An Introduction to Consciousness

An introducon to consciousness

Camilla Derchi

Lorenzo Ga

Marisa Saggio

Topics

Today: Introducon to consciousness and aenon The sensorymotor conngency (OReagan and No 2001) Introducon to neural correlates of consciousness (Tononi & Koch 2008)

Thursday: The integrated informaon theory Consciousness in dreams (Nir & Tononi 2010) Discussion

Brain & consciousness

The words conscious and consciousness are umbrella terms that cover a wide variety of mental phenomena

Both are used with a diversity of meanings: the adjecve conscious is heterogeneous in its range, being applied both to whole organisms (creature consciousness) and to parcular mental states and processes (state consciousness) (Rosenthal 1986, Gennaro 1995, Carruthers 2000)

Conscious mental state: at least six major opons

1) States one is aware of States in which some informaon is available for control of behaviour and for guiding verbal reports (Chalmers 1996)


1) States one is aware of 2) Qualitave states States that involve qualitave or experienal properes of the sort oen referred to as qualia or raw sensory feels


1) States one is aware of 2) Qualitave states 3) Phenomenal states


1) States one is aware of 2) Qualitave states 3) Phenomenal states 4) What-it-is-like states


1) States one is aware of 2) Qualitave states 3) Phenomenal states 4) What-it-is-like states 5) Access consciousness A states being conscious is a maer of its availability to interact with other states and of the access that one has to its content (Nagel 1995)


1) States one is aware of 2) Qualitave states 3) Phenomenal states 4) What-it-is-like states 5) Access consciousness 6) Narrave consciousness

Qualia Perceptual experiences (seeing green, hearing loud trumpets, tasng liquorice, )

Bodily sensaons (feeling a twinge of pain, feeling an itch, feeling hungry, having a stomachache, )

Felt reacons or passions or emoons (feeling delight, lust, fear, love, feeling grief, jealousy, ...)

Felt moods (feeling elated, depressed, calm, bored, tense, ...)

Explanatory gap

Qualitave, phenomenic aspect of experience

vs

Representaonal, intenonal and funconal aspect of experience

Its not possible to explain the subjecve, felt aspects of experience in behavioral, physical or funconal terms

A sensorimotor account of vision and visual consciousness

ORegan & No

2001

The explanaon of ORegan & No

Qualia are meant to be properes of experiental states or events. But experiences are not states: they are ways of acng and things we do

There is no introspecbly available property determining the character of ones experienal states

Qualia are an illusion, and explanatory gap is not a real gap at all

The sensorimotor conngency

Proposal Seeing as a way of acng: parcular way of exploring the environment. The experience of seeing occurs when the organism masters the governing laws of sensorimotor conngency

The sensorimotor conngency

Proposal Seeing as a way of acng: parcular way of exploring the environment. The experience of seeing occurs when the organism masters the governing laws of sensorimotor conngency

Advantages Provides a natural and principled way of accounng for visual consciousness and for dierences in perceived quality of the experience in dierent sensory modalies

Brain & vision General idea For every perceptual state there is a neural correlate sucient to produce it. Its funcon is to produce sensory experience by generang a representaon corresponding to the content of the experience

Brain & vision General idea For every perceptual state there is a neural correlate sucient to produce it. Its funcon is to produce sensory experience by generang a representaon corresponding to the content of the experience Sensorimotor conngency theory Seeing is a skillful acvity. The brain supports vision by enabling mastery and exercise of knowledge of sensorimotor conngencies

Brain & vision General idea For every perceptual state there is a neural correlate sucient to produce it. Its funcon is to produce sensory experience by generang a representaon corresponding to the content of the experience Sensorimotor conngency theory Seeing is a skillful acvity. The brain supports vision by enabling mastery and exercise of knowledge of sensorimotor conngencies

Visual consciousness It is not a special kind of brain state or a special quality of informaonal states of the brain: its something we do

The neural correlates of consciousness

An update

Tononi & Koch

2008

Neural correlates of consciousness

Using the tools of neuroscience to shed light on the minimal neural structures and acvity paerns that underlie consciousness

Neural correlates of consciousness

How?

1)Measuring how brain acvity changes when a smulus is experienced or not

2)Considering condions in which consciousness is globally diminished such as sleep or anesthesia: what has changed in the brain?

