Alpha and theta oscillations: Conscious control of information processing in the human brain?

Alpha and theta oscillations: Conscious control of information processing in the human brain?

Wolfgang KlimeschUniversity of Salzburg

Austria

May conference on ‚Consciousness, brain rhythms and the perception-action cycle‘

Memphis, May 3rd – 4th 2008

(1) Oscillations: Timing and spatial organization of information processes. Oscillations provide mechanisms that allow the emergence of spatially and temporally organized firing patterns in neural networks.

(2) Slow frequency oscillations: Conscious control of information processing. Slow frequency oscillations in the theta and alpha range (of about 4 – 13.5 Hz) are associated with the top-down control of two large processing systems, a working memory system and a a complex knowledge system, allowing semantic orientation in a constantly changing environment.

Theta and alpha oscillations exhibit a variety of different synchronization processes (e.g., amplitude increase, phase coupling, event-related phase reorganization) that reflect different types of control processes and different aspects of the timing of cognitive processes.

(3) Process binding and consciousness

(4) Conclusions

Oscillations and the control of information processing:Outline of the

structure of argumentation and proposed hypotheses

Part 1.1Timing of neuronal activity and information

processing

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Oscillations reflect rhythmic fluctuations of the membrane potential (of the dendritic tree and soma).

They have a strong influence on the timing of neural firing.The influence of oscillations depends on the excitatory level of

affected cells and on the magnitude of their amplitudes.

Basics: Inhibition, Excitation and Timing

Large amplitudes tend to entrain many neurons

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Basics: Inhibition, Amplitude and Timing

Example 1: Alpha-like oscillations control the timing of sensory coding

Nicolelis & Fanselow, (2002). Thalamcortical optimization of tactile processing according to behavioural state. Nature Neurosci. 5 (6), 517-523.

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a) Top-down control of sensory encoding during exploratory behavior

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Individual alpha frequency (IAF) varies to a large degree between subjects (in a range of about 7.5 and 13.5 Hz) and is related to the speed of information processing. This have been shown very early in EEG research: e.g., Surwillo, W. (1961). Frequency of the alpha rhythm, reaction time and age, Nature 191, 823-824. Klimesch, W. (1996). Alpha frequency, reaction time and the speed of processing information, J. Clin. Neurophysiol. 13, 511-518.

Example 2: Alpha oscillations and the timing of information processing

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A) Average alpha frequency in a large sample of subjects is at about 10 Hz

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Range of variation

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Interindividual differences in alpha frequency vary with age and memory performance. (A) From early childhood to puberty, alpha frequency increases from about 5.5 to more than 10 Hz but then starts to decrease with age. (B) As compared to bad memory performers, good performers have a significantly higher alpha frequency, even in Alzheimer demented subjects.

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IAF increases and declines with age just as processing speed, cognitive performance and brain volume does

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Example 2: Alpha oscillations and the timing of information processing

Part 1.2Oscillations and the spatio-temporal organisation

of information processing

First half retention interval

Second half retention interval

Manipulation Retention

Upper alpha phase coherence: leading and trailing sites

Sauseng, P., Klimesch, W., Doppelmayr, M., Pecherstorfer, T., Freunberger, R., Hanslmayr, S., (2005). EEG alpha synchronization and functional coupling during top-down processing in a working memory task. Hum. Brain Mapp. 26, 148-155.

Part 2 Slow frequency oscillations: Conscious control

of information processing. The functional meaning of theta and alpha

(i) A brief phasic event-related increase in theta power probably reflects encoding/retrieval of new (episodic) information.

(ii) A long lasting event-related increase probably reflects top-down control associated with central executive functions. Examples:- The maintenance of information in WM- Spatial navigation (exploratory behavior)- Sustained attention

Part 2.1 ThetaTheta appears to be related to different functions of a complex working memory (WM) system. At least two types of task-related responses can be distinguished :

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Evoked theta; recogn. hits

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Evoked upper alpha; recogn. hits

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Frequency specificity and functional meaning of theta for episodic encoding. Klimesch et al (2001). Episodic retrieval is reflected by a process specific increase in human theta activity. Neuroscience Letters, 302, 49-52.

