Addiction Biology
HUMAN/CLINICAL STUDY
doi:10.1111/j.1369-1600.2010.00312.x
Activation of the mesostriatal reward pathway with
exposure to ultraviolet radiation (UVR) vs. sham UVR
in frequent tanners: a pilot study
Cynthia R. Harrington1, Tracy C. Beswick2, Michael Graves1, Heidi T. Jacobe1,3,
Thomas S. Harris4, Shadi Kourosh1, Michael D. Devous Sr5 & Bryon Adinoff3,5
Department of Dermatology, University of Texas Southwestern Medical Center, USA1, Department of Dermatology, University of Oklahoma Health Science
Center, USA2, VA North Texas Health Care System, Dallas VAMC, USA3, Department of Radiology, University of Texas Southwestern Medical Center, USA4
and Department of Psychiatry, University of Texas Southwestern Medical Center, USA5
ABSTRACT
adb_312
1..7
Frequent and excessive tanning persists despite a growing understanding of its associated morbidity and mortality,
suggesting that ultraviolet radiation may impart rewarding effects beyond the assumed cosmetic benefits. To empirically measure putative centrally rewarding properties of ultraviolet radiation (UVR), we assessed the effects of a
commercially available tanning bed upon regional cerebral blood flow (rCBF), a measure of brain activity, using
single-photon emission computed tomography (SPECT). Seven frequent salon bed tanners were placed under a UVA/
UVB tanning light during two sessions; one session with UVR and the other with filtered UVR (sham UVR). Session
order was randomized and subjects were blinded to study order. During the UVR session, relative to sham UVR session,
subjects demonstrated a relative increase in rCBF of the dorsal striatum, anterior insula and medial orbitofrontal
cortex, brain regions associated with the experience of reward. These changes were accompanied by a decrease in the
subjective desire to tan. These findings suggest that UVR may have centrally rewarding properties that encourage
excessive tanning.
Keywords Neuroimaging, reward, single-photon emission computerized tomography, striatum, tanning,
ultraviolet radiation.
Correspondence to: Bryon Adinoff, UT
E-mail: [email protected]
Southwestern
Medical
INTRODUCTION
Almost 30 million Americans, including 20% of 18- to
39-year olds, visit indoor tanning salons each year
(Levine et al. 2005). The voluntary exposure to sunlight
continues unabated despite progressively increasing rates
of ultraviolet radiation (UVR)-induced illness and death
(Levine et al. 2005). Between 50 and 90% of skin cancers
are caused by UV radiation. In 2000, the WHO estimates
that there were 200 000 cases of melanoma and 65 000
melanoma-associated deaths worldwide, coupled with
2.8 million squamous cell and 10 million basal cell carcinoma cases (WHO 2009).
The use of tanning beds to administer UVR is a particularly prevalent form of exposure. Ten annual tanning
bed visits increases the risk of developing malignant
Center,
5323
Harry
Hines
Blvd,
Dallas, TX
75390-8564,
USA.
melanoma almost eightfold for those under 30 years of
age (Westerdahl et al. 1994). Although persons using
tanning beds exhibit a high level of knowledge about the
risks of UVR exposure, often more than non-users, the
awareness of these adverse effects does not decrease or
alter tanning activity, especially for those in their teens
and 20s (Mawn & Fleischer 1993; Arthey & Clarke 1995;
Robinson et al. 1997a). In fact, while public knowledge
regarding the hazards of sun exposure grew from 1986
to 1996, sun-burning and the regular use of tanning
beds also increased (Robinson, Rigel & Amonette 1997b).
Persistent tanning, despite both perceived and experienced adverse consequences, has led some investigators
to suggest that tanning has ‘addictive’ properties (Nolan
& Feldman 2009). Over half of the persons who endorse
frequent sunbathing (Warthan, Uchida & Wagner 2005)
© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction
Addiction Biology
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Cynthia R. Harrington et al.
and the use of tanning beds (Harrington et al. 2011)
report behaviors consistent with addictive disorders,
including an inability to decrease their tanning frequencies, compulsive tanning and continued tanning despite
adverse consequences. In fact, the term ‘tanorexia’ has
been coined to refer to persons who compulsively tan
(Warthan et al. 2005). Underlying these behaviors is the
implication that UVR has physiologic reinforcing properties distinct from any known psychosocial benefits of
having a tan (Feldman et al. 2004). For instance, two of
the top most frequent reasons selected by the indoor
tanners were to ‘feel good’ and for ‘relaxation’ (the top
reason being cosmetic) (Harrington et al. 2011). Importantly, the perceived rewarding effects of UVR was reportedly blocked by an opioid receptor antagonist (Kaur et al.
