10_Up_to_consciousness

10_Up_to_consciousness - Terminology Chapter 10: Up to...

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Unformatted text preview: Terminology Chapter 10: Up to consciousness Sensation (gewaarwording) Perception (waarneming, ervaring) Attention Intention Consciousness Sensation ~ gewaarwording Perception ~ waarneming, ervaring Arousal, wakefullness ~ wakkerheid: non-specific activation of the cortex in relation to sleep-wake state Alertness ~ alertheid, opmerkzaamheid: includes some cognitive processing. Vigilance ~ vigilantie, waakzaamheid: sustained (tonic) attention. Awareness ~ besef Perception, illusions and hallucinations Sensation, perception Illusion An illusion is a distortion of what is sensed. • Sensation detection of physical energy from objects transmitted to the brain • Perception interpretation of that physical energy, into meaningful sensory experiences (making sense) The Müller-Lyer illusion Hallucination The perception of something that can not be sensed externally. In hallucinations, there are correlations between particular kinds of hallucination (e.g. visual) and activity in the appropriate (visual) centres that normally subserve real phenomena of the same kind. 1 Perception and illusions The cube of Necker Perception and illusions The cube of Necker More alternations after stimulanting drugs (cafeine, speed…) Watching actively: Extravert persons alternate more (feel rapidly bored) Looking passively: Introvert persons alternate more (more brain activity at rest) Perception and illusions Perception and illusions Top-down (from brain expectation to periphery) disturbs buttom-up 2 Perception and illusions How can perception be formed? Key ideas from a simple neurologist •Although an illusion, the brain does exactly what we want E.g. objects look nearer than they are (evolutionary: advantage to flight early seeing a lion at distance) •The world is a product of perception, not a cause of it Transactionalist theory Sensation is the process of bridging the physical energy and the brain. Perception involves making sense of sensation. Perception is a product of both - bottom-up sensory processes (from periphery to brain) - top-down processing (from expectation to periphery) Crevits, 2005 Intention Perception vs Intention Intention The subjective experience of intention allows us to recognize whether an external event is linked to our own action or not. The parietal and frontal lobes jointly develop, monitor and refine the motor commands for intentional action. 3 Intention Intention arises as a direct consequence of pre-movement brain activity in the frontal and parietal motor areas. The supplementary motor area is a particularly important site for intention. Fried et al. J. Neurosci. 1991, 11, 3656-66 Intention The motor commmand on its own can produce the hallucination of movement When volunteers with an anaesthetised arm are asked to move their arm, they report the sense of movement. ⇒ The brain only has to send a command to a limb (intention) to create the sense of movement (i.e. a hallucination of movement) When the SMA is stimulated, subjects report the sensation of an urge to move their limb. More intense stimulation at the same locations provokes physical movements of the corresponding limb. Intention A pre-motor stimulation (SMA) can produce the sensation of an urge to move the limbs. J. Neurosci. 1991, 11, 3656–3666. The motor commmand on its own can produce the sense of movement. J Physiology, 2006, 571, 703-10 J. Physiology, 2006, 571:703-10 Hierarchy of action - Non-intentional: (reflexive) the lower system produces an action not set by the higher system - Intentional: higher system sets up the lower system. Intention: translates goals and desires into behavior. - absent-minded intentional action: (autonomous, automatic) action runs unmonitored. Action is appropriate to stimulus if appropriate conditions are met. - fully executive-controlled intentional action: (voluntary) higher system plans, triggers and monitors execution of action, overriding when necessary Adapted from Trends in Cognitive Sciences, 2005,9, No.6 June 4 From Sensation and Perception to Consciousness through Attention Multimodal Reflexive Automatic Voluntary Non-intentional Intentional, absent minded Intentional, fully controlled (Crevits, 2007) Attention ATTENTION PRE CONSCIOUS CONSCIOUS INATTENTION perception may proceed pre-consciously Attention Approximately 99% of all information entering through the senses is dropped (Wolfe, 2001) Factors that influence attention are meaning and emotion The process by which the brain - actively selects environmental information to pass on to higher levels of processing or - actively processes internal information (ie. visceral cues or thoughts). More generally, attention can be defined as an ability to - focus (selective attention) and - maintain interest in a given task managing distractions (vigilance). 