Consciousness and sensory input/motor output

Consciousness might be ghtly linked to the ongoing interacon we maintain with the world and the body

However:

We are conscious of our thoughts, which do not seem to correspond to anything out there (smulus-independent thoughts)

During dreams, we are virtually disconnected from the environment. Nevertheless, we are vividly conscious (Hobson, 2009)

Consciousness and self-reecon

Consciousness might arise through the ability to reect on our own percepons: our brain would form a scene of what it sees but we experience it subjecvely only when we, as subject of experience, watch that scene from the inside.

However:

When we are immersed in the rapid ow of experience (for example watching and engrossing movie) we are vividly conscious, without any need for reecon or introspecon.

Consciousness and aenon When a subjects pay aenon to an object they become conscious of its various aributes; when the focus of aenon shis away, the object fades from consciousness

Are aenon and consciousness same phenomenon or are they disnct phenomena with disnct funcon and neuronal mechanisms?

Recent evidence argues in favor of a dissociaon between selecve aenon and consciousness (Bahrami et al. 2007)

Bahrami et al. 2007

Bahrami et al. 2007

The dierent fMRI response in V1 for the two condions

Aenon without consciousness

Results show that availability of aenonal capacity determines neural representaons related to unconscious processing of connuously suppressed smuli in V1.

Spillover of aenon to corcal representaons of invisible smuli cannot be a sucient condion for their awareness

Consciousness in the absence of aenon

Using the idencal renal layout, the subject either performs the central task, the peripheral task, or both simultaneously (Sperling & Dosher 1986; Braun & Sagi 1990; Braun & Julesz 1998)

In a dual-task paradigms, the subjects aenon is drawn to a demanding central task, while at the same me a secondary smulus is ashed somewhere in the periphery (Braun & Julesz 1998)

Consciousness & aenon: summary The existence of aenon without consciousness and consciousness without aenon, should not be surprising when considering their dierent funcons

Aenon: mechanisms whereby the brain selects a subset of incoming sensory informaon for higher level processing, while nonaended parts are analyzed at a lower bandwidth. It can be directed by boom-up, exogenous cues or by top-down endogenous features and can be applied to a spaally restricted part of the image (focal, spotlight of aenon), an aribute (e.g., all red objects), or to an enre object

Consciousness: involved in providing a kind of execuve summary of the current situaon that is useful for decision making, planning, and learning

An important disncon

Changes in level of consciousness

(the degree to which

we are conscious)

How does brain acvity change when level of

consciousness changes?

An important disncon


(the degree to which

we are conscious)

How does brain acvity change when level of

consciousness changes?

Changes in content of consciousness

(the parcular experience

we are having)

How does brain acvity change when specic

content of consciousness changes?


Many situaons where the level of consciousness can decrease:

Sleep

Anesthesia

Coma and vegetave states

Seizures

Sleep

The brain isnt (completely) shut down: vivid conscious experiences in REM or late NREM sleep (dreams)

Sleep

The brain isnt (completely) shut down: vivid conscious experiences in REM or late NREM sleep (dreams)

So what are the dierences between NREM and REM?

Part of the brain inacve (frontal & parietal areas)

Slow (1 Hz) up-down oscillaons in corcal and

thalamic neurons (Steriade et al. 2001)

TMS response (Massimini et al. 2005, 2007)

Steriade et al. 2001

Why is NREM not conscious?

A rst explanaon based on these slow oscillaons:

Changes in level of consciousness might be related to the degree of bistability of thalamocorcal networks (Tononi 2004, Massimini et al. 2007)

Massimini et al. 2004, 2005, 2007

TMS during NREM:

in lateral corcal regions remains localized to the smulaon site and lasts for

Massimini et al. 2005

Wakefulness

NREM sleep

TMS

TMS

Why is NREM not conscious?

The experiment show that during NREM connecvity among corcal regions break down, and so does corcal integraon

This suggests that during sleep brain becomes bistable:

part of it breaks down in casually independent modules (premotor cortex)

another part shows a global stereotypical response (sensorimotor cortex)

It loses the ability to enter states that are both integrated and dierenated, typical of wakefulness

Anesthesia

How do anesthecs cause (brusque) loss of consciousness (LOC)?

They reduce thalamic methabolism and blood ow, but also a global 30%-60% reducon.