2006).
To our knowledge, the central nervous system (CNS)
effects of UVR have not been explored. As UVR is passively experienced, UVR administration may assist not
only in understanding compulsive tanning but provide a
novel method to assess reward-related CNS processes.
We therefore assessed the neural response to UVR in frequent tanners using a methodology developed by
Feldman et al. (2004). In this paradigm, subjects were
exposed to UVR in a tanning bed in the presence of a
filter that did or did not remove UVR (UVR or sham
UVR), such that the only experiential difference between
sessions was the subject’s reception of UVR (or not).
Using this procedure, we hypothesized that UVR, relative
to sham UVR, would elicit activation in the brain
regions associated with reward. Specifically, we predicted that striatal regions, including the nucleus
accumbens, caudate and putamen, would be activated
during UVR exposure relative to sham-UVR exposure.
We utilized single-photon emission computed tomography (SPECT) to measure the effect of UVR (relative to
sham UVR) on brain perfusion.
MATERIALS AND METHODS
Study subjects
After protocol approval by the University of Texas
Southwestern Medical Center (UTSW) Institutional
Review Board, subjects were recruited from frequent
tanners responding to a notice in two local tanning
salons (see Harrington et al. 2010 for further details).
The notice asked for volunteers for a study on tanning if
they like to tan in a tanning bed at least three times a
week and if maintaining a tan was important to them.
Subjects contacting the clinic were requested to fill out
self-administered surveys assessing: (1) demographic
information, prescription medications and supplements, and past medical and psychiatric history; (2)
information on tanning behaviors, including age at first
tanning bed use, frequency of tanning bed use and individual reasons for tanning; and (3) a modified Diagnostic and Statistical Manual of Mental Disorders IV (DSMIV) Criteria for Substance Dependence Disorder. Eight
items from the DSM-IV criteria for Substance Dependence Disorders (Warthan et al. 2005; Kourosh, Harrington & Adinoff 2010) were modified to reflect
tanning behaviors rather than substance dependence.
Following completion of the survey, subjects were
offered the opportunity to be contacted to participate in
additional research. Subjects were contacted if they
regularly tanned in a tanning bed at least twice per
week over the past 90 days and if they endorsed at least
three of the seven modified criteria (Harrington et al.
2010). Twenty subjects were contacted and eight agreed
to participate in the study. Consent was obtained and
subjects were financially compensated for their participation. One of these was subsequently excluded because
of concurrent illicit drug use.
Additional medical and psychiatric history was
obtained by self-administered health report form. Subjects were excluded from the study if they self-reported
major psychiatric disorders or active substance use disorders, the use of any medication with central nervous
system effects, or were females who were pregnant,
breast-feeding or sexually active without birth control.
All female participants were required to have a negative
urine pregnancy test during initial assessment and just
prior to each scanning session.
Scanning procedure
On the two subsequent visits, the subjects were imaged
via SPECT while exposed to either UVR or sham UVR.
Sessions for each subject were conducted in the afternoon
or early evening and between 2 and 8 days apart
(6.3 ⫾ 2.1 days). Tanning was conducted in a Sunquest
3000S tanning canopy, which includes both UVA and
UVB wavelengths. Irradiance at the exposure site was
measured using probes for UVA and UVB radiation positioned at 12 in. from the bulbs. Fluence rate of UVA was
0.1 W/cm2 and UVB was 0.061 W/cm2. Two matching,
visually identical (Kucenic et al. 2002) plastic/acrylic
filters, obtained from Dr. Steven Feldman, were placed
over the tanning bed panel and tested as previously published (Feldman et al. 2004). These filters were transparent to visible/infrared light; one blocked UVR (Polycast
UF3, Sterling Industries, Shawnee, KS, USA) and the
other was transparent to UVR (Polycast SUVT, Sterling
Industries, Shawnee). As the filters were transparent to
infrared light, the same heat load was provided during
both sessions. Fluence rate for UVA with the transparent
filter (active session) was 0.1 w/cm2; with UVR blocked
© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction
Addiction Biology
Mesostriatal activation in frequent tanners
filter (sham session) 0.001 w/cm2. Fluence rate for
UVB with transparent filter was 0.047 w/cm2; with UVR
blocked filter 0.0 w/cm2. The estimated dose delivered to
each subject for the UVR transparent filter was 6 J/cm2
UVA and 0.282 J/cm2 UVB; for the UVR blocked filter
0.06 J/cm2 UVA and 0 J/cm2 UVB. The order of shamUVR and UVR tanning sessions were pseudo-randomly
determined and subjects were blinded to session order.
