1. Methods in Cognitive Neuroscience I

2. The Emergence of Cognitive Neuroscience Fueled by the development of powerful new imaging instruments and techniques Formulation of questions based on discoveries with older, more established methods Relies critically on converging operations between new methods and older established methods

3. Older Methods Cognitive Psychology –Behavior is the basic unit of study –Phenomena must be well characterized

4. Cognitive Psychology Has benefitted as a science by the development of a circumscribed set of methods and techniques

5. Measurement of Human Performance in Information Processing Tasks Much work has been done to establish the validity and reliability of these measurements W. W. Norton Basic Units of measurement: Reaction time Accuracy

6. Characteristics of Human Performance Positively skewed distribution of Reaction Times Speed/Accuracy Trade-off

7. Cognitive Psychology Basic methods have yielded a circumscribed number of phenomena in need of explanation

8. The Posner Task Results demonstrate that multiple representations are activated by a single stimulus

9. Posner Task RT decreases as time between letter presentations increases

10. The Word Superiority Effect A target letter can be identified more quickly when it is imbedded in a word than when it appears among a random letter string

11. The Sternberg Task RT increases monotonically with increasing memory set- size Similar RT slopes for both “yes” and “no” responses

12. Implications of Sternberg Task Results Memory retrieval is a serial comparison process between items in memory and those in the world Each comparison takes a fixed amount of time Mental operations can be quantified in terms of the amount of time they take

13. The Stroop Effect Subjects take longer to name a color word (e.g., red) when it is printed in a color that does not match the word

14. Implications of the Stroop Effect Multiple representations “Privileged access” of some representations over others

15. Older Methods Neuropsychology The study of cognitive deficits following brain damage

16. Older Methods Neuropsychology The “lesion method” The role of a missing brain region may be inferred from what the patient cannot do after it is removed

17. The Lesion Method Laid the empirical foundation for modern cognitive neuroscience –Broca: Left hemisphere language dominance –Luria: Posterior visuospatial dominance

18. The Lesion Method Logic is based on a localizationist perspective An “additive factors” logic Does not take into account the adaptive “parallel” nature of brain function

19. Neuropsychology Methods Basic question: Is brain region X important for Task A?

20. Single Dissociation Task ATask B Patients w/lesion to region X Controls 70%92% 90% 94% 1 Patient group, 1 Control group Two tasks, Difference between groups only occurs in Task A

21. Inference Problems with Single Dissociations Both tasks assumed to be equally sensitive to group differences Single dissociation may result from general effects of trauma, not specific effect of lesion

22. Double Dissociation Task ATask B Patients w/lesion to region X Controls 70%92% 90% 94% 2 Patient groups 1 Control group Patient groups differ on task affected, control group unaffected Patients w/lesion to region Y 89%64%

23. Newer Methods Electroencepholography –Records overall electrical activity secondary to neural activity Transcranial Magnetic Stimulation –For “virtual lesions” Positron Emission Tomography –Records metabolic activity secondary to neural activity Magnetic Resonance Imaging –Records Radio-frequency differences between types of tissue –Records blood flow increases secondary to neural activity

24. EEG Cinically useful as distinct brain states show characteristic EEG signal

25. EEG Cinically useful in determining the focus of epileptic seizure Normal Activity Seizure Activity

26. EEG Background EEG signal can be removed by trial- averaging revealing the response of a brain region to stimuli “Event-related Potentials”

27. Electroencepholography Poor spatial localization due to recordings made at the scalp Excellent temporal localization due to continuous recording Better suited to answering questions about “when” cognitive processes work not “where” they work

28. Transcranial Magnetic Stimulation Coil placed over target brain region Cognitive failures recorded

29. Positron Emission Tomography Subjects injected with radioactive isotope Where blood flow concentrates, so do isotopes As isotopes decay they are detected by scanner permitting inferences about active brain regions Capitalizes on blood-flow or “hemodynamic” properties of brain

30. Positron Emission Tomography Type of tracer determines type of activity detected – 15 O radioactive oxygen, is injected into bloodstream with water Measures blood flow –Radioactive Sugar Measures metabolism

31. Magnetic Resonance Imaging Manipulates the behavior of Hydrogen protons to yield radio signal Generates high resolution structural images Generates high resolution functional images

32. MRI Subject placed in standing magnetic field RF pulses applied to manipulate H protons

33. Structural MRI Takes advantage of the fact that different types of tissue produce different RF signals

34. Functional MRI Takes advantage of the fact that neural activity is followed by blood flow in a highly predictable manner Altered blood flow alters RF signal from active brain regions

35. Functional MRI Permits examination of brain regions that become active during cognitive performance baseline cognitive task Facilitates comparison of brain activity in younger and older

36. Functional MRI Analysis methods take advantage of known hemodynamic properties of the brain