|Year : 2021 | Volume
| Issue : 3 | Page : 204-208
Exploration of electroencephalographic signatures of non-dominant handwriting task
Yogesh Singh1, Jayvardhan Singh2, Rajesh Kathrotia3
1 Department of Physiology, AIIMS, Rishikesh, Uttarakhand, India
2 Department of Physiology, GSVM Medical College, Kanpur, Uttar Pradesh, India
3 Department of Physiology, AIIMS, Rajkot, Gujarat, India
|Date of Submission||09-May-2020|
|Date of Decision||10-Sep-2020|
|Date of Acceptance||24-May-2021|
|Date of Web Publication||28-Dec-2021|
Dr. Rajesh Kathrotia
Department of Physiology, AIIMS, Rajkot - 360 005, Gujarat
Source of Support: None, Conflict of Interest: None
Background: Handwritten language is one of the key learned expertises of the human brain and preferred modes for long-distance communication. The dexterity and hand dominance in written language are well-known phenomenon. Normally, we are accustomed to writing with one hand only. Literature suggests that the dual task of attention interferes with the performance of one task and/or the other, as these tasks use the same attentional resources. Aim: The aim of this study was to investigate the quantitative electroencephalographic (EEG) correlates of non-dominant handwriting (NDHW) as an attentionally demanding task. Materials and Methods: We conducted a study on 35 male native Hindi speakers, well accustomed to reading and writing. The intervention consisted of 5-min writing with the DHW and NDHW with concurrent EEG recording. The EEG electrodes were applied according to the 10–20 international system of electrode placement. EEG signals were analysed offline. The outcome measures were fast Fourier transform transformed absolute power in delta (1–4 Hz), theta (4–8 Hz), alpha (8–14 Hz), beta (14–30 Hz) and gamma (30–50 Hz) frequency bands at 19 electrode positions. Medians of 10 epochs from artefact-free regions of EEG during NDHW and DHW were statistically analysed. Results: The task of NDHW was associated with decreased absolute powers in frontal and occipital leads mainly in delta and theta frequency bands and at frontocentral leads in the alpha band. Absolute powers in the beta frequency band were increased mainly at frontal and decreased posteriorly, while there was a generalised increase in gamma-band power. Conclusions: NDHW task as compared to the DHW task has distinct EEG correlates suggestive of a stressed attentive mental state.
Keywords: Fast Fourier transform, Quantitative electroencephalography, Writing task, Stressed attentive mental state
|How to cite this article:|
Singh Y, Singh J, Kathrotia R. Exploration of electroencephalographic signatures of non-dominant handwriting task. J Med Evid 2021;2:204-8
| Introduction|| |
Brain oscillations during various cognitive tasks have been extensively researched. Electroencephalographic (EEG) correlates of cognitive tasks during meditation have provided valuable insight into the neurophysiology of the brain, particularly attention and its control. Attention has many components, for example, the capacity to focus, maintaining the focus of attention as well as noticing small and rapid shifts to what we experience.,,
Literature suggests that the dual task of attention interferes with the performance of one task and/or the other. Based on these observations, researchers have tried to explain the role of eye movements in the 'Eye Movement Desensitization and Reprocessing therapy' for the post-traumatic stress disorder patients, where eye movement was shown to decrease the vividness and emotional valence associated with the autobiographical memories, as both the eye movement and the autobiographical memories were demanding the attention from the same attentional pool.
We hypothesise that writing with a non-dominant hand will be more attention demanding than writing with the dominant hand as the participants will have to maintain the visual imagery of the words in the working memory and also try hard to write the words correctly – and not just mirror image of words – which may happen when we try to write with the non-dominant hand. Therefore, we hypothesise that writing a traumatic experience with the non-dominant hand may also have the potential to benefit emotional trauma patients.
