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Research Article

A method for using video presentation to increase thevividness and activity of cortical regions during motor
imagery tasks
https://doi.org/10.4103/1673-5374.313058
Date of submission: September 3, 2020
Date of decision: September 29, 2020

Kengo Fujiwara1, 2, Masatomo Shibata1, Yoshinaga Awano1, Koji Shibayama1,
Naoki Iso3, Moemi Matsuo2, Akira Nakashima2, Takefumi Moriuchi2,
Wataru Mitsunaga2, Toshio Higashi2, *Date of acceptance: October 15, 2020

Graphical Abstract Changes in motor imagery (MI) vividness and hemodynamic changes

in the cerebral cortex during MI performance under the following three
conditions in near-infrared spectroscopy

Date of web publication: April 23, 2021

MI only

No video
Inverse video of other person’s dominant hand

AO + MI(other hand)

Inverse video of the participants own dominant hand
AO + MI(own hand)

Abstract
In recent years, mental practice (MP) using laterally inverted video of a subject’s non-paralyzed upper limb to improve the vividness ofpresented motor imagery (MI) has been shown to be effective for improving the function of a paralyzed upper limb. However, no studies have
yet assessed the activity of cortical regions engaged during MI task performance using inverse video presentations and neurophysiologicalindicators. This study sought to investigate changes in MI vividness and hemodynamic changes in the cerebral cortex during MI performance
under the following three conditions in near-infrared spectroscopy: MI-only without inverse video presentation (MI-only), MI with action
observation (AO) of an inverse video presentation of another person’s hand (AO + MI (other hand)), and MI with AO of an inverse video
presentation of a participant’s own hand (AO + MI (own hand)). Participants included 66 healthy right-handed adults (41 men and 25 women;mean age: 26.3 ± 4.3 years). There were 23 patients in the MI-only group (mean age: 26.4 ± 4.1 years), 20 in the AO + MI (other hand) group(mean age: 25.9 ± 5.0 years), and 23 in the AO + MI (own hand) group (mean age: 26.9 ± 4.1 years). The MI task involved transferring 1 cm × 1
cm blocks from one plate to another, once per second, using chopsticks held in the non-dominant hand. Based on a visual analog scale (VAS),
MI vividness was significantly higher in the AO + MI (own hand) group than in the MI-only group and the AO + MI (other hand) group. A main
effect of condition was revealed in terms of MI vividness, as well as regions of interest (ROIs) in certain brain areas associated with motor
processing. The data suggest that inverse video presentation of a person’s own hand enhances the MI vividness and increases the activity of
motor-related cortical areas during MI. This study was approved by the Institutional Ethics Committee of Nagasaki University Graduate Schoolof Biomedical and Health Sciences (approval No. 18121303) on January 18, 2019.
Key Words: action observation; cortical activity; inverse video presentation; mental practice; motor imagery; motor palsy; paralysis; recovery;
rehabilitation; stroke
Chinese Library Classification No. R493; R364; R741

Introduction
S e ve ra l m e t h o d s h ave b e e n e m p l o ye d to i m p ro ve
rehabilitation of paralyzed upper limbs post-stroke, including
motor therapy, functional electrical stimulation, repeatedmental practice (MP) with motor imagery (MI), action
observation (AO), and brain machine interfaces (BCIs) (Sharma
et al., 2006; Ruffino et al., 2017; Lin and Dionne, 2018;

Buchignani et al., 2019; Coscia et al., 2019). MP is a safe, costeffective strategy, with unlimited opportunities for practice(Kho et al., 2014). Most studies have shown that MP reduces
impairments and improves functional upper limb recovery
post-stroke (Nilsen et al., 2010), although those with motor
paralysis had significantly lower MI vividness than healthy
subjects (de Vries et al., 2011), and MP may not enhance
motor recovery in the early period post-stroke (Ietswaart et1

Department of Clinical Services, Nagasaki Rehabilitation Hospital, Nagasaki, Japan; 2Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki,
Japan; 3Department of Rehabilitation, Faculty of Health Sciences, Tokyo Kasei University, Tokyo, Japan*Correspondence to: Toshio Higashi, PhD, higashi-t@nagasaki-u.ac.jp.
https://orcid.org/0000-0002-4562-068X (Toshio Higashi)
How to cite this article: Fujiwara K, Shibata M, Awano Y, Shibayama K, Iso N, Matsuo M, Nakashima A, Moriuchi T, Mitsunaga W, Higashi T (2021) A method forusing video presentation to increase the vividness and activity of cortical regions during motor imagery tasks. Neural Regen Res 16(12):2431-2437.

