EELECTROENCEPHALOGRAPHIC LECTROENCEPHALOGRAPHIC (EEG) COHERENCE STUDY OF (EEG) COHERENCE STUDY OF

WORKING MEMORY BRAIN WORKING MEMORY BRAIN OSCILLATIONSOSCILLATIONS

Dr. Dr. Simon BreSimon Brežanžan

Institute of Clinical Neurophysiology,Institute of Clinical Neurophysiology, University Medical Centre Ljubljana, Ljubljana, Slovenia University Medical Centre Ljubljana, Ljubljana, Slovenia

coauthors:coauthors: Vita ŠtukovnikVita Štukovnik,, Veronika Rutar,Veronika Rutar, Jurij Dreo, Vito Logar, Blaž Koritnik, Grega Jurij Dreo, Vito Logar, Blaž Koritnik, Grega Repovš, Blaž Konec, Janez Zidar Repovš, Blaž Konec, Janez Zidar

INTERNATIONAL NEUROSCIENCE CONFERENCE, INTERNATIONAL NEUROSCIENCE CONFERENCE, SINAPSA, LJUBLJANA 2005SINAPSA, LJUBLJANA 2005

WORKING MEMORY (WM)WORKING MEMORY (WM) memory processes: encoding, storage, recallmemory processes: encoding, storage, recall

memory structure: sensory memory (attention)memory structure: sensory memory (attention)>> short-term short-term memory (rehearsal/replacement)memory (rehearsal/replacement)>> long-term memory long-term memory

active role of short term memory – working memory- active role of short term memory – working memory- central for intelligent goal-directed behaviour, coherent central for intelligent goal-directed behaviour, coherent thoughts, language etc. thoughts, language etc.

DEFINITION: DEFINITION: complex of cognitive processes for complex of cognitive processes for time- and time- and capacity- limited capacity- limited maintenance, manipulation and utilization maintenance, manipulation and utilization of mental representationsof mental representations

MODEL OF WORKING MEMORY (BADDELEY, 2000)MODEL OF WORKING MEMORY (BADDELEY, 2000)

central executive (CE)central executive (CE): : attentional control of subsystems, manipulation of attentional control of subsystems, manipulation of information, planning, strategy selection, inhibitioninformation, planning, strategy selection, inhibition

slave subsystems: slave subsystems: • phonological loopphonological loop:: 2 separated components: storage and rehearsal of 2 separated components: storage and rehearsal of

verbal informationverbal information• visuospatial sketchpadvisuospatial sketchpad: separated storage and rehearsal of visual and : separated storage and rehearsal of visual and

spatial informationspatial information• episodic bufferepisodic buffer: integration of information from other subsystems and : integration of information from other subsystems and

episodic long-term memoryepisodic long-term memory

CENTRAL EXECUTIVE

VISUOSPATIAL SKETCHPAD

EPISODIC BUFFER

VISUAL SEMANTICS LANGUAGE

EPISODIC MEMORY

PHONOLOGICAL LOOP

CENTRAL EXECUTIVE

VISUOSPATIAL SKETCHPAD

EPISODIC BUFFER

VISUAL SEMANTICS LANGUAGE

EPISODIC MEMORY

PHONOLOGICAL LOOP

NEUROPHYSIOLOGICAL NEUROPHYSIOLOGICAL AND AND NEUROANATOMICAL NEUROANATOMICAL BASIS OF WORKING MEMORYBASIS OF WORKING MEMORY

NEUROPHYSIOLOGICAL VIEWNEUROPHYSIOLOGICAL VIEW

basic neurophysiological mechanismbasic neurophysiological mechanism of WM: of WM: repeated repeated reverberations of electrical impulses in reverberational reverberations of electrical impulses in reverberational (feedback) loops (Štrucl, 1999)(feedback) loops (Štrucl, 1999)? ?

rrepeated excitation of a synapse in excitational loopepeated excitation of a synapse in excitational loop>> increase of excitatory postsynaptic potential (EPSP) – increase of excitatory postsynaptic potential (EPSP) – postsynaptic facilitationpostsynaptic facilitation. .

• postsinaptic facilitation – preservation/maintenance ofpostsinaptic facilitation – preservation/maintenance of specific informatiospecific information in WM?n in WM?

• role of active repeating?role of active repeating?

NEUROANATOMICAL VIEWNEUROANATOMICAL VIEW

CCell electrophysiological ell electrophysiological and and functional brain imaging studiesfunctional brain imaging studies (Fletcher and Henson, 2001, etc.)(Fletcher and Henson, 2001, etc.)

vvarious components of working memoryarious components of working memory: : different different anatomically separated neuronal networksanatomically separated neuronal networks

specific brain aspecific brain activityctivity: : • ((prepre))frontal (frontal (VLFCVLFC, , DLFC, AFC) cortex DLFC, AFC) cortex • ppremotorremotor cortex cortex• llimbicimbic cortex and other subcortical structures cortex and other subcortical structures• posterior association parietal areasposterior association parietal areas

hypothetical hypothetical lateralization of functionlateralization of functions (s (Postle et al., 2000):Postle et al., 2000):• verbal information verbal information (phonological loop): (phonological loop): left hemisphereleft hemisphere• vvisuospatial information (visuospatial sketchpad)isuospatial information (visuospatial sketchpad):: right right

hemispherehemisphere

ccentral executiveentral executive:: heteromodal association cortex of heteromodal association cortex of ((prepre))frontal brain regionsfrontal brain regions ( (Gathercole, 1999)Gathercole, 1999)??

