Long-Wave Infrared Functional Brain Imaging in Human: A Pilot Study

Abstract

Although some authors suggest to use Long-Wave Infrared (LWIR) sensors to evaluate brain functioning, the link between emissions of LWIR and mental effort is not established. The goal of this pilot study was to determine whether frontal LWIR emissions vary during execution of neuropsychological tasks known to differentially activate the pre-frontal cortex (simple color presentations, induction of the Stroop effect, and a gambling task with real money). Surprisingly, LWIR emissions as measured with bilateral frontal sensors in 47 participants significantly differed between tasks, in the supposed direction (Color<Stroop<Gambling), in spite of counterbalanced presentations. This pilot study suggests that investigations of convergent validity with other types of brain imaging techniques can be initiated with LWIR imaging. If confirmed, this technique would offer a simple and accessible method to evaluate frontal cortex activation.

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The Open Neuroimaging Journal, 2013, 7, 1-3 1
1874-4400/13 2013 Bentham Open
Open Access
Long-Wave Infrared Functional Brain Imaging in Human: A Pilot Study
Christian C Joyal
1,2,*
and Mylene Henry
2
1
Université du Québec à Trois-Rivières, Canada
2
Institut Philippe-Pinel de Montréal, Canada
Abstract. Although some authors suggest to use Long-Wave Infrared (LWIR) sensors to evaluate brain functioning, the link
between emissions of LWIR and mental effort is not established. The goal of this pilot study was to determine whether frontal
LWIR emissions vary during execution of neuropsychological tasks known to differentially activate the pre-frontal cortex
(simple color presentations, induction of the Stroop effect, and a gambling task with real money). Surprisingly, LWIR
emissions as measured with bilateral frontal sensors in 47 participants significantly differed between tasks, in the supposed
direction (Color<Stroop<Gambling), in spite of counterbalanced presentations. This pilot study suggests that investigations of
convergent validity with other types of brain imaging techniques can be initiated with LWIR imaging. If confirmed, this
technique would offer a simple and accessible method to evaluate frontal cortex activation.
Keywords: Long-wave, passive, infrared, brain imaging.
INTRODUCTION
Infrared (IR) light is electromagnetic radiation of
wavelengths invisible to the human eye (0.75 to 300 µm).
Long-Wave Infrared (LWIR) emissions represent a IR
specific spectrum (8 to15 µm) associated with thermal
modification. The development of infrared cameras and
sensors sensitive to LWIR allows Infrared Thermography
(IRT), a temperature-based imaging technique used in
different domains, including military (e.g. target acquisition,
guiding missile technology, night human detection),
industrial (e.g. thermal efficiency analyses, remote
temperature sensing, localization of over-heating parts),
domestic (e.g. alarm systems and movement detection), and
emergency services (e.g. nonvisual and distant localization
of fire bases, heat leaks, warm-blooded animal; see [1] for a
review). IRT is also used in medicine as a diagnostic aid for
vascular, tumor, or cancer-related pathologies [2, 3]. Given
that brain activation is associated with small variations of
local cerebral blood flow [4] and thermal radiation [5], it is
theoretically possible to use IRT as a crude technique of
brain functional imaging [6]. This idea is certainly not new
[7], but it was abandoned because of methodological
difficulties [8]. More recently, some authors proposed the
use of infrared cameras to deduce human brain functioning
from temperature variation of the scalp [6, 9, 10], and
multiple-contact [11] or single non-contact [12] infrared
head-mounted sensors have also been used. Still, the link
between functional activation of the cortex and temperature
modification of the scalp is not established. Temperature
increases of the skin might be associated with other factors,
including ambient temperature, peripheral activation, waking
*Address correspondence to this author at the Université du Québec à Trois-
Rivières, Canada; Tel: 819-376-5011; Fax: 819-376-5195;
E-mail: christian.joyal@uqtr.ca
state, etc. Another issue is that functional cortical T increases
might be less localised than previously believed, affecting
adjacent areas as well [13]. Thus, before conducting
concomitant or construct validity studies with the LWIR and
other types of functional brain imaging, basic assumptions
related with the approach should be tested. The first
assumption to assess is that frontal LWIR emissions vary as
a function of the cognitive load. The goal of this pilot study
was to determine whether frontal LWIR emissions would
significantly change during the execution of
neuropsychological tests known to differentially activate the
prefrontal cortex.
MATERIALS AND METHODOLOGY
Forty-seven volunteers participated in this study (36♀-11
♂, mean age: 27.4 ± 11.0, range 21 to 63; mean number of
years of education: 16.8 ± 2.4, range 14 to 27). Each
participant was individually assessed in a closed, mildly lit,
sound-attenuated experimental room at constant ambient
temperature (20
0
C). Participants were seated behind a desk,
in front of a 52” flat screen monitor (2 m), connected to two
control computers placed in the back of the room. Two
LWIR sensitive sensors embedded in a headgear (TT-pIR
HEG device, Thought Technology Ltd, Montreal) were
placed at a one-inch distance from the skin on each side of
the forehead midline (Fp1 and Fp2 positions of the 10-20
international EEG system corresponding to left and right
prefrontal regions). The signal was transformed with a
ProComp Infinity encoder, processed in real time with the
Biograph software, and analysed offline with the Physiology
suite (Thought Technology, Ltd). A block design experiment
with counterbalanced presentations of three classic
neuropsychological tasks was used with Stim2 (Neuroscan
Inc, Charlotte, NC). The first task was a simple presentation
of colored rectangles (25 X 40 cm) placed in the center of
the screen (colors: blue, red or green, presented in pseudo-

