M.N. Rusalova “EEG FRONTAL – OCCIPITAL ASYMMETRY IN THE SITUATION OF ANXIETY” (P. 46-55)

M.N. Rusalova

EEG FRONTAL – OCCIPITAL ASYMMETRY IN THE SITUATION OF ANXIETY

Institute of higher nervous activity and neurophysiology, RAS, Russia

 

EEG FRONTAL – OCCIPITAL ASYMMETRY IN THE SITUATION OF ANXIETY
M.N. Rusalova
A study was run on 32 subjects, aged 18-24.  The subjects were  to perform  the following functional tasks: mental  representation of a state of joy, listening to an extract of  a text, mental representation of  an expected painful stimulus, an expectation of  an electrical skin stimulation. Data obtained showed that 7 subjects of 32 Ss had an inversion of frontal-occipital asymmetry when expecting an electrical stimulation,  owing to which the occipital cortical regions were more activated as compared to the frontal regions. This fact testifies to a decrease in the general cortical activation of the brain in those subjects  who were expecting an unpleasant stimulation.
Key words: emotions, EEG asymmetry.
 
DOI: http://dx.doi.org/10.18454/ASY.2016.10.3553

 

Human brain functional asymmetry is an object of numerous studies (Bekhtereva N.P., Danko S.G., Starchenko M.G.,2001;Posner, 1995; Rusalova, 2004; Fokin, 2007) in other works,   this problem is investigated in the development of various psycho-physiological issues (Kiroy, Vladimirskiy, Aslanyan et al., 2010; Tambiev, Aslaniyan, 2016). The overwhelming majority of authors   describe EEG left-right asymmetry and study its dynamics in various  tests.

In the present work we paid attention to the dynamics of EEG frontal-occipital  assymmetry (FOA).

Methods. The object of the present study was to reveal the FOA dynamics  under different testing conditions.  The study was run on 32 subjects, aged 18-24.  The subjects were  asked to perform  the following functional tasks: mental  representation of a state of joy, listening to an extract of  a text, mental representation  of an electric painful skin stimulus, an expectation of   a “real” electrical skin stimulation, (which in reality was never delivered because we studied the state of anxiety), and  the mental representation of an  electrical skin stimulus 2 minutes after the expectation of the ‘real’ painful stimulus.

EEG was recorded according to the international 10-20 % scheme from 16 derivations: Fp1, Fp2, F3, F4, F7, F8, СЗ, С4, РЗ, Р4, ТЗ, Т4, Т5, Т6, О1, О2. A united earlobe electrode was used as a reference. The frequency of digitization was  500 c/sec. The bandwidth was 0.3 – 80 c/sec.

The EEG recording was done on the 21-channel amplifier, consisting of the computer.  To eliminate electrical noises, a  special rejection  filter (50 c/sec) was

apparatus-program complex for topographic mapping of  brain electrical  activity «NEURO-KM» made by the Scientific-medical firm «Statokin» and a personal

used. The data obtained were treated with the help of the program «BRAINSYS» (Scientific-production firm  «Neurometrix», Moscow, author  A.A. Mitrofanov).

Spectral amplitudes (with the subsequent calculation of spectral power) using discrete Fourier  transformation in summary alpha rhythm  (8-13 c/sec) were -calculated. Separate brain maps (powers of alpha-rhythm) were made for every subject for each testing condition.

 

Results. The analysis of the brain maps in  7 subjects,  when expecting an electrical skin stimulus, showed an FOA inversion  of the EEG powers alpha-rhythm power. In other subjects, similar effect was absent. On the basis of this phenomenon, the sample  was divided into two groups: the group 1(7 persons) in whom the inversion was observed and the  group 2 (25 persons) in whom the inversion was absent.

In the present work  we shall describe only the results obtained for the group 1 because the problem of the FOA is reflected insufficiently in the literature. (The results for other  25  persons will be given later in further publications).

As the brain maps in different subjects were different, in particular, the focus of the biggest alpha-rhythm powers could be observed in the very different parts of the brain  (Figure 1), we considered it inexpedient to average the results for all 7 subjects. Instead, we will give the results of only one subject (Yu.A.)  as an example.

 rusalova_8_3_2016 rusalova_7_3_2016 rusalova_6_3_2016 rusalova_5_3_2016 rusalova_4_3_2016 rusalova_3_3_2016 rusalova_2_3_2016 rusalova_1_3_2016

Fig.1. Examples mapping of EEG alpha-rhythm power    in 4 subjects when  expecting of  a real painful stimulus.

