Neuroimaging of high-level visual functions. Visual awareness

Transcription

1 Neuroimaging of high-level visual functions Visual awareness

2 Phylosphy of mind Art AI Normal and abnormal states Coma Drugs Hypnosis Religion Cosciousness 2 Unconscious processes Normal and abnormal contents attention Memory emotion Thinking Intention language

3 Introduction for the non-philosopher Definition Components Levels Prerequisites Why??? 3

4 Definition of consciousness (for the nonphilosopher) continous pursuit and controll of the self responding capacity of the brain, awareness state state of wakefullness, responsiveness and activity of the whole brain 4

5 Components of consciousness ability to interact with our enviroment awareness, attention formation of abstract ideas self consciousness recognition of being formation and recognition of aesthetic and etical categories 5

6 Levels of human consciousness 1. no sharp boundaries conscious states coma, "a state of unresponsiveness from which an individual has not yet been aroused", deep vigilant coma 6

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8 Cerebral glucose metabolism Controls n=110 mean age: 42y Vegetative state n=33 mean age: 42y 8

9 Levels of human consciousness 2. Sleep slow-wave sleep (stages 2,3,4) REM sleep (stage 1), dreaming, lucid-dreaming 9 Kognitív pszichológia 2.

10 Brain metabolism during sleep Awake REM Sleep Slow Wave Sleep 10

11 Levels of human consciousness 3. Awake states -undisturbed actively following ideas 11

12 Prerequisites of consciousness 1. neocortex desynchronized EEG ascending pathways of the reticular formation 12

13 Prerequisites of consciousness comissures 2. (?) substrate of consciousness: mutual activation of several CNS areas 13

14 Why are we conscious? Produces the best interpretation of the enviroment Makes this interpretation directly available to other CNS structures 14

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16 Visual awareness Blindsight The on-line system Neglect Binocular rivalry Ambigous stimulation Implicit processes NCC

17 Blindsight 1. Visual behavior in the absence of visual consciousness (contrasts residual seeing) Such behaviors include pointing to single targets wavelength naming or discrimination direction of motion and speed discrimination shape and object recognition is not possible 17 (Weiskrantz, 1997).

18 Blindsight Unilateral V1 lesion Kognitív pszichológia 2.

19 Blindsight. Neural correlates Collicular projections Extrageniculate thalamic projections Cooling V1 leads to complete loss of neural responses in the ventral pathway, but parietal functions are not touched (via colliculus or extrageniculate thalamus) 19

20 Blindsight. fmri of Blindsight patient reveals different areas for awareness (Br46) and unawareness (SC) Ventral pathway is essential for visual consciousness 20 Sahraie et al, 1997)

21 Visual awareness Blindsight The on-line system Neglect Binocular rivalry Ambigous stimulation Implicit processes NCC

22 Perception vs. Action or The on-line system 1. eye movements, arm movements, body posture adjustments unconscious mainly dorsal path (Milner & Goodale, 1995) HOW vs. What or action vs. perception the zombie part of you 22

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24 Dorsal pathway responds to invisible stimuli too Fang and He (2005) Binocular rivalry with visible and invisible conditions: Invisible visible

25 Visual awareness Blindsight The on-line system Neglect Binocular rivalry Ambigous stimulation Implicit processes NCC

26 neglect 26

27 Neglect is object based figure/ground completion 27

28 Visual awareness Blindsight The on-line system Neglect Binocular rivalry Ambigous stimulation Implicit processes NCC

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30 Binocular rivalry 30 Kognitív pszichológia 2.

31 Binocular rivalry human fmri study rivalry with faces and houses Fusiform face area parahippocampal place area FFA and PPA activity correlated with perception ambiguous information is resolved by reaching FFA & PPA 31 Tong et al, 1998

32 Binocular rivalry Greater ratio of neurons following perception at higher areas in the cortex These neurons are beyond the resolution of ambiguitis, reflecting the brain s internal views of the objects Multiple extrastriate areas are involved in awareness Q: (Are neurons following perception form NCC?) 32

33 Bin. Riv in monkeys?? Logothethis 33 et al (1998)

34 Bin. Riv in monkeys V1/V2 20 % V4 40 % V5 IT 50 % 90 % 34

35 Visual awareness Blindsight The on-line system Neglect Binocular rivalry Ambigous stimulation Implicit processes NCC

36 Ambigous images 36

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38 38 Kognitív pszichológia 2.

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40 Bistable percepts - Ambiguous figures Monkey perceive the same way as humans do. Bradley et al (1998) Field of moving dots, percept of a rotating cilinder, with changing direction of rotation. 50 % of MT neurons fire if monkey reports one direction but fires much less in the opposite direction. Britten et al, (1992) made monkeys to discriminate direction of motion of visual noise patterns. In 50 % of the MT neurons the behavior of the neurons reliably signalled the behavior of the animal. half of the neurons in MT reflects not the image of the retina, but what the animal perceives. 40

41 ? 41 Bradley et al (1998)

42 V5 Stimulus Percept 50 Neuron % %

43 Bistable percepts- Ambiguous figures Kleinschmidt et al (1998) human fmri of ambiguous fig. Activations due to flip in percept in bilat.middle fusiform g., posterior intraparietal and ventral prefrontal cortex. Decrease in V1, n. pulvinar Visual areas remote from early visual processing, both categorical and spatial. Widespread cooperation of multiple cortical areas in visual awareness of bistable percepts 43 Kognitív pszichológia 2.

44 Microstimulation V5 Stimulus Percept Neuron Electric stim.? 44

45 50% 50 % Controll Electric stim 45

46 2.5 Electrical brain stimulation and conscious behaviour 2. Salzman et al (1990) directly stimulated MT neurons electrically during a motion direction discrimination task. The performance of the animals shifted towards signalling the preferred direction of the motion of the stimulated neurons stimulation of a small group of (MT) neurons could modify the final decision of the animal could this area contribute to conscious processing of motion? 46

47 Kanwisher, 2001 Cognition

48 Face recognition without FFA

49 Amygdala, Impl. Sem. Priming

50 2.7. NCC-Neural correlate of consciousness Consciousness is mediated by specific groups of neurons (? all encoding neurons)- NCC NCC is explicit different percept-different NCC small groups of neurons 50

51 What are the Neural Correlates of Consciousness (NCC)? - special neurons? - single neurons, firing rate overcoming a given threshould (activation hypothesis)? - cell assemblies, way of activation, synchrony?