The Neurobiology of Consciousness Professor Christof Koch

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Virgil Sparks
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1 California Institute of Technology 1 Science explains many things very well 2 3 1

2 4 5 Yet science has no idea how consciousness comes about! Some philosophers say that consciousness is not logically supervenient to physics 6 2

relationship between the immaterial, conscious

3 In lieu of a definition - look! Bonneh, Cooperman & Sagi in Nature (2001) 7 First person account versus third person account 8 The mind-body problem What is the nature of the relationship between the immaterial, conscious mind and its physical basis in the electro-chemical interactions in the body? 9 3

4 The mantra of the science of consciousness Measure what is measurable, and make measurable what is not so Gallileo Gallilei 10 What do we know about C? C is associated with some complex, adaptive, biological networks It is not associated with the immune system Nor with the enteric nervous system C does not require behavior e.g., dreaming C does not require emotions C does not require language nor self-consciousness Most of us, most of the time are not very self-conscious Our self awareness is reduced when doing demanding activities (e.g.. rock climbing, riding a motorcycle etc.) C can occur in one cerebral hemisphere Destruction of localized brain regions interferes with specific content of C As in prosopagnosia after a stroke As in achromatopsia, i.e. the loss of color perception 11 A conceptual distinction The content of consciousness must be distinguished from states of consciousness - wakefulness, REM & non-rem sleep Enabling factors are necessary for any form of consciousness Intralaminar nucleus of the thalamus cholinergic pathways from the brainstem & basal forebrain Mesencephalic reticular formation (ascending reticular activating system) Specific factors are required for any one particular conscious percept; That is, the content requires enabling factors as well as a dominant neuronal coalition in the cortex and thalamus to express any one specific conscious content 12 4

Ascending reticular activating system ARAS - sometimes also known as

Modern view of the ARAS 2x40 nuclei in the human Parvizi & Damasio

profoundly disturbed (coma) or permanently absent (persistent

5 Ascending reticular activating system ARAS - sometimes also known as the (mesencephalic) reticular formation Moruzzi & Magoun (1949) 13 Modern view of the ARAS 2x40 nuclei in the human Parvizi & Damasio (2001) 14 Pathologies in states of consciousness Consciousness can be profoundly disturbed (coma) or permanently absent (persistent vegetative state) Terri Schiavo see at

6 When does consciousness begin? Lagercrantz & Changeux in Pediatric Research (2009) 16 Consciousness begins with the baby s first cry Mellor et al., in Brain Res. Rev. (2005) 17 Consciousness in mammals 18 6

Consciousness in non-human animals Assumption that C occurs in other species because: Similarity of behavior Similarity of brain architecture Close evolutionary kinship The main

comp. Neurol. (2005) 20 What do we not know about C?

7 Consciousness in non-human animals Assumption that C occurs in other species because: Similarity of behavior Similarity of brain architecture Close evolutionary kinship The main specialization of homo sapiens is highly developed self-consciousness 19 Consciousness in insects? Bees have highly evolved behavior The 3-D Honeybee Brain Brandt et al., in J. comp. Neurol. (2005) 20 What do we not know about C? We do not know the minimal brain size necessary for C to occur We do not know whether C requires a body We do not know whether C can be instantiated in any system with the same functional relationships as in the brain We do not have a widely accepted theory of consciousness But a theory is needed 21 7

8 Search for the minimal neuronal mechanisms jointly sufficient for any one conscious perception, the neuronal correlates of consciousness (NCC) Crick & Koch (1990, 1995) 22 For every conscious percept, there exists some such correlates in the brain Crick & Koch in Nature (1995) 23 The cerebellum is not part of the NCC Frontal lobe Parietal lobe Occipital lobe Temporal lobe Brain stem Cerebellum 24 8

retina The retina is not part of the NCC The retina is necessary for normal seeing but that s not where consciousness happens 25 Primary

Horton 26 Consciousness and planning The function of consciousness is to complement on-line zombie systems: our second assumption is

best current interpretation of the visual scene, in the light of past experience either of ourselves or of our ancestors (embodied in our

outputs (of one sort or another) Crick and Koch in Nature (1995) From this hypothesis and the neuroanatomical observation in the macaque

