Research Article

Comparison of cerebral activation between motor
execution and motor imagery of self-feeding activity
Received: November 20, 2019

Moemi Matsuo1, 2, Naoki Iso3, Kengo Fujiwara1, 4, Takefumi Moriuchi1,
Daiki Matsuda1, 5, Wataru Mitsunaga1, 6, Akira Nakashima1, Toshio Higashi1, *Peer review started: December 12, 2019

Abstract

Accepted: June 2, 2020

Motor imagery is defined as an act wherein an individual contemplates a mental actionof motor execution without apparent action. Mental practice executed by repetitive
motor imagery can improve motor performance without simultaneous sensory input orovert output. We aimed to investigate cerebral hemodynamics during motor imagery andmotor execution of a self-feeding activity using chopsticks. This study included 21 healthy
right-handed volunteers. The self-feeding activity task comprised either motor imagery
or motor execution of eating sliced cucumber pickles with chopsticks to examine eightregions of interest: pre-supplementary motor area, supplementary motor area, bilateralprefrontal cortex, premotor area, and sensorimotor cortex. The mean oxyhemoglobin
levels were detected using near-infrared spectroscopy to reflect cerebral activation. The
mean oxyhemoglobin levels during motor execution were significantly higher in the left
sensorimotor cortex than in the supplementary motor area and the left premotor area.
Moreover, significantly higher oxyhemoglobin levels were detected in the supplementary
motor area and the left premotor area during motor imagery, compared to motor
execution. Supplementary motor area and premotor area had important roles in the motor
imagery of self-feeding activity. Moreover, the activation levels of the supplementary
motor area and the premotor area during motor execution and motor imagery are likely
affected by intentional cognitive processes. Levels of cerebral activation differed in someareas during motor execution and motor imagery of a self-feeding activity. This study wasapproved by the Ethical Review Committee of Nagasaki University (approval No. 18110801)
on December 10, 2018.
Key Words: Activities of Daily Living; brain function; hemodynamics; imagery(psychotherapy); mental practice; motor cortex; near-infrared neuroimaging; neuroscience;
rehabilitation; spectroscopy

https://doi.org/10.4103/1673-5374.295333

Published online: October 9, 2020

Chinese Library Classification No. R445; R741.04; R742

Introduction
Motor imagery (MI) is an act wherein an individual
contemplates mental action of motor execution without
obvious action (Decety, 1996; Blefari et al., 2015). Mental
practice (MP), executed by repetitive MI, aims to improve
motor performances without any simultaneous sensory
input or overt output (Decety and Ingvar, 1990). MP cancomplement physical exercise because it can be undertaken
by patients who are in acute recovery, wherein they cannot
conduct motor execution (ME) due to reduced voluntary
movement post-injury. Moreover, MP can be executedsafely anywhere and has been shown to improve upper
limb function after stroke (Park et al., 2018). In addition, a
combination of MP and physical practice can improve motor
performance more than physical practice alone (Wriessnegger
et al., 2014).
The effects of MP have been demonstrated by many studies
that compared cerebral activity during ME and MI, andreported that near-identical brain areas were activated during

ME and MI (Jeannerod, 1995; Decety, 1996; Wriessnegger etal., 2008; Wang et al., 2014). A meta-analysis of activationlikelihood estimation suggested that MI relies on a network
involving motor-related regions, including the premotor
area (PMA), supplementary motor area (SMA), parietal
lobule, cerebellum, and basal ganglion, which supports
the view that ME and MI are very similar processes (Hetuet al., 2013). However, most of these reports used simple
movements as tasks; only a few reports, to date, have usedcomplex movements that are essential in clinical scenarios inrehabilitation medicine.
A thorough understanding of cerebral hemodynamics during
MI of complex movements is essential to use MP in relevant
clinical scenarios. Cerebral hemodynamics during MI of theself-feeding activity task, one of the activities of daily living,remain unclear. We selected self-feeding as the MI task
because it is frequently used for stroke patients undergoingrehabilitation, and it is a complex activity that engages various
movements, including arm and finger movements, chewing

