A schematic design of an epidermal touch
panel is shown in Fig. 4A. The epidermal touch
panel was built on a 1-mm-thick VHB film (3M,
Maplewood, MN) so as to insulate the panel from
the body. Because VHB film was originally developed as an adhesive, the panel could be attached to an arm without using extra glues (Fig.
4B). The epidermal touch panel was fully transparent so that it could convey visual content
behind the touch panel. Moreover, the panel
was mechanically soft and stretchable so that
a user is comfortable with movement while
wearing it. The currents measured before and
after attachment are plotted in Fig. 4C. The baseline currents increased after the attachment owing to a leakage of charges through the VHB
substrate. The thicker insulating layer generated
a smaller baseline current. The effect of thickness of the insulating layers on the baseline currents is shown in fig. S8. The sensitivity to touch
decreased after the attachment; however, the
touching current was still sufficient to be detected. As shown in Fig. 4D, we subsequently
touched from TP#1 to TP#4 on the epidermal
touch panel, and the current was measured with
the A1 current meter. The correlation between
the measured currents and the touched position was not influenced by the attachment. The
epidermal touch panel could successfully perceive various motions, such as tapping, holding,
dragging, and swiping. Thus, various applications can be easily managed by integrating the
panel. As shown in Fig. 4, E to G, writing words
(Fig. 4E), playing music (Fig. 4F), and playing
chess (Fig. 4G) were accomplished via adequate
motions on the epidermal touch panel (movies
S3 to S6).
We have demonstrated a highly stretchable
and transparent ionic touch panel. We used a
PAAm hydrogel containing 2 M LiCl salts as
an ionic conductor. We investigated the mechanism of position-sensing in an ionic touch panel with a 1D strip. The ionic touch strip showed
precise and fast touch-sensing, even in a highly
stretched state. We expanded the position-sensing mechanism to a 2D panel. We could
draw a figure using the 2D ionic touch panel.
The ionic touch panel could be operated under
>1000% areal strain. An epidermal touch panel
was developed based on the ionic touch panel.
The epidermal touch panel could be applied onto
arbitrarily curved human skin, and its use was
demonstrated by writing words and playing the
piano and games.
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This work was supported by the National Research Foundation of
Korea (NRF) grant funded by the Korean Government (MSIP)
(2015R1A5A1037668). J.-Y.S. and H.-H.L. acknowledge the support
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Materials and Methods
Figs. S1 to S11
Movies S1 to S6
14 April 2016; accepted 19 July 2016
Local modulation of human brain
responses by circadian rhythmicity
and sleep debt
Vincenzo Muto,1,2,3 Mathieu Jaspar,1,2,3 Christelle Meyer,1,2 Caroline Kussé,1,2
Sarah L. Chellappa,1,2 Christian Degueldre,1,2 Evelyne Balteau,1,2
Anahita Shaffii-Le Bourdiec,1,2 André Luxen,1,2 Benita Middleton,4 Simon N. Archer,5
Christophe Phillips,1,2,6 Fabienne Collette,1,2,3 Gilles Vandewalle,1,2
Derk-Jan Dijk,5† Pierre Maquet1,2,7†‡
Human performance is modulated by circadian rhythmicity and homeostatic sleep pressure.
Whether and how this interaction is represented at the regional brain level has not been
established. We quantified changes in brain responses to a sustained-attention task during
13 functional magnetic resonance imaging sessions scheduled across the circadian cycle,
during 42 hours of wakefulness and after recovery sleep, in 33 healthy participants. Cortical
responses showed significant circadian rhythmicity, the phase of which varied across brain
regions. Cortical responses also significantly decreased with accrued sleep debt. Subcortical
areas exhibited primarily a circadian modulation that closely followed the melatonin profile.
These findings expand our understanding of the mechanisms involved in maintaining cognition
during the day and its deterioration during sleep deprivation and circadian misalignment.
Forgoing sleep and staying up at night, be it for professional or recreational reasons, is highly prevalent in modern societies (1). Acute sleep loss leads to deterioration of multiple aspects of cognition (2) and is associated
with increased risk of human errors and health
hazards (3). These effects are often attributed to
the mere lack of sleep. However, despite the pro-
gressive buildup of sleep pressure during wake-
fulness, human performance remains remarkably
well preserved until wakefulness is extended into
the biological night. This is attributed to a puta-
tive circadian alerting signal that increases during
the day and reaches its peak in the early evening,
close to the rise of melatonin concentration, to
counter the mounting homeostatic sleep pressure
(4–6). Cognition deteriorates rapidly and substan-
tially when wakefulness is extended into the night
and early morning hours. This is attributed to the
accumulated sleep pressure and the dissipation of
the circadian alerting signal (6, 7). Whether and
how this interaction between homeostatic sleep
pressure and circadian rhythmicity is represented
at the regional brain level is not known. Single–time
SCIENCE sciencemag.org 12 AUGUST 2016 • VOL 353 ISSUE 6300 687
1GIGA-Cyclotron Research Centre–In Vivo Imaging, University of
Liège, Liège, Belgium. 2Walloon Excellence in Life Sciences and
Biotechnology ( WELBIO), Liège, Belgium. 3Psychology and
Cognitive Neuroscience Research Unit, University of Liège,
Liège, Belgium. 4Faculty of Health and Medical Sciences,
University of Surrey, Guildford, UK. 5Sleep Research Centre,
Faculty of Health and Medical Sciences, University of Surrey,
Guildford, UK. 6Department of Electrical Engineering and
Computer Science, University of Liège, Liège, Belgium.
7Department of Neurology, CHU Liège, Liège, Belgium.
*These authors contributed equally to this work. †These authors
contributed equally to this work. ‡Corresponding author. Email:
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