The neural correlates of conscious awareness during successful retrieval are reflected by a late event-related synchronization (ERS) in theta.

An early EEG synchronization in the theta band predicted knowing, and a later remembering. Moreover, early and late event-related potentials were also found to predict knowing and remembering, respectively.

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Klimesch, W., Doppelmayr, M., Yonelinas, A., Kroll, N.E.A., Lazzara, M., Roehm, D., & Gruber, W. (2001). Theta synchronization during episodic retrieval: neural correlates of conscious awareness. Cognitive Brain Research, 12, 33-38.

75 words are presented, 45 items are repeated (old),

30 not repeated (new)Yes/no recognition and confidence judgment.

Stimulus onset every 3.5 sec

30 items 45 itemsnot repeated repeated (new words) (old words)

15 itemsLag 1656 sec

25 itemsLag 828 sec

15 itemsLag 27 sec

Retrieval from Retrieval from WM intermediate memory

Block 1 Block 2…………….. Block 8

Continous Word Recognition Paradigm

A decaying episodic trace is associated with decreased theta Klimesch, W., Hanslmayr, S., Sauseng, P., Gruber, W., Brozinski, C., Kroll, N.E.A., Yonelinas, A., & Doppelmayr, M. (2006c). Oscillatory EEG correlates of episodic memory trace decay. Cerebral Cortex, 16 (2), 280-290.

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Lag effect: Theta, mean over all electrodes

Evoked theta in P2 time window (around 300 ms)

Low resolution electromagnetic tomography LORETA (Pascual-Marqui et al., 1994)

LORETA (Pascual-Marqui et al., 1994).

The P3 component elicited stronger activity for Lag-2 than Lag-16 in left superior temporal gyrus and middle temporal gyrus, posterior cingulated gyrus, bilateral lingual gyrus, and, most interesting, in right hippocampus and parahippocampal gyrus (t > 3.77, p < .05 corrected). There were no significant differences between lag-2 and lag-8, nor between lag-8 and lag-16.

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WM comprises an anterior-posterior network

Attentional Control/Central executive Phonological loopprimarily located in left hemisphere, including- articulatory rehearsal system (BA 44)- temporary STORAGE system (BA 40): ‚Verbal-acoustic‘ STM‘

Visuospatial sketchpad primarily located in right hemisphere, including- frontal areas (BA 6, 47) and- posterior areas (BA, 19, 40): ‚visual STM‘

From Sarnthein, Petsche, Rappelsberger, Shaw &Von Stein (1998). Synchronization between prefrontal and posterior association cortex during human working memory. PNAS, 95, 7092-7096.

Enhanced coherence in the theta range (4-7 Hz) during retention. Connections between electrode sites represent significant increases of coherence above control (P< 0.05 or better). The shaded areas indicate the range of positions of individual electrodes as determined in an MRI study. Note that the occipital electrodes (01, 02) are placed not over primary visual areas, but closer to the parieto-temporo-occipital association region. (a) During retention of character strings in memory, enhanced coherence appeared between prefrontal and posterior cortex. In posterior cortex, the left hemisphere was predominantly involved. (b) coherence- increases during retention of abstract line drawings in memory. Patterns of encanced coherence were similar n both tasks, but more connections appeared in the right hemisphere in the visual task. For convergent evidence see Weiss & Rappelsberger (2000)

A) character strings B) line drawings

Functional interplay in theta frequency between prefrontal and posterior regions

Is the ‘interplay’ between anterior and posterior regions due to executive functions operating on storage areas?

Study by Sauseng, Klimesch, Gruber, Doppelmayr, Stadler, W., & Schabus (2002)

Issue of interest: Retrieval processes from LTM (or intermediate memory) activated from WM.

Design: Three tasks were performed, a learning, ‘recognition’ and selective retrieval task. First, subjects had to learn a verbal label (numbers between 1-8) for each of a set of 8 abstract pictures. Second, the pictures were presented and subjects had to name the label. Third, in the selective retrieval task, two labels were presented sequentially. Now in response to each label, the respective picture had to be retrieved. To guarantee that subjects are actually retrieving the corresponding pictures they had to perform an imagery task after the presentation of the second label.

