EEG alpha rhythm spatial distribution depending on level of motor activity

Фотографии: 

ˑ: 

PhD A.V. Kabachkova1
Postgraduate G.S. Lalaeva1
Postgraduate A.N. Zakharova1
Professor, Dr.Med. L.V. Kapilevich1, 2
1National Research Tomsk State University, Tomsk
2National Research Tomsk Polytechnic University, Tomsk

Keywords: EEG, motor activity, cyclic exercise, static exercise, hypodynamia.

Introduction. The activity of various regions of the cerebral cortex and subcortical structures reflects the intensity of different electroencephalographic (EEG) rhythms, their ratio and topical representation [3]. The nature of their relationship varies depending on a situation [1, 5, 7, 9], which is an important integrative indicator of brain activity in general [3]. With each movement, the central nervous system processes a large amount of information related to the proprioceptive afference of muscles. As a result, the functional status of the cerebral cortex and subcortical centers improves, and the excitation and inhibition processes become more intense and balanced [8].

Physical activity (PA) has a strong tonic effect on man’s physical and emotional state, increases the activity of the central neurotransmitter systems [4]. And it is the level of MA that is important here. Thus, the study data on PA of Tomsk State University students has revealed that the weekly activity of about 1/3 of students of both sexes is above average (about 10 hours per week, while the conditional norm is 9 hours per week) [2].

Objective of the study was to estimate the alpha-activity of the cerebral cortex in individuals with different levels of PA.

Methods and structure of the research. The study involved 40 men aged 17 to 20 without any mental or neurological diseases (all - right-handers). We formed 4 uniform groups with the same number of participants but various levels of PA [6]:

– low physical activity (LPA) - less than 9 hours per week;

– moderate physical activity (MPA) - 9 hours per week;

– high physical activity dominated by dynamic exercise (HPAd) - more than 9 hours per week;

– high physical activity dominated by static exercise (HPAs) - more than 9 hours per week.

EEG was carried out using the software and hardware complex "Neuron-Spectrum 3" ("Neurosoft" LLC, Russia). The electrodes were placed according to the international circuit "10-20" (monopolar installation, ear-clip reference electrodes): frontal polar (FP), central sulcus (C), temporal (T), occipital (O) leads. The measurements were taken in a sitting position with the eyes closed, in a state of relative rest (baseline sample) and during standard tests - "eye opening / eye closing". Each EEG was followed by the reinstallation and filtration in the band from 1 to 150Hz and elimination of 50Hz hum pickup. Each EEG was automatically scanned for possible artifacts. The EEG segments with the amplitude over 200 mcV within the range of 640 ms were marked as a bad channel; the segments with the amplitude over 140 mcV were treated as a motion artifact (NetStationsoftware).

The data were statistically processed using the STATISTICA 8.0 software, which implied determination of the sampling descriptive parameters, assessment of the normality of data distribution (Shapiro-Wilk’s test), comparative analysis of independent (Mann-Whitney test) and dependent (Wilcoxon test) samples. P£0.05 was taken as a statistically significant difference.

Results and discussion. Alpha-rhythm is a rhythmic sinusoidal oscillation, modulated in a spindle-like way, with a frequency of 8-13Hz and an amplitude of 100 mcV [3]. The alpha-rhythm average amplitude in all examined groups, in the state of relative rest and during the eye-opening and eye-closing tests, is presented in Table 1 and Figure 1.

In the state of relative rest, there were no significant differences in the average amplitude in all groups (p>0.05). We registered the predominance of the rhythm in the occipital leads and amplitude decay from back to front (G → C → FP → T). The rhythm was symmetrical in frequency and amplitude in both hemispheres. There was a functional asymmetry of the rhythm with a slight excess of the average amplitude in the right hemisphere in all the examined groups (MPA - from 0.03 to 0.11 mcV; HPAd - from 001 to 0.14 mcV; HPAs - from 0.03 to 0.08 mcV), except for the LPA group (there was an increase in the average amplitude on the left to 0.20 mcV). This distribution of alpha-oscillations is treated as an indicator of the brain functional interhemispheric asymmetry (FIA): it is the hemisphere (or the region in ​​the brain), in which the alpha-rhythm amplitude is lower, that is considered functionally more active [4]. Therefore, in the LPA group there was a right sided FIA, unlike other groups with the left-sided FIA.