BINDING PROBLEMBINDING PROBLEM

BINDING PROBLEM: TBINDING PROBLEM: The he mechanisms for mechanisms for functional functional integration (‘binding’) of different brain areas, responsible integration (‘binding’) of different brain areas, responsible for specific (for specific (WMWM) functions) functions??

Paralell and distributed processing of information in the Paralell and distributed processing of information in the brain:brain:

• Functional integration - coupling (visual perception, Functional integration - coupling (visual perception, complex motor patterns, visuo-motor integration, complex motor patterns, visuo-motor integration, cognitive functions): key for understanding brain cognitive functions): key for understanding brain functioningfunctioning

• The code for functional coupling: synchronised The code for functional coupling: synchronised oscillations of neuronal networks between anatomically oscillations of neuronal networks between anatomically separated brain areas? separated brain areas?

Measure of synchronised brain oscillations: EEG coherenceMeasure of synchronised brain oscillations: EEG coherence

ELECTROENCEPHALOGRAPHYELECTROENCEPHALOGRAPHY (EEG), SIGNAL (EEG), SIGNAL ANALYSIS: EEGANALYSIS: EEG COHERENCE AND POWER SPECTRA COHERENCE AND POWER SPECTRA

EEG: EEG: repeated, periodic electrical activity of repeated, periodic electrical activity of (pyramidal) (pyramidal) cortical neurons cortical neurons

activity of many neuronsactivity of many neurons (synaptic EPSPs, IPSPs) –ionic (synaptic EPSPs, IPSPs) –ionic currentscurrents>> field potentials, macropotential (EEG signal)field potentials, macropotential (EEG signal)::• intrinsic qualities of neuronsintrinsic qualities of neurons, , dynamic interactions between dynamic interactions between

neuronal networksneuronal networks-- changing pattern of synchronization and changing pattern of synchronization and desynchronization of regional brain cellsdesynchronization of regional brain cells-- amplitude changes of amplitude changes of specific frequencyspecific frequency bands. bands.

EEGEEG - - great time resolution great time resolution (milisec), (milisec), distinct patterns of distinct patterns of activity activity

brain rhythms, brain rhythms, frequency bands for frequency bands for oscillations oscillations (delta: (delta: 0,5-4 Hz,0,5-4 Hz, theta: theta: 4-7 Hz4-7 Hz, alpha: , alpha: 8-13 Hz8-13 Hz, beta: , beta: 13-30 13-30 HzHz, , ggamma: 30amma: 30-50-50 Hz) Hz)

specific functionaspecific functional,l, behavioral behavioral, spatial, spatial correlates correlates- s- switching witching neural networks between different functional statesneural networks between different functional states- - activating or inhibiting neural systemsactivating or inhibiting neural systems??

EEGEEG COHERENCE AND POWER SPECTRA COHERENCE AND POWER SPECTRA

PPOWER SPECTRUMOWER SPECTRUM - - degree of representation degree of representation (power) (power) of specific of specific frequency band infrequency band in the signalthe signal; basic input data for coherence calculation; basic input data for coherence calculation

> > different levels of regional cortical activity or different level of different levels of regional cortical activity or different level of regional regional synchronizationsynchronization-activation or inhibition of neural networks-activation or inhibition of neural networks

EEG EEG COHERENCECOHERENCE – – measure of measure of degree of similarity, phase-locking degree of similarity, phase-locking (“synchronization”) of 2 distant signals for specific frequency band(“synchronization”) of 2 distant signals for specific frequency band

> > different degrees of different degrees of long-range long-range synchronization synchronization of oscillations of oscillations between between separate cortical regionsseparate cortical regions for specific frequency band for specific frequency band

measure of measure of functional coupling – binding and communication functional coupling – binding and communication between between separatedseparated brain centers brain centers

2 2 different operational systems of the braindifferent operational systems of the brain

Φxy(ω)- value of cross-correlation power spectrum of signals x, yΦxy(ω)- value of cross-correlation power spectrum of signals x, yΦxx(ω)- value of auto-correlation power spectrum of signal xΦxx(ω)- value of auto-correlation power spectrum of signal xΦyy(ω)- value of auto-correlation power spectrum of signal yΦyy(ω)- value of auto-correlation power spectrum of signal y

Cxy(ω): coherence value between signals x and y

WORKING MEMORY AND SYNCHRONIZED BRAIN WORKING MEMORY AND SYNCHRONIZED BRAIN OSCILLATIONS – POWER SPECTRA AND EEG OSCILLATIONS – POWER SPECTRA AND EEG

COHERENCE STUDIESCOHERENCE STUDIES

synchronous oscillationssynchronous oscillations-- correlat correlationion with specific with specific behavioural contexts and cognitive tasks behavioural contexts and cognitive tasks – numerous – numerous studiesstudies

The neurophysiological theory of (working) The neurophysiological theory of (working) memory:memory:

Brain oscillations in different frequency bands subserve Brain oscillations in different frequency bands subserve specific (memory) functions and operate over different specific (memory) functions and operate over different spatial scales. spatial scales.

Multiple superimposed synchronized (coherent) oscillations Multiple superimposed synchronized (coherent) oscillations in different frequency bands with different spatial patterns in different frequency bands with different spatial patterns and functional correlates govern specific mental functions. and functional correlates govern specific mental functions.

