Failure of tDCS to impact militarised threat-detection in a military cohort
Nicholas S. Willmota,乙, Li-Ann Leowb, Hannah L. Filmerb, Paul E. Duxb
aDepartment of Defence, 爱丁堡, 澳大利亚
bSchool of Psychology, The University of Queensland, St Lucia, 澳大利亚
通讯作者: Nicholas S. Willmot (nicholas.willmot1@defence.gov.au)
抽象的
Transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, has become a focus of military
organisations due to its reported positive effects on cognitive and motor performance. 然而, the majority of tDCS
research in this space is conducted with civilian participants and/or uses abstract tasks. 此外, of the small subset
of studies that have used military participants or military-relevant tasks, few have employed both, and none with a con-
siderable sample size. 这里, we extend on previous work by exploring whether tDCS to the right inferior frontal gyrus
(rIFG) enhances the performance of a large military cohort during a militaristic threat-detection task. 98 participants aged
之间 18 和 45 were randomly assigned to one of three conditions: (1) 2 mA anodal tDCS to the rIFG; (2) Sham
stimulation to the rIFG; 或者 (3) 2 mA anodal tDCS to the visual cortex (V1). Participants viewed serially presented, virtually
generated militaristic images, and responded Yes/No via keypress to a threat being present. tDCS was applied for
25 min during the first two training blocks of the 50 min task. Results showed evidence for the null hypothesis: tDCS did
not influence mean accuracy or reaction time across the task, in contrast to previous work. We discuss possible meth-
odological and population factors that may explain why previously published effects of tDCS were not reproduced.
关键词: tDCS, 前额皮质, visual search, 军队, cognitive performance
1. 背景
An individual’s ability to perceive and detect targets within
their visual field is vital in military operations, where per-
sonnel may find themselves searching for a hidden target
(例如, via camouflage) from the cockpit of an aircraft, 这
bridge of a ship, or the turret of a tank. While personnel in
these roles receive extensive training, including on optimal
visual search tactics, there exists considerable interest in
interventions that may boost generalised performance
during sustained visual search tasks.
Transcranial direct-current stimulation (tDCS), a form
of non-invasive brain stimulation, is one such interven-
tion that already features heavily in military-related
research where it has been shown to combat fatigue
(McIntire et al., 2017), augment working memory
(Nelson et al., 2016), enhance navigational efficiency
(Brunyé et al., 2014) and most importantly, for the pres-
ent work, improve performance in visual search tasks
(Clark et al., 2012; Falcone et al., 2012; Nelson et al.,
2015). 的确, Clark and colleagues (2012) used fMRI to
identify the brain regions involved when participants
attempted to identify threats in a series of militarized
图片. Brain scans were taken as the participants
cycled through the threat images, with these scans
showing that two regions, the right inferior frontal gyrus
(rIFG) and right parietal cortex, were consistently acti-
vated in participants as they progressed from novice to
intermediate performance. In the next stage of their
学习, the authors applied tDCS at varying intensities to
these two regions during the first half of the threat-
检测任务 (for a period of 25 min). Participants who
已收到: 6 六月 2023 公认: 6 六月 2023 Available Online: 19 七月 2023
Imaging Neuroscience, 体积 1, 2023
https://doi.org/10.1162/imag_a_00004
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© 2023 麻省理工学院. 根据知识共享署名发布 4.0 国际的 (抄送 4.0) 执照. Research ArticleN.S. Willmot, L.-A. Leow, H.L. Filmer et al.
Imaging Neuroscience, 体积 1, 2023
received 2 mA tDCS to the rIFG (F10) or the right parietal
cortex (P4) showed up to 50% greater improvement in
accuracy than those receiving 0.6 mA or sham stimula-
的. Subsequent studies by the same group suggest
that this effect of rIFG tDCS may have been due to
increases in alerting attention (Coffman et al., 2012) 和
perceptual sensitivity (Falcone et al., 2012) brought on
by tDCS. Such results are consistent with the theorised
role of the right inferior frontal cortex in attentional
(Chong et al., 2008; Hampshire et al., 2010) and inhibi-
tory control (Aron et al., 2004, 2014), with several other
inhibition
studies also finding
(Jacobson et al., 2011) and regulation (Herrmann et al.,
2016) following similar rIFG tDCS protocols. 然而,
tDCS enhancement research has repeatedly faced criti-
cism for its lack of reproducible results due to inade-
quate methodological designs and limited sample sizes
(Hill et al., 2016; Horvath et al., 2016). 更远, it has
been previously demonstrated that an individual’s level
of skill and ability can significantly impact their response
to paired tDCS and training (Brunyé et al., 2014) thus it
remains to be seen if the threat-detection improvements
observed by Clark and colleagues (2012) would be
observable in a much larger military cohort using a task
analogous to their training.
improved response
In this pre-registered, large-scale study we expand on
the extant literature by exploring whether the significant
effects of tDCS to the rIFG would be observed in a cohort
consisting of trained military personnel performing a
visual search task relevant to their primary role. 虽然
the present study was designed to be an extension,
rather than a replication, of previous findings showing
positive effects of rIFG stimulation (Clark et al., 2012;
Falcone et al., 2012; McKinley et al., 2013) we nonethe-
less attempted to match stimulation parameters, task dif-
ficulty and session schedule as best we could, 与
majority of differences in protocol arising from the practi-
cal considerations in the use of brain stimulation within
military contexts. We also improved upon the ecological
validity of the training task through a consultative pro-
cess with our target population, used double-blinding
method for the rIFG conditions, and included an addi-
tional control stimulation group. Based on previous find-
英格斯 (Clark et al., 2012; Falcone et al., 2012; 麦金莱
等人。, 2013) our primary hypothesis was that anodal tDCS
to the rIFG would upregulate the targeted region and
thereby lead to increased attentional control resulting in a
significant behavioural effect (IE。, increased threat-
detection accuracy), and that this effect may be influ-
enced by years of experience and role.