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Research Articleal., 2011). A meta-analysis demonstrated promising benefitsof MP in post-stroke rehabilitation; however, the optimal
amount of MP, the method of video presentation, and theeffects of visual and kinesthetic MI, and imagery perspective
have not been elucidated (Nilsen et al., 2010).
Therefore, research to improve vividness of MI during video
presentation has attracted attention. Independent use of MI
and AO has been largely effective, and there is evidence thatthe two processes can elicit similar motor system activity
changes (Eaves et al., 2016). Recent neuroimaging studies
demonstrated enhanced cortical activity and improved
performance when AO and MI were performed concurrently(“AO + MI”), compared to either AO or MI being performed
alone (Vogt et al., 2013; Taube et al., 2015). Others haveassessed differences in visual perspectives used in AO,
showing that the first-person perspective is more effective
than the third-person perspective in inducing brain activity
in motor processing areas (Ruby and Decety, 2001, 2003).
AO of a subject’s own hand induces greater primary motor
area (PMA) activity than video presentation of anotherperson’s hand (Maeda et al., 2001). Clinically, however, somepatients are unable to move paralyzed upper limbs, making it
impossible to film their actions. Mirror therapy (MT) produces
muscular movement sensations in the paralyzed upper limb
by reflecting the movement of the non-paralyzed counterpart
using a mirror box (Altschuler et al., 1999), providing patientswith a “proper” visual input and giving the illusion that theaffected arm is moving unimpaired. A meta-analysis indicatedthat combining MT with another rehabilitation method toimprove upper extremity motor function post-stroke is better
than relying solely on monotherapies (Luo et al., 2020). In
recent years, MP using laterally inverted video presentationof a subject’s non-paralyzed upper limb to improve MI
vividness has been effective in improving paralyzed upper limb
function (Iso et al., 2016b); this effect was maintained after
therapy ended. Although MP with inverse video presentation
was effective in a single case intervention study, none havebeen conducted on a large number of subjects or assessed
cortical activity during MI processing using neurophysiologicalindicators, such as near-infrared spectroscopy (NIRS).
This study aimed to investigate changes in MI vividness
and hemodynamic changes in the cerebral cortex during
MI performance under the following three conditions innear-infrared spectroscopy: MI-only (without inverse video
presentation), MI with inverse video presentation of anotherperson’s hand, and MI with inverse video presentation of aparticipant’s own hand.

Participants and Methods
ParticipantsParticipants were right-handed, healthy adults with nohistory of neurological disease, respiratory disease, stroke,or dementia, who had provided informed consent prior toenrollment.
This study was approved by the Institutional Ethics Committeeof Nagasaki University Graduate School of Biomedical and
Health Sciences (approval No. 18121303) on January 18, 2019.
Recruitment was conducted from February 2019 to February
2020, and participants were informed about the study andsigned a consent form before participating in the study. All
study procedures were conducted in accordance with the
Declaration of Helsinki (World Medical Association, 2013).
Participants were administered the Edinburgh Handedness
Inventory (el Maniani et al., 2016). All were right-handed. The
total sample size required was determined statistically using
G* Power software (Erdfelder et al., 1996); a two-way analysis
of variance (ANOVA) yielded a power of 0.8 for a probabilityof error of 0.05 and an effect size of 0.4, giving a total sample