1

Unit of Medical Science, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan; 2Center for Child Mental Health Care and Education,
Nagasaki University, Nagasaki, Japan; 3Department of Rehabilitation, Faculty of Health Sciences, Tokyo Kasei University, Saitama, Japan; 4Zeshinkai General
Incorporated Association, Nagasaki Rehabilitation Hospital, Nagasaki, Japan; 5The Japanese Red Cross, Nagasaki Genbaku Hospital, Nagasaki, Japan; 6Unit of
Rehabilitation, Nagasaki University Hospital, Nagasaki, 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: Matsuo M, Iso N, Fujiwara K, Moriuchi T, Matsuda D, Mitsunaga W, Nakashima A, Higashi T (2021) Comparison of cerebral activation
between motor execution and motor imagery of self-feeding activity. Neural Regen Res 16(4):778-782.

778 ｜NEURAL REGENERATION RESEARCH｜Vol 16｜No.4｜April 2021

and swallowing, and using cutlery (e.g., chopsticks). Therefore,
MP with MI of self-feeding is likely beneficial for patients withdominant-hand hemiplegia.
In our previous research, we investigated differences incerebral hemodynamics between self-feeding MI using
chopsticks with the right and left hands. However, we did notcompare the ME and MI of the task (Matsuo et al., 2019).
Among the previous studies involving tool-use MI, a functional
magnetic resonance imaging-based assessment indicatedthat near-identical cerebral regions were excited with either
tool-use ME or MI, although differences in excitability wereobserved (Higuchi et al., 2007). However, a study of nearinfrared spectroscopy (NIRS) suggested that MI task with tool
use can significantly increase oxyhemoglobin (oxyHb) levels
in motor-related cerebral areas than MI task without tooluse (Oikawa et al., 2017). Thus, our main objective was toinvestigate the cerebral hemodynamics associated with the MI
and ME of a self-feeding activity with chopsticks.

Subjects and Methods
Subjects
This observational study recruited 21 right-handed volunteers,
14 females and 7 females, aged 29.4 ± 10.2 years, from
Nagasaki University via recruitment advertisement. The righthandedness of participants was confirmed by the Edinburgh
Handedness Inventory (Oldfield, 1971). The safety regulationsof this research work were explained to all participants. All
participants assured that none of their identifying information
would be disclosed. Therefore, all participants provided
written informed consent for study participation. Additional
informed consent was also obtained from all individual
subjects whose identifiable information was included in thisstudy. None of the study participants had a history of major
physical disorders, including neurological illness, brain injury,
or psychiatric illnesses. This study was approved by the
Ethical Review Committee of Nagasaki University (approvalNo. 18110801) on December 10, 2018 and was performed inaccordance with the principle of the Declaration of Helsinki(World Medical Association, 2013) and its later amendments.
Experimental Protocol
Task
The participants were required to eat sliced cucumber
pickles with the right hand using chopsticks, which involve
actions including reaching to the mouth, chewing, andthen swallowing. Participants were asked to execute serial
movements of the task within 20 seconds. These movements
were conducted under ME and MI conditions.
All participants practiced each movement before theexperimental session until they could undertake the task
sufficiently well during the experiment. The participants
checked the actual slices of cucumber pickles on a dish withchopsticks, and repeated the task practice while monitoring
the time required to perform it using a stopwatch.
Experimental setup
The participants sat on a chair with a backrest in a silent room.
They placed their forearms in an intermediate and relaxed
position on the table and were instructed to carry out theactual self-feeding activity with their eyes open during the
ME condition, and to imagine the task with their eyes closed
without other movements during the MI condition. Moreover,they were instructed not to move their head, to maintain thesame posture as much as possible, and not to speak during
both conditions throughout the experiment. In addition, they
were asked to maintain the same posture and relax without