2. 方法
2.1. 参加者
Participants were recruited from two separate units of the
Australian Army’s Royal Australian Armoured Corps
(RAAC) 和 98 defence members completing the full
学习 (mean age = 26.5, SD = 4.9, range = 19-42, 6
女性). The sample comprised 32 drivers/loaders, 28
gunners, 和 38 crew commanders of both armoured
fighting vehicles (ASLAV, Boxer) and main battle tanks
(M1A1 Abrams). Drivers/loaders, gunners, and crew
commands have differing levels of training and experi-
恩斯. 一般来说, drivers and loaders are newer soldiers
和 <4 years of experience, gunners are more experi-
enced with>4 years of service and more advanced train-
英, and crew commanders are the most trained members
of the crew and hold the greatest responsibility for the
平台, although age and experience varies more
between crew commanders as this role contains both
non-commissioned and commissioned officers. 我们
deliberately recruited a cross-section of crew roles to
additionally investigate whether soldier experience and
level of training influenced task performance.
A tDCS Safety Screening Questionnaire was employed
to screen for tDCS contraindications. 具体来说, 印迪-
viduals with a family history of psychiatric or neurological
状况(s), current psychoactive medication use, signif-
icant alcohol or drug use, or recent concussion were
excluded from participating in the study. 参加者
were also provided a written information sheet on the
study and given the opportunity to ask any questions
before providing
informed consent. The Australian
Departments of Defence and Veteran’s Affairs Human
Research Ethics Committee approved all study proto-
cols, and the work was carried out in accordance with
Declaration of Helsinki.
2.2. Sample size rationale
We were given support to recruit up to a maximum of 120
volunteers from the Australian Army. We chose to divide
this sample into three conditions of n = 40 in order to
maximise the strength of the study. In determining the
sample size we estimated an effect size of Cohen’s
d = 1.2 between active and sham conditions at 1 小时
后续行动 (Clark et al., 2012; 吉布森等人。, 2020). 使用
G*Power version 3.1, we determined that a sample of 34
participants/group would provide 90% 力量, at an alpha
level of 0.05, to detect a smaller effect of Cohen’s d = 0.8.
Subsequent calculations using the BFDA package
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2
N.S. Willmot, L.-A. Leow, H.L. Filmer et al.
Imaging Neuroscience, 体积 1, 2023
(Schönbrodt & Stefan, 2018) in R showed similar results,
和 88% of replications terminating at a boundary of
BF10 = 6 for a fixed-n design of n = 40 and effect size of
Cohen’s d = 0.8.
2.3. Conditions
Participants were allocated to three stimulation condi-
系统蒸发散: 2 mA tDCS to the right inferior frontal gyrus (n = 33),
Sham tDCS to this same site (n = 34), 和 2 mA to the
primary visual cortex (n = 31). To ensure balanced repre-
sentation of roles across the three conditions, partici-
pants were assigned to groups based on their role and
time of day (AM/PM) using a custom MATLAB script.
2.4. Threat detection task
Our goal when designing this paradigm was to stay as
close as possible to the Clark et al. 任务, while adapting
the stimuli for the targeted cohort and the primary task
they perform in their military role. This study employed a
threat-detection task using images generated with the
Australian Army’s simulation software, VBS3 (BISim,
澳大利亚). The task was programmed and delivered using
PsychoPy open-source software (Peirce et al., 2019).
Most images (85%) showed a vehicle gunner’s view of a
complex landscape, with images being either natural
light or thermal filtered. 15% of images were from a bird’s
eye view to simulate the visual feed a soldier may receive
from an unmanned aerial vehicle (UAV). There were two
reasons for including these aerial images. 第一的, they pro-
vided a novel image type for our sample, which was more
familiar with the gunner’s view. 第二, they were more
analogous to images used in similar studies exploring
training and tDCS on target detection in military person-
nel (Blacker et al., 2020; McKinley et al., 2013). Half of the
images contained a threat/potential target such as an
enemy armoured vehicle, tank, or grounded aircraft.
Threats were distributed pseudo-randomly (see Fig. 1
E-G) and were between 5 和 10 mm in size. We con-
sulted experienced crew commanders and gunners
during the selection of the image sets, to ensure the
scenes depicted were relevant to the target population,
and that the difficulty of detecting the threats was consis-
tent across images. This experienced cohort were serially
presented with the full bank of threat images in an
untimed manner and were asked to respond when they
identified the threat. We used the median response times
to identify images which were too difficult (>5 sec median
response time) or too easy (<2 sec median response
time). Those images that remained were then used as
templates for further image generation. The completed
task was piloted with a small cohort of soldiers (n
=17)
who did not receive tDCS, to ensure the ran intended and
difficulty level appropriate population. Lastly, we included post-study sur-
vey
capture individual ratings perceived relevance.
As shown in Figure 1A, similar Clark et al. (2012), each trial
participants presented an 3 sec, required respond quickly accu-
rately possible whether or threat
is present using “A” “L” key, this contingency counterbalanced across
participants. In there can be one four outcomes. (1) Misses (target but missed) will evoke negative feedback. (2) Hits detected) positive
(3) False alarm absent participant indicated it present) (4)
Correct rejections: partic-
ipant correctly absence target. Feed-
back given via voice feedback
message indicating correct incorrect presence>