EEGEEG WORKING MEMORY STUDIES WORKING MEMORY STUDIES

EEG COHERENCE changesEEG COHERENCE changes

increases increases mainly mainly in thetain theta, alpha and gamma band, alpha and gamma band ((working memory working memory processesprocesses) ) (Serrien et al., 2003; Sauseng et al., 2004; Sarnthein et al, 1998; Jensen et al., 2002, etc.)(Serrien et al., 2003; Sauseng et al., 2004; Sarnthein et al, 1998; Jensen et al., 2002, etc.)

changes of power spectra and coherencechanges of power spectra and coherence with different memory load with different memory load (Gevins et al., 1997, Jensen, 2000, etc.)(Gevins et al., 1997, Jensen, 2000, etc.)

POWER SPECTRA changesPOWER SPECTRA changes

decrease in lower alpha banddecrease in lower alpha band (non-specific effect of attention, mental effort)(non-specific effect of attention, mental effort) (Klimesch et al., 1998, etc.)(Klimesch et al., 1998, etc.)

decrease in upper alpha banddecrease in upper alpha band (correlate of semantic processing) (correlate of semantic processing) (Basar et al., (Basar et al., 2000, etc.)2000, etc.)

or or increaseincrease in alpha band in alpha band (active inhibition of disturbing neural networks not (active inhibition of disturbing neural networks not needed for the memory taskneeded for the memory task) ) (Klimesch et al., 1998, etc.)(Klimesch et al., 1998, etc.)

increase increase in theta bandin theta band: frontal midline theta r: frontal midline theta rhhythythm m ((memory memory maintenance, attention, mental effortmaintenance, attention, mental effort) ) (Klimesch et al.; Gevins et al. 1997, etc.,)(Klimesch et al.; Gevins et al. 1997, etc.,)

increase in increase in gamma bandgamma band (sensory, perceptional (sensory, perceptional, , attentional, working memory attentional, working memory processes)processes) (Jensen, 2000; Babiloni et al., 2004, etc.)(Jensen, 2000; Babiloni et al., 2004, etc.)

SPATIAL SCALES OF COHERENCE CHANGES IN WM SPATIAL SCALES OF COHERENCE CHANGES IN WM TASKSTASKS

MAINLY (MAINLY (PRE)FRONTO- TEMPORO- PARIETALPRE)FRONTO- TEMPORO- PARIETAL INCREASES OF INCREASES OF THETA, THETA, ALPHA COHERENCE ALPHA COHERENCE

MAINLY MAINLY FRONTOCENTRAL INCREASES OF THETAFRONTOCENTRAL INCREASES OF THETA AND GAMMA AND GAMMA OSCILLATIONS- OSCILLATIONS- POWER SPECTRUMPOWER SPECTRUM INCREASES (FRONTAL MIDLINE INCREASES (FRONTAL MIDLINE THETA RHYTHM); THETA SOURCE??THETA RHYTHM); THETA SOURCE??

→ → ININ ACCORDANCE WITH BADDELEY’S MODEL OF WMACCORDANCE WITH BADDELEY’S MODEL OF WM: SEPARATE : SEPARATE SYSTEMS FOR SYSTEMS FOR STORAGE (POSTERIOR)STORAGE (POSTERIOR) AND AND ACTIVE MAINTENANCEACTIVE MAINTENANCE, , UPDATING OF INFORMATION UPDATING OF INFORMATION (FRONTAL BRAIN AREAS)(FRONTAL BRAIN AREAS) in modal in modal specific subsystemsspecific subsystems

NEED FOR INFORMATION EXCHANGE, COOPERATION, NEED FOR INFORMATION EXCHANGE, COOPERATION, FUNCTIONAL FUNCTIONAL COUPLING BETWEEN ANTERIOR AND POSTERIOR BRAIN REGIONS COUPLING BETWEEN ANTERIOR AND POSTERIOR BRAIN REGIONS

LONG RANGE- SLOW RHYTHMS, SHORT RANGE- FAST RHYTHMSLONG RANGE- SLOW RHYTHMS, SHORT RANGE- FAST RHYTHMS

TOP-DOWN CONTROL-TOP-DOWN CONTROL- CENTRAL EXECUTIVE CENTRAL EXECUTIVE

OUR STUDY OF WORKING MEMORY AND BRAIN OUR STUDY OF WORKING MEMORY AND BRAIN OSCILLATIONSOSCILLATIONS

AIMAIM

To examine the neurophysiological mechanisms of working To examine the neurophysiological mechanisms of working memory processesmemory processes

To To investigatinvestigatee task-related coherence task-related coherence (and power spectra) (and power spectra) changes for changes for different EEG frequenciesdifferent EEG frequencies during the processes of working memory during the processes of working memory

Search for possible differences in coherence (and power spectra) Search for possible differences in coherence (and power spectra)

changes between maintenance and manipulation processes in working changes between maintenance and manipulation processes in working memory. memory.

HYPOTHESESHYPOTHESES

Increases in fronto-posterior coherence in working memory tasksIncreases in fronto-posterior coherence in working memory tasks Increases in bilateral (pre)frontal coherence for manipulation vs. Increases in bilateral (pre)frontal coherence for manipulation vs.

maintenance-only processes of working memory (prefrontal maintenance-only processes of working memory (prefrontal central executive?)central executive?)