size requirement of 64 participants.
Participants were randomly assigned to one of the following
three groups using the software’s Excel function RAND: agroup that was not presented with a laterally inverted video
during the MI task (MI-only), a group that was presented
with an inverse video of another person’s hand (AO + MI
(other hand)), and a group that was presented with an inverse
video of the participant’s own hand (AO + MI (own hand)).
It has been reported that cerebral hemodynamics decreaseduring visualization of MI when subjects are fatigued or sleep
deprived (Suda et al., 2009). Participants were only allowed
to participate in the experiment after confirming that they did
not feel sleep deprived or fatigued.
The participants consisted of a total of 66 healthy, righthanded adults (41 men and 25 women; mean age: 26.3 ±4.3 years). There were 23 participants in the MI-only group(mean age: 26.4 ± 4.1 years), 20 in the AO + MI (other hand)group (mean age: 25.9 ± 5.0 years, and 23 in the AO + MI (ownhand) group (mean age: 26.9 ± 4.1 years).
Study design
The MI task involved transferring 1 cm × 1 cm blocks fromone plate to another every second using chopsticks held in
the non-dominant hand. The experimental protocol is shownin Figure 1. Before the MI task, the participants were asked
to practice transferring twenty 1 cm × 1 cm blocks between
plates based on the rhythm of a metronome (1 Hz; i.e., one
block per second) (Avanzino et al., 2015) using chopsticks
held in the dominant hand. As soon as each participant wasable to accomplish this, the MI task was performed to assess
MI vividness with chopsticks held in the dominant hand.
The subjective MI vividness was assessed using a Visual
Analogue Scale (VAS) (Malouin et al., 2008; Mizuguchi et al.,2019). This is a subjective assessment of how well the MI was
performed with the non-dominant hand, using chopsticks tocarry the block, and how vivid the MI was. Briefly, participants
were asked to mark a location on a 100 mm horizontal line
according to the vividness of the MI they experienced, thetwo ends of which were labeled “0 = no MI at all,” and “100 =very vivid MI.”In order to create a video to be presented during the MI
task, we used a smartphone (iPhone XS, Apple, Cupertino,
CA, USA) to film an individual moving blocks from plateto-plate using chopsticks held in the dominant hand. The
video was edited with a free application (SymPlayer, Masiyo
Tachikawa, Japan; iMovie, Apple) to create a presentation
video of a non-dominant hand moving a block from plate-toplate with chopsticks once per second (Figure 2). Two inverse
videos were created: one showing a block being moved using
chopsticks held in a participant’s own hand and the other withthe chopsticks held in another person’s hand. For the latter,
videos of the dominant hands of a man and a woman in their
60s were filmed. This was done purposefully so that the hands
were clearly different in age and of the opposite sex comparedwith the participants’ own hands.
In the experiment, the performances of the three randomly
assigned groups were compared. The use of chopsticks heldin the non-dominant hand was conducted once without
practice to evaluate performance, and the MI vividness wasassessed with chopsticks held in the non-dominant hand.
In this MI task, participants were instructed to performthe task using kinesthetic MI (Jackson et al., 2006), as if
they were actually performing the movement, but without
contracting the muscles. The participants were instructed
to maintain the same position and to try to relax without
thinking during the resting period. Immediately after the nearinfrared spectroscopy (NIRS) measurements were completed,
we assessed the subjective vividness of MI. During themeasurement, the MI-only group was instructed to look at