Label 1 Label 2

Retrievepicture 1

Retrievepicture 2 and perform imagery task

x = positive maximumo = negative maximum

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Evoked theta behaves like a travelling wave. After a label is presented several cycles of theta can be observed travelling from frontal to occipital sites. At about 774 ms (on average) the direction reverses. This ‚latency‘ is correlated with memory performance (number of correct labels in recognition task): r = .39 p < .05.

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Example of an evoked, ‘traveling’ theta wave, one subject, negative polarity is in blue

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Upper Alpha Desynchronization (ERBP) over occipital sites as a function of theta reversal

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Part 2.2 Alpha

Part 2.2.1 The key for the functional understanding of alpha: The onset of

Alpha ERD reflects retrieval from memory

Episodic processing mode:A phasic process concentrated

on a specific event

Semantic processing mode: A continuous, automatic

process

In a conventional, event-related memory task episodic and semantic memory proccesses are required

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Part 2.2.1 The functional dissociation between theta

and alpha

The behaviour of alpha is puzzling and remarkable in several ways: (i) Whereas other frequencies reliably show an increase in power (event-related synchronization, ERS) in response to a stimulus/event, alpha shows a decrease (event-related desynchronization, ERD) in many tasks. (ii) More recently, it became clear that certain types of tasks reliably elicit alpha ERS.

We have suggested recently that the key for understanding alpha is the fact that the onset of upper alpha ERD indicates the onset of access to and retrieval of a trace from LTM (Klimesch et al. 2007).

Sample: 22 right handed volunteers (8 males, mean age = 22.88; SD = 3.34; 14 females, mean age = 23.79; SD = 4.41). Each subject had to perform first the reading and then the semantic task.

READING TASK: Subjects were instructed to silently read and to pronounce the sentence right after a question mark would appear.

SEMANTIC TASK: Subjects were instructed to read the sentence in order to search a super-ordinate concept for the noun of the third chunk and to pronounce the super-ordinate concept after the question mark appeared.

First chunk:subject

‚Ein Hase‘,A rabbit

Second chunk:finite verb and a

reflexive pronoun ,hat sich‘

‚is‘

Third chunk:object

‚in der Schachtel‘‚in the box‘

Fourth chunk:verb

,versteckt‘‚hiding‘

?

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Evidence for hypothesis that semantic memory is related to upper alpha ERD

From: Röhm, D., Klimesch, W., Haider, H., Doppelmayr, M. (2001). The role of theta and alpha oscillations for language comprehension in the human electroencephalogramm. Neuroscience Letters, 310, 137-140.

Experimental design:

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Evidence for hypothesis that semantic memory is related to upper alpha ERDSignificant increase in upper alpha ERD during retrieval from semantic long-term memory and semantic processing - although sentences were already presented in

the preceding reading task.

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Theta ERS and Upper Alpha ERD scaled in red

Part 2.2.2 Alpha and Perception No ERD but phase locking during ‘re-activation

of a trace’

Experimental design:

Example of a trial. The subjects were instructed to respond as fast as possible to two target stimuli (p, q) by pressing one of four buttons.

Hanslmayr, S., Klimesch, W., Sauseng, P., Gruber, W., Doppelmayr, M., Freunberger, R., Pecherstorfer, T., 2005. Visual discrimination performance is related to decreased alpha amplitude but increased phase locking. Neurosci. Lett. 375, 64-68. For similar findins see: T. Ergenoglu, T. Demiralp, Z. Bayraktaroglu, M. Ergen, H. Beydagi, Y. Uresin, Alpha rhythm of the EEG modulates visual detection performance in humans, Cognitive Brain Res. 20 (2004) 376-383. These findings were replicated in Hanslmayr et al. (2007).

Mean reaction time ~ 500 ms

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No upper alpha ERD in perception taskAre good and bad performers using different strategies of top-down control?