thinking for the remainder of the session.
After the MI task, the visual analog scale was used toinvestigate MI vividness, which has been previously described(Lotze et al., 2003; Lotze and Halsband, 2006; Malouin etal., 2008; Ikeda et al., 2012). All participants assessed thevividness of the MI task, which they marked on the visual
analog scale: range from 0 to 100 mm (0%; none, 100%; very
vivid).
NIRS measurements
Cerebral activation was investigated using the NIRS,
which has been applied in clinical scenarios. The levels of
oxyHb, deoxygenated hemoglobin, and total hemoglobin
were measured with the 24-channel ETG-4000 (Hitachi
Medical Co., Tokyo, Japan). The 24-channel ETG-4000 has
8 emitters and detectors, and comprises 4 × 4 probe sets.
Every probe was positioned 3 cm away from each otherand placed in accordance with the international 10–20
electroencephalography placement method (Okamoto etal., 2004). Then, Cz was marked as a reproducible marker inthe probes, as described previously (Okamoto et al., 2004;
Saimpont et al., 2015; Figure 1).
Eight regions of interests (ROIs) were examined: the presupplementary motor area (Pre-SMA), SMA, the bilateralprefrontal cortex (PFC), PMA, and sensorimotor cortex (SMC;
Figure 1). The activation of the Pre-SMA, SMA, and left andright PFC (L-PFC/R-PFC) was detected by channels 2, 5, 6,
and 9; channels 9, 12, 13, and 16; channels 1 and 4; andchannels 3 and 7, respectively. The activation of the left andright PMA (L-PMA/R-PMA) was detected by channels 8, 11,
and 15 and by channels 10, 14, 17, respectively, whereas
the activation of the left and right SMC (L-SMC/R-SMC) was
detected by channels 18 and 22, and by channels 21 and 24,
respectively (Hatakenaka et al., 2007; Sagari et al., 2015; Isoet al., 2016; Matsuo et al., 2019). The levels of oxyHb anddeoxygenated hemoglobin were calculated based on thelevels of hemoglobin detected by the modified Beer–Lambertapproach (Cope and Delpy, 1988; Obrig and Villringer, 2003).
After completion of the task practice session, NIRS
measurements were taken with three cycles of 20-second task
and 30-second rest in a blocked design (Figure 2) as described
previously (Iso et al., 2016; Matsuo et al., 2019). The blocked
design was used in each condition; thus, there were threecycles of the task each under MI and ME conditions. All
participants were assessed under each condition, with thecondition order (ME or MI) equilibrated. The participants were
instructed to execute or imagine eating a pickle once for a
20-second duration. Under the MI condition, the participants
were instructed to imagine they were eating the pickle. Thus,
this study involved the participants imagining a first-personview with kinesthetic imagery, which included sounds. The
timing of the task or rest was indicated by the words “start” or“stop”, spoken by the examiner.
Data analysis
Changes in the concentration of oxyHb were used to indicate
brain activation during tasks, because oxyHb is the mostsensitive parameter for detecting cerebral activity (Hoshi etal., 2001). We used the 5-second moving average method to
exclude short-period motion artifacts from the analyzed data,
and analyzed the data using the integral mode to calculate
average values.
For data analysis, we considered the data measured at 5
seconds before the task as the pre-task baseline, and the datameasured at 5 seconds after the task was completed as the

NEURAL REGENERATION RESEARCH｜Vol 16｜No.4｜April 2021｜779

Research Article
post-task baseline; thereafter, we applied linear fitting to thedata between these baselines. Moreover, we excluded thefirst 5 seconds of tasks from the analyses to ensure the data
were unaffected by the time required for cerebral activation
to occur. Thus, we included the last 5 to 20 seconds of thetask duration for analyses (Figure 3). Next, we calculated datafrom three cycles with the signal-averaging technique. The
3-Hz high-pass filter of the wave analysis marked channels
that included high noise levels to exclude noise such as
hyperactivation caused by skin and blood dynamics (Takahashi
et al., 2011).