5 Attention Attention Neurobiology of attention: Different approches Some leading theories Neural structures involved in attention Mesulam, 1981 Attention Attention “conscious control” SAS selects according to -level of activation, which is determined by trigger conditions of the schema -lateral inhibition / excitation between schemata. The Norman & Shallice model (1986) The central executive in the working memory model manages attention The Baddeley model 6 (NOR) (dopamine) Attention DLPFC Supervisory Attentional System ~ Central Executive ~ executive function ~ prefrontal cortex ~ DLPFC Sup. colliculus Ant. system: detection and response-selection (overt): DLPFC, ACC Post. system: automatic allocation of spatial attention (covert) thalamus (pulvinar thalami): engages attention to new location PPC: disengages attention colliculus superior: displaces attention Crevits, 2005 Selective Attention The Posner-Peterson model Selective Attention • Attention can modulate the efficacy of information processing • Attention can be selectively directed to various stimulus features LIP: lateral intraparietal sulcus MT: medial temporal cortex Selection requires top-down feedback about what is important. Parietal neurons increase activity in (focused) selective spatial attention. Studied by neurophysiologic (ERP), metabolic (PET) and cellular (single unit) methods Science, 2007, 316, 1612-5 7 Attention Brain regions involved in attention ARAS: alertness and arousal superior colliculus: automatically orienting attention to a particular location thalamus: - selection of incoming information - activation of the cortex posterior parietal lobe: - spatial frame of reference - binding features together (eg. color and form) cingulate cortex: - selection of motor responses - processing attentionally demanding tasks prefrontal cortex: - top-down attentional control - motor aspects of attentional control Finally…consciousness: a neurobiological approach Crevits, 2006 The concept of “consciousness” has different meanings… Example: in sleep, we are unconscious (1), but our experiences in dreams are vividly conscious (2). Consciousness takes two forms: transitive and intransitive Intransitive consciousness has no object; being awake (1). It can be lost and recovered. Transitive consciousness is a matter of being conscious of something or of another (2). To be conscious of a percept is to be aware of it. This requires attending to. Perception per se is not a form of consciousness, but becoming aware and retaining an awareness, is. (1) Wakefulness, arousal: elementary, biological substrate. A non-specific activation of the cortex in relation to sleep-wake. (1) Wakefulness, arousal: elementary, biological substrate. A non-specific activation of the cortex in relation to sleep-wake. (2) Awareness: sensory and emotional experience ~ psychological, phylosophical content. (2) Awareness: sensory and emotional experience ~ psychological, phylosophical content. 8 Terminology Transitive consciousness: To be conscious (to be aware) is to have one’s attention caught and held. But one can be attentive without being aware, because separate neural networks subserve attention. Attentional networks are found in the fronto-parietal regions. Sensation ~ gewaarwording Perception ~ waarneming, ervaring Arousal, wakefullness ~ wakkerheid: non-specific activation of the cortex in relation to sleep-wake state Alertness ~ alertheid ~ opmerkzaamheid: includes some cognitive processing. Vigilance ~ vigilantie, waakzaamheid: sustained (tonic) attention. Awareness ~ besef Adapted from: Clinical Neurophysiology, 2006, 117, 1885-1901 Consciousness: Wakefulness, arousal (level) and awareness (content) Conscious content: the continually changing phenomenal content (e.g. qualia such as redness and warmth) and intentional content (e.g. explicitly held beliefs, conscious knowledge) that is present to varying degrees at non-zero conscious levels. Conscious level: refers to a scale ranging from total unconsciousness (e.g. death and deep coma) to vivid wakefulness. A “conscious organism” is one that is capable of having non-zero conscious levels. A non-zero conscious level indicates the presence of some conscious content. Cell Press 2008, in press, doi:10.1016/j.tics.2008.04.008 9 Consciousness: (three) necessary brain structures Primary consciousness: (sensory consciousness) conscious content consisting of a multimodal scene composed of basic perceptual and motor events. Higher-order consciousness: refers to awareness of being in a mental state. In humans it is usually associated with language and an explicit sense of selfhood. In higher-order theories, it