METHODSMETHODS

PARTICIPANTSPARTICIPANTS

11 healthy right-handed volunteers (4 males, 7 females); informed consent, aged 11 healthy right-handed volunteers (4 males, 7 females); informed consent, aged between 20-35between 20-35

average number of set repetition per each task/person= 38 average number of set repetition per each task/person= 38 10 min training of paradigm before recording10 min training of paradigm before recording

EEG RECORDINGEEG RECORDING

Dark quiet room, projection of different tasks on computer screen- cca. 80 cm from Dark quiet room, projection of different tasks on computer screen- cca. 80 cm from the eyesthe eyes

EEG cap (E1-S Electro-Cap) - 29 electrodes, standard 10-20 International electrode EEG cap (E1-S Electro-Cap) - 29 electrodes, standard 10-20 International electrode system with system with extra electrodes: Fp1, Fp2, Fz, FCz, Cz, CPz, Pzextra electrodes: Fp1, Fp2, Fz, FCz, Cz, CPz, Pz; impedance below 5k; impedance below 5kΩΩ

EEG aparat: Medelec (Profile Multimedia EEG System, version 2.0, Oxford Instruments EEG aparat: Medelec (Profile Multimedia EEG System, version 2.0, Oxford Instruments Medical Systems Division, Surrey, England)Medical Systems Division, Surrey, England)

EOG measurement (6 additional eye electrodes, Croft 2000)- 20 min calibration taskEOG measurement (6 additional eye electrodes, Croft 2000)- 20 min calibration task

Synchroniztation signal between 2 computersSynchroniztation signal between 2 computers

Presentation software for paradigm programmingPresentation software for paradigm programming

COGNITIVE WM PARADIGMCOGNITIVE WM PARADIGM

Modified Sternberg paradigmModified Sternberg paradigm of working memory of working memory

CONTROL + 2 EXPERIMENTAL CONDITIONS: CONTROL + 2 EXPERIMENTAL CONDITIONS: alternating the type of task coincidentaly during recording sessions!alternating the type of task coincidentaly during recording sessions!

““WAIT”:WAIT”: control task with ‘no’ memory demands (ignore the set, fixate the cross, relax) control task with ‘no’ memory demands (ignore the set, fixate the cross, relax)TASK: matching the serial position of goal stimulus with simultaneosly presented set of TASK: matching the serial position of goal stimulus with simultaneosly presented set of lettersletters

SETSET (M, D, O) (M, D, O) TASK instructionTASK instruction (WAIT) (WAIT) FIXATION (5500ms) FIXATION (5500ms) GOAL GOAL (3 D) (3 D) ANSWER ANSWER (NO)(NO)ANALYSIS!ANALYSIS! SET SET (M D O) (M D O)

““MEMORIZE”:MEMORIZE”: rehearsal (retention) of information in WM rehearsal (retention) of information in WMTASK: matching the serial position of goal stimulus with rehearsed originally presented set TASK: matching the serial position of goal stimulus with rehearsed originally presented set

SETSET (F, J, C, I, Z) (F, J, C, I, Z) TASK instructionTASK instruction (MEMORIZE) (MEMORIZE) RETENTION (5500ms)RETENTION (5500ms) GOAL GOAL (1 F) (1 F) ANSWER ANSWER (YES)(YES) ANALYSIS!ANALYSIS!

““REORDER”REORDER”: : manipulationmanipulation and rehearsal (retention) of information in WM and rehearsal (retention) of information in WM TASK: matching the serial position of goal stimulus with TASK: matching the serial position of goal stimulus with alphabetical orderalphabetical order of presented set of presented set

SETSET (K, C, M, A) (K, C, M, A) TASK instructionTASK instruction (REORDER) (REORDER) RETENTION (5500ms)RETENTION (5500ms) GOAL GOAL (2 M) (2 M) ANSWER ANSWER (NO)(NO) ANALYSIS! ANALYSIS!

DATA ANALYSISDATA ANALYSIS

Special independent computer programmes were designed Special independent computer programmes were designed for coherence and power spectra analysis: for coherence and power spectra analysis:

• Borland Delphi 7.0 (with EOG artefact correction- modified Borland Delphi 7.0 (with EOG artefact correction- modified Croft correction procedure) and Matlab software (no EOG Croft correction procedure) and Matlab software (no EOG correction) correction)

• .edf conversion of EEG recordings.edf conversion of EEG recordings

Analysis of 5500ms retention/fixation periods in all 3 types Analysis of 5500ms retention/fixation periods in all 3 types of tasks, selection of artefact-free epochs of tasks, selection of artefact-free epochs

Our analytical procedure

• Measuring EEG volatage and recording them in .EDF files • Correcting EEG voltages with the RAAA EOG correction method• Dividing the 5 secod retention periods for all sets of every task into five 1

second periods.• Transforming the time-domain EEG signal of all five 1 second periods into a

frequency-domain signal via a Fast Fourier Transform alghoritm.• Averaging the frequency-domain EEG signals for all five 1 second periods for

every set of every task to obtain the Average-frequency-domain signal for that set of that task for each person.

• Calculating Power-Spectra and Coherence for every set of every task for each person.

• Averaging of Power-Spectra and Coherence for every task from all the sets in that task for every person. Thus obtaining the Average-task PS and C for every person.

• Averaging of Power-Spectra and Coherence for all persons for every task Thus obtaining the Average-person PS and C.

• Averaging the Power-Spectra and Coherence in the desired frequency bands. Thus obtaining the Average-band PS and C that are displayed in our results.

• Optionally comparing Average-band PS and C for two different tasks.