Statistical analysis
The mean oxyHb levels under the ME and MI conditions
were calculated, and data were converted to the Z-score. We
obtained mean 0 and up to 1 standard deviation (Tsunashima
and Yanagisawa, 2009), also the higher score indicates higher
oxyHb, through calculations undertaken in the ETG-4000. The
two-way repeated measures analysis of variance (ANOVA) wasused taking “ROIs” (Pre-SMA, SMA, L- and R-PFC, L- and R-PMA,
as well as L- and R-SMC) and “conditions” (ME and MI) as
factors to compare differences in the Z-scores. Furthermore,
the Bonferroni test was used to compare the Z-scores. SPSS
22.0 (IBM, Tokyo, Japan) was used for data analysis. A level of
P < 0.05 was considered statistically significant.

Results

Figure 1 ｜ NIRS probe sets.
The NIRS probes were placed in the similar way of the international 10–20
electroencephalography placement method. The Cz was marked as a
replicable point in the probes. The two pairs of black circled numbers 1–18
indicate optode probes: emitters and detectors. The numbers 1–24 indicate
channels that consist of optode probes. The Pre-SMA, SMA, PFC, PMA, and
SMC were examined. NIRS: Near-infrared spectroscopy; PFC: prefrontal
cortex; PMA: pre-motor area; Pre-SMA: pre-supplementary motor area; SMA:
supplementary motor area; SMC: supplementary motor cortex.

Figure 2 ｜ Experimental protocol.
The experiment was performed with a blocked design consisting of threecycles of the 20-second task and the 30-second rest. The task practice session
was finished before the NIRS measurements were started. NIRS: Near-infrared
spectroscopy.

Figure 3 ｜ Method of calculating OxyHb changes.
Linear fitting was used to the periods of the pre-task (blue arrow) to posttask (green arrow). The pink background is the task duration, and the skincolor background is the rest duration. The vertical axis indicates the oxyHb
levels (mMmm), and the horizontal axis indicates the time of one cycle. The
first 5-second duration of the task was excluded, and the final 5–20 seconds
duration of the task was used for the analyses.

In addition, surface electromyography was applied to ensurethat participants did not move under the MI condition. The
surface electromyography electrodes were positioned over
the right masseter and the first dorsal interosseous musclesof the right hand, and signals were amplified and filtered at 5
to 3 kHz of bandwidth with the Neuropack Sigma MEB-5504
digital signal processor (Nihon Kohden, Tokyo, Japan). An A/D
converter transferred the signals to a PC for offline analysis(PowerLab16/30, AD Instruments, Sydney, Australia). During
surface electromyography measurements, we ensured thatthe finger and face postures of all participants were immobile,
without overt muscle movement. Therefore, all the data wereused for analyses.

Handedness and the vividness of MI
The mean ± SD Edinburgh Handedness Inventory score of allparticipants was 88.6 ± 12.0; in addition, 76% of participants
answered “always using the dominant hand” to thequestion relevant to self-feeding. Furthermore, none of theparticipants answered “always using the non-dominant hand”.
All participants self-reported that they have used chopsticks
with their dominant hand nearly every day for approximately
20 years or more, indicating that they had a proficient levelof skill in using chopsticks. Moreover, the mean visual analog
scale value (vividness of the MI task) of all participants was
73.1 ± 10.4 mm.
Comparison of cerebral hemodynamics between ME and MI
Figure 4 shows the grand average waveforms of oxyHb during
tasks for all subjects. During tasks, the oxyHb levels increased
over the baseline value in most ROIs. The significant main
effect of “ROIs” (F(7,14) = 4.918, P = 0.000, η2 = 0.193), and asignificant “ROIs *conditions” interaction (F(7,14) = 2.221, P =0.036, η2 = 0.114) were revealed by two-way ANOVA, whereas
there was no main effect of “conditions” (F(1,20) = 0.002, P= 0.968, η2 = 0.000). Based on the main effect of ROI andinteraction of ROI*conditions, we assessed Z-score differenceswith the Bonferroni test, and found that the Z-score under
the ME condition was significantly higher in the L-SMC thanin the SMA (P = 0.033) and L-PMA (P = 0.039), whereas there
were no apparent differences between ROIs during the MI.
Furthermore, significantly higher oxyHb levels were detectedin the SMA (P = 0.017) and L-PMA (P = 0.012) during MI, in
contrast to the levels that were observed during the ME;
however, there were no apparent differences in the other
ROIs (Figure 5).