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the block on the plate with their eyes open, while the AO + MI
(other hand) and AO + MI (own hand) groups were instructed
to watch the video. The study is open-label, and no blinding
was performed.
NIRS measurements and analyses
The NIRS measurements were conducted using an optical
topography system (ETG4000, Hitachi Medical Corp.,
Tokyo, Japan). Participants were assessed in a quiet, private
evaluation room (room temperature: 24°C) at Nagasaki
Rehabilitation Hospital. The measurements were conductedwith the participant seated in a chair with both upper limbs
on the table; the table had chopsticks and a plate with ablock in front of it. The participants were seated with theirhips pressed to the back of the chair, their spines against thebackrest, the soles of their feet in contact with the floor, andboth upper limbs placed with the forearm and palm facing
down on the table.
The NIRS probes were placed in a 4 × 4 optode probe
configuration with respect to Cz, according to theinternational 10–20 method (eight incident lights and eightdetector fibers), resulting in a total of 24 channels, with aninter-optode distance of 3.0 cm (Okamoto et al., 2004), as
shown in Figure 3. The continuous wave NIRS system emitted
at two different wavelengths (625 and 830 nm) over the scalp,
and the relative change in absorption of the near-infrared
light were measured. These values are based on the modified
Beer-Lambert (Cope and Delpy, 1998; Obrig and Villringer,
2003; Baker et al., 2014), oxygenated hemoglobin (Oxy-Hb),and deoxygenated hemoglobin (Deoxy-Hb) concentrations.
It has been reported that there is no difference in the optical
path length of the left and right target region for this NIRS
probe (Cope and Delpy, 1998). NIRS measurements have beenreported to be non-invasive, safe, and reproducible (Ito et al.,
2000; Kakimoto et al., 2009).
The regions of interest (ROIs) were the sensorimotor cortex(SMC), the pre-motor area (PMA), the prefrontal cortex(PFC), the pre-supplementary motor area (pre-SMA), andthe supplementary motor area (SMA) (Figure 3). Based on
our previous studies, we have identified channels 18 and22 as recording above the left SMC, channels 21 and 24
recording above the right SMC, channels 9, 12, 13, and 16
above the SMA, and channels 2, 5, and 6 above the preSMA (Hatakenaka et al., 2007; Amemiya et al., 2010; Sagari
et al., 2015; Iso et al., 2016a). Channels 8, 11, and 15 wereabove the left-PMC, channels 10, 14, and 17 channels wereabove the right-PMA. Channels 1 and 4 were above the leftPFC, channels 3 and 7 were above the right PFC. Channels
19, 20, and 23 were not further analyzed (Hatakenaka etal., 2007; Amemiya et al., 2010; Sagari et al., 2015; Iso etal., 2016a). For the SMC, studies using NIRS experiments
have treated the sensory area and motor cortex as a whole(Hatakenaka et al., 2007; Amemiya et al., 2010; Sagari et al.,2015). The NIRS measurements were based on a block design,with three consecutive cycles of alternating 20 second MI
tasks and 30 second resting periods for each condition (Isoet al., 2016a). Since it has been reported in a previous NIRS
signal study of the rat brain that Oxy-Hb concentration is anindicator of changes in regional cerebral blood volume anda more sensitive parameter for measuring brain activation
than Deoxy-Hb (Hoshi et al., 2001), we adopted the change
in Oxy-Hb concentration occurring during the MI task as anindicator of regional changes in cerebral hemodynamics.
Both NIRS and functional magnetic resonance imaging (fMRI)
studies exhibited similar changes in cerebral hemodynamics
during the task, and the results are not affected by bloodflow of the skin (Sato et al., 2013). The data were analyzed
for changes in Oxy-Hb concentrations in each region in an
integral mode, which averages three cycles of data. For thebaseline measurement, the average of the 5 second period

immediately before and after the end of the task was used
(Marumo et al., 2009; Pu et al., 2012). Considering the time
until cerebral blood flow increased in accordance with neuralactivity, the usable performance data were collected from 5
seconds after the start of the task to 20 seconds after the endof the task (Bakalova et al., 2001; Figure 4).
The measured data were filtered using a 3 Hz high-pass filter,
which was 0.1 standard deviation above the wave analysis, as
previously reported (Iso, 2016; Matsuo et al., 2019). This filter
was used to exclude noise such as hyperactivity due to skinand blood dynamics, marking the channels with higher noiselevels (Takahashi et al., 2011). When obvious artifacts were
found, they were removed from the waveform. The average
waveform was calculated by integral analysis. In addition,
the Oxy-Hb values in each of the regions were converted toZ-scores for comparisons.
Statistical analysis
Statistical Package for the Social Sciences software (SPSS
version 22.0, IBM, Armonk, NY, USA) was used for statisticalanalysis. One-way analysis of variance (ANOVA) was conductedto compare the number of blocks transferred between dishes
using chopsticks with the non-dominant hand and VAS scoresamong the three video presentation groups outlined above.
A two-way ANOVA was conducted to compare Z-scores of the
ROI measurements in the brain regions (PFC, PMA, pre-SMA,
SMA, and SMC) and the three video presentation conditions.
Bonferroni post hoc test was used in all cases when warrantedby the results of the ANOVAs. All levels of significance wereset at P < 0.05.