During the eye-opening test, the alpha-activity in all groups decreased by more than 25% in the occipital leads and by 10-25% in the temporal ones. Moreover, in the temporal region, the level of the rhythm average amplitude on the left did not change in individuals with the low level of MA. In the central sulcus region, a significant decrease (>25%) was observed in the average amplitude in the MPA and HPAd groups, while in the HPAs and LPA groups it decreased by less than 25%. The change in the alpha-rhythm amplitude in the frontal polar leads in the groups was multidirectional. For example, in the MPA and HPAd groups, no changes were observed, while in the HPAs group we registered a significant increase in the rhythm, and in the LPA group – its weakening. The predominance of alpha-activity was recorded in the frontal polar leads in all examined groups. The alpha-oscillation amplitude gradient during the eye-opening test in the HPAd and HPAs groups can be represented as follows: FP → O → C → T (from the highest to the lowest). In the MPA group, the gradient was the same, but FP = O. In the LPA group, the indices were the same on the right; however, on the left FP → T → C → O.

During the eye-closing test, the alpha-activity in all the examined groups increased by more than 25% in the occipital leads. In the central sulcus region, we observed a significant increase (>25%) of the average amplitude in the MPA and HPAd groups, while in the HPAs and LPA groups - an increase by 10-25%. The change in the alpha-rhythm amplitude in the frontal polar and temporal leads in the groups was multidirectional. There were no changes in the amplitude in the frontal polar leads - MPA, as well as an increase by 25% - HPAd and a decrease by more than 25% - HPAs. There was an increment in activity by 25% in the temporal leads - MPA and HPAd, no changes - HPAs, an increase on the right and a decrease on the left - LPA. The predominance of alpha-activity was detected in the occipital leads in all the examined groups. The alpha-oscillation amplitude gradient during the eye-opening test in all the examined groups can be represented as follows: O → C → FP → T.

Conclusion. These findings suggest that the intensity and nature of MA affect the laws of formation of alpha-activity patterns of the cerebral cortex. According to the baseline sample, it is the left-sided alpha-rhythm asymmetry that predominates in individuals with the average and high levels of MA, while in individuals with the low level of MA it is the right-sided one. Lability (the degree of response to the eye-opening and eye-closing tests) is significantly more pronounced in the groups with the moderate and high physical activity dominated by dynamic exercise. Of special note is a marked increase in the alpha-activity in the frontal polar region in the group where static exercise prevailed. 

Table 1. Alpha-rhythm average amplitude in the examined groups, mcV

Lead

Examined group

Test

MPA

HPAd

HPAs

LPA

FP

left

0.87 (0.74; 0.94)

1.03 (0.78; 1.30)

0.85 (0.70; 1.08)

1.09 (0.85; 1.35)

baseline sample

0.88(0.66; 1.09)

0.96 (0.67; 1.21)

1.34 (1.12; 1.61)1

0.99 (0.60; 1.20)

eye opening

0.88(0.66; 1.09)

1.02 (0.79; 1.21)

0.91(0.75; 1.10)

1.03 (0.91; 1.20)

eye  closing

right

0.90(0.81; 1.06)

1.06 (0.80; 1.36)

0.92 (0.86; 1.11)

1.09 (0.90; 1.34)

baseline sample

0.83(0.66; 0.95)

0.93 (0.71; 1.22)

1.28 (1.10; 1.62)

0.97 (0.62; 1.16)

eye opening

0.98(0.74; 1.20)

1.04 (0.82; 1.21)

0.95(0.85; 0.22)

1.03 (0.86; 1.19)

eye  closing

C

left

1.11(0.92; 1.14)

1.22 (0.82; 1.58)

1.12 (0.84; 1.41)

1.37 (1.10; 1.88)

baseline sample

0.84(0.72; 0.98)

0.82 (0.70; 0.95)

0.96 (0.84; 1.05)