The same tanning canopy (with either the UVR or nonUVR filter) was used for both sessions. Four subjects
received the sham-UVR filtered radiation on their first
sessions.
Upon arrival to each session, subjects changed into
bathing suits of their choice. An intravenous line was
then placed into each subject’s left arm. Subjects were
then brought into the study room and immediately lay
down on the tanning bed. Prior to turning on the tanning
bed, subjects were asked to rate ‘how much you feel like
tanning right now’ on a 10 cm visual analogue Likert
scale, from ‘Not at all’ to ‘More than I ever have’. Opaque
eye shields were then placed over the eyes and the tanning
bed was turned on. Lamps were placed 12 in. above the
subjects. One minute after turning on the tanning light,
20 mCi of 99mTc HMPAO (GE Healthcare, Princeton, New
Jersey) was administered intravenously over 30 seconds
and followed by a 10 ml saline flush over 30 seconds.
[99mTc HMPAO assesses regional cerebral blood flow
(rCBF) from 1 to 3 minutes following administration].
Tanning sessions lasted ten minutes, which was consistent with the subjects’ usual practice. After the tanning
light was turned off, the eye covering and intravenous
lines were removed. While still on the tanning bed and
prior to being able to view their skin color, subjects filled
out two questionnaires about the tanning session, the
first again asking how much they wanted to tan and the
second asking ‘How much did you like this tanning bed?’
[from ‘not at all’ (1) to ‘excellent’ (5)] and ‘How much tan
do you expect to get from this tanning bed?’ [from ‘no tan’
(1) to ‘the perfect tan’ (4)]. Following the second session,
subjects were also asked whether they preferred the first
tanning session, the second tanning session or had no
preference. As subjects exposed to sham UVR might
notice that they did not tan, subjects were asked to cover
exposed body areas with Oil of Olay A Touch of Sun
immediately following termination of the tanning
session.
SPECT scans were obtained in the Nuclear Medicine
Center at UTSW 90 minutes following 99mTc HMPAO
administration to allow time for tracer activity to clear
from blood and non-brain tissues. Because 99mTc HMPAO
is extracted during the first arterial pass and remains distributed in the brain in proportion to rCBF for many hours,
this perfusion image represents rCBF at the time of
radiotracer administration and not at the time of the scan.
3
SPECT images were acquired on a PRISM 3000S 3-headed
SPECT camera (Picker International, Cleveland, OH, USA)
using ultra-high-resolution fan-beam collimators (reconstructed resolution of 6.5 mm) in a 128 ¥ 128 matrix in
three-degree increments. For our system, voxels in reconstructed images were 1.9 mm3. Reconstructed images
were smoothed with a sixth-order Butterworth threedimensional filter, and attenuation was corrected using
a Chang first-order method with ellipse size adjusted
for each slice.
Statistical analysis
Demographic and clinical data
Basal and post-light exposure changes in Desire to Tan
were assessed using repeated measures analysis of variance with post hoc paired t-tests for both within sessions
(pre- and post-light exposure) and between sessions (UVR
versus sham UVR) using delta responses (post-light
versus pre-light scores).