Borland Delphi 7.0 data analysisBorland Delphi 7.0 data analysis

Statistical analysisStatistical analysis To calculate the border coherence-difference values that are significant at desired p-levels we To calculate the border coherence-difference values that are significant at desired p-levels we

created from 50.000 to 100.000 (depending on the frequency band) randomly distributed simulated created from 50.000 to 100.000 (depending on the frequency band) randomly distributed simulated EEG measurements that fit our experimental design exactly:EEG measurements that fit our experimental design exactly:

a total of 11 people, 4 with 56 sets per person, 7 with 28 sets a total of 11 people, 4 with 56 sets per person, 7 with 28 sets of one task of one task per personper person per each set an average of five 1 second retention periodsper each set an average of five 1 second retention periods a 1 Hz resolution in the a 1 Hz resolution in the FFourier transformourier transform

From these simulations we obtained a sampling distribution curve that fits From these simulations we obtained a sampling distribution curve that fits our experiment design as accurately as possible. The border-coherence our experiment design as accurately as possible. The border-coherence values that are significant at desired p-levels were then estimated through values that are significant at desired p-levels were then estimated through a two-tailed a two-tailed tt-test-test by calculating the area under the sampling distribution by calculating the area under the sampling distribution curve that fits the desired p-level.curve that fits the desired p-level.

FB 1: Delta (1-4 Hz), Theta (4-7 Hz), Alpha 1 (7-10 Hz), Alpha 2 (10-13 Hz)FB 1: Delta (1-4 Hz), Theta (4-7 Hz), Alpha 1 (7-10 Hz), Alpha 2 (10-13 Hz) FB 2: Beta (13-30 Hz)FB 2: Beta (13-30 Hz) FB 3: Gamma (30–50 Hz)FB 3: Gamma (30–50 Hz)

Border coherence-difference values at desired p-levels for different frequency

bands

p-level Coh. diff. FB 1

Coh. diff. FB 2

Coh. diff. FB 3

< 0.5 > 0.0186 > 0.0091 > 0.008

< 0.1 > 0.0452 > 0.0221 > 0.020

< 0.05 > 0.0542 > 0.0263 > 0.022

< 0.01 > 0.0722 > 0.0348 > 0.030

RESULTSRESULTS

Increases and decreases of coherence for different Increases and decreases of coherence for different frequency bands with differences between 3 tasks will be frequency bands with differences between 3 tasks will be showed: only for showed: only for statistical significance p statistical significance p << 0.1 FOR ALL 0.1 FOR ALL IMAGESIMAGES

New schematic model of the head with coherence value New schematic model of the head with coherence value TASK DIFFERENCES presentedTASK DIFFERENCES presented

Colour scale: Colour scale:

warm colours- coherence increases between electrodeswarm colours- coherence increases between electrodes

cold colours- coherence decreases between electrodescold colours- coherence decreases between electrodes

COHERENCE CHANGESCOHERENCE CHANGESMEMORIZE VS. WAIT (CONTROL) TASK (P MEMORIZE VS. WAIT (CONTROL) TASK (P << 0.1) 0.1)

ALPHA 1ALPHA 1

EXPLAINATION OF SCHEME!EXPLAINATION OF SCHEME!

(Pre)fronto-central (Pre)fronto-central fronto-parietalfronto-parietal fronto-occipital fronto-occipital

increases increases Interhemispheric Interhemispheric

bitemporal increasesbitemporal increases Temporo- parietal Temporo- parietal

increasesincreases

MEMORIZE VS. WAIT MEMORIZE VS. WAIT

ALPHA 2ALPHA 2

Fronto-central increases Fronto-central increases

interhemispheric interhemispheric frontotemporal increasesfrontotemporal increases

fronto-parieto-occipital fronto-parieto-occipital increasesincreases

Temporo-parietal Temporo-parietal increasesincreases

MEMORIZE VS. WAITMEMORIZE VS. WAIT

GAMMAGAMMA

Less intensive increases, Less intensive increases, dominant:dominant:

fronto-parietalfronto-parietal fronto-temporal fronto-temporal fronto-central increasesfronto-central increases

MEMORIZE VS. WAITMEMORIZE VS. WAIT

THETATHETA

Fronto- central increasesFronto- central increases Fronto- occipital increasesFronto- occipital increases

Interhemispheric Interhemispheric bitemporal increasesbitemporal increases

Frontotemporo-Frontotemporo-parietooccipital increasesparietooccipital increases

REORDER VS. WAITREORDER VS. WAIT

ALPHA 1ALPHA 1

(pre)fronto-centro-(pre)fronto-centro-parietal increasesparietal increases

temporo- central temporo- central

interhemisheric interhemisheric bitemporalbitemporal

parieto-occipital parieto-occipital increases increases

REORDER VS. WAITREORDER VS. WAIT

ALPHA 2ALPHA 2

Prefronto-central increasesPrefronto-central increases

Fronto-centro-parietalFronto-centro-parietal

Fronto-temporalFronto-temporal

Centro-temporalCentro-temporal

Interhemispheric Interhemispheric bitemporalbitemporal

Temporo-occipitalTemporo-occipital

REORDER VS. WAITREORDER VS. WAIT

GAMMAGAMMA

Less intensive butLess intensive but

simmilar pattern of simmilar pattern of coherence increasescoherence increases

REORDER VS. WAITREORDER VS. WAIT

THETATHETA

Fronto-centralFronto-central

Fronto-parietalFronto-parietal

Frontotemporo-occipital Frontotemporo-occipital increasesincreases

REORDER VS. MEMORIZEREORDER VS. MEMORIZE

ALPHA 1ALPHA 1

Centro-temporal increaseCentro-temporal increase Occipito-temporal Occipito-temporal

increaseincrease

Decreases of coherenceDecreases of coherence

REORDER VS. MEMORIZEREORDER VS. MEMORIZE

ALPHA 2ALPHA 2

Fronto-centralFronto-central

Fronto-temporo-parietal Fronto-temporo-parietal

Parieto-occipital increasesParieto-occipital increases

Interhemispheric bitemporal Interhemispheric bitemporal increasesincreases

Decreases of coherenceDecreases of coherence

REORDER VS. MEMORIZEREORDER VS. MEMORIZE

GAMMAGAMMA

Less intensive increasesLess intensive increases

Prefronto-centro-parieto-Prefronto-centro-parieto-occipital axis increases occipital axis increases