Thalamus might be a consciousness switch (Alkire et al. 2000)

Thalamus might be eecng the corcal circuits (deacvaon of cortex alone can cause LOC, acvaon of thalamus alone cannot maintain it) (Velly et al. 2007)

Alkire et al. 2000

Intersecon of eect between halothane and isourane anesthesia


Apart from lesions, LOC caused by impairment in cells acvaon in intralaminar nuclei, which enable interacons among corcal regions

Brain metabolism reduced by 50%-60%, especially in posterior cingulate cortex and precuneus (Laureys et al. 2004; Schi 2006). These areas acvate most reliably if paent recovers

Schi 2006

Acvaon paerns in response to

passive language presentaons

Forward speech

Reversed speech

Overlap


In paents with great part of the thalamocorcal system intact, normal acvaon paerns can be induced by cognive smuli (Laureys et al. 2004; Schi 2006) or even by thoughts (Owen et al. 2006)

Owen et al. 2006 Acvaon paerns during tennis and moving around a house imagery.

Seizures

All types of seizures with momentary LOC show:

Increased upper brainstem and medial thalamus acvity

Decreased anterior and posterior cingulate, medial frontal cortex and precuneus acvity

Altered acvity in the lateral and orbital front cortex, and in the lateral parietal cortex

LOC appears when neurons are excessively and synchronously acve (Blumenfeld & Taylor 2003)

Blumenfeld & Taylor 2003

Level of consciousness: summary

Status Region aected

Sleep Inacve frontal and parietal areas. Slow oscillaons in corcal and thalamic neurons

Anesthesia Reduced methabolism in thalamic area, but also everywhere else

Coma Reduced posterior cingulate cortex and precuneus acvity. Might show consciousness signs if thalamocorcal system is intact

Seizures Increased upper brainstem and medial thalamus acvity Decreased anterior and posterior cingulate, medial frontal cortex and precuneus acvity

Changes in content of consciousness

The ulmate goal is to idenfy the NCC (neural correlates of consciousness)

Mainly done with visual smuli because

Easy to manipulate Visual area is the best known in primates

Uses techniques (masking, binocular rivalry, change blindness, ) to disrupt the smulus-percept associaon and its resulng neural acvity

Masking Binocular rivalry

The NCC in visual cortex

There is good evidence (Wolfe 1984; Leopold & Logothes 1996; Logothes 1998) that the inferior temporal cortex responds to the percept instead of the smulus.

The NCC in visual cortex

Many experiments seem to show that V1 contains perceptually suppressed informaon (Haynes & Rees 2005; Bahrami et al. 2007)

Probably, much of the neural acvity in V1 does not belong to the NCC (and this could be true for all the primary sensory corces)

Consciousness and neural dynamics

Most of the cortex is acve during early NREM, anesthesia and generalized seizures, but there is no consciousness

This suggests that addional dynamic features of neural acvity are necessary to generate consciousness

Models of neural dynamics

Three proposed models:

Substained vs Phasic acvity Neural acvity needs to last a minimum amount of me (propagaon me?) in appropriate areas.

Or maybe its the onset and oset discharge that correlates with consciousness, and masking smulus overlap the on and o phases and so are suppressed



Substained vs Phasic acvity Reentrant vs Feedforward acvity Simple smulus percepon is the rst, feedforward acvity, but consciousness is due to a reentrant wave.



Substained vs Phasic acvity Reentrant vs Feedforward acvity Synchronizaon and oscillaons Consciousness might require ne synchronizaon between distributed populaon of neurons. Phase locking could be a disambiguang factor between mulple objects

A theorecal framework

The integrated informaon theory (Tononi 2004) tries to estabilish

What consciousness is



What consciousness is How we can measure it



What consciousness is How we can measure it What is required to generate it in any physical system

What is consciousness?

When we experience a conscious state, we rule out other alternave experience

So, consciousness is informaon, because it lowers our level of uncertainty

Why integrated informaon theory?

The level of consciousnes of a physical system is related to the repertoire of causal states (informaon) avaiable to the system as a whole (integraon)

Integrated because the experience is an integrated whole, it cannot be subdivided into indipendently experienced components

How to measure it?

We can dene a measure of integrated informaon that quanes the reducon of uncertainty

If a system has a posive value of its called a complex, which is connected to other elements by means of ports-in and ports-out

Since integrated informaon is generated within a complex, this implies subjecvness of conscience.

What does consciousness require?

Computer simulaons (Tononi 2004, 2005) show that high requires networks that conjoin funconal specializaon with funconal integraon

This would explain, for example, why consciousness is related to the thalamo-corcal systems but not for the cerebellum (which, despite its large number of neurons, does not contribute much to consciousness because its made of quasi-independent modules)

Evidence for this models?


None.


None.

But

its validity [] rests on its ability to account coherently for some phenomenological observaons and for some elementary but puzzling facts about consciousness and the brain

Documents

An Introduction to Consciousness