EEG correlates of non-dominant handwriting (NDHW) task are interesting and naïve areas and its role as an attention-demanding task has not been explored. In the present study to explore the effects of NDHW on attention, we investigated the EEG signatures of NDHW as compared to the DHW task. We selected an emotionally neutral paragraph for writing as the emotional valence has been shown to affect the cognitive processes and EEG.
| Materials and Methods|| |
We conducted the study on 35 male native Hindi speakers, without any difficulty in reading and writing, recruited from ongoing research in a neurophysiology laboratory. Handedness scores were assessed by the Edinburgh Handedness Inventory. Ethical clearance obtained - letter no. IEC/IM/17/RC15. dated 20/03/2014, from Institutional Ethics Committee, AIIMS Rishikesh for the study was obtained from the institutional ethics committee for the participation of human subjects. We briefed the participants about the study protocol and obtained written informed consent. Only participants with no recent history of medical or surgical illness were recruited for the study. Participants were asked to report at 10 am on the day of study, to abstain from smoking, alcohol and caffeine-containing beverages and to avoid heavy physical or mental exercise before the experimental session.
We requested the participants to report to the laboratory on the day of the experiment with shampooed hair without the application of any conditioner or oil. Participants were made to sit comfortably in a chair and EEG electrodes were placed according to the 10–20 system of electrode placement. The intervention consisted of a 5-min writing task that involved writing of a preselected emotionally neutral paragraph with the DHW and NDHW with concurrent EEG recording. One-min rest with eye closed was given between the test conditions. Participants were asked to refrain from undue body movements during the experiment session.
We instructed participants to carry out the writing tasks in an upright sitting position on a chair fitted with a writing pad. Participants were also requested to carry out the writing task in a straight line at a normal pace on a lined paper with the help of a ballpoint pen.
Electroencephalographic signal acquisition
Twenty-three electrodes were placed according to the 10–20 international system of electrode placement with an impedance of <5 kΩ. EEG signal was acquired at a sampling frequency of 256 Hz using high (0.5 Hz), low (99 Hz), and notch (50 Hz) pass filters on the RMS EEG-19 Superspec system.
Signals were analysed offline. We identified the movement and eye-blink artefacts manually and excluded them from the analysis. The first 10-s record was excluded to remove any effect of expectancy. We selected 10 epochs, each of 2-second duration from each test condition. The outcome measures were fast Fourier transform transformed absolute power expressed in microvolts squared in the delta, theta, alpha, beta and gamma frequency bands at 19 electrode positions. Medians of the absolute power of 10 epochs during DHW and NDHW were statistically analysed.
The statistical analysis were done by R Software version 3.1. The distribution of the data was found to be non-Gaussian type; therefore, a non-parametric test (Wilcoxon Signed-rank test) was applied. To overcome the problem of multiple comparisons (85 variables), a false discovery rate test was applied. p <0.05 was considered significant.
| Results|| |
The mean age of participants was 30.15 years. The education status of all participants was graduates and above, with good command of Hindi-writing motor skills. Thirty participants were right handed with an average handedness score of 100%, while the rest five were left handed with an average handedness score of 80% (ranging from 60% to 100%).
The result of absolute power in various frequency bands during NDHW and DHW is presented in [Table 1] and [Supplementary Figure Box Plot 1]. The task of NDHW was associated with decreased absolute powers in frontal and occipital leads mainly in delta and theta frequency bands and at frontocentral leads in the alpha band. Absolute powers in the beta frequency band were increased mainly at frontal and decreased posteriorly while there was a generalised increase in gamma-band power.
|Table 1: Difference of absolute power in non-dominant hand versus dominant hand|
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The p value histograms are representations of signal strength during NDHW and DHW conditions in various domains of EEG analysis [Figure 1].
|Figure 1: P value histogram for differences in a) absolute power, b) relative power, c) peak power frequency and d) mean power frequency. In each of 4 histogram, X-axis is P value of differences in non-dominant hand versus dominant hand and Y-axis is frequency of P value|
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The relative power changes of NDHW were nearly similar to absolute power (except in a few electrode positions). The median power frequency and peak power frequency increased during the NDHW task in the same bands' locations as in absolute power and relative power but in fewer electrode positions [Supplementary Figures Box Plot 2], [Supplementary Figures Box Plot 3], [Supplementary Figures Box Plot 4].
| Discussion|| |
During NDHW, as compared to DHW, we found a decrease in absolute powers of delta frequency bands mainly at frontal and occipital leads, a decrease of theta power mainly at frontal and posterior leads and also a decreased power at frontocentral leads in the alpha band. Absolute power in the beta frequency band was increased mainly at the frontal and decreased posteriorly while gamma-band power was increased in most of the electrode positions.