Discussion
In this study, we investigated the cerebral hemodynamics
during ME and MI of a self-feeding activity with chopsticks
using NIRS. A previous study using a simple finger-tappingtask suggested that increases in oxyHb levels in the SMA andPMA during MI were similar to those observed during ME(Iso et al., 2016), although another study that used the sametask suggested that the PFC was more activated during MI
than during ME, whereas the left SMA was more activatedduring ME than MI (Wu et al., 2018). Furthermore, an fMRI
study suggested that stronger cerebral activations wereobserved in the PMA and the SMA during ME than during
MI of swallowing, which is a simple task (Kober et al., 2019).
As such, many previous MI studies using simple tasks havesuggested that near-identical brain areas are activated during
MI and ME, although the brain areas were more activatedduring ME than during MI. However, our results suggested
that, although MI and ME of self-feeding activity as a tooluse complex task activated mostly overlapping cerebral

780 ｜NEURAL REGENERATION RESEARCH｜Vol 16｜No.4｜April 2021

nerve activation levels; however, low activity can also imply
better task proficiency (Debarnot et al., 2014).
All participants were familiar to the self-feeding activity using
chopsticks with the right hand, which was used in the present
study because they had executed the task nearly every day
for at least 20 years. Thus, the task was easy for them andparticipants could carry it out expertly and did not need tointentionally implement the cognitive process. Thus, SMA
and PMA activation might have been reduced during ME, andthe differences in the SMA and PMA activation between ME
and MI might be related to a need for intentional cognitive
processes. Overall, our results further expand the knowledge
with regard to MI and may be useful in developing MP in
rehabilitative fields.
Figure 4 ｜ OxyHb time course.
All participants’ grand average wave forms of oxyHb during tasks are shown.
The vertical axis indicates the oxyHb levels, and the horizontal axis indicatestime. The blue line is oxyHb levels of the MI condition, and the red line is
oxyHb levels of the ME condition. The gray background is the task duration(5–25 seconds), and the white background indicates the rest duration (25–50
and 0–5 seconds). L: Left; ME: motor execution; MI: motor imagery; oxyHb:
oxyhemoglobin; PFC: prefrontal cortex; PMA: pre-motor area; Pre-SMA: presupplementary motor area; R: right; SMA: supplementary motor area; SMC:
supplementary motor cortex.

*

Research limitations
The participants were all right-handed volunteers who wereskilled in the use of chopsticks; therefore, it is unclear whether
our results can be generalizable to individuals unskilled in theuse of chopsticks, left-handed people, or patients with motor
diseases or disabilities. Furthermore, the task was limited
to a self-feeding activity; thus, it is unclear whether cerebral
hemodynamics during other complex tasks are similar to
those observed during the self-feeding activity. In addition,
our study only included a small number of participants.
Because of these limitations, future studies should include
more subjects with various conditions for MP, as well as lefthanded subjects, and investigate cerebral activation during
various tasks, including other complex tasks to confirm theeffectiveness of MP in rehabilitation.

*

Figure 5 ｜ Comparison of cerebral Hemodynamics between ME and MI.
The oxyHb signal data were expressed as the mean ± SD and analyzed using
two-way ANOVA with the Bonferroni test. The blue line is the oxyHb Z-score of
the MI condition, while the red line is the oxy-Hb Z-score of the ME condition.
The oxyHb levels were significantly higher during MI than during ME in the
SMA and the L-PMA. Bonferroni test *P < 0.05 (n = 21). ANOVA: Repeatedmeasures analysis of variance; L: left; ME: motor execution; MI: motor
imagery; oxyHb: oxyhemoglobin; PFC: prefrontal cortex; PMA: pre-motorarea; Pre-SMA: pre-supplementary motor area; R: right; SMA: supplementary
motor area; SMC: supplementary motor cortex.

