Spatial representation and parietal cortex

1. Spatial representation and parietal cortex Marlene Behrmann Department of Psychology, CMU and CNBC • Contact: behrmann@cnbc.cmu.edu • 268-2790 • URL: http://www.cnbc.cmu.edu/~behrmann

3. Division of labour in human visual cortical system

4. Mishkin and Ungerleider

8. Inferior Parietal lobule Angular gyrus Supramarginal gyrus The parietal lobes: • “crossroads of the brain” • (Critchley, 1953) • well situated • topographically • multimodal • requisite cortical and subcortical connectivity • Distribution of MCA, little collateral supply

9. Neglect

10. Federico Fellini (1920-1993)

11. Neglect * * • Asymmetry in incidence: RH (66%) in humans not monkeys • Inferior parietal lobule • Areas 39 and 40; • non-human primate analog: IPL (7) vs STS • bimodal: short-lived vs persistent • Affects different sensory modalities • Not sensory deficit

12. Not just parietal • Distributed network: (Mesulam; Heilman) • dorsolateral prefrontal, medial frontal (cingulate, thalamus, basal ganglia, white matter). • Same network activated in eye movement studies • Close relationship between attention and eye movements (Corbetta et al.) • Other terminology • Extinction • Allesthesia • anosagnosia

13. Extent of effect • Other sensory modalities • Auditory • Olfactory • Tactile • Mental imagery • Piazza del Duomo (Bisiach and Luzzatti) • Affects output: not surprisingly

14. Vision and eye movements(Behrmann et al.) • 45 x 36 degrees visual angle • magnetic scleral coil in right eye • indicate number of As in display

15. Lesions: neglect patients

16. Lesions: BD controlswith hemianopia

17. Location and duration of fixations

18. Eye movements reflect left-sided neglect

21. What can we learn about parietal cortex? • What determines what information is neglected? • What gives rise to neglect? • What happens to the information that is neglected?

22. What can we learn about parietal cortex? • What determines what information is neglected? • What gives rise to neglect? • What happens to the information that is neglected?

23. Possible frames of reference: what defines ‘left’?

24. Visual neglect in allocentric coordinates

26. Depiction of environmental neglect

27. Visual neglect in allocentric and egocentric coordinates

28. Tactile and visual neglectMoscovitch and Behrmann

29. Tactile neglect in allocentric co-ordinates

30. Range of possible frames of reference

31. Neglect with respect to object midline • Target • Copy

32. Behrmann and Tipper right object right space left object right space

33. Object-based neglect: inhibition for right and facilitation for left targets

34. Directional selectivity of neuronsOlson and Gettner (1995, 1998) L/R of bar L/R eye movement

35. Neurons fire for left or right of bar independent of direction of movement

36. Paradigm: object and environ- neglect square circle

38. Simultaneous object- and environ-based neglect

39. Multiple reference frames in eye movements too

40. Normal: no errors in reading

41. Neglect: errors and eye movements

42. Another example

43. Hemianopic: no reading errors

44. Frames of reference • Egocentric (dependent on viewer) • But also allocentric (independent on viewer) • Not only in vision, also in tactile • Multiple coordinate frame • Also evident in eye movements

45. What can we learn about parietal cortex? • What determines what information is neglected? • What gives rise to neglect? • What happens to the information that is neglected?

46. What gives rise to neglect? gradient Gradient consistent with neuronal distribution: 68 bilateral, 29 contra, 3 ipsi

47. Suggests competition too:bad on left, too good on right

48. Visual search paradigm

49. Normal subjects

50. Patients with LHD