Brain cognitive-specific functional states studied with quantitative

EEG

Bechtereva N.P., Danko S.G. Institute of the Human Brain, Russian Academy of

Sciences, Sankt-Petersburg, Russia.

Initially functional state of the central nervous system was defined and treated as a background to the behavioural activities of humans and animals (e.g. Sokolov, 1975)

“Functional states regulated by modulating system of the brain are a mandatory component of any activity and behavior” (Danilova, 2001 - from Textbook on Psychophysiology, ed Y.Alexandrov ).

From: Bechtereva N.P. The neurophysiological aspects of human mental activity. Leningrad:, Meditsina, 1971. (in Russian) Bechtereva N.P. The neurophysiological aspects of human mental activity. NY;Oxford: Univ. Press, 1978

“A well-known difference [with conditioned reflex activity] is the great discontinuity and polimorphism of the changes in the EEG during tests that are strictly psychological. …although local changes can be noted during psychological tests, the development of these local changes is always a part of the general modification of bioelectric activity. Thus, EEG changes during mental activity reflect not so much the active state of individual structures as they reflect general changes in the brain, which evidently optimize the conditions for activity.”

The main ideas feeding the studies in question are:

1. Cognitive activities include not only short-term transitions of the information processed but are based also on specific interactions of network brain systems underlying basic psychic functions such as vigilance, attention, memory.

2.There are some necessary integrations of the brain systems which result in certain functional states of brain characteristic to certain cognitive activities

3. There should be certain manifestations in EEG processes related to a functional state supposed.

The term “quantitative electroencephalography –qEEG” should be understood so that both digital processing of EEG raw data and statistical evaluation of observed differences are mandatory.

When using term “state-related qEEG” mean values of EEG parameters are assumed to be constant during certain functional states. The states under considerations here are differed according to cognitive/emotional activities to be controlled. And the states should be durable enough to allow statistical estimations of mean values with acceptable accuracy and they can be discriminated from transitory processes and acts on this base.

The volunteers who undergone computer EEG registration presumably in different functional states were of both sexes, aged 17-27, university students and graduates, right-handed, without acute problems with health and without CNS injuries or diseases in their past.

EEG was recorded from 19 sites (International 10-20 system), monopolar with reference to earlobes.

Mean values of EEG power and coherence for each subject in each state were calculated in frequency bands (1,5-3,5Hz), (4-7Hz), 1 (7,5-9,5Hz), 2 (10-12,5Hz), 1 (13-18Hz), 2 (18,5-30Hz). In the last investigations low (30-40Hz) was added.

EEG records were processed on intervals 1-3s duration corresponding to different states under investigation, 20-40 intervals for each state were taken for processing

Statistical analysis of the values was conducted not as testing of certain hypotheses but as screening of the all data available using multi-way Anova and within subjects design.

Frequency bands, states and zones were considered as effective factors. Greenhouse-Geisser correction was applied for evaluation of main effects and their interactions significance.

Statistical significances of differences between means in certain frequency bands, states and zones were tested with post hoc tests (multiple comparisons). Tukey HSD test was used as more conservative and less sensitive, Fisher LSD test – as less conservative and more sensitive.

Commonly used paradigm of psychophysiological investigation is based on comparisons of test situations as close as possible except for an element being investigated.

That’s a very productive paradigm indeed especially if one is sure about physiological interpretation of the parameters controlled. That is the case in rCBF tomography studies but unfortunately not so with EEG

In the situation it’s desirable to anticipate the results related to cognitive-specific FS with a result of qEEG application to well-known physiological states – quiet rest with eyes open and eyes closed

D T A1 A2 B1 B2 G

State-related statistically significant EEG power changesContrast “eyes closed – eyes open”

EC-EO

**

N=57

Tukey HSD

P<5*10-2 P<10-2 P<10-3 P<10-4 P<10-5 ** <0.01* <0.05;p GG corrected:

Red colors - values higher in the first of the

compared states, blue – lower.