Image analysis
SPECT images were resliced to 2 mm3 voxels, co-registered
to Montreal Neurologic Institute (MNI) space using the
MNI T1 SPECT template, smoothed to a final resolution of
10 mm and normalized to whole brain counts (to correct
for individual variability in global cerebral blood flow).The
accuracy of spatial normalization of functional brain
images [(SPECT, positron emission tomography and functional magnetic resonance imaging (fMRI)] is limited by
the spatial resolution of the original data (6 mm for these
data), by partial volume effects and by the limits of the
normalization algorithm used. Thus, the accuracy of normalization in our data is about 2–4 mm, and the anatomic
designations assigned to observed rCBF effects are constrained by these limitations, as well as by our spatial
resolution and partial volume effects. Voxel-wise analyses
(voxel z score at P < 0.01, cluster size >50 voxels) comparing UVR versus sham-UVR effects were conducted
using Statistical Parametric Mapping (SPM5; University
College, London, England). Regions reaching our statistical threshold were overlaid on the MNI MRI template.
Regions are identified by x, y, z MNI coordinates and
cluster size. Regions of interests (ROIs) defined by cluster
boundaries for four regions we considered relevant to
reward processes were also identified (see Table 1) and the
average rCBF within each cluster was determined for each
subject in each condition. Differences between sessions
were obtained by paired t-test and Pearson product
moment correlation was used to assess the association
between clusters and Desire to Tan. RCBF responses are
relative; that is, a region showing increased rCBF reflects
© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction
Addiction Biology
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Cynthia R. Harrington et al.
either an increase in rCBF during UVR compared with
sham UVR, a decrease in sham UVR relative to UVR or a
combination of both.
the previous ninety days. All subjects reported tanning
on a regular basis two to three times per week.
Change in rCBF following UVR versus
No-UVR exposure
RESULTS
Subjects
The seven subjects (four females) consisted of five
Caucasians and two Asians. Subjects were 30.7 ⫾
9.0 (mean ⫾ SD) years old, started regular tanning at
21.4 ⫾ 8.9 years old and had tanned 26.9 ⫾ 6.0 days in
Table 1 Brain regions demonstrating increased (P < 0.01)
regional cerebral blood flow (rCBF) following ultraviolet radiation (UVR) compared with sham UVR in frequent tanners.
MNI coordinates
Identified region
x
y
Caudate, leftb
Putamen, rightb
Anterior insula, left, extending
dorsally to inferior/middle
frontal gyrusb
Orbitofrontal cortex, lateral,
left, extending to dorsolateral
prefrontal cortex
Orbitofrontal cortex, left
Orbitofrontal cortex, medialb
Superior temporal gyrus
(BA42), left
Dorsolateral prefrontal cortex,
right
-12
0
26 -16
-36 20
-40
kEa
z
Z score
18 56 2.96
14 78 3.68
36 231 3.54
34 -18 333 3.47
-12 46 -16 85 3.41
12 24 -14 68 3.09
-62 -34 20 575 4.36
52
36
10
72 3.41
a
Cluster size. bRegions considered in cluster-derived region of interest
analyses.
The rCBF response to UVR was compared with the rCBF
response to sham UVR (MNI coordinates and cluster size
in Table 1 except as noted). Increases in rCBF were
observed during UVR exposure, relative to sham UVR, in
the left caudate, right putamen and left anterior insula,
extending up to the boundary between the inferior frontal
gyrus (BA 44) and middle frontal gyrus (BA 9) (Fig. 1).
Three regions show a relative increase in the orbitofrontal
cortex (OFC): medial OFC; lateral left OFC extending
superiorly to the left dorsolateral prefrontal cortex; and
a smaller, more medial left cluster. Other regions of
increased rCBF included a large region of the left superior
temporal gyrus (Brodman Area 42) and left dorsolateral
prefrontal cortex. The only relevant area of decreased
rCBF following UVR relative to the sham UVR was a small
area in the left OFC (-30, 54, -18; 75).
SPM-derived clusters showed a significant increase in
the left dorsal caudate [t = 4.5, degrees of freedom
(d.f.) = 6, P = 0.004], medial OFC (t = 5.0, d.f. = 6, P =
0.002) and left anterior insula (t = 6.7, d.f. = 6, P =
0.0005), but not right putamen (t = 1.4, d.f. = 6,
P = 0.21), during the UVR relative to sham UVR session.
Subjective responses
Desire to Tan significantly changed from basal to postUVR measures (F = 16.1, d.f. = 12, P = 0.002) and there
was a significant time ¥ session (UVR versus sham UVR)
interaction (F = 12.70, d.f. = 12, P = 0.004) (Fig. 2).