Period of 100 ms = 10 Hz

Large alpha phase-locking is associated with a large P1 and N1 component in the EEG

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Prestimulus alpha synchronization

cf Hanslmayr et al. 2006, 207)

Prestimulus alpha synchronization may reflect different strategies of top-down control that lead to differences in performance

Perceivers (P+) : Group of subjects (n = 15) with a performance that lies significantly above chance (25%). Mean detection rate: 58%

Non-Perceivers (P-) : Group of subjects (n = 15) with a performance that is not significantly different from chance. Mean detection rate: 26 %

Correlation between alpha power (8 – 12 Hz) and detection performance. Both scales are transformed to ranks.

prestimulus power (- 500 to 0 ms)

c) For the group of Perceivers (P+), the ongoing prestimulus EEG (- 500 to 0 ms) shows larger phase coupling in trials when subjects failed to perceive the stimulus. d) topography of electrode pairs with larger phase coupling for incorrect as compared to correct responses. e) Number of couplings for each electrode.

Resting condition, eyes open

Part 2.2.3 Alpha ERS reflects control of search area/ blocking of retrieval

Upper Alpha, Temporal sites, Hits

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ENCODING RETENTION RETRIEVALCognitive processes:

Task sequence:

Upper alpha exhibits a load dependent increase in ERS during encoding and retention in memory scanning tasks (Klimesch et al., 1999; Jensen et al.,

2002; Schack & Klimesch, 2002; Busch & Herrmann, 2003; Cooper et al., 2003; Herrmann et al., 2004a; Sauseng et al., 2005b)

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InterpretationAlpha synchronization reflects inhibitory top-down control to

block retrieval of interfering information When the stored memory trace has to be retrieved, however, a

strong ERD can be observed.

In a memory scanning task, a subject is in an encoding and retrieval mode.

Trial k B 2 H 5 4 L K R 1 F H?

Trial k + 1: 3 1 L 4 8 6 R K C 8 F?

Suppression of retrieval of items from previous trialshelps to reduce interference

The separately performed TMS experiment revealed that the amplitude of the motor evoked potential (MEP) at the hand was reduced during INH as compared to ACT and a baseline condition.

Further Evidence comes from findings about motor behavior and the mu.rhythm:In a study by Hummel et al. (2002) subjects had - in response to visual cues - to perform sequential finger movements on an electrical keybord. The task was either to actually perform the movements (ACT condition) or to

look at the cues but to inhibit a response (INH condition). Upper alpha ERD was observed during ACT but ERS during INH

Part 2.2.4 Alpha phase and top-down control

Memory set500ms

Retention Interval 2500ms

Probe & ResponseMatch or no match?

Ret

enti

onM

anip

ulat

ion

pure retention

retention + manipulation (rotation around vertical midline)

2 analysing intervals(0 – 1000 ms and 1000 - 2000 ms after

memory item offset)

Sauseng, P., Klimesch, W., Doppelmayr M., Pecherstorfer, T., Freunberger, R., Hanslmayr, S. (2005). EEG alpha synchronization and functional coupling during top-down processing in a working memory task. Human Brain Mapping, in press.

Visuo-spatial working memory task

First half retention interval Second half retention interval

Upper Alpha between 9.8 and 12.7 Hz

First half retention interval

Second half retention interval

Manipulation Retention

Upper alpha coherence: leading and trailing sites

Part 3: Process binding and consciousness

Event-related phase reorganization (ERPR)and between frequency phase coupling

may reflect binding of different processes that are controlled by consciousness

ms-500 0 500

ms-500 0 500

ms-500 0 500ms

Hz

-1000 -500 0 500

5

10

15

20

ms

Hz

-1000 -500 0 500

5

10

15

20

ms

Hz

-1000 -500 0 500

5

10

15

20

Who

le P

ower

Evo

ked

Pow

erPL

I

F7, set size 4 O2, set size 4

loga

rith

mic

sca

le f

or p

ower

PL

I

Upper Alpha Sync.during retention

6 Hz

12 Hz

6 Hz

12 Hz

Theta : upper alpha phase coupling in a Sternberg task (load 2 and load 4); Schack, Klimesch & Sauseng (2005). Internat. Journal of Psychophysiology, in press.

theta: s4-s2 11.719 ms 23.438 ms 35.156 ms 46.875 ms 58.594 ms 70.312 ms 82.031 ms 93.75 ms

105.469 ms 117.188 ms 128.906 ms 140.625 ms 152.344 ms 164.062 ms 175.781 ms 187.5 ms 199.219 ms