As is seen in the Fig. 1, in subjects, in the situation of  expectation of a real  electrical skin stimulus, different EEG segments with increased alpha rhythm power  were observed.    Similar differences were also found in other 3 persons, in this case the inversion of the FOA was characteristic of all the persons:  the alpha-rhythm power in occipital regions was lower than in the frontal ones.

 rusalova_2_3_2016

 

Fig.2.  Background. Subject Yu.A.

The Fig. 2 shows a map and a EEG segment in the background. As is seen from this Figure, a typical picture is observed for all the background recordings: in occipital derivations alpha-rhythm power is higher, as compared to the frontal recordings, and in the right hemisphere alpha-rhythm power is higher than in the left hemisphere.

 rusalova_3_3_2016

Fig.3. Mental  representation of an expected electrical skin stimulus. Subject Yu. A.

    The fig. 3 is an example of  EEG segment  and mapping under the mental  representation of an expected electrical skin stimulus. As is seen from this figure, a lower power of alpha-rhythm in the left hemisphere remains only in derivations Fp1, F7 и F3 and,  thus, in the majority of derivations a right hemisphere alpha-rhythm inversion is observed.    The  right hemisphere inversion  was observed  many times in our previous studies under the conditions of reproduction of emotionally charged images (Rusalova, 2015).

 rusalova_4_3_2016

Fig 4. Listening to a speech segment. Subject Yu.А.

      When listening to a speech segment, an alpha-rhythm blockade was observed in all the derivations, a greater activation of the left hemisphere remaining in the  overwhelming number of derivations, besides С4 and Р4.

 rusalova_5_3_2016

Fig. 5. Mental representation of joy. Subject Yu. А.

 

Under the mental representation of joy (figure 5),  an inversion  was observed in occipital  brain regions (О2, Т6, Р4 иС4).

rusalova_6_3_2016

Fig. 6. Expectation of a real  electrical skin stimulus. Subject Yu.А.

When expecting of a real electrical skin stimulus  (fig. 6) we observed  a decrease of  alpha-rhythm power as compared with background. Here an inversion of the FOA was revealed: the power in the brain fontal regions was significantly higher  than in the occipital regions.

 rusalova_7_3_2016

 

Fig. 7.  Mental  representation of the expected painful  stimulus one minute after    expectation  of a real painful stimulus. Subject Yu.А.

     It is interesting to note that under the condition of expectation of electrical skin stimulus  (fig.7)  one  minute after  the expectation of a real stimulus, the FOA inversion  remains, and the EEG pattern is different from that of in the Fig. 2 , where  similar effect was absent. Moreover, this effect remains two minutes after the expectation of a painful stimulation (Fig. 8).

rusalova_8_3_2016

Fig. 8 . An EEG map 2 minutes after the expectation  of electrical  stimulus. Subject Yu.A.

The figure 8 shows that in the associative regions, an increased alpha-rhythm powers  have lasted  for 2 minutes, as compared to the background values of alpha-rhythm, which  testifies to their  inhibitory  state.

         Conclusion.

  Data obtained showed that  7 subjects (the group 1),  when expecting a  painful stimulation. had an inversion of the FOA. This means that the occipital regions of the brain were   more activated, as compared to the frontal regions. This fact testifies to a decrease in general cortical activation (Rusalova, 2004) in these subjects. We could suggest the following explanation for this phenomenon. Animals. in case of impossibility of avoiding a dangerous situation, switch on a mechanism of  “withdrawing into oneself”, or passive – defensive reaction. It was shown  that  the level of activation of amygdala in these animals  was higher, and the right amygdala being dominant (Pavlova, Rysakova, 2013). It is quite possible that a  similar mechanism takes place in our subjects from  the group 1.

      Data obtained   showed the possibility of changing a  normal course of EEG processes  in the human cortex in case of negative passive  emotions, which could remain also after the cessation of a traumatic situation. 

                           

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