty navigating through the corridors of the hospital to get to the bathroom. On one occasion, she was frustrated to find herself back where she started without reaching her destination:

13. d. Examine a known impairment (cont’d)

14. d. Examine a known impairment (cont’d) • What kinds of situations are most difficult for these individuals? • Does the problem affect only vision, or other senses too? • What happens when head and body are at different angles? • What factors can help a patient attend to the left side of space? Questions to ask:

15. Lesion Method: Problems and Issues Underlying assumption of this method: performance = normal performance – function impaired i.e. The “subtractivity” assumption

16. Lesion Method: Problems and Issues • Compensation • Premorbid differences • Anatomical co-occurrence error • The problem of group averaging

17. Lesion Method: Problems & Issues (cont.) • i. Compensation • P uses alternative strategy • e.g. P with STM deficit uses visual mnemonics • P with word retrieval prob. uses writing • Dangers: • - may underestimate importance of damaged structure/component • - performance may have unusual qualities • e.g. gnome -> gome

18. Lesion Method: Problems & Issues (cont.) • ii. Premorbid differences HM: Temporal lobe damage resulted from surgery for epilepsy. BUT epileptics -> "atypical" brain localisation

19. Lesion Method: Problems & Issues (cont.) • iii. Anatomical Co-occurrence Error • Functions appear to be associated, but this is just • due to anatomical proximity. • e.g. Broca's aphasia: • articulation problems • problems with sentence planning

20. Lesion Method: Problems & Issues (cont.) • Group data can reveal spurious "syndromes": • e.g. Broca's aphasia: articulation + central language prob's • Gerstmann's syndrome: finger agnosia + agraphia + alexia iv. The Problem of Group Averaging

21. Lesion Method: Problems & Issues (cont.) • Group trends may not reflect each individual:

22. Lesion Method: Problems & Issues (cont.) • Alternative: • - Present each individual separately. • - Only report what's true for most/all individuals.

23. Lesion Method: Problems & Issues (cont.) Single case studies have their own challenges:

24. B. Experiments with Intact Humans Use existing information about brain organisation to design a study. Example: Can take advantage of contralateral organisation of primary visual cortex:

25. Visual half-field technique:- choose a task (e.g. word naming)- present stimulus to one half-field: B. Experiments with Intact Humans • +

26. Visual half-field technique:- choose a task (e.g. word naming)- present stimulus to one half-field: B. Experiments with Intact Humans • CAT

27. B. Experiments with Intact Humans • Which hemisphere is first to receive this stimulus? Left hemisphere Can compare RT’s to words in left vs. right visual field (e.g. lexical decision task) Result: Words on the right approx. 100msec faster than on left. Q: What does this tell us?

28. Four Main Methods • A. Lesion (or subtraction) method • B. Experiments with intact humans • C. Functional imaging studies • D. Electrical recording techniques