0.89 (0.74; 1.00)

eye opening

1.15(0.90; 1.33)

1.18 (0.75; 1.45)

1.13(0.90; 1.44)

1.32 (1.04; 1.59)

eye  closing

right

1.13(0.98; 1.18)

1.23 (0.89; 1.69)

1.18 (1.04; 1.50)

1.30 (1.05; 1.76)

baseline sample

0.78(0.72; 0.85)

0.79 (0.67; 0.88)

0.94 (0.85; 1.00)1

0.88 (0.72; 1.14)

eye opening

1.15(0.95; 1.33)

1.19 (0.82; 1.51)

1.14(0.99; 1.46)

1.30 (1.10; 1.58)

eye  closing

О

left

1.75(1.14; 2.03)

1.62 (1.24; 1.94)

1.53 (0.96; 2.32)

1.87 (1.48; 2.15)

baseline sample

0.86(0.75; 0.96)

0.81 0.63; 0.89)

0.85 (0.74; 0.94)

0.88 (0.72; 1.05)

eye opening

1.76(1.43; 2.12)

1.79 (1.35; 2.23)

1.53(0.97; 1.11)

2.14 (1.55; 2.5)

eye  closing

right

1.82(1.39; 2.13)

1.76 (1.19; 2.29)

1.56 (1.27; 2.07)

1.76 (1.28; 2.25)

baseline sample

0.82(0.74; 0.86)

0.87 (0.71; 1.11)

0.92 (0.75; 1.02)

0.85 (0.60; 1.06)

eye opening

1.88(1.65; 2.07)

1.92 (1.35; 2.40)

1.50(1.33; 1.88)

1.94 (1.65;2.28)

eye  closing

Т

left

0.80(0.67; 0.89)

0.93 (0.67; 1.26)

0.84 (0.57; 1.01)

0.94 (0.65; 1.25)

baseline sample

0.68(0.60; 0.70)

0.66 (0.54; 0.84)

0.82 (0.64; 0.97)

0.96 (0.55; 0.77)

eye opening

0.85(0.72; 0.99)

0.93 (0.63; 1.27)

0.84(0.61; 1.14)

0.79 (0.66; 1.07)

eye  closing

right

0.91(0.83; 0.94)

1.00 (0.64; 1.36)

0.92 (0.91; 1.03)

0.74 (0.62; 0.91)

baseline sample

0.71(0.60; 0.71)3

0.66 (0.53; 0.76)

0.75 (0.66; 0.87)3

0.52 (0.45; 0.62)

eye opening

0.93(0.80; 1.08)

0.98 (0.63; 1.33)

0.90(0.81; 1.10)

0.72 (0.63; 0.92)

eye  closing

Note. The sampling data recording is presented in the form of Me (Q25; Q75); FP- frontal polar leads, C - central sulcus leads, O – occipital leads, T - temporal leads; MPA - moderate physical activity, HPAd - high physical activity dominated by dynamic exercise, HPAs - high physical activity dominated by static exercise, LPA - low physical activity.

1 – statistically significant differences between the indicators compared to the MPA group (p≤0.05),

2 – statistically significant differences between the indicators in the HPAd and HPAs groups (p≤0.05),

3 – statistically significant differences between the indicators compared to the LPA group (p≤0.05).
 

Fig. 1. Changes in the gradient of alpha-activity in the examined groups.

Note. MPA – moderate physical activity, HPAd – high physical activity dominated by dynamic exercise, HPAs – high physical activity dominated by static exercise, LPA – low physical activity; blue is for the region of alpha-rhythm domination, an arrow is for the gradient direction from the highest to the lowest.

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Corresponding author: kapil@yandex.ru

Abstract

Physical activity has a strong tonic effect on the physical and emotional state in man, increases the activity of the central neurotransmitter systems. And it is the level of physical activity that is important here.

The intensity and nature of physical activity influence the rules of formation of brain alpha-activity patterns. The differences in the functional interhemispheric asymmetry of the brain in people with low physical activity were identified. The changes in functional mobility in groups with middle and high (mostly dynamic nature of loads) levels of physical activity were shown in the paper.