what can electrophysiology (and brain rythms) tell us about ‘meditation’ ? jean-philippe lachaux

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

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

Mind’s Dynamic

Plasticity of AttentionGrasping, Frozen Mind,

Overexcitment, …

Mind’s Dynamic

Deeply Rooted into a Large-Scale Non-linear Dynamical System under constant external

perturbations(reactivity vs. inertia)

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

temporal resolution

sp

ati

al re

solu

tion

neurons

cms

ms minutes

meg -eeg

seeg

petfmri

EEG/MEG in Humans

Evoked Potentials EEG Oscillations‘spontaneous EEG’

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 ? …

G M response K

Gatingof the THETA band

How is the spontaneous EEG modified during meditative states ?

EEG Oscillations :

it’s more complicated than that ….

… But more interesting for our main topic

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….)

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

Background

Study of EEG at the intracerebral levelIn humans, in a variety of cognitive tasks

Visual perceptionMemoryAttentionLanguageMovement

…

And how it related to

visual attentionthe notion of ‘brain availibility’and visual imagery

A simple face perception paradigm ….

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

mean

std

F5-F4 : Fusiform Gyrus

121 trials

Very little freedom ….

Pat1, fusiform gyrus

I

III

II

IV

-500 0 500 1000

0

10

20

30

40

50

time [ms]

z-sc

ore

Pat1, fusiform gyrus

Mean Deviation[50 – 200 Hz]

PNP

-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

O’E’

FUSIFORM GYRUS PRIMARY VISUAL CORTEX

PRIMARYVISUAL

CORTEX

Sorry, my brain is busy, I can’t get your call right now …

Fusiform gyrus

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 …

OK, you have my full attention, now

And now, MENTAL IMAGERY and the BETA range

from ( Tallon-Baudry et al., 01 )

Yes

Yes

And how it related to

self (executive) control

A simple occulo-motor paradigm ….

Saccade Anti-Saccade

timeLook Away !

« 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

And how they related to

‘the little voice in the head’

Two simple language paradigms ….

le il etait foisunepetit chat

time 1s

adapted from Nobre et al. 1998

AMPLITUDE MODULATIONBETWEEN 30 AND 150 Hz(z-score / ligne de base[-500ms : -100ms])

Left Motor Operculum

: GREEN TARGET

: RED TARGET

: GREEN IGNORED

: RED IGNORED

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

Amplitude Modulation between 30 and 150 Hz(z-score / base line[-500ms : -100 ms])

Broca Area

Motor Operculum

Associative Auditory Cortex

Inferior Frontal Gyrus

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

THE FUTURE

Real-time Feedback

Non-invasive dynamic mapping using EEG/MEG and source modelling