Results
Comparison of MI performance using non-dominant hands
In the MI task, we evaluated the number of times participants
were able to transfer one block per second using chopsticks
with the non-dominant hand as a real action. The MI-onlygroup had a mean number of transfers of 9.3 (± 1.0), the AO+ MI (other hand) had a mean of 11.05 (± 1.3), and the AO +MI (own hand) had a mean of 9.6 (± 1.2), with no significant
difference between the groups (Figure 5).
MI vividness
MI vividness was assessed using a VAS after performing NIRS
measurements. A main effect of condition was observed; theMI-only group had a mean score of 48.8 mm (± 4.9), the AO +MI (other hand) had a mean score of 45.2 mm (± 6.0), and the
AO + MI (own hand) group had a mean score of 74.4 mm (±5.0). Furthermore, the post hoc test showed that MI vividness
was significantly lower in the MI-only and AO + MI (otherhand) groups compared to the AO + MI (own hand) group (P <0.01; Figure 6).
Activity of cortical areas during performance of the MI task
Over the time course of the MI task, each ROI we assessed
was activated in all three conditions: MI-only, AO + MI (otherhand) and AO + MI (own hand) groups (Figure 7). In the MI
task, we compared the Z-scores of the ROIs across the three
conditions to identify the best way to improve the vividnessof MI and the activation of cortical regions engaged by
MI task performance. The results showed a main effect ofcondition on ROIs measured in the assessed brain regions, but
no interaction was observed. For this reason, comparisons
between conditions and ROIs were conducted in follow-up
post hoc comparisons. The values were significantly higher inthe AO + MI (own hand) group than in the MI-only and AO +MI (other hand) groups (Figure 8). Significant differences were
found between ROIs, in particular the right PFC, right SMC,
and SMA (Figure 9).

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Research Article

Figure 1 ｜ Experimental protocol.
The experimental protocol consisted of three conditions: MI-only, or MI with
AO, with presentation of a video depicting the participant’s own hand (AO+ MI (own hand)) or another person’s (AO + MI (other hand)). AO: Action
observation; MI: motor imagery; NIRS: near-infrared spectroscopy; VAS: visual
analog scale.

Figure 4 ｜ Analysis of NIRS waveforms using the integral method.
The red curve represents one case of a false NIRS waveform. The average
waveforms were created by determining the mean of data measured ina three-cycle block design. The vertical axis shows Oxy-Hb concentration(mM•mm) and the horizontal axis shows the time course of one cycle oftask performance and rest periods. The average value of Oxy-Hb measured
between 5 and 20 seconds during the task (15 seconds, yellow line in the
averaged graph) was calculated. NIRS: Near-infrared spectroscopy; Oxy-Hb:
oxygenated hemoglobin.
MI tasks for the non-dominant hand
**
**

90

20

80
VAS score (mm)Actual movements using chopsticks(count)Figure 3 ｜ Diagram showing the channel configuration of the 4 × 4 optode
probe set.
The NIRS probes were arranged with reference to Cz according to theinternational 10–20 method. The red and blue circles indicate the locations of
the NIRS sensors and detectors, respectively. The regions of interest were the
SMC, PMA, PFC, pre-SMA, and SMA. Based on our previous studies, channels
18 and 22 were above the left SMC, and channels 21 and 24 were above theright SMC. Channels 9, 12, 13, and 16 were above the SMA, and channels
2, 5, and 6 were above the pre-SMA. Channels 8, 11, and 15 channels wereabove the left-PMA, and channels 10, 14, and 17 were above the right-PMA.
Channels 1 and 4 were above the left-PFC, and channels 3 and 7 channels
were above the right PFC. Channels 19, 20, and 23 were not further analyzed.
NIRS: Near-infrared spectroscopy; PFC: prefrontal cortex; PMA: pre-motorarea; pre-SMA: pre-supplementary motor area; SMA: supplementary motorarea; SMC: supplementary motor cortex.

Figure 2 ｜ Examples of laterally inverted video presented to a participantof either his or her own dominant hand or another person’s.
The video was recorded with a smartphone, and then the video was invertedwith free application software. Therefore, the inverse video showed a
depiction of chopsticks being held in a participant’s non-dominant hand as
small blocks were transferred from one plate to another at a rate of one persecond. For the condition where the videos depicted another person’s hand,the dominant hands of a man and a woman in their 60s were filmed to assess
differences in task performance between conditions.