316.406 ms 328.125 ms 339.844 ms 351.562 ms 363.281 ms 375 ms 386.719 ms 398.438 ms 410.156 ms

421.875 ms 433.594 ms 445.312 ms 457.031 ms 468.75 ms 480.469 ms

Difference of phase-locking index at 6 Hz: load 4 – load 2

permutation test (1000 perm.) for PLI at F7 (0-400 ms): tsum=0.038

no univariate differences

0 ms 11.719 ms 23.438 ms 35.156 ms 46.875 ms 58.594 ms 70.312 ms 82.031 ms 93.75 ms



316.406 ms 328.125 ms 339.844 ms 351.562 ms 363.281 ms 375 ms 386.719 ms 398.438 ms 410.156 ms

421.875 ms 433.594 ms 445.312 ms 457.031 ms 468.75 ms 480.469 ms

permutation test (1000 perm.) for PLI at O2 (100-500 ms): tsum=0.022;

No univariate sign. diff.: 200-500 ms

Difference of phase-locking index at 12 Hz: load 4 – load 2

m:n phase synchronization; F7 / O2

ERP‘s Sternberg yes response, load 2 (blue) and load 4 (red)

-2

0

2

4

6 µ

V

85 ms11.8 Hz

250 500 ms 170 ms 5.9 Hz

RT, load 2400 ms

RT, load 4524 ms

P3

-4

-

2

0

2

4

µV

250 500 msF7

O2

ERP‘s generated (in part) bynested theta and upper alpha.

Phase reversal between left frontaland right posterior sites.

F7 dominated by theta

O2 dominated by upper alphaand theta

Significant theta and upper alpha PLI and significant phase coupling suggest nested oscillations as illustrated below.

P1 N1 P1 N1

Phase locking index

Evoked Power

Event-related Potential

O2M+ M-

PLI

Gabor wavelet estimate (µV)

0 0.6

20

5

10

5

10

Hz

Hz

-10

0

10

µV

-1 -0.5 0 0.5 1Time (sec)

0

5

10

15

20

Freq

uenc

y (H

z)

Stimulus

Good memory performers (M+) show a significantly larger phase locking in the N1 time window as compared to bad performers (M-)

A) Alpha: 10 Hz Sinus

0 50 100 150 200

-

+P1 at 100 ms

N1 at 150 ms

Resetting at 25 ms

B) Theta:, 6 Hz Sinus-

+

N1 at 150 ms

Resetting at 24.9 ms

24.9 66.6 108.3 ms

P1

0 50 100 150 200

Period = 166.7 ms,

0 50 100 150 200

C) Phase alignment at N1

N1 at 150 ms

D) Superposition

0 50 100 150 200

P1 latency is 86 ms

N1 at 150 ms

Interpeak latency is 150-86 = 64ms 7.8 Hz

The basic properties of the P1-N1 complex can be described by a superposition of an evoked theta and alpha wave

Part 3.1 Instantaneous Phase Alignment (IPA)

between frequencies generates event-related potentials (ERP‘s)

Picture encoding and retrieval task. Data and methods from: Gruber,W., Klimesch, W., Sauseng, P. & Doppelmayr M. (2004). Alpha phase synchronization predicts P1 peak latency and amplitude size. Cerebral Cortex, in press.

N1

P1

Time [ms]

Vol

tage

[µ

V]

Event-related potentiala

c

-500 -250 0 250 500 750 1000

0

-10

-20

10

20

Time [ms]

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quen

cy [

Hz]

Gab

or e

stim

ates

max

min

Evoked powerb

d

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Time [ms]

Fre

quen

cy [

Hz]

Whole power

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Time [ms]

Fre

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Hz]

Significant PLI (α = 10 %)

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Sig

n. P

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Recording site O1, example for one subject

Fre

quen

cy [

Hz]

P1 N1

Phase angle; pos. peak, neg. peak

(1) Test for circular unimodal distribution of the phase angle (Hodges-Ajne test)

(2) For selected frequencies at each time point the mean phase angle was determined.

