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Attention and neglect. Neurophysiology of Attention The Superior Colliculus MT, MST and PPC V2, V4 and IT.

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Presentation on theme: "Attention and neglect. Neurophysiology of Attention The Superior Colliculus MT, MST and PPC V2, V4 and IT."— Presentation transcript:

1 Attention and neglect

2 Neurophysiology of Attention The Superior Colliculus MT, MST and PPC V2, V4 and IT

3 Neurophysiology of Attention The Superior Colliculus MT, MST and PPC V2, V4 and IT

4 The Superior Colliculus Receptive Field

5 The Superior Colliculus Saccadic Enhancement Receptive Field

6 The Superior Colliculus Receptive Field

7 Is the saccadic enhancement in the superior colliculus due to attention or to a motor intent?

8 The Superior Colliculus Attention alone can increase the firing rate Receptive Field

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11 Response enhancement could correspond to the selection of the attended target This enhancement seems to be independent of the behavior

12 Physiology of Attention The Superior Colliculus MT, MST and PPC (the posterior parietal cortex) V4 and IT (the infero temporal cortex)

13 Treue and Maunsell, MST

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16 Response to the attended stimulus is enhanced Enhancement is stronger when the distractor and the target are in the same receptive field The response to the distractor is decreased

17 PPC: Gottlieb and Goldberg, 1998 Firing Rate Time Cue: Triangle Time Cue: Circle + * Cue * + 1 st Saccade Firing Rate 1 st Saccade 2 nd Saccade

18 Cells in MT and PPC: Attention boosts the gain of the response to the attended stimulus while reducing the response to the unattended stimulus.

19 Physiology of Attention The Superior Colliculus MT and PPC (the posterior parietal cortex) V2, V4 and IT

20 Reynolds et al, 1999 Monkey attends preferred stimulus of the cell

21 Reynolds et al, 1999 Monkey attends null stimulus for the cell

22 McAdams and Maunsell, 1999 Colored Gaussian

23 McAdams and Maunsell, 1999

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25 What’s going on? Maunsell: –Gain modulation –No baseline shift –Seen everywhere although strongest when the distractor and the target are in the same receptive field Desimone: –Not gain: normalization –Baseline shift –Seen only when the distractor and the target are in the same receptive field

26 Neglect

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28 Line Cancellation

29 Line Bisection

30 Patient: Frederico Fellini

31 Karnath et al., 1993 Patients: Right Parietal Task: Shape Identification Condition 1 Condition 2

32 Prediction for Retinocentric Neglect Condition 1 Condition2 Right Target Left Target % Correct

33 Prediction for Trunk-centered Neglect Condition 1 Condition2 Right Target Left Target % Correct

34 Patients % Correct Patient 1 Patient 2 C1 C2

35 Frames of reference for neglect: Trunk-centered?

36 Left hand is neglected Left hand is still neglected even though it is now on the right

37 Can neglect be object-centered?

38 Object-centered or relative neglect?

39 Draw the black half Draw the white half Object-centered or relative neglect?

40 Main axis Hard Easy Driver et al, Neuropsychologia, 1994 Axis-centered neglect

41 Frames of Reference of Neglect Neglect always affects a mixture of egocentric frames of reference for all behaviors Neglect is always relative In some patients, it can also be axis- centered (object-centered).

42 Can we relate the behavior of hemineglect patients to the response of neurons involved in spatial representations? What do we know of the response properties of neurons involved in spatial representations?

43 Retinal Location (deg) Activity Eye Position (Andersen et al., 1985) e x = -20 e x = 0 e x = –

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45 Motor commands, M, are non linear functions of sensory inputs, S, and posture signals, P: M = f(S,P) Such functions can be approximated by linear combinations of basis functions, B i (S,P): M =  c i B i (S,P) Claim: parietal neurons compute basis functions

46 Retinal Location (deg) Activity Eye Position e x = -20 e x = 0 e x = 20 Retinal Location (deg) Activity Eye Position (deg) -40 –

47 Eye MovementsReaching Basis Function Layer (Parietal Cortex) Retinal Location Eye Position Units Retinotopic Map Visual Cortex Eye Position Premotor Cortex Head-Centered Map Superior Colliculus Retinotopic Map

48 Can we generalize the basis function theory of spatial representations to object-centered representations?

49 Left of the object Right of the object Neuronal Activity Trials

50 Left of the object Right of the object Left of the objectRight of the object Saccades Direction (deg) Neuronal Activity Activity Trials

51 Explicit object-centered neurons or gain modulated neurons?

52 Left of the object Right of the object Left of the objectRight of the object Saccades Direction (deg) Neuronal Activity Activity Trials

53 It appears that the parietal cortex uses basis functions for spatial representations in: Egocentric coordinates (eye-, head-, body- centered) Object-centered coordinates

54 Eye MovementsReaching Basis Function Layer (Parietal Cortex) Retinal Location Eye Position Units Retinotopic Map Visual Cortex Eye Position Premotor Cortex Head-Centered Map Superior Colliculus Retinotopic Map

55 Basis Function Layer Eye Position Right Left Retinal Position Right Left Map Eye Position Right Left Retinal Position Right Right Map Premotor Cortex Head-Centered Map Superior Colliculus Retinotopic Map Eye Position Units Retinotopic Map Visual Cortex

56 Main assumptions of the hemineglect model: Parietal neurons compute basis functions Basis function units are distributed across hemispheres according to contralateral gradients

57 Basis Function Layer Eye Position Right Left Retinal Position Right Left Map Eye Position Right Right Map Premotor Cortex Head-Centered Map Superior Colliculus Retinotopic Map Eye Position Units Retinotopic Map Visual Cortex Left Retinal Position Right

58 Saliency: summed activity in the basis function layer Saliency Retinal Location Eye Position Left Right Left

59 Line Length Line Orientation Line Length Error Model Patients Model

60 Karnath et al., 1993 Patients: Right Parietal Task: Shape Identification Condition 1 Condition 2

61 Model Condition 1 Condition 2 Right Target Left Target

62 Retinal Location Head Position Left Right Left Left Stimulus Right Stimulus C2 C1

63 Left hand is neglected Left hand is still neglected even though it is now on the right

64 General principle: any change of posture toward the ipsilesional side results in an improvement in performance (extreme case: vestibular recovery)

65 Relative neglect

66 Draw the black half Draw the white half

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70 Object-centered neglect

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72 Activity in the Basis Function Layer Hard Easy Main axis

73 Conclusions Parietal neurons compute basis functions of their inputs. As a result, they encode the location of objects in multiple frames of reference simultaneously A lesion of a basis function representation leads to a syndrome similar to hemineglect if the basis functions are distributed across hemispheres according to contralateral gradients This approach can be generalized to object- centered representations


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