REORDER VS. MEMORIZEREORDER VS. MEMORIZE

THETATHETA

MainlyMainly

(Pre)fronto-parietooccipital (Pre)fronto-parietooccipital axis increasesaxis increases

ADDITIONAL DATA ANAYLSIS AND DIFFERENT WAY ADDITIONAL DATA ANAYLSIS AND DIFFERENT WAY OF DATA PRESENTATION OF DATA PRESENTATION

////MATLAB SOFTWARE (no MATLAB SOFTWARE (no EOG correction)EOG correction)

The influence of The influence of EOG correction EOG correction procedures on EEG procedures on EEG coherence? coherence?

>>SIMMILAR TRENDS >>SIMMILAR TRENDS IN COHERENCE IN COHERENCE VALUES VALUES

Memorise vs. wait task Memorise vs. wait task

THETA coherence changesTHETA coherence changes

Reorder vs. wait taskReorder vs. wait taskTHETA coherence changesTHETA coherence changes

Reorder vs. memorize taskReorder vs. memorize taskTHETA coherence changesTHETA coherence changes

SUMMARY OF RESULTSSUMMARY OF RESULTS

WM TASKS: COHERENCE INCREASESWM TASKS: COHERENCE INCREASES MAINLY IN MAINLY IN ALPHA 2, ALPHA 1, THETAALPHA 2, ALPHA 1, THETA (AND ALSO GAMMA) (AND ALSO GAMMA) FREQUENCY BANDSFREQUENCY BANDS

FOR MEMORIZE (WM MAINTENANCE) VS. WAIT (CONTROL) FOR MEMORIZE (WM MAINTENANCE) VS. WAIT (CONTROL) TASK TASK

FOR REORDER (WM MANIPULATION) VS. WAIT (CONTROL)FOR REORDER (WM MANIPULATION) VS. WAIT (CONTROL) SPATIAL SCALESSPATIAL SCALES OF INCREASES: MAINLY OF INCREASES: MAINLY FRONTO-FRONTO-

POSTERIOR, FRONTOTEMPORAL, BITEMPORAL LONG- POSTERIOR, FRONTOTEMPORAL, BITEMPORAL LONG- RANGERANGE CONNECTIONS CONNECTIONS IN THE BRAININ THE BRAIN

REORDER (WM MANIPULATION) VS. MEMORIZE REORDER (WM MANIPULATION) VS. MEMORIZE (MAINTENANCE-ONLY): COHERENCE INCREASES(MAINTENANCE-ONLY): COHERENCE INCREASES MAINLY IN MAINLY IN ALPHA2 AND THETAALPHA2 AND THETA BAND BAND

SPATIAL SCALES:ALSO SPATIAL SCALES:ALSO ANTERIO-POSTERIOR BRAIN AXISANTERIO-POSTERIOR BRAIN AXIS, , BITEMPORAL INTERHEMISPHERICALLYBITEMPORAL INTERHEMISPHERICALLY, BUT , BUT NO NO (PRE)FRONTAL INTERHEMISHERIC INCREASES(PRE)FRONTAL INTERHEMISHERIC INCREASES

DECREASES OF COHERENCE– OTHER AREASDECREASES OF COHERENCE– OTHER AREAS

INTERPRETATION OF RESULTSINTERPRETATION OF RESULTS

Greatest coherence (synchronization) increases Greatest coherence (synchronization) increases --retention retention WM WM periods in periods in ALPHA AND THETAALPHA AND THETA ((and gammaand gamma)) frequency bands frequency bands

widespread widespread fronto-parietal association brain areasfronto-parietal association brain areas involved- involved- in in accordance accordance with other studies and Baddeley’s modelwith other studies and Baddeley’s model of WM!+ of WM!+

temporal interhemispheric connections?temporal interhemispheric connections?

Different EEG frequencies appear to have different Different EEG frequencies appear to have different functional correlatesfunctional correlates? ?

LIJ (Lisman, Idiart, Jensen, 1998) WM MODEL!!!LIJ (Lisman, Idiart, Jensen, 1998) WM MODEL!!!

The increased The increased theta theta coherencecoherence --working memory processes working memory processes (storage, rehearsal and scanning)(storage, rehearsal and scanning)

Alpha bandAlpha band directly involved in directly involved in memory processesmemory processes or reflects or reflects increased mental effort, attention?increased mental effort, attention? Role not known yet, results Role not known yet, results contradictive in different studiescontradictive in different studies

GGamma bandamma band is believed to be correlated with is believed to be correlated with sensory sensory processing and the very content of informationprocessing and the very content of information processing, but processing, but could also reflect increased attentivenesscould also reflect increased attentiveness..

LATERALIZATION?LATERALIZATION?