2 The Open Neuroimaging Journal, 2013, Volume 7 Joyal and Henry
random order during 2000 ms with an inter-trial interval of
1000 ms, 64 stimuli, total duration of approximately 5
minutes). Passive presentation of colors is classically
associated with activation of posterior parts of the cortex,
especially occipital regions (e.g. [14, 15]). The second task
involved the well-known Stroop effect, closely associated
with fronto-medial structures (most notably the anterior
cingulate and the medial frontal cortices), and the posterior
parietal cortex [16-18]. In the present study, a virtual version
of the Stroop task was used [19], in which color blocks
(blue, red or green) or color words (blue, red or green) were
visually presented while names of colors (blue, red or green)
were simultaneously and verbally enunciated (72 stimuli, 36
congruent and 36 non congruent; total duration of 10
minutes). Participants had to click the left (or right) button of
a mouse only when visual and audio stimuli matched. The
third task was an improved version of the Balloon Analog
Risk Task (www.millisecond.com), a gambling game known
to recruit widespread prefrontal regions, including the
ventral, medial, and dorsolateral cortices [20, 21]. A balloon
(blue, red or green) was presented in the center of the screen
and participants had to click the left (or right) button of the
mouse to put virtual air into it. Each click corresponded to a
pump, which gradually inflated the balloon. The goal of the
game is to maximally inflate the balloon without exploding
it. The maximal number of pumps allowed before explosion
varied pseudo-randomly between each trial. Each pump was
associated with real money (25 cents) to enhance interest or
anxiety related with the task, and an explosion was related
with the loss of money gain for that trial (participants made
$13.00 on average, $1.25 min and $25.50 max, total duration
of approximately 10 min). Thus, the three task were chosen
as a function of their various association with frontal cortex
activation (lowest to highest: color bock < Stroop <
Balloon). The order of presentation of the tasks was counter-
balanced across participants so that half of the group
received the color block condition first and the other half
received the Balloon condition first. Given the exploratory
nature of this preliminary experiment, there was no a priori
hypothesis. However, if infrared sensors are sensitive to any
frontal lobe activation, the average amplitude of frontal
LWIR emissions (area under the curve) should significantly
differ across conditions as a function of their known frontal
lobe activation properties.
RESULTS
The dependant variable was the area under the curve
recorded during the experiment. On average, it differed
between each condition in the expected directions: color
presentation (98.2 ± 3.1) < Stroop task (102.6 ± 26.4) <
Balloon task (129.2 ± 99.3). The differences were significant
F (2, 138) = 3.67, p < 0.05 with a medium effect size (η
2
=
0.052; [22]). LSD post-hoc analyses confirmed the presence
of significant differences between the Balloon and both the
Color (p = 0.01) and the Stroop conditions (p = 0.03). Order
of presentation had no effect upon these differences (Fig. 1).
Given that variation of the variable (standard deviations) also
differed across the conditions (increasing as a function of the
complexity: Color<Stroop<Balloon), behavioral results were
taken into consideration, and a significant positive
correlation was found between reaction time at the Stroop
task and the T area under the curve (2-tailed Pearson r =
0.46; p < 0.01).
CONCLUSION
These preliminary data suggest that LWIR emitted from
the forehead might vary as a function of cortical frontal
activation (perhaps reflecting blood flow modification), as it
was first proposed by Lombard [7]. Concomitant validity
studies using other brain imaging approaches with LWIR are
warranted. If LWIR emitted from the scalp are truly
associated with cortical activation, the use of sensors
sensitive to LWIR might not only serve as a
neuromodulating technique (e.g. to treat migraine; [12]), but
also as a crude, yet simple, low-cost, easy-to-use instrument
to evaluate cortical response in clinical settings. Only studies
with larger groups of clinical and nonclinical participants
will allow to test this possibility.
CONFLICT OF INTEREST
The authors confirm that this article content has no
conflicts of interest.
Fig. (1). Area under the curve (mean) during the three conditions after merging (dashed bar) the two subgroups of participants. (counter
balanced order of presentations; n=23 in each order).
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120
140
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olor
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ACKNOWLEDGEMENTS
Declared none.
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Received: November 10, 2012 Revised: December 06, 2012 Accepted: December 07, 2012
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