Post-hoc analyses demonstrated similar Desire to Tan
Figure 1 Areas of relative increases and
decreases in regional cerebral blood flow
(rCBF) following ultraviolet radiation
(UVR), relative to sham UVR, in frequent
tanners (n = 7). Transverse images are on
top row, sagittal image in bottom left, and
coronal image in bottom right. Red areas
reveal voxels increased following URV relative to sham UVR and blue areas reveal
voxels decreased following UVR relative to
sham UVR. MNI coordinates noted at the
bottom left of each image. L = left. R = right.
OFC = orbitofrontal cortex. STG = superior
temporal gyrus. All transverse, sagittal and
coronal images are available in Supporting
Information Appendix S1
© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction
Addiction Biology
Mesostriatal activation in frequent tanners
Figure 2 Change in Desire to Tan in individual subjects pre- and
post-sham ultraviolet radiation (UVR) and UVR exposure sessions
measures prior to UVR (mean ⫾ SD; 59.7 ⫾ 23.3) and
sham UVR (62.1 ⫾ 23.7) sessions (t = 0.50, d.f. = 6,
P = 0.64). A significant decrease in Desire to Tan was
observed following UVR exposure (t = -5.63, d.f. = 6,
P < 0.0007) but not following sham UVR (t = -0.05,
d.f. = 6, P = 0.96). The difference in the pre- and postsession Desire to Tan (DDesire to Tan) was greater following UVR (-38.6 ⫾ 18.1) relative to the no UVR exposure
(-0.42 ⫾ 21.5) (t = -3.84, d.f. = 6, P = 0.01). When
asked which bed was preferred, five selected the UVR
session, one had no preference and one chose the nonUVR session. Only the two subjects of East Asian race did
not prefer the UVR session. No significant correlations
between Desire to Tan and SPM-derived regions (caudate,
putamen, insula and OFC) rCBF were identified.
DISCUSSION
These findings reveal that UVR exposure via a commercially available tanning bed, relative to sham UVR,
increases mesostriatal activity in frequent tanners. Furthermore, we have confirmed the findings of Feldman
et al. (2004) revealing that most frequent tanners can
successfully identify UVR from sham UVR based solely
upon their subjective response. These findings strongly
suggest that frequent tanning may involve CNS reward
and/or reinforcement over and above the oft-stated goal
of ‘getting tan’.
The epidermis and nervous system both emerge from
the ectoderm germ layer and there are well recognized
associations between dermatologic and psychiatric disorders (Locala 2009). In fact, the term ‘psychodermatology’ has been used to describe the mind–skin connection.
From an evolutionary perspective, it is reasonable to
suggest that sunlight may have centrally rewarding properties given the importance of UV-mediated synthesis of
5
vitamin D for human survival. Biological mechanisms
underlying the connection between UVR and neural
activity may include UVR-induced changes in the gene
p53, which upregulates the transcription of POMC in
keratinocytes. POMC is cleaved into a-melanocytestimulating hormone that induces melanogenesis,
increasing the free-radical absorbing molecule melanin
and thereby the photoprotective mechanism represented
by a suntan (Pathak & Fanselow 1983; Riley 1997;
Bykov, Marcusson & Hemminki 2000; Cui et al. 2007)
and b-endorphin, an opioid-receptor agonist. bendorphin may act peripherally on the skin to induce the
relief from pain and irritation or centrally to induce relaxation or euphoria. UVR can also alter serotonin levels, a
neurotransmitter strongly implicated in anxiety disorders
and depressive disorders, through light-induced changes
in pineal N-acetyltransferase (Klein et al. 1997). Interestingly, over 80% of female undergraduate students who
frequently tan (ⱖ40 times per year) report symptoms
consistent with seasonal affective disorder (SAD) or subsyndromal SAD compared with 46% of non-tanners
(Hillhouse, Stapleton & Turrisi 2005).
Clinically relevant brain regions showing changes
following UVR included the dorsal striatum (i.e.
caudate, putamen), medial OFC and left anterior insula.
The ventral striatum, or nucleus accumbens, is typically
associated with drug-induced reward (Drevets et al.
