Heart rate variability of left-handed and right-handed children in three different situations was compared. The first record was made in quite situation; the second one was made when child answered the questions about rewards in family and the third one when she (he) answered the questions about punishment. We have shown that heart rate variability of lefthanded children in three situations did not change significantly, but regulation of heart rate variability of righthanded children in emotional situations changed significantly.
The development of handedness is one of the most
intriguing problems of contemporary science. A preference
for one or another extremity has been documented on an
individual level for many mammals, and among humans it is
characteristic to divide the population unevenly into those
who prefer the left hand and those who prefer the right
It turns out that among many animal species those that
have pronounced motor asymmetry exhibit greater cognitive
capabilities
In the European part of Russia, the majority of the
population favor their right hand when involved in various
activities. By contrast, as a number of authors have
revealed, natives of the Far North favor their left hand
In these harsh, inhospitable regions of Russia, oil extraction takes place, and it involves the use of a rotational working schedule in which workers from other, often faraway, regions come to work for two weeks and then return home, where they also spend two weeks, thus alternating their stays at home with work stints. It turns out that the number of left-handers who enter these jobs does not differ from their number in the general European population. After seven years of working such shifts, however, there is a sharp increase in the number of lefthanders. As it happens, right-handers do not simply quit such jobs; they do so because of a steady increase in blood pressure.
These statistics allow us to assume that there is a
causative connection between handedness and the process of
adapting to complex conditions within a person’s
surroundings. It is known that when there are new
environmental conditions to contend with, the right
hemisphere of the brain is activated
It has been shown that for right-handers central regulation
of the sympathetic nervous system is also a function of the
right hemisphere
Furthermore, it has been proven that for left-handers
many functions of the brain are less specialized
This begs the question as to how early differences in the primary regulation of the heart develop. Can we detect such differences in elementary school children during the period when they are adapting to the educational process? Is it possible that the development of right-handed attributes during the formulation of handedness will increase intensive changes in the heart rate when a person recalls emotional states?
In order to answer these questions, 145 schoolchildren (they were an average of 7.2 ± 0.4 years old) were surveyed. Here and elsewhere, the results are given in the [Mean] ± [SD]) format. The conditions for inclusion in the experiment were the following: the absence of chronic disease, the presence of a sine heart rate and written permission from the parents to take part in the research, along with an explanation of what will happen at every step along the way. Those children whose parents did not given permission to participate were not included.
Before the study began, it was determined which hand
was dominant for each of the children by administering a
series of tests: the Interlocked Fingers Test, the Napoleon
Pose Test
In addition, these tests were conducted once: Drawing a Circle and Square with Closed Eyes and The Hand That Holds the Pen and Pencil, as well as the Tapping Test (Nikolaeva et. al., 2008). These tests were chosen because it had earlier been shown that the performance of these activities was a reasonably stable indicator for children of this age.
The results of all the tests were assigned a numerical rating: left-handed performance was given a score of 0; symmetrical performance (the child performed the activity first with one hand and then, when the test was repeated, with the other) a score of 1; and right-handed performance a score of 2. Children with an average value within the range of 0.0-0.7 were considered to be left-handed; those within the range of 1.3-2.0, right-handed; and the rest, mixedhanded.
Power analysis
Department of Applied Physics of the University of Eastern Finland, in Kuopio, Finland. Statistical analysis was performed by using the IBM SPSS Statistics program (version 23).
Recording of the heart rates was conducted individually, and it consisted of three stages. Electrodes were placed on a child’s arm, in the area of the wrist, with the contact pad on the inside. At the point of the contacts, the skin was doused with water. The child sat in a comfortable chair. At each stage, 300 consecutive heart beats were recorded (from this point on, heart beats are taken into account after the processing of technical and biological artifacts on the electrocardiogram recording, the time between R peaks on the ECG is called the NN interval, and the standard deviation from their average value is noted as SDNN). Such a prolonged ECG recording was chosen so that the entire assessment, beginning with the placing of the electrodes and ending with the recording of the answers, would take no longer than ten minutes. The heart rates were recorded using the Omega Medicine hardware and software system (the Dinamika Company, St. Petersburg, Russia).
In Stage 1, the heart rate was recorded with the child at
rest. In Stage 2 (the valence of the emotional state = “+”),
the heart rate was registered while the child was recalling
situations of encouragement made possible by their parents.
In Stage 3 (the valence of the emotional state =“ – "), the
heart rate was noted while the child was recalling situations
involving punishment. The child’s answers were recorded
on the data sheet. The questions used in the conversation
were taken from the E.
It is extremely difficult to create conditions that generate
an emotional response, especially in children. Talking about
punishment or encouragement does not presuppose any sort
of investigation into the real situation inside a family; it is
simply a way of discovering the child’s perception of this
situation. It has been proven that it is the perception of a
situation that evokes an emotional response from a child
It can be assumed that the dynamics of the heart rate will be minimally intense for left-handed children and will be at its peak for right-handers.