In our experimental paradigm of writing task, alertness, attention and fine motor execution were the main cognitive processes exercised, so we expected to find similar trends. The results of the current study are discussed in terms of models grounded in working memory and meditation literature.
Increased goal-directed mental activity and higher social involvement are associated with decreased power in the 8–13 Hz frequency range mainly in central locations. Decreased alpha power in centroparietal regions during the NDHW task condition may be reflective of a higher requirement of top–down cognitive processes and mental absorption of the participants in the task.
Increased power in frontal midline theta has been reported during tasks involving attentional processes,,,,, working memory, retention and mental imagery. Power in frontal midline theta is also shown to increase a few seconds before a self-initiated hand movement and reaches the peak immediately after the movement. Frontal midline theta is also expected to increase in monitoring of ongoing experience without high levels of control or manipulation of the contents of experience. A decrease in theta power in the current study again along with the decrease in alpha power may show the mental absorption of the participants in the task.
Gamma oscillations are important building blocks of synchronisation of the electrical activity of the brain and reflect local processing within short-range connections, and when participants have to actively maintain the short-term memory for attended stimuli. An increase in gamma power during NHW tasks may reflect the expectancy during the task condition. However, the possibility of some contribution to increased gamma power by the contamination of EMG artefacts cannot be ruled out.
We selected a traditional beta band ranging from 14 to 30 Hz. Some researchers have further subdivided this band into two sub-bands beta-1 (12–20 Hz) and beta-2 band (20–30 Hz). Widespread increases in beta-2 power are associated with tasks requiring increased attention. Tasks requiring a high degree of focused attention are associated with higher activity in beta-2 and gamma bands. In the present study during the NHW task condition, increased power in the gamma band and frontal-central beta may be reflective of sustained allocation of attention. Literature findings suggest that differential power changes in beta-1 across the region of the electrodes play a role in unified perception and experience.
Significant power changes in beta and gamma bands during the task may also be reflective of motor coordination and binding of the various modalities. A decrease in the beta band power in the posterior leads during NDHW may be due to the wider inclusion range of traditional beta band (14–30 Hz) in our study.
Delta band activity is mainly seen during sleep. Delta wave is characteristic of slow-wave sleep. Thus, decrease power in the delta band during NDHW is suggestive of an aroused state during the odd handwriting task.
While farfetched, the predictions from our study indicate that writing traumatic experiences with NDHW may show benefits. The NDHW being an attentional demanding task may decrease the image vividness and corresponding emotional valence of the traumatic experience similar to how eye movement is thought to work in Eye Movement Desensitization and Reprocessing therapy. Moreover, the added component of writing can also benefit from the emotional disclosure of the experience.
Finally, the results of the study may be context specific to the type of participants selected and their perception of the writing task in the laboratory settings. Writing speed in words per minute was lesser in NDHW as compared to DHW, and this difference in speed and associated movement can also affect EEG.
| Conclusions|| |
NDHW task as compared to the DHW task has distinct EEG correlates suggestive of a stressed attentive mental state.
We would like to acknowledge and thank Dr. Nilotpal Chowdhury, Additional Professor, Department of Pathology and Laboratory Medicine, All India Institute of Medical Sciences Rishikesh, for his valuable contribution in making of box plots for the EEG analysis and representation.
Financial support and sponsorship
The present work was supported from the intramural grant (Number: IEC/IM/15/RC17) of AIIMS Rishikesh.
Conflicts of interest
There are no conflicts of interest.
| Electronic Supplementary Material|| |
The following Box Plots 1-4 represent differences of absolute power, relative power, mean power frequency and peak power frequency during non-dominant handwriting and dominant handwriting tasks. In the box-plots colour codes for different EEG, bands are in the following manner: Green = delta, Blue = theta, Yellow = alpha, Purple = beta, Orange = gamma. In the X-axis electrodes and bands' names are abbreviated using the following scheme: Electrodes name precedes the band name. Electrode name is full however for the different band initials are taken in the abbreviated form: For Example, 'FP1T' represents the comparison of the Theta band at the FP1 electrode.
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