Modulation of local and long-distance Mental Processes and Brain Activation Lab. INSERM U280, Lyon, France bertrand@lyon.inserm.fr 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

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

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

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

Visual short-term memory

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

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

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. 1999 Tallon-Baudry, Bertrand, Fischer 2001

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

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

frequency discrimination Auditory frequency discrimination

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

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

Frequency discrimination task 40 - 80 Hz profile evoked induced on off induced response pat. NG HG PT evoked response

Frequency discrimination task 40 - 80 Hz profile evoked induced on off induced response pat. NG HG PT induced response

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)

evoked induced induced evoked Frequency discrimination task 40 - 80 Hz HG PT induced 40 - 80 Hz depth profile 26 - 40 Hz depth profile evoked induced 10 mm pat. NG induced response

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

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

Frequency discrimination task Heschl’s gyrus patient #2 patient #1 Superior temporal gyrus Planum Temporale 25-70 Hz 130-300 ms

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 130-300 ms 5 patients late vs early standard tones

Multiple foci of induced gamma oscillations high-gamma (40-80 Hz) HG1 PT 130 - 500 ms synchronized low-gamma (25-30 Hz) STG amplitude and phase-synchrony modulated by attention

Local and large-scale oscillatory synchronization multiple gamma (25-40, 40-80 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

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