10

70
60
50

0

MI-only

AO + MI(other hand)

AO + MI(own hand)

Figure 5 ｜ The average number of actual movements performed totransfer blocks from one plate to another once per second using chopsticks
held in the non-dominant hand for each condition.
The white bar shows data for the performance of the MI task without AO.
The gray and black bars show data for MI performance with AO, with a video
presentation of another person’s hand and the participant’s own hand,
respectively. A one-way analysis of variance was performed for the numberof blocks transferred from plate-to-plate using chopsticks with the nondominant hand in the MI-only group (23 participants), AO + MI (other hand)group (20 participants), and AO + MI (own hand) group (23 participants). Data
are expressed as the mean ± SE. AO: Action observation; MI: motor imagery.

40

MI-only

AO + MI(other hand)

AO + MI(own hand)

Figure 6 ｜ Vividness of MI evaluated for each condition (without AO or
with AO with a video depicting the participant’s own hand or anotherperson’s) using a VAS.
The vertical axis represents the value of MI vividness, where “0 = No MI at all,”and “100 = very vivid MI.” 23, 20, and 23 participants in the MI-only, AO + MI
(other hand), and AO + MI (own hand) group, respectively. Data are expressedas the mean ± SE. **P < 0.01 (one-way analysis of variance followed by
Bonferroni post hoc test). AO: Action observation; MI: motor imagery; VAS:
visual analog scale.

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Figure 7 ｜ Time course of changes in
Oxy-Hb concentration in various brain
regions during MI task performance.
The vertical axes show the changes in
Oxy-Hb concentration and the horizontal
axes shows the time courses. The solid
red line indicates the group performing
the MI with AO with a video presentationof the participant’s own hand (AO + MI
(own hand)), the solid blue line indicatesthe group performing the MI task with
AO with a video presentation of anotherperson’s hand (AO + MI (other hand)),and the dotted line indicates the groupperforming the MI alone without AO.
The gray shaded area indicates the timeover which the task was performed. The
time courses were averaged across all
participants. 23, 20, and 23 participantsin the MI-only, AO + MI (other hand),and AO + MI (own hand) group,
respectively. AO: Action observation;
MI: motor imagery; Oxy-Hb: oxygenatedhemoglobin; PFC: prefrontal cortex; PMA:
pre-motor area; SMC: supplementary
motor area.
Different methods of inverse video presentation**
Comparison between ROIs

**
0.5

1.0

*

Oxy-Hb (Z-score)

Oxy-Hb (Z-score)*0

MI only

AO + MI(other hand)

0.5

0AO + MI(own hand)

Figure 8 ｜ Z-score of all regions of interests (PFC, PMA, Pre-SMA, SMA,
and SMC) during MI of the upper extremity in the MI-only group (23participants), AO + MI (other hand) group (20 participants), and AO + MI
(own hand) group (23 participants).
The vertical axis indicates the value of Oxy-Hb in MI. With respect to thecomparison between conditions, the value in the AO + MI (own hand)group was significantly higher than that in the MI-only group and AO + MI
(other hand) group (two-way analysis of variance followed by Bonferroni
post hoc test). Data are expressed as the mean ± SE. **P < 0.01. AO: Action
observation; MI: motor imagery; Oxy-Hb: oxygenated hemoglobin; PFC:
prefrontal cortex; PMA: primary motor area; pre-SMA: pre-supplementary
motor; SMA: supplementary motor area; SMC: sensorimotor cortex.

Discussion
In this study, we investigated changes in the cerebral
hemodynamics of cortical regions, as well as vividness during
MI task performance.
MI vividness
As a means to increase the vividness of MI, research into
combining MI and AO has attracted attention, and studies
on video presentation have been performed. Such studies
using video presentations have shown differences based on
the perspective used in AO; a first-person perspective wasmore effective than a third-person perspective in inducing
activity in the somatosensory cortex of the brain (Ruby etal., 2003). Furthermore, studies have also shown that video
presentation of another person’s hand induces lesser changes
in brain activity in the PMA than when a person’s own handis presented (Maeda et al., 2001). In a study of the effect ofhand angle in the presented image, a medial-lateral effect wasobserved in that the responses were faster for images where
the third finger was rotated toward the midline of the body