D T A1 A2 B1 B2 G

EC-EO

**

N=57

Tukey HSD

P<5*10-2 P<10-2 P<10-3 P<10-4 P<10-5 ** <0.01* <0.05;p GG corrected:

1. Occipital and parietal zones are most involved. 2. The changes are unidirectional in all frequency bands considered. 3. So decrease of rCBF in the visual cortex (Gebhardt et al., 2001,2002) corresponds to EEG synchronization in every of the frequency band

State-related statistically significant EEG power changesContrast “eyes closed – eyes open”

MM-EO

MR-EO

MM-MR

P<5*10-2 P<10-2 P<10-3 P<10-4 P<10-5 ** <0.01* <0.05;p GG corrected:

Red colors - values higher in the first of the compared

states, blue –

lower.

D T A1 A2 B1 B2 G**N=57

State-related statistically significant EEG power changesContrasts: “memorizing(MM) – eyes open rest(EO)”; “memory retrieval(MR) –EO”; “MM-MR”

Tukey HSD

MM-EO

MR-EO

MM-MR

P<5*10-2 P<10-2 P<10-3 P<10-4 P<10-5 ** <0.01* <0.05;p GG corrected:

Red colors - values higher in the first of the compared

states, blue –

lower.

D T A1 A2 B1 B2 G**N=57

State-related statistically significant EEG power changesContrasts: “memorizing(MM) – eyes open rest(EO)”; “memory retrieval(MR) –EO”; “MM-MR”

1. Both MM-EO and MR-EO patterns are rather similar: desynchronization in alpha and synchronization in beta2 and gamma – looks like classical non-specific activation. 2. But in MM-MR no difference in alpha and prominent difference in beta2 and gamma – non-specific activation should be omitted. 3. In MM-EO and MR-EO the changes in alpha 2 and gamma are rather widespread.

State-related statistically significant EEG power changesContrasts: “positive induced emotions(P) – time count(C)”; “negative induced emotion(N) – C”; “P-N”

Delta Theta Alfa1 Alfa2 Beta1 Beta2

P-N

P-C

N-C

N=16*

P<5*10-2 P<10-2 P<10-3 P<10-4 P<10-5 ** <0.01* <0.05;p GG corrected:

Red colors - values higher in the first of the compared

states, blue –

lower.Fisher LSD

State-related statistically significant EEG power changesContrasts: “positive induced emotions(P) – time count(C)”; “negative induced emotion(N) – C”; “P-N”

Delta Theta Alfa1 Alfa2 Beta1 Beta2

P-C

P-C

N-C

N=16*

P<5*10-2 P<10-2 P<10-3 P<10-4 P<10-5 ** <0.01* <0.05;p GG corrected:

Red colors - values higher in the first of the compared

states, blue –

lower.

1. Both P-C and N-C patterns are unidirectional in all the frequency bands concerned. 2. But in N-C the changes are much less pronounced and that is confirmed in P-N contrast

GammaAlfa1 Alfa2 Beta1 Beta2ThetaDelta

Tukey HSD test

*

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

** <0.01* <0.05;p GG corrected: Red colors - values higher in the first

of the compared states, blue –

lower.

State-related statistically significant EEG power changesContrast: “complicated verbal task (search for a word changing the proverb sense) – non-complicated verbal task (remembering of the certain word missing in the proverb)

N=67

GammaAlfa1 Alfa2 Beta1 Beta2ThetaDelta

Tukey HSD test

*

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

** <0.01* <0.05;p GG corrected: Red colors - values higher in the first

of the compared states, blue –

lower.

State-related statistically significant EEG power changesContrast: “complicated verbal task (search for a word changing the proverb sense) – non-complicated verbal task (remembering of the certain word missing in the proverb)

N=67

1. Even in a situation when main and control tasks are intentionally close one using srqEEG can reveal significant changes between the states corresponding to the tasks performed 2. Here the changes are unidirectional and concentrated in gamma and beta2 bands.

Conclusions:

1. Brain functional states cognitive-specific states included can be separated using srqEEG with good statistical reliability.

2. In the situations investigated the differences were widespread in space indeed and were present in a variety of frequency bands considered.

3. Both unidirectional and bidirectional statistical significant differences could be observed.

4. So potentially EEG power values in several frequency bands can serve as a tool for multiscale (not only regional and general cortex activation/deactivation) rating of brain functional states.

We greatly appreciate contributions of N.V.Shemiakina, M.G.Starchenko, M.L.Solovjeva and Y.A.Boitsova in the studies presented

Thank you for your kind attention!

