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.
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.
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.
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).
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.
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).
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.
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).
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.
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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