is possible to have higher-order thoughts that are not themselves (higher-order) conscious, but in virtue of which other (primary) contents are conscious. cortex (awareness) (sensory relais selective attention) (ARAS; NOR, Dopamine) (arousal) Cell Press 2008, in press, doi:10.1016/j.tics.2008.04.008 Consciousness: a modular view Consciousness: network (conceptual view) Attention 10 Consciousness: network (neurological basis) Consciousness: network (neurolobiogical theories) 1. Thalamo-cortical network (sensorial information to cortex) 2. Cortico-subcortical loops (polysynaptic) 3. Projections from brainstem to cortex (the “ancient” neurotransmission) Consciousness: network cortices cortex Some neurobiological challenges (ARAS) Crevits, 2005 11 A chimere: ½ self-face ½ Clinton face Some neurobiological challenges The right hemisphere is critical for the sense of self Comparision of viewing the self-face, with viewing the face of Bill Clinton. If the right hemisphere is anesthetized, the subject sees Clinton, not himselve. When the left hemisphere anesthetized, the subject still recognizes his own face. Emotion and consciousness Some authors argue that emotion consists of - an emotional state - as well as feelings (the conscious experience of the emotion) Analogous to consciousness that consists of - level (e.g. coma, vegetative state); arousal, wakefulness - and content (what it is we are conscious of); awareness. Some neurobiological challenges Not only is consciousness important to aspects of emotion, but structures that are important for emotion (brainstem nuclei and midline cortex), overlap with those that regulate the level of consciousness. Trends in Cogn Sc 2007, 11, 158-67 12 The Libet et al. experiments The Libet experiment brainpotential…………….. voluntary will ……… voluntary action 0 ms 350 ms 550 ms At time 0, a brain potential can be recorded (readiness potential). Only 350 ms later, we are aware we want to perform a certain action. Another 200 ms later, the voluntary action is initiated. Libet: brain activity begins before willed judgement A brain potential is measured before willed judgement: a readiness potential (Bereitschaftspotenzial) As causes necessarily precede effects, conscious intention cannot be the cause of the neural processes that lead to action. Libet, neuropsychologist, 1970, California The Libet et al. experiments “Die freie Wille ist eine Illusion“ Some neurobiological challenges Are we are puppets on a string? (Crevits) 13 The Crevits et al. ‘zombie* experiments’ The Freudian concepts Light stim. When a target has moved during a saccade (the subject being blind in that time), he adjusts the trajectory without consciously having seen the second target. *A zombie: a hypothetical human being without consciousness ATTENTION U N C O N S C I O U S PRE CONSCIOUS CONSCIOUS INATTENTION Unconsciousness subliminal: a condition of information inaccessibility where bottom-up activation is insufficient to become aware preconscious: potentially conscious, but not now because of lack of attention (topdown) SUBLIMINAL Consciousness Trends in Cognitive Sciences, 2006, 10, 204-211 14 Subliminal visual stimuli evoke a strong activation in extrastriate visual cortex, but their intensity quickly decrease in higher visual areas Only conscious stimuli trigger a late surge of activation in a global prefronto-parietal network. PLoS Biology, 2007, 5, 10, e260, 2408-23 2006, 10, 204-11 Proposed distinction between subliminal, preconscious, and conscious processing defined by bottomup stimulus strength (vertical axis) and top-down attention (horizontal axis). Shades of color: the amount of activation in local areas. Small arrows: the interactions among them. Large arrows: the orientation of top-down attention to the stimulus, or away from it (‘task-unrelated attention’). Dashed curves: a continuum of states. Thick lines with separators: a sharp transition between states. During subliminal processing, activation propagates but remains weak and quickly dissipating. “Consciousness”: an approach trough visual neuroscience During preconscious processing, activation can be strong, durable, and can spread to multiple specialized sensori-motor areas. When attention is oriented away from the stimulus (large black arrows), activation is blocked from accessing higher areas and establishing long-distance synchrony. During conscious processing, activation invades a parieto-frontal system, can be maintained ad libidum in working memory, and becomes capable of guiding intentional actions including verbal reports. The transition between preconscious and conscious is sharp. 