Statistically significant EEG differences between states of creative and non-creative thinking with various tests

Alfa1 Alfa2 Beta1 Beta2ThetaDelta

1.Sense changing word

2.Storymaking

3.Logical chains

4.Original definitions

5.Drawing pictures from a restricted set

of elements

**

* * *

V e

r b

a l

* *

*

*

Statistically significant EEG differences between states of creative and non-creative thinking with various tests

Alfa1 Alfa2 Beta1 Beta2ThetaDelta

1.Sense changing word

2.Storymaking

3.Logical chains

4.Original definitions

5.Рисунки из набора элементов

**

* * *

V e

r b

a l

* *

*

*

Posterior psychological analysis highlighted a number of factors presumably responsible for the scatter of EEG results with the verbal tests: time frames, involvement of remote associations and of mental imagery, emotion-producing tension etc. It looks like the factor of creative load is not so effective in modulating EEG power in the frequency bands δ - β if compared with aforementioned ones.

Alfa1 Alfa2 Beta1 Beta2 GammaThetaDelta

Gr.1N=22

Gr.2N=25

Gr.3N=20

Variants of statistically significant EEG differences between states of creative and non-creative thinking in 3 groups of subjects

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

* *

** <0.01* <0.05;p GG corrected: Red colors - values higher in the first

of the compared states, blue –

lower.

Emotional components remarkably influence EEG power during creative thinking

C-NC

(C+PE)-NC

* * *Alfa1 Alfa2 Beta1 Beta2ThetaDelta

(C+NE)-NC

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

** <0.01* <0.05;p GG corrected: Red colors - values higher in the first

of the compared states, blue –

lower.

A simple task (search for grammar mistakes in a presentation) added to the creative task influences EEG power statistical significant differences between states of creative and non-creative thinking

Alfa1 Alfa2 Beta1 Beta2 GammaThetaDelta

C-NC

(C+S)-NC

* *

(C+S)-C

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

** <0.01* <0.05;p GG corrected: Red colors - values higher in the first

of the compared states, blue –

lower.

GammaAlfa1 Alfa2 Beta1 Beta2ThetaDelta

Tukey HSD test

EEG power

Statistically significant EEG differences between states of creative (search for a word

changing the proverb sense) and non-creative (remembering of the certain missing word)

thinking

*

EEG coherence

* ***

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

** <0.01* <0.05;p GG corrected:

Red colors - values higher in the first

of the compared states, blue –

lower.

GammaAlfa1 Alfa2 Beta1 Beta2ThetaDelta

Tukey HSD test

EEG power

Statistically significant EEG differences between states of creative (search for a word

changing the proverb sense) and non-creative (remembering of the certain missing word)

thinking

*

EEG coherence

* ***

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

** <0.01* <0.05;p GG corrected:

The results of the test can be guardedly treated as argumentative of activation in memory scanning system (γ synchronization) and in memory control zones (β synchronization in temporal areas) in creative thinking state.

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

Alfa1 Alfa2 Beta1 Beta2 GammaThetaDeltaEEG power

EEG coherence

Statistically significant EEG differences between states of creative and non-creative thinking with two statistical post hoc tests used

C-NCFisher LSD

C-NC

Tukey HSD

C-NCTukey HSD

C-NC

Fisher LSD

Red colors - values higher in the first of the

compared states, blue – lower.

P<5*10-2

P<10-2

P<10-3

P<10-4

P<10-5

Alfa1 Alfa2 Beta1 Beta2 GammaThetaDeltaEEG power

EEG coherence

Statistically significant EEG differences between states of creative and non-creative thinking with two statistical post hoc tests used

C-NCFisher LSD

C-NC

Tukey criterium

C-NCTukey HSD

C-NC

Fisher LSD criterium

Red colors - values higher in the first of the

compared states, blue – lower.

Number of 70 in a group seems enough for reliable results with conservative test Tukey. For EEG power the results reflect characteristic patterns recognizable in subgroups. For EEG coherence the conservative test in such a group doesn’t reveal characteristic patterns.

Today we consider quantitative EEG as a helpful instrument for versatile screening of numerous groups of subjects in evaluation of hypotheses, psychological tests and research methods related to basic mechanisms of cortex functioning.