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What can Electrophysiology (and Brain Rythms)tell us about ‘Meditation’ ?
Jean-Philippe LACHAUX
CNRS - LENA - PARISINSERM – U280 – LYON
Stirling Workshop June 11-12, 2004 Buddhist inspired Models of the Mind
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GENERAL FRAMEWORK
‘Meditation(s)’ … ?
Varieties of attention-Focal (‘external’ or ‘internal’ targets)
- Open attention (whatever happens, happens)
If we can talk about the dynamic of the mindThen meditation has to do with the fine tuning
of parameters that determine this dynamic
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Mind’s Dynamic
Plasticity of AttentionGrasping, Frozen Mind,
Overexcitment, …
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Mind’s Dynamic
Deeply Rooted into a Large-Scale Non-linear Dynamical System under constant external
perturbations(reactivity vs. inertia)
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If the dynamic of the Mind has to do with the dynamic of the Brain,
Then
it should be possible to understand, or at least witness,the effects of meditation on this dynamic via brain imaging
Optimally, it would be nice to describe the neural dynamic at a time-scale that is compatible withthe time-scale of subjective experience
And at a spatial scale compatible with the spatial scale of the brain’s functional architecture
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temporal resolution
sp
ati
al re
solu
tion
neurons
cms
ms minutes
meg -eeg
seeg
petfmri
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EEG/MEG in Humans
Evoked Potentials EEG Oscillations‘spontaneous EEG’
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EEG Oscillations
Several characteristic frequency bands with different functional specificities (more or less)
Synchronization of large neural populations
(<4Hz) (4-7 Hz) : working memory, mental load ? (7-14 Hz) : relax ? ‘idle rythm?’ (15 – 30 Hz) : sustained attention ? Relax ? (> 30 Hz) : attention ? Visual processing ? Motor ? …
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G M response K
Gatingof the THETA band
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How is the spontaneous EEG modified during meditative states ?
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EEG Oscillations :
it’s more complicated than that ….
… But more interesting for our main topic
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The function of EEG Oscillations depends on where they originate from
Then, we should be able to understand what they tell us about meditation
My main point
Therefore, they must be studied and understood at the level of functionally homogeneous neural populations (at first….)
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Select a set of cognitive tasks ….
Some proposals on how to use electrophysiology to study meditation
In which expert meditators perform much better than ‘normal’ subjects
With well-known electrophysiological characteristics(functional anatomy + dynamics)
Compare those characteristics between the two groups
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Background
Study of EEG at the intracerebral levelIn humans, in a variety of cognitive tasks
Visual perceptionMemoryAttentionLanguageMovement
…
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And how it related to
visual attentionthe notion of ‘brain availibility’and visual imagery
A simple face perception paradigm ….
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Stimuli: 'Mooney' faces
Readily recognized when presented in upright orientation
Usually seen as meaningless
black and white spots when
presented upside-down.
Brain Oscillations during the perception of visual objects
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mean
std
F5-F4 : Fusiform Gyrus
121 trials
Very little freedom ….
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Pat1, fusiform gyrus
I
III
II
IV
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-500 0 500 1000
0
10
20
30
40
50
time [ms]
z-sc
ore
Pat1, fusiform gyrus
Mean Deviation[50 – 200 Hz]
PNP
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-500 0 500 1000
0
10
20
30
40
50
time [ms]
sta
ndard
devia
tion
-500 0 500 1000-20
0
20
40
time [ms]
pote
ntial [m
icro
V]
Pat2, Inferior temporal gyrus BA37 (Bipole e’7e’8)
Mean Deviation[50 – 200 Hz]
Evoked Potential
PNP
PNP
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O’E’
FUSIFORM GYRUS PRIMARY VISUAL CORTEX
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PRIMARYVISUAL
CORTEX
Sorry, my brain is busy, I can’t get your call right now …
Fusiform gyrus
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The Attentional blink : how to hide things to the brain
Do seasoned meditators Blink attentionally ?
Sorry, my brain is busy, I can’t get your call right now …
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OK, you have my full attention, now
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And now, MENTAL IMAGERY and the BETA range
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from ( Tallon-Baudry et al., 01 )
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Yes
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Yes
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And how it related to
self (executive) control
A simple occulo-motor paradigm ….
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Saccade Anti-Saccade
timeLook Away !
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« This ability to control behaviour flexibly, responding automatically to stimuli in one situation and suppressing this automatic response in favour of an alternative response in a different situation, is the hallmark of executive control.
In this review, we describe how the antisaccade task can
be used to investigate the volitional control of action »
Munoz et al. Nature Reviews Neuroscience 2004
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And how they related to
‘the little voice in the head’
Two simple language paradigms ….
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le il etait foisunepetit chat
time 1s
adapted from Nobre et al. 1998
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AMPLITUDE MODULATIONBETWEEN 30 AND 150 Hz(z-score / ligne de base[-500ms : -100ms])
Left Motor Operculum
: GREEN TARGET
: RED TARGET
: GREEN IGNORED
: RED IGNORED
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SEMAN : living entity or not ?
PHONO : final sound : vowel or cons. ?
ORTHO : twice the same letter ?
VISUAL : twice the same item ?+
+
+
+
nefoul
cheval
xwsxkz
adapted from Bentin et al. 1999
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Amplitude Modulation between 30 and 150 Hz(z-score / base line[-500ms : -100 ms])
Broca Area
Motor Operculum
Associative Auditory Cortex
Inferior Frontal Gyrus
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Select a set of cognitive tasks ….
Some proposals on how to use electrophysiology to study meditation
In which expert meditators perform much better than ‘normal’ subjects
With well-known electrophysiological characteristics(functional anatomy + dynamics)
Compare those characteristics between the two groups
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THE FUTURE
Real-time Feedback
Non-invasive dynamic mapping using EEG/MEG and source modelling