9 retina The retina is not part of the NCC The retina is necessary for normal seeing but that s not where consciousness happens 25 Primary visual cortex Human ocular dominance columns J. Horton 26 Consciousness and planning The function of consciousness is to complement on-line zombie systems: our second assumption is based on the broad idea of the biological usefulness of visual awareness (or, strictly, of its neural correlate); This is to produce the best current interpretation of the visual scene, in the light of past experience either of ourselves or of our ancestors (embodied in our genes), and to make it available, for a sufficient time, to the parts of the brain that contemplate, plan and execute voluntary motor outputs (of one sort or another) Crick and Koch in Nature (1995) From this hypothesis and the neuroanatomical observation in the macaque that V1 does not project into the frontal lobes, we conclude that the NCC does not reside in V1; Conscious vision can be dissociated from V1 activity This may be also true for primary somatosensory and auditory cortex (Laureys et al.) 27 9

What is the relationship between visual consciousness and V1 activity? Is V1 necessary for conscious vision? Is V1 necessary and sufficient (at least under some conditions) for visual perception?

10 What is the relationship between visual consciousness and V1 activity? Is V1 necessary for conscious vision? Is V1 necessary and sufficient (at least under some conditions) for visual perception? Is feedback to V1 necessary for conscious vision? Evidence suggests that V1 is neither necessary nor sufficient but often co-varies with conscious vision (Haynes & Rees Nature Neurosci. 2005; Lee, Blake & Heeger Nature Neurosci. 2007; Maier et al., Nature Neurosci. 2008) Pollen in Cerebral Cortex (1999) 28 Various proposed NCCs While there is some agreement about what are not NCC, there is much less agreement on what NCC are: 40 Hz synchronized firing NMDA activity Layer 5 cells Slow cortical potentials Cortical re-entry Feedback between visual cortices and prefrontal cortex Default cortical networks Right anterior insula Why this matters Not any cortical activity is sufficient for conscious percept Some cortical regions have a more privileged position with regard to the NCC Possibly none of the primary sensory areas support NCC Some measurable progress in the questions of the NCC 30 10

Many brains inside your head Many - if not most - behaviors occur in the absence of conscious sensations, or consciousness occurs after the fact: Spinal reflexes Posture adjustments Any over-trained

11 Many brains inside your head Many - if not most - behaviors occur in the absence of conscious sensations, or consciousness occurs after the fact: Spinal reflexes Posture adjustments Any over-trained routine: shaving, dressing, tennis, video games, keyboard typing, driving, rock-climbing, dancing Reaching and grabbing (Milner & Goodale 1996) Generating speech Dissociation between what the eyes see and conscious perception High-level decision making (e.g., choice blindness) 31 Francis Crick and I call them zombie agents Zombie agents perform well without conscious awareness What is common about these different zombie system? Koch & Crick in Nature (2001) 32 Continuous flash suppression Left eye Right eye Percept Tsuchiya & Koch in Nature Neurosci. (2005) 33 11

Looking at invisible nudes Jiang et al., in Proc. Natl. Acad. Sci.

Attention and consciousness Attention and consciousness are distinct neuronal processes, with distinct functions (Iwasaki

12 Looking at invisible nudes Jiang et al., in Proc. Natl. Acad. Sci. USA (2006) 34 Processing invisible stimulus requires top-down attention Bahrami, Lavie & Rees in Current Biology (2007) 35 Attention and consciousness Attention and consciousness are distinct neuronal processes, with distinct functions (Iwasaki 1993; Baars 1997; Hardcastle 1997; Crick & Koch 2003; Naccache et al., 2002; Lamme 2003; Kentridge et al., 2004; Bachman 2006; Dehaene et al., 2006) Often one becomes conscious of what one attends to However, one can attend to objects or events without becoming necessarily conscious of any or even all of their attributes Likewise, one can become conscious of something without attending to it Koch & Tsuchiya in Trends Cog. Sci. (2007) 36 12

Recording from neurons in the human medial temporal lobe All recordings

Medical School UCLA G. Kreiman, R. Quian-Quiroga, L. Reddy, F. Morman, M.