LPFC

PreSMA RPFC

LPMA

SMA

RPMA

LSMC

RSMC

Figure 9 ｜ Oxy-Hb values in the MI task in 66 subjects were calculated by
Z-score for each ROI, and mean values of Z-score for each ROI.
Quantification of Oxy-Hb concentrations by regions of interest in certain brain
areas. The vertical axis indicates the Oxy-Hb concentrations during upper limb
MI task performance. Significant differences were found between the RPFC
and RSMC and SMA. 23, 20, and 23 participants in the MI-only, AO + MI (otherhand), and AO + MI (own hand) group, respectively. Data are expressed as themean ± SE. *P < 0.05 (one-way analysis of variance followed by Bonferroni
post hoc test). LPFC: Left prefrontal cortex; LPMA: left primary motor area;
LSMC: left sensorimotor cortex; MI: motor imagery; Oxy-Hb: oxygenatedhemoglobin; PreSMA: pre-supplementary motor area; ROI: region of interest;
RPFC: right prefrontal cortex; RPMA: right pre-motor area; RSMC: rightsensorimotor cortex; SMA: supplementary motor area.

than in images where it was rotated in the opposite direction,
and we inferred that an MI strategy was primarily employed(ter Horst et al., 2010; Nagashima et al., 2019). To summarize
what has been reported in previous studies, the video
presentation should ideally be shown from the first-person
perspective (kinesthetic MI) and should be of a subject’s own
hand, not another person’s hand. In addition, the hand in
the biomechanically constrained position is considered to be
more susceptible to MI. In this MI task, we filmed the imagesof hands of others and the participants’ own hands from thefirst-person, subjective perspective from the angle in which
the hands would be used in daily life. Therefore, we believethat MI vividness was significantly higher in the AO + MI (ownhand) group.
Activation of cortical regions in different video presentation
conditions
The greatest change in Oxy-Hb values was found in corticalregions for all three presentation conditions. Post hoc results
showed that Oxy-Hb concentrations in cortical areas weresignificantly higher in the AO + MI (own hand) group than in

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Research Article
the MI-only and AO + MI (other hand) groups. As mentioned
above, brain activity in the PMC was greater when AO was
performed using the video of a participant’s own handthan that of another person’s hand (Maeda et al., 2001).
Furthermore, in a study assessing concomitant AO + MI task
performance, dart throwing, basketball tossing, and golfing
tasks were performed under the AO-only, MI-only, and AO +MI conditions, with the results showing that the performanceof the AO + MI group was better than that of AO alone or MI
alone in all assessed tasks (Wright et al., 2018; Smith et al.,2019; McNeill et al., 2020a, b). From these studies, it could beconcluded that the conditions for better performance werethe use of the participant’s own hand video and the combined
use of AO + MI. Therefore, it can be presumed that the corticalarea was activated under the condition of own hand AO + MI
in the present experiment.
Activity in cortical areas during the MI tasks
In a study using NIRS to compare the activity of corticalregions based on changes in concentration of hemoglobin
during the finger tapping tasks with motor execution (ME)and kinesthetic MI, greater activation was observed for the
ME condition in the motor cortex, including in the PMA, SMA,
PMC, and SMC. Also, in the MI condition, more activation wasobserved in the motor cortex, including the SMC, which isconsistent with previous observations in studies using fMRI
(Batula et al., 2017; Wu et al., 2018). Therefore, we believethat the SMA and right SMC were active in the MI task in thisexperiment.
In an NIRS study using smartphone flick input tasks, the left
SMC, SMA, and right PFC exhibited significant changes incerebral blood flow dynamics as the task cycles progressed,
indicating motor learning over time. These changes in activity
likely reflect distinct aspects of acquisition of the motor task,such as increased finger momentum, motor inhibition, andvisual working memory in the left SMC, SMA, and right PFC,
respectively (Sagari et al., 2015). Therefore, the fact that theactivity of the right PFC region was higher than that of theright SMC and SMA in the present experiment may be dueto the fact that it was at an early stage of learning the MI
task. This NIRS study provided us with further informationon the activity of cortical regions during MI in different video
presentations. In contrast, the functional MRI studies allow
us to analyze a wide range of areas active during MI, except
for the cerebral cortex. Thus, our study could reveal basic
knowledge to inform research using MRI for developing MP
methodologies in the future.
Clinical application of MI using inverse video presentation
These results may provide a means of improving the vividnessof MI during rehabilitation in stroke patients, which has beena problematic issue with MP performance, as described inprevious studies. It has been reported that MP can be applied
to each stage of stroke rehabilitation, permitting patientsto begin training earlier, even in states of flaccid paralysis(Zimmermann-Schlatter et al., 2008; Tong et al., 2017).
This indicates that MP can be performed in clinical settings,
regardless of the severity of motor palsy affecting the upper
limb.
Most studies have shown that MP reduces impairments
and improves functional upper limb recovery post-stroke.
However, it has been noted that further research is neededon the effects of appropriate amounts, methods of video
presentation, and video perspectives (Nilsen et al., 2010). In
this study, we were able to solve the problem of the video
presentation method and the viewpoint of the images. Also,
although the MI task used in this study was performed on theupper extremities, there are reports of improved performancein the lower extremities, as well, with combined AO + MI
treatment (Villiger et al., 2013). With regard to the future