Figure 1 shows the trajectory of the conditions of the
heart rate within a range from quiet state to “recollection of
encouragement” to “recollection of punishment”
During recollection of encouragement within the family (axis Y), the span of the heart rate for a left-handed child does not change, but for a right-hander its lower limit changes from 65 to 105 bpm. During recollection of a situation involving punishment (axis Z), the upper limit of the heart-rate span changes for both groups: for left-handers, from 55 to 95, and for right-handers, from 65 to 110 bpm. Based on this data, it can be supposed that the dynamics of the heart rate for a right-handed child during a shift to an emotional state are more pronounced that are those of a lefthanded child. As a result, the three-dimensional point cloud of heart-rate conditions for a right-handed child “shifts” when compared to that of a left-hander.
At the beginning of the experiment, the average HR value was 72.5 ± 8.7 bpm (for the left-handed children) and 77.3 ± 10.0 bpm (for the right-handed children), the difference being at the level of p <<< 0.001, power = 1.000. At the end of the experiment, the average HR value was 72.8 ± 11.1 bpm (for the left-handers) and 87.8 ± 9.4 bpm (for the righthanders), the difference being at the level of p <<< 0.001, power = 1.000. Thus, it can be observed that the heart rate for a left-handed child at the beginning of the experiment (quiet state) and at the end of the experiment (after the first emotional state and at the end of the second, which had the opposite valence) did not show a significant change (p>>0.05). By comparison, the HR for a right-handed child in the same situation increased by 10 beats a minute (p <<< 0.001; power = 1.000), which would correspond to an intensive stress load during physical activity (an increase in the HR should not exceed 12 beats a minute in relation to quiet state).
Figure 2 presents the trajectory of the conditions of the
heart rate for those children in the plane of embedding (a
Poincaré plot) from “quiet state” to “recollection of
punishment” (i.e., from the beginning to the end of the
experiment) with a configuration of the dispersion ellipse
The picture for a right-handed child is different (Fig 2): the point clouds of the heart-rate conditions at the beginning and at the end of the experiment are out of line with each other. Although the configurations of the diversion ellipses are similar, the centers of the ellipses have shifted (p <<< 0.001; power = 1.000).
There are no any differences between stages of left-and mixed- handed children. Power analysis confirms the differences of heart rate both between background and recalling situations of encouragement and background and recalling situations of punishment.
We have received the differences just for right-handed children. It could be assumed that there is no enough a discriminant power of one parameter – handedness (but it describes the most part of dispersion). Maybe we need some more parameters of lateral preferences, for example eyeness, footedness, ear-ness.
Thus, an analysis of the results (see the tables) shows that the intensity of the heart-rate dynamics among 7-8 year-old children when they are in emotional states of different valences increases along the line from left-hand dominance to mixed-hand dominance to right-hand dominance.
Left/n=35 Mixed/n=64 Right/n=46 background A 84.32±20.14 85.69±17.72 87.74±14.64 “+” (B) 86.14±20.04 87.53±18.90 91.32±15.26 “–“ (C) 85.96±20.96 87.41±17.53 91.76±14.84 W (B–A) p= 0.017* p<0.001* p<0.001* Power (B–A) 0.719 0.914* 0.995* W (B–A) p=0.599 p=0.636 p=0,285 Power (C–B) 0.053 0.057 0.096 W (C–A) p=0.123 p=0.004* p<0.001* Power (C–A) 0.328 0.735 0.992* Notes: There are no any differences between groups for heart rate (U Mann-Whitney) and distribution (F Fisher, Moses Test); the differences between stages in a group for heart rate (W-test Wilcoxon, Į =0,05; exact 2-tails); Power = (1–ȕ err Prob), Į = 0,05; 2-tails; “+” – a stage of two, recalling reward; “–“ – a stage tree, recalling punishment; * – p<0,05; Power 0,80.
Our findings are in keeping with the hypothesis that there is a difference in the regulation of the heart rate between people with different types of handedness. While in righthanded children emotional stress is extensively reflected in their heart rate variability, in left-handers there is no link between emotional stress and autonomic manifestations. In adulthood, this means that serious changes in the regulation of emotional stress leads to myocardial infarction more often with people who have all of the right-side attributes: right-hand, right-foot, right-eye and right-ear dominance.
Further research might focus not only on an analysis of how cardiological changes are linked to the characteristics of handedness but of how they are related to other lateral attributes as well.
An examination of these mechanisms allows us to comprehend the evolutionary workings involved in the phenomenon of lateral preferences in the sensory and motor spheres and, at the same time, to understand how people with such attributes are distributed in various climatic and geographical conditions.
The work was supported by rant of RGNF 14-06-00195