Verbal memoryVerbal memory tasks tasks seem tseem to o activate activate primarly left brain primarly left brain hemisphere, but hemisphere, but visuospatial memory visuospatial memory tasks activate tasks activate predominantly right predominantly right brain hemispherebrain hemisphere- - we we didn’t demonstrate didn’t demonstrate significant significant lateralization lateralization patterns!patterns!

possible reasons?possible reasons?volume conduction, low volume conduction, low spatial resolution, spatial resolution, visuospatial strategiesvisuospatial strategies

The neuronal The neuronal synchronization synchronization (increased (increased coherence)coherence)– – functional couplinfunctional couplingg

role in role in interaction of interaction of posterior association posterior association cortexcortex ( (where sensory where sensory information is storedinformation is stored)), , and (pre)frontal and (pre)frontal cortex, where relevant cortex, where relevant current information is current information is held, rehearsed and held, rehearsed and updatedupdated (Baddeley’s (Baddeley’s model, phonological model, phonological looploop) )

Decreases of coherenceDecreases of coherence: : functional decoupling of functional decoupling of disturbing processes, disturbing processes, selective attention?selective attention?

Manipulation- CE functionManipulation- CE function

We found increases of coherence in fronto- parietal We found increases of coherence in fronto- parietal loops also compared to memorize onlyloops also compared to memorize only

Central executive also demands funtional integration Central executive also demands funtional integration of anterio-posterior neural circuits- brain regions of anterio-posterior neural circuits- brain regions and not primarily prefrontal interhemispheric and not primarily prefrontal interhemispheric communication?communication?

Role of interhemispheric connections in temporal Role of interhemispheric connections in temporal brain regions (alpha 2- semantic memory?)brain regions (alpha 2- semantic memory?)

LIJ NEUROPHYSIOLOGICAL MODEL OF WORKING LIJ NEUROPHYSIOLOGICAL MODEL OF WORKING MEMORY (MEMORY (Lisman, IdiartLisman, Idiart and and Jensen, 1998Jensen, 1998))

Figure Figure ----.. C Concept of LIJ working memory model. oncept of LIJ working memory model.

Three memory items (A, B, C) are loaded in memory buffer, the theta period Three memory items (A, B, C) are loaded in memory buffer, the theta period increases by one gamma period with each item added. In retention interval increases by one gamma period with each item added. In retention interval (delay period), items are maintained by activity-dependent intrinsic properties of (delay period), items are maintained by activity-dependent intrinsic properties of the neurons coding these items. After probe presentation the items can be the neurons coding these items. After probe presentation the items can be scanned – compared with the probe as they are activated. After scanning, motor scanned – compared with the probe as they are activated. After scanning, motor response and answer can be initiated. RT – reaction timeresponse and answer can be initiated. RT – reaction time

Figure Figure ----. LIJ model as a multi-item short-term memory buffer. . LIJ model as a multi-item short-term memory buffer.

Theta and gamma oscillations play an important role in the concept. An Theta and gamma oscillations play an important role in the concept. An afterdepolarization (ADP) is triggered after a cell fires (sensory input) and it causes afterdepolarization (ADP) is triggered after a cell fires (sensory input) and it causes depolarizing ramp that serves to trigger the same cell to fire again after delay. These depolarizing ramp that serves to trigger the same cell to fire again after delay. These ramps are temporarily offset for different memories, an offset that causes different ramps are temporarily offset for different memories, an offset that causes different memories to fire in different gamma cycles. The key function of this buffer is to memories to fire in different gamma cycles. The key function of this buffer is to perpetuate the firing of cells in a way that retains serial order. The repeat time is perpetuate the firing of cells in a way that retains serial order. The repeat time is determined by theta oscillations due to external input. Gamma oscillations arise from determined by theta oscillations due to external input. Gamma oscillations arise from alternating global feedback inhibition and excitation (the cell with most depolarized alternating global feedback inhibition and excitation (the cell with most depolarized ramp will fire again) because of separate firing of different memory codes. ramp will fire again) because of separate firing of different memory codes.

DISCUSSION – CRITICAL APPROACHDISCUSSION – CRITICAL APPROACH

BETTER STATISTICAL SIGNIFICANCE?- PROBLEM OF CONTROL- BETTER STATISTICAL SIGNIFICANCE?- PROBLEM OF CONTROL- WAIT TASK (absolute coherence values!): WAIT TASK (absolute coherence values!): spontaneous non-spontaneous non-intentional memory set repetition?- encoding before instruction; intentional memory set repetition?- encoding before instruction; inhibitory instruction context (WM?), ‘working space’ preparation; inhibitory instruction context (WM?), ‘working space’ preparation; resting state correlated networks?resting state correlated networks?

PROBLEM OF VOLUME CONDUCTION- electrical charge flowPROBLEM OF VOLUME CONDUCTION- electrical charge flow>> voltage/ signal masking effectvoltage/ signal masking effect

INFLUENCE OF EOG CORRECTION PROCEDURE?INFLUENCE OF EOG CORRECTION PROCEDURE?

LOW SPATIAL RESOLUTION IN EEG, occipital-parietal transfer LOW SPATIAL RESOLUTION IN EEG, occipital-parietal transfer of signal, interhemispherically? NO of signal, interhemispherically? NO LATERALIZATION IN VERBAL TASK?LATERALIZATION IN VERBAL TASK?

