1. Modulation of local and long-distance
Mental Processes and Brain Activation Lab.
INSERM U280, Lyon, France
Modulation of local and long-distance
beta/gamma oscillatory synchronization
observed in human intracranial recordings
O. Bertrand
Functional modulations of local and long-distance beta/gamma oscillatory
synchronization: evidence from direct intracranial recordings in humans.
COMMUNICATION IN BRAIN SYSTEMS
Communication in Brain System – Cold Spring Harbor – May, 2004

2. beta/gamma oscillatory synchronization
perception, attention,
learning, memory,
sensory-motor integration, …
Working hypothesis
Oscillatory synchronization could be a general mechanism for the dynamic cooperation of neural networks
underlying various sensory and cognitive processes
effective coupling / de-coupling of brain regions
by synchronization / de-synchronization
Puisque des oscillations gamma on été vues dans de nombreuses structures alors généralisation du phénomène de synchro de réseau
Tallon-Baudry & Bertrand 1999, Varela et al. 2001, Engel & Singer 2001

3. Human intracranial recordings
depth electrodes in epileptic patients
during pre-surgical functional evaluation
Visual working memory task
Auditory discrimination task
Intra : auditory
collaboration with C. Fischer, Neurological Hospital, Lyon

4. Wavelet-based time-frequency analysis
T-F
ERP
averaging •
power
averaging
induced gamma ms Hz
T-F
evoked
gamma ms Hz
+µV 2
-µV
Time-freq evoked and induced
Bertrand et al. 1996

5. Visual short-term memory

6. Visual memory task - intracranial recordings
lateral occipital sulcus
fusiform gyrus
S2=S1?
memory
condition S1 S2
delay
dimming?
control
condition
Tallon-Baudry, Bertrand, Fischer, J. Neurosci., 2001

7. Visual memory task – gamma / beta oscillations
lateral occipital sulcus
fusiform gyrus
memory S1 S1 20 30 60
100 Hz 15 40
-400
400
800
1200
1400 ms
control
Tallon-Baudry, Bertrand, Fischer, J. Neurosci., 2001

8. Phase-synchrony detection in the time-frequency domain
power
complex value
(ampl. & phase)
N trials
trial 1
chan#1
chan#2
trial N
synchrony factor =
modulus of the mean vector
(ranging from 0 to 1)
phase
difference
freq.
time
Synchrony 1
Lachaux et al Tallon-Baudry, Bertrand, Fischer 2001

9. Visual memory task – phase synchronization
lateral occipital sulcus
fusiform gyrus S1 S1 2 µV
-µV S1 S1
synchronization
during
memory retention S1
synchrony factor 1
Tallon-Baudry, Bertrand, Fischer, J. Neurosci., 2001

10. Visual memory task – phase synchronization
lateral occipital sulcus
fusiform gyrus S1 S1 2 µV
-µV S1 S1
beta synchronization
during
memory retention
randomization
statistics
(yellow: p<0.05)
Tallon-Baudry, Bertrand, Fischer, J. Neurosci., 2001

11. frequency discrimination
Auditory
frequency discrimination

12. Frequency discrimination task
distractor
1080 Hz
target
1040 Hz
button
press
STD
1000 Hz
ISI : 1.4 s
50 ms tones
Discrim : protocol

13. Frequency discrimination – intracranial recordings
pat. NG
standard tones
ERPs
Heschl’s Gyrus (HG)
Planum Temporale (PT) HG PT HG PT H1
STG

14. Frequency discrimination task
Hz profile
evoked
induced on
off
induced
response
pat. NG HG PT
evoked
response

15. Frequency discrimination task
Hz profile
evoked
induced on
off
induced
response
pat. NG HG PT
induced
response

16. Frequency discrimination task evoked
induced
response
off
pat. NG
induced
(170ms) HG PT on
40-80Hz high-gamma
induced
response
26-40Hz low-gamma
evoked
(220 ms)

17. evoked induced induced evoked Frequency discrimination task 40 - 80 HzHG PT
induced Hz
depth profile Hz
depth profile
evoked
induced
10 mm
pat. NG
induced
response

18. Frequency discrimination task
ISI : 1.4 s
50 ms tones
STD
1000 Hz
target
1040 Hz
distractor
1080 Hz
late STD
early STD
increased attention
Discrim : protocol

19. Effect of attention on induced gamma
Frequency discrimination task
Effect of attention on induced gamma
1400 ms
STD
(late)
STD
STD
(early)
Target
. . .
24-40 Hz
pat. CG

20. Frequency discrimination task
Heschl’s gyrus
patient #2
patient #1
Superior
temporal
gyrus
Planum
Temporale
25-70 Hz ms

21. 2 gamma foci in the auditory cortex late vs early standard tones
Frequency discrimination task
2 gamma foci in the auditory cortex
primary
area
secondary
areas
no attention
effect
modulation
by attention
25-80 Hz ms patients
late vs early standard tones

22. Multiple foci of induced gamma oscillations
high-gamma (40-80 Hz)
HG1 PT ms
synchronized
low-gamma (25-30 Hz)
STG
amplitude and phase-synchrony
modulated by attention

23. Local and large-scale oscillatory synchronization
multiple gamma (25-40, Hz) and beta (15-25 Hz) sites
local synchrony in the vicinity of the electrodes
beta when evoked response and gamma
task-modulated medium-scale gamma synchrony (30 Hz)
task-modulated long-distance beta synchrony (15-20 Hz)
The same neural population can switch from gamma to beta oscillatory modes, each one being related to distinct functional processes: encoding, target selection, maintenance in memory

24. Mental Processes and Brain Activation Lab.
INSERM U280, Lyon, France
INSERM Lyon
Aurélie Bidet-Caulet, Françoise Bauchet
Pierre-Emmanuel Aguera
Jean-Philippe Lachaux
Catherine Fischer
Catherine Tallon-Baudry
Neurological Hosp. Lyon
CNRS Paris