prospects of the use of NIRS, a systematic review showed thatNIRS is a viable tool to detect functional differences between
patients with chronic neurological diseases and older adults(Bonilauri et al., 2020). Therefore, we consider NIRS to be oneof the effective methods to objectively evaluate brain activity.
Along with the present results, this supports the utility of
inverse video presentation when performing MP with AO +MI in patients with stroke with motor palsy of the upper orlower limbs. We can also use NIRS to measure brain activity incortical regions of AO + MI using an inverted video of the nonparalyzed upper and lower limbs, which can be communicatedusing objective data.
Limitations
In the present study, healthy adults performed an MI taskusing chopsticks held with the non-dominant hand. However,
not all tasks that are difficult to perform in the non-dominant
hand result in the same changes in cortical area activity. In thepresent MI task, there was no interaction between the MIonly, the AO + MI (other hand), and the AO + MI (own hand)conditions and ROIs. From this, it was not clear which regions
were more active under the AO + MI (own hand) condition.
In this study, the only neurophysiological indicator used toanalyze the activity of cortical regions, mainly motor-relatedareas, is NIRS. Thus, the activity in other cortical areas is not
yet well known; in addition, it remains unclear whether otherneurophysiological indicators such as MRI scans may show
similar results as those which were observed in this study.
Conclusions
The group that was presented with the video of theparticipant’s own hand exhibited significantly higher values
for MI vividness and significantly greater activation incortical areas than the MI-only group and the group thatwas presented with video of another person’s hand. In thisstudy, we presented an inverse video of the participant’s own
hand in an MI task that is difficult to perform with the nondominant hand. Performing AO + MI with video of a subject’s
own hand can increase the vividness of MI and activate motor
areas during the MI task to improve post-stroke rehabilitation.
Thus, to improve rehabilitation after stroke, AO + MI using the
subject’s own hand images may improve the clarity of MI and
activate the motor cortex during the MI task, and furthermore,practicing this may improve performance.
Author contributions: Study concept and design: KF, MS, YA, KS, NI, MM,
AN, TH and WM. Experiment implementation: KF, MS, YA, KS, and TH.
Data analysis: KF, TM and TH. Manuscript preparation: KF and TH. All
authors approved the final version of this study.
Conflicts of interest: The authors declare that they have no conflicts ofinterest.
Financial support: None.
Institutional review board statement: This study was approved by theInstitutional Ethics Committee of Nagasaki University Graduate School of
Biomedical and Health Sciences (approval No. 18121303) on January 18,
2019. All experimental procedures were conducted in accordance with the
Declaration of Helsinki (World Medical Association, as amended 2013).
Declaration of participant consent: The authors certify that they haveobtained all appropriate participant consent forms. In the forms theparticipants have given their consent for their images and other clinicalinformation to be reported in the journal. The participants understandthat their names and initials will not be published and due efforts will bemade to conceal their identity.
Reporting statement: This study followed the STrengthening theReporting of OBservational studies in Epidemiology (STROBE) statement.
Biostatistics statement: The statistical methods of this study werereviewed by the biostatistician of Nagasaki University in Japan.
Copyright license agreement: The Copyright License Agreement has beensigned by all authors before publication.
Data sharing statement: Datasets analyzed during the current study areavailable from the corresponding author on reasonable request.
Plagiarism check: Checked twice by iThenticate.
Peer review: Externally peer reviewed.

2436 ｜NEURAL REGENERATION RESEARCH｜Vol 16｜No. 12｜December 2021

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C-Editor: Zhao M; S-Editor: Li CH; L-Editor: Song LP; T-Editor: Jia Y

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