Steps for determining a significant phase alignment between frequencies (for each time point and frequency bin):

(3) By using confidence intervals it was tested whether the phase angle of each selected frequency bin deviates significantly from mean phase angle.(4) From all selected cases only those with a significant increase in PLI were considered.

Phase alignment between frequencies, example for one subject (data from Gruber et al. 2004)

e

h Phase alignment and ERP over all subjects

Circular histogram of phase angle at P1 / N1

counts0 1

P1

N10°

90°

180°

270°

30°

60°120°

150°

210°

240°300°

330°

g

Time [ms]

Fre

quen

cy [

Hz]

pos. peak (360°)

neg. peak (180°)

po

s. g

oin

g n

eg. g

oin

g

pos. goingneg. going

Sign. phase alignment

ER

P [µ

V]

-20

+20

5

10

15

20

40 80 120 160 200 240

f

pos. peak (0°)

Timet1 t2 t3

Prestimulus Stimulus Poststimuus

Theta

UpperAlpha

Phase reset

Phase reset Co-activation of both networks:

Information exchange?

Part 3.2 The P1 may reflect alpha-ERPR

Hypothesis: The P1 is the earliest manifestation of a top-down process during early sensory processing in sensory-semantic long-term memory which is functionally associated with alpha activity. The general idea is that under conditions where sensory processing is guided by a specific expectancy e.g., about the spatial location and/or type of stimulus, the P1 amplitude will be larger than under conditions where specific expectancies are lacking.

For a Review see: Klimesch, Sauseng & Hanslmayr (2007). EEG alpha oscillations: The inhibition/timing hypothesis. Brain Research reviews.

-15

-10

-5

0

5

10

15

[µV]

0 50 100 150 200 250 300 350 400 450 500 [ms]

O2 GA-ERP-L1 GA-ERP-L2 GA-ERP-L3 GA-ERP-L4

-15

-10

-5

0

5

10

15

[µV]

0 50 100 150 200 250 300 350 400 450 500 [ms]

Oz GA-ERP-L1 GA-ERP-L2 GA-ERP-L3 GA-ERP-L4

Degraded picture recognition task; Data analysis in progress

Example 1:The P1 is not a sensnory component.

It is missing if expectancy/early categorization is missing

Recording site Oz Recording site O2

Completely degraded picture

Not degraded picture

P1 appears graduelly as expectancy becomes more specific

The circle represents the ‚stimulus space‘ ~ All possible stimuli that may appear in a particular task/condition.

If the P1 is generated by evoked alpha, the P1 should reflect inhibition as alpha does

Highly specifc expectancy Specifc expectancy Vague expectancy

The P1 may be related to the inhibition of access to irrelevant stimuli

inhibition inhibition inhibition

Picture categorization task: Objects vs. Scrambled objects

Example 2:The P1 may reflect top-down induced inhibition

-16

-12

-8

-4

0

4

8

12

16

[µV]

-50 0 50 100 150 200 250 300 350 400 450 [ms]

Oz OBJ-ERP SCR-ERP

P1

N1

ERP at Oz

The average median for the response times for objects was 490.1 ms (SD=0.65 ms) and 506.1 ms for scrambled objects. Difference is not significant.

Objects

ScrambledObjects

Larger evoked alpha for scrambled objects in time window of P1

..

......

..

......

..

..

Cue: Arrow, 34 ms; Random SOA (600-800 ms); Target 50 ms

The cue indicates the most likely side (p = .75; valid trials).

Spatial Cue Paradigm after Posner

Hemifield presentation of two targets (short and long bar)

..

......

..

......

..

..

Cue: Arrow, 34 ms; Random SOA (600-800 ms); Target 50 ms

VALID Trial, Example:

INVALID Trial, Example:

Po3 Target Valid

Ipsi = Target is expected and processed ‘at’ PO4

Contra = Target is expected and processed ‘at’ PO3

9

8

7

6

5

4

3

2

1

0

-1

-2

-3

-4

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-8

-9

[µV]

-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 [s]

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+

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8

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1

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-9

[µV]

-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 [s]

-

+

Po3 Target Invalid

Ipsi = Target is expected ‘at’ PO3 but processed ‘at’ PO4

Contra = Target is expected ‘at’ PO4 but processed ‘at’ PO3

Po3 Target VALID

Po3 Target INVALID

Ipsi = Target is expected and processed ‘at’ PO4

Contra = Target is expected and processed ‘at’ PO3

Ipsi = Target expected ‘at’ PO3 but processed ‘at’ PO4

Contra = Target expected ‘at’ PO4 but processed ‘at’ PO3

100 ms

Time course of changes in upper alpha power

Example 3:The P1 behaves like a traveling, evoked alpha wave.