, Cerebral microdialysis combined with single neuron and

Neurosurg. 91: 697-705 (1999) All surgeries carried out by Dr.

13 Recording from neurons in the human medial temporal lobe All recordings are carried out in the clinic and laboratory of Itzhak Fried at the Medical School UCLA G. Kreiman, R. Quian-Quiroga, L. Reddy, F. Morman, M. Cerf C. Koch 37 Around 100 microwires per patient Fried, I et al., Cerebral microdialysis combined with single neuron and electroencephalographic recording in neurosurgical patients; J. Neurosurg. 91: (1999) All surgeries carried out by Dr. Fried at UCLA 38 The human medial temporal lobe Hippocampus Amygdala Parahippocampal gyrus Entorhinal cortex 39 13

14 A patient on Dr. Fried s ward 40 Left posterior hippocampus neuron 40 Hz 1sec Quian-Quiroga, Reddy, Kreiman, Koch & Fried in Nature (2005) 41 Right anterior hippocampus neuron 40 Hz 1sec C) Quian-Quiroga, Reddy, Kreiman, Koch & Fried in Nature (2005) 42 14

15 Right anterior hippocampus neuron (2) 40 Hz 1sec Quian-Quiroga, Reddy, Kreiman, Koch & Fried in Nature (2005) 43 Left anterior hippocampus neuron Quian-Quiroga, Kraskov, Koch & Fried in Current Biology (2009) 44 Entorhinal cortex neuron Quian-Quiroga, Kraskov, Koch & Fried in Current Biology (2009) 45 15

Amygdala neuron Quian-Quiroga, Kraskov, Koch & Fried in Current Biology (2009) 46 Data from 21 sessions in 8 patients

8% of images shown Invariant units: 52 [38% of resp.

this selective Each particular stimulus can activate up to one million discrete neurons The same neurons could be

suppressed image The 1/3 neurons that did not follow the percept responded selectively during the monocular presentation

16 Amygdala neuron Quian-Quiroga, Kraskov, Koch & Fried in Current Biology (2009) 46 Data from 21 sessions in 8 patients Units: 998 (~48 per recording session;) Responsive: 137 [14%] +5std baseline Sparse firing: Responded to 2.8% of images shown Invariant units: 52 [38% of resp. units] +99 ROC surrogates Responsive Non-responsive Responsive + invariant It is only a small minority of neurons that are this selective Each particular stimulus can activate up to one million discrete neurons The same neurons could be activated by other stimuli 47 The effect of masking on these neurons No MTL neuron responded selectively to a perceptually suppressed image The 1/3 neurons that did not follow the percept responded selectively during the monocular presentation but not during suppression; This might be due to sparse firing and therefore weak statistics MTL neurons do not represent perceptually suppressed information Kreiman, Fried & Koch in Proc. Natl. Acad. Sci. USA (2002) 48 16

17 The need to move from correlation to causation Transcranial magnetic stimulation Selective surgery Direct electrical stimulation Injecting drugs Opto-genetic techniques Introducing photoreceptors into genetically characterized populations of neurons using viruses Introducing light (by using optical fibers) to these areas, will activate the photoreceptors and will lead to spiking in these neurons 49 In summary Studying the neuronal basis of consciousness has moved from philosophical speculation and deduction into the realm of the empirical, the scientific A functioning brain is sufficient to generate consciousness Progress in the science of consciousness will enable to rigorously define and measure the extent of the size of conscious, subjective states in humans, across developmental stages and in diseases, and in other animals Such a research program also tell us how to create conscious artifacts

The Nervous System. Divisions of the Nervous System. Branches of the Autonomic Nervous System. Central versus Peripheral

The Nervous System. Divisions of the Nervous System. Branches of the Autonomic Nervous System. Central versus Peripheral The Nervous System Divisions of the Nervous System Central versus Peripheral Central Brain and spinal cord Peripheral Everything else Somatic versus Autonomic Somatic Nerves serving conscious sensations