areas, these activations were not identical, with MI inducing
higher activation levels in some areas compared to ME. The
Z-scores during ME were significantly higher in the L-SMC
than in the SMA and the L-PMA. Moreover, cerebral activationdifferences were observed between ME and MI conditions,with significantly higher oxyHb levels detected under the MI
condition than the ME condition in the SMA and the L-PMA;
these results were not identical to those reported with simple
MI tasks.
The SMA and PMA are known to play roles in motor planning,motor preparation, and motor learning (Hoshi and Tanji, 2004;
Nakayama et al., 2008; Wang et al., 2016). MI is equivalent to
the motor planning and preparation for ME (Tong et al., 2017).
A previous study suggested that SMA activation was mainly
observed in MI, with partially overlapping activation during
ME and MI (Stephan et al., 1995). Moreover, other studies
suggested that SMA activation affected the inhibition of the
SMC during MI (Di Rienzo et al., 2014; Gao et al., 2014). Someneurons of the PMA may be solely involved in the MI task
(Raffin et al., 2012); the PMA serves as a hub that connects
cognition and motor activities (Hanakawa, 2011). Both SMA
and PMA activations during ME and MI are affected by thetask experiences and the task-proficiency levels; moreover,they are dependent on the task specificity and are changeable
by the degree of practice. Thus, low activity may indicate low

Conclusion
Levels of cerebral activation differed in some areas during ME
and MI of a self-feeding activity. SMA and PMA have importantroles in the MI of self-feeding activity. Furthermore, levelsof activation in the SMA and PMA during ME and MI wereaffected by the necessity of intentional cognitive processes.
Our findings expand the knowledge base of MI, and provides
further understanding of the use of MI in rehabilitation for
activities of daily living. Therefore, this study might contributeto the application of MP in clinical situations.
Acknowledgments: We would like to thank a statistician Dr. Sumihisa
Honda for supporting and giving us knowledge about statistical analysis.
Author contributions: MM contributed to the research concept,
design, definition of intellectual content, literature search, experimental
studies, data acquisition and analysis, statistical analysis, manuscript
preparation, editing, and review. NI and KF contributed to the researchconcept, design, definition of intellectual content, literature search, andexperimental studies. TM contributed to definition of intellectual content,
statistical analysis, manuscript editing and review. DM contributed toexperimental studies. WM and AN contributed to literature search. TH
contributed to the research concept, design, definition of intellectual
content, literature search, statistical analysis, manuscript editing andreview. All authors approved the final version of this paper.
Conflicts of interest: The authors declare that they have no conflicts ofinterest.
Financial support: None.
Institutional review board statement: This study was approved by
the Ethical Review Committee of Nagasaki University (approval No.
18110801) on December 10, 2018 and was performed in accordance withthe principles of the Declaration of Helsinki (World Medical Association,2013) and its later amendments.
Declaration of participant consent: The authors certify that they haveobtained all appropriate participant consent forms. In the form 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 the

NEURAL REGENERATION RESEARCH｜Vol 16｜No.4｜April 2021｜781

Research Article
Reporting of OBservational studies in Epidemiology (STROBE) statement.
Biostatistics statement: The statistical methods of this study werereviewed by the biostatistician of Sumihisa Honda, Nagasaki University inJapan.
Copyright license agreement: The Copyright License Agreement has
been signed 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.
Open access statement: This is an open access journal, and articles are
distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak,
and build upon the work non-commercially, as long as appropriate credit
is given and the new creations are licensed under the identical terms.
Open peer reviewer: Ryota Nishiyori, University of Southern California,
USA; Jianjun Sun, Third Hospital of Peking University, China.
Additional file: Open peer review report 1.

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782 ｜NEURAL REGENERATION RESEARCH｜Vol 16｜No.4｜April 2021

P-Reviewers: Nishiyori R, Sun J; C-Editor: Zhao M; S-Editor: Li CH; L-Editor:
Song LP; T-Editor: Jia Y