Table 1P1 and N1 latencies in ms

ComponentPz P3 P4 PO3 PO4 P7 P8 O1 O2

P1 138 128 132 120 122 116 108 113 112

N1 183 170 175 166 163 162 159 162 163

Difference 45 42 43 46 41 46 51 49 51

0

9

-9

-500 0 500 1000

0

PzO1

0

9

-9

-500 0 500 1000

0

PzO1

Stroop task; Klimesch et al 2007The task is to respond only to ink color but to ignore the meaning of the presented words

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

PO3-0.5

-1.0

-1.5

P8-0.5

-1.0

-1.5

[µV]

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

-0.5

-1.0

-1.5

[µV]

O1

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

-0.5

-1.0

-1.5

[µV]

PO4

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

P4-0.5

-1.0

-1.5

[µV]

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

-0.5

-1.0

-1.5

[µV]

Pz

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

P7-0.5

-1.0

-1.5

[µV]

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

-0.5

-1.0

-1.5

[µV]

P3

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

-0.5

-1.0

-1.5

[µV]

-40 -20 0 20 40 60 80 100 120 140 160 180 200 220 [ms]

P1 O1 P1 Pz

0 - 16 ms 17 - 33 ms 33 - 49 ms

50 - 66 ms 67 - 83 ms 84 - 100 ms

100 - 116 ms 117 - 133 ms 134 - 150 ms

151 - 167 ms 167 - 183 ms 184 - 200 ms

-1.0 µV 1.0 µV0 µV

Filtered ERP (7 to 10 Hz)

Topography of filtered ERP

C D

2

4

6

8

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20

0

3

-1000 -800 -600 -400 -200 0 200 400 600 800 ms

Hzm

/sMean Travel Speed (m/s)

-800 -400 0 400 800 ms0

0.2

Correlation of Single Trial Phase-differences with P1 Latency

B C

2

4

6

8

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200

0.2

Correlation of Single Trial Phase-differences with N1 Latency

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-800 -400 0 400 800 ms

Hz Hz

Part 4: Conclusions

4. 1. ThetaFor theta the interpretation appears straight forward: This oscillation appears functionally related to processes in a complex WM-system that operates under direct conscious (top-down) control

4.2 Alpha Synchronized (upper) alpha reflects control processes in a complex long-term memory (LTM, or ‘knowledge system’) system that may either operate under top-down control or may be running automatically in a default-like mode. An important function of these control processes is to keep us semantically oriented in our environment with respect to its meaning, location and time.

The reactivity, topography and functional meaning of alpha is similar to that of posterior parts of a default mode network as proposed by Gusnard & Raichle (2001). Raichle and colleagues assume that activity in the posterior cingulate and precuneus during a baseline state (in which no specific task performance is required) is related to the ‘representation (monitoring) of the world around us’. For posterior lateral parts of the default mode network the authors assume a specific role for the monitoring of targets at unfamiliar or unexpected locations. It should be emphasized that the default network plays an important role for consciousness as patient studies with lesions in posterior parts of the default network indicate.

Gusnard, D.A. & Raichle, M.E. (2001). Searching for a baseline: Functional imaging and the resting human brain. Nature Reviews Neuroscience, 2, 685-694.

Is alpha part of the default mode network? The reactivity, topography and functional meaning of alpha is similar to that of posterior parts

of a default mode network. (i) Activity decreases in a variety of different tasks; (ii) Resting activity is larger over posterior brain regions, (iii) Both systems are associated with ‚semantic

orientation‘.

The default mode network (Gusnard and Raichle, 2001)

Oscillations and joy:Peaks are more enjoyable than troughs

Documents

Alpha and theta oscillations: Conscious control of information processing in the human brain?