2001; Martinez et al. 2003). However, several studies
have implicated the dorsal striatum in the affective experience of both reward and punishment (Balleine,
Delgado & Hikosaka 2007; Delgado 2007). A strong correlation is observed between dopamine release in the
dorsal caudate (P < 0.001) and putamen (P < 0.05)
with the elation/euphoria experienced after nicotine
inhalation (Barrett et al. 2004). Dopamine transmission
in both the left medial caudate (the same region of
change observed in the present study) and putamen also
show increased dopamine release following monetary
rewards (Zald et al. 2004). The medial OFC is thought
to monitor the reward value of several different reinforcers (Kringelbach & Rolls 2004). Neuroimaging
studies using fMRI have shown increased medial OFC
responses to monetary rewards (Elliott & Deakin 2005;
Elliott, Agnew & Deakin 2010), to methamphetamine
administered to healthy controls (Vollm et al. 2004) and
to cocaine administered to cocaine-addicted subjects
(Kufahl et al. 2005). The insula, particularly the anterior insula, is preferentially involved in the evaluative,
experiential or expressive aspects of internally generated
emotions (Reiman et al. 1997; Craig 2003) and
anterior/middle insular activation has been observed
during the ingestion of chocolate in ‘chocolate lovers’
(Small et al. 2001) and cocaine administration (Kufahl
et al. 2005).
© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction
Addiction Biology
6
Cynthia R. Harrington et al.
The strengths to our design included the blinded
administration of UVR and sham UVR, including the use
of self-tanning cream to prevent the subject’s ability to
objectively determine UVR exposure. The use of SPECT
allowed us to assess brain reactivity early in the tanning
sessions during the circumscribed (1–3 minutes) period
of time most expected to coincide with subjective rewarding effects. Nevertheless, the small n, coupled with apparently distinct groups of subjects (Asian and Caucasian)
and responses (high versus low Desire to Tan, high versus
low dorsal striatal rCBF), limit the significance and interpretation of our findings. The absence of skin phototype
assessments did not allow us to consider skin tone as
a covariate. Salon tanning obtained by participants
between their two study sessions, which ranged from 2 to
8 days, may also have affected the findings. Limits of
spatial resolution and the ability to only determine relative measures of limbic activation are inherent in our
SPECT methodology and camera. It should also be noted
that the SPECT technique assessed relative (to whole
brain), not absolute, rCBF differences between groups.
Larger studies assessing neural processing of UVR in both
frequent and infrequent tanners of various racial backgrounds are clearly indicated to determine the role of
UVR exposure (both frequency and years of tanner) and
skin type (Fitzgerald 1975) upon brain reactivity. Future
studies would also benefit from a more thorough assessment of skin phototype and other co-morbid psychiatric
pathology, such as other substance use, SAD and body
dysmorphic disorder (Phillips et al. 2006), that may effect
the central rewarding response to UVR. Although fMRI
would offer the advantage of assessing neural activity
during the whole tanning session, the metal in a tanning
bed would not allow its use in an fMRI environment.
Our findings of dorsal striatal activation by UVR, relative to sham UVR, provide a unique approach to our
understanding of persistent tanning. Despite the near
universal awareness of skin cancer risk and the acceleration of the skin’s aging process, the use of tanning salons
continues to increase. If CNS reward mechanisms, similar
to those observed in other additive disorders, are involved
in frequent tanning, novel and more dramatic behavioral
and pharmacologic treatment approaches to tanning may
be useful in preventing morbidity and mortality.
Acknowledgements
The authors thank Vanessa Casanova and Shelley Redfern
for their help with data collection and Paul R. Bergstresser,
MD, for his guidance on study design and paper preparation. We are particularly indebted to Dr. Steven R. Feldman
at Wake Forest University for his donation of the UVR
filters. This study was funded, in part, by the James N.
Gilliam, MD, Chair in Dermatology Endowment.
Authors Contributions
CRH, HTJ, MDD and BA were responsible for study concept
and design. CRH and BA were responsible for paper preparation. TSH was responsible for obtaining SPECT imaging
and SPECT analysis. TCB, MG and SK were responsible for
subject recruitment, data collection and monitoring of all
imaging sessions. HTJ and MDD provided critical revision
of the paper. All authors critically reviewed content and
approved final version for publication.
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SUPPORTING INFORMATION
Additional Supporting Information may be found in the
online version of this article:
Appendix S1 Complete transverse, sagittal and coronal
images showing areas of relative increases and decreases
in regional cerebral blood flow (rCBF) following UVR,
relative to sham UVR, in seven frequent tanners.
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