15 Consciousness and visual pathways V1 is necessary for conscious vision (cf cortical blindness). but, V1 is not sufficient for “conscious” vision (sensation). (V1 may be active in vegetative state) Consciousness and visual pathways Dorsal route: Unconscious Consciousness and visual pathways V5 (MT) Consciousness and visual pathways Potential actions Visual features Potential actions Visual features Ventral route: Conscious Recognition The classical view: dorsal ~ unconscious, ventral ~ conscious Neglect Recognition Neurology: neglect bridging the dorsal and ventral streams 16 Consciousness and visual pathways OFC orbitofrontal cortex IT inferior temporal cortex LSF low spatial frequency V1 Potential actions Visual features Attention Recognition Neurological view: attention as a bridge between Consciousness and visual pathways • No single area, pathway or locality appears to be the neural correlate for (visual) consciousness. Adapted from Journal of Cognitive Neuroscience 2003, 15, 600-9 -A partially analyzed version of the input image (V1) (i.e., a blurred image) is projected rapidly from early visual or subcortical areas directly to the orbitofrontal cortex. -This coarse representation activates in the OFC expectations about the most likely interpretations of the input image, which are then back-projected as an ‘‘initial guess’’ to the inferior temporal cortex to be integrated with the bottom-up analysis. -Bottom-up analysis is processed through the ventral visual route. -Both pathways integrate in IT. The top-down process (OFC) facilitates recognition by substantially limiting the number of object representations that need to be considered and speeds up time when a quick response is necessary. Attention and awareness of visual percepts Attentional networks are found in the fronto-parietal regions. • It is widely agreed that the ventral pathway, interacting with areas of prefrontal, parietal and temporal cortex, forms the basic circuit. e.g. vision Within this parieto-frontal network, it is likely that visual target selection involving attention to a salient target is associated first with firing of neurons in the lateral intraparietal area. In contrast, top-down selection, involving volitional acts of attention, is associated first with firing of neurons in the frontal eye fields. Australian and New Zealand Journal of Psychiatry, 2008,42:11,915-31 17 Attention and awareness of visual percepts (a) In the absence of attention, percepts evoke only slight activity in the visual extrastriate cortex. (b) If the visual percepts are salient, networks in lateral intraparietal cortex are activated that increase the extrastriate visual pathway activity; slightly later, the frontal eyefield attentional area of the brain is active, also contributing to activity in the extrastriate pathway. (c) If attention is held, activity in the superior parietal and DLPFC is enhanced. This is graded with an increase in extrastriate visual cortex activity, until a threshold is reached. At that time there is a sudden non-graded large increase in activity in DLPFC as well as in superior parietal cortex, which drives a very large late increase in extrastriate visual cortex. The increase in the extent of recruitment of extrastriate visual cortex and of activity in the DLPFC and sup. parietal cortex is associated with being conscious of the percepts; the subject reports awareness of these. Attention and awareness are category-specific (visual, auditive…) Visual attention is supported by activity in lateral intraparietal and frontal (eyefield) cortical areas. Auditory attention is supported by activity in inferior parietal and dorsolateral prefrontal cortex. Attention and awareness of visual percepts If attention is held, activity in the superior parietal and DLPFC is enhanced. This is graded with an increase in extrastriate visual cortex activity (peak at 200 ms, signals 1,2), until a threshold is reached (signal 3). At that time there is a sudden non-graded large increase in activity in DLPFC (signal 4) as well as in superior parietal cortex, which drives a very large late increase in extrastriate visual cortex. The increase in the extent of recruitment of extrastriate visual cortex and of activity in the DLPFC and sup. parietal cortex is associated with being conscious of the percepts; the subject reports awareness of these. Finally… Much of our behavior is initiated and directed by nonconscious processes (awareness is not always necessary) • Activation of superior parietal and dorsolateral prefrontal cortex are necessary for visual awareness, together with (of course) activation of a distributed set of regions for the different components of the visual scene in primary visual cortex and ventral visual areas. Auditory awareness requires activity in prefrontal and superior temporal cortex. • Conscious control is limited (it does not feel that way) L. Crevits, 2005 18 ...
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