ELECTROMAGNETIC INFLUENCES, OTHER ARTEFACTS- SIGNAL ELECTROMAGNETIC INFLUENCES, OTHER ARTEFACTS- SIGNAL TO NOISE RATIOTO NOISE RATIO

FUTURE PERSPECTIVESFUTURE PERSPECTIVES

‘‘LAPLACE’ CORRECTION (Nunez) FOR VOLUME LAPLACE’ CORRECTION (Nunez) FOR VOLUME CONDUCTIONCONDUCTION

ADDITION OF NEW ‘PURELY’ SENSORY-PERCEPTIVE ADDITION OF NEW ‘PURELY’ SENSORY-PERCEPTIVE CONTROL TASKCONTROL TASK

ELECTRODE POSITIONING DETERMINATIONELECTRODE POSITIONING DETERMINATION HIGHER SAMPLING RATE HIGHER SAMPLING RATE choosing appropriate cognitive paradigms and choosing appropriate cognitive paradigms and

neuropsychological testsneuropsychological tests-- possible to study physiological possible to study physiological and patophysiological aspects of cognitive, motor and and patophysiological aspects of cognitive, motor and sensory brain functionsensory brain function!!!!!!

new future perspectives for possible search of new future perspectives for possible search of patophysiological mechanisms and etiological patophysiological mechanisms and etiological factors contributing to many different neurological factors contributing to many different neurological diseasesdiseases!!

MAIN REFERENCESMAIN REFERENCES

Baddeley, A. (2000). The episodic buffer: a new component of working memory? Baddeley, A. (2000). The episodic buffer: a new component of working memory? Trends in cognitive Trends in cognitive science, 4(11)science, 4(11), 417-423. , 417-423.

Jensen O, Tesche CD Jensen O, Tesche CD (2002). Frontal theta activity in humans increases with memory load in a working (2002). Frontal theta activity in humans increases with memory load in a working memory task.memory task.. Eur J Neurosci. 2002;15(8):1395-9. . Eur J Neurosci. 2002;15(8):1395-9.

Jensen, O. in Lisman, J.E. (1998). Jensen, O. in Lisman, J.E. (1998). An oscillatory short-term memory buffer model can account for data on An oscillatory short-term memory buffer model can account for data on the Sternberg task. The journal of neuroscience, 18(24), 10688-10699. the Sternberg task. The journal of neuroscience, 18(24), 10688-10699.

Babiloni, C., Carducci, F., Vecchio, F., Rossi, S., Babiloni, F., Cincotti, F., Cola, B., Miniussi, C. in Rossini, Babiloni, C., Carducci, F., Vecchio, F., Rossi, S., Babiloni, F., Cincotti, F., Cola, B., Miniussi, C. in Rossini, P.M. (2004). P.M. (2004). Functional frontoparietal connectivity during short-term memory as revealed by Functional frontoparietal connectivity during short-term memory as revealed by high resolution EEG coherence analysis. Behavioral neurosciencies, 118(4), 687-697.high resolution EEG coherence analysis. Behavioral neurosciencies, 118(4), 687-697.

Klimesch W. Memory processes, brain oscillations and EEG synchronization. Internal journal of Klimesch W. Memory processes, brain oscillations and EEG synchronization. Internal journal of psychophysiology (1996); 24: 6-100psychophysiology (1996); 24: 6-100..

Klimesch, W., Doppelmayr, M., Schwaiger, P. Auinger in Winkler, Th. (1999). Klimesch, W., Doppelmayr, M., Schwaiger, P. Auinger in Winkler, Th. (1999). „Paradoxical“ alpha „Paradoxical“ alpha synchonisation in memory task. Cognitive brain research, 7, 493-501.synchonisation in memory task. Cognitive brain research, 7, 493-501.

Sarnthein, J., Petsche, H., Rappelsberger, P., Shaw, G.L. in von Stein, A. (1998). Synchronization between Sarnthein, J., Petsche, H., Rappelsberger, P., Shaw, G.L. in von Stein, A. (1998). Synchronization between prefrontal and posterior association cortex during human working memory. Neurobiology, 95, prefrontal and posterior association cortex during human working memory. Neurobiology, 95, 7092-7096. 7092-7096.

Sauseng, P., Klimesch W., Doppelmayr, M., Hanslmayr, S., Schabus, M. in Gruber, W.R. (2004). Theta Sauseng, P., Klimesch W., Doppelmayr, M., Hanslmayr, S., Schabus, M. in Gruber, W.R. (2004). Theta coupling in the human electroencephalogram during a working memory task. Neuroscience coupling in the human electroencephalogram during a working memory task. Neuroscience letters, 354, 123-126.letters, 354, 123-126.

Serrien, D.J., Pogosyan A.H. in Brown, P. (2003). Influence of working memory on patterns of motor Serrien, D.J., Pogosyan A.H. in Brown, P. (2003). Influence of working memory on patterns of motor related cortico-cortical coupling. Experimental brain research. Dostopno na spletni strani related cortico-cortical coupling. Experimental brain research. Dostopno na spletni strani

Stam, C.J., van Cappellen van Walsum, A.M. in Micheloyannis, S. (2002). Variability of EEG Stam, C.J., van Cappellen van Walsum, A.M. in Micheloyannis, S. (2002). Variability of EEG synchronization during a working momory task in healthy subjects. International journal of synchronization during a working momory task in healthy subjects. International journal of psychophysiology, 46, 53-66.psychophysiology, 46, 53-66.

ABSOLUTE VALUES OF THETA COHERENCE-ABSOLUTE VALUES OF THETA COHERENCE-WAIT VS. MEMORIZE TASKWAIT VS. MEMORIZE TASK

ABSOLUTE VALUES OF THETA COHERENCE- ABSOLUTE VALUES OF THETA COHERENCE- WAIT VS. REORDER TASKWAIT VS. REORDER TASK