Leptin replacement alters brain response to food cues
in genetically leptin-deficient adults
Kate Baicy†, Edythe D. London†‡§¶, John Monterosso†, Ma-Li Wong?, Tuncay Delibasi†, Anil Sharma†, and Julio Licinio?
†Department of Psychiatry and Biobehavioral Sciences and Semel Institute, and‡Department of Molecular and Medical Pharmacology, David Geffen School
of Medicine, University of California, Los Angeles, CA 90024;?Center for Pharmacogenomics, Department of Psychiatry and Behavioral Sciences, University of
Miami Miller School of Medicine, Miami, FL 33136; and§Biomedical Engineering Interdepartmental Faculty, University of California, Los Angeles, CA 90024
Edited by Marcus E. Raichle, Washington University School of Medicine, St. Louis, MO, and approved August 21, 2007 (received for review July 10, 2007)
A missense mutation in the ob gene causes leptin deficiency and
morbid obesity. Leptin replacement to three adults with this
mutation normalized body weight and eating behavior. Because
the neural circuits mediating these changes were unknown, we
paired functional magnetic resonance imaging (fMRI) with presen-
tation of food cues to these subjects. During viewing of food-
related stimuli, leptin replacement reduced brain activation in
regions linked to hunger (insula, parietal and temporal cortex)
while enhancing activation in regions linked to inhibition and
satiety (prefrontal cortex). Leptin appears to modulate feeding
behavior through these circuits, suggesting therapeutic targets for
functional MRI ? obesity ? hunger ? prefrontal cortex ? insula
(1). A recessive missense mutation (c313C?T Arg105Trp) in the
ob gene was identified in three adults (two women and one man)
and one child from a family in Turkey (2). The only other known
mutation producing congenital leptin deficiency is a frame
shift/premature stop (c398delG ?133G), identified in three
families of Pakistani origin (3). Before treatment with leptin
supplement was initiated, the adults with the Arg105Trp muta-
tion were morbidly obese and hypogonadal, and one of them had
type-2 diabetes mellitus. Concomitant with weight loss, replace-
ment of leptin to the adults with the Arg105Trp mutation
normalized endocrine and other health measures (4) and pro-
duced a 50% reduction in food intake (during the first 15 weeks)
that correlated with ratings of hunger and desire to eat (5).
Moreover, supplementation was associated with sustained in-
creases in brain gray matter concentration in the anterior
cingulate gyrus, inferior parietal lobule, and cerebellum (6).
Leptin treatment had similar effects on body weight and health
measures for patients identified with the ?133G mutation (7) as
well as mice that bear a homologous gene mutation (ob/ob
Consistent with a direct action in the brain, leptin receptors
are found in the cerebral cortex, hippocampus, basal ganglia,
hypothalamus, brainstem, and cerebellum (9). However, the
neural circuits through which leptin alters human feeding be-
havior are not known. We addressed this question by pairing
functional magnetic resonance imaging (fMRI) with presenta-
tion of food images to the three leptin-deficient adults with the
Arg105Trp mutation with and without leptin treatment. In
healthy adults, presentation of food increases ratings of hunger
and cerebral glucose metabolism, particularly in the orbitofron-
tal cortex, somatosensory cortex, superior temporal cortex,
occipital cortex, insula, basal ganglia, and thalamus (10); images
of high-calorie foods increase ratings of hunger and activate a
network of brain regions, including the medial and dorsolateral
prefrontal cortex (PFC), corpus callosum, amygdala, thalamus,
hypothalamus, and cerebellum (11). We hypothesized that leptin
replacement would alter ratings of hunger induced by the
eptin, the primary signaling hormone from adipocyte energy
stores, regulates feeding behavior and energy expenditure
in activation of the previously identified brain regions by the
food-related cues in the congenitally leptin-deficient research
Ratings of Hunger and Body Mass Index (BMI).Self-reportsofhunger
in response to images of food presented during fMRI scanning
were generally higher when subjects were not receiving leptin
supplementation than during leptin treatment (Table 1).
ANOVAs indicated a significant effect of test session in two
participants [F(2, 63) ? 11.2, P ? 0.001, and F(2, 63) ? 16.1, P ?
0.001, respectively] and a near significant effect in the third [F(2,
63) ? 3.0, P ? 0.058]. Post hoc analyses indicated that all three
participants reported significantly lower hunger when tested
during supplementation for 57 months than when not receiving
leptin (all P values were ?0.05). After only 2 weeks of supple-
mentation, ratings of one participant (P ? 0.001), but not the
others (P ? 0.09 and 0.21, respectively) were significantly lower.
Hunger ratings after 57 months were significantly lower than
after 2 weeks of supplementation for one participant (P ? 0.01)
but not for the other two (P values ?0.5). The increase in hunger
rating was accompanied by an increase in BMI (average from
27.7 to 29.6, P ? 0.009); BMI did not change after 2 weeks of
leptin reinstatement (Table 2).
Neuroimaging Data. Compared with the neutral stimuli condition,
high-calorie foods activated the middle, inferior, superior, and
medial frontal gyri and regions of the occipital, temporal, limbic,
and parietal lobes, insula, amygdala, putamen, thalamus, midbrain,
and cerebellum (P ? 0.05, corrected FDR, t ? 2.75, z score 2.72,
extent ?10 voxels). These findings were consistent with those
obtained in healthy volunteers, using a similar paradigm (11).
When patients were not receiving leptin (vs. during supple-
mentation), activity related to the contrast of high-calorie ?
Author contributions: E.D.L., J.M., M.-L.W., and J.L. designed research; J.M., M.-L.W., T.D.,
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations: fMRI, functional MRI; PFC, prefrontal cortex; BMI, body mass index; EPI,
echoplanar imaging; BOLD, blood oxygen level-dependent.
¶To whom correspondence should be addressed. E-mail: email@example.com.
© 2007 by The National Academy of Sciences of the USA
Table 1. Mean (standard deviation) rating of hunger in response
to images of high-calorie food presented during fMRI scan (1 ?
not at all, 7 ? very hungry)
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low-calorie was greater in the insula and other parietal regions
(Fig. 1) as well as occipital, limbic, and temporal regions (Table
3). In comparison, leptin supplementation accompanied signif-
icantly greater activation in the medial, superior, and middle
frontal gyri, cingulate gyrus, occipital cortex, midbrain, pons,
and cerebellum (Fig. 2 and Table 4). In the region of interest
analysis of a subset of clusters, each subject showed an activation
pattern resembling the group results (Fig. 3).
As expected, leptin supplementation reduced self-reports of
cue-induced hunger, more consistently after 57 months than
after 2 weeks. In addition, removal of leptin treatment increased
BMI and altered the brain response to food-related cues. In the
contrast high-calorie ? low-calorie, leptin deficiency was asso-
ciated with enhanced activation of areas in the parietal (espe-
cially insula), temporal, and occipital lobes.
The insula functions as the primary gustatory cortex (12) and
is activated during the presentation of food (10), with increases
during hunger and decreases after satiation (13–15). These
findings may reflect the role of the insula in representing
information about the internal bodily states as conscious emo-
tional feelings, or interoception (16). Our results suggest that
leptin deficiency may enhance insular interoception of cue-
induced feelings of hunger.
Hunger also elicits activation in the temporal and parietal
cortices of healthy adults (13), and there is clinical evidence of
temporal involvement in the sensation of hunger (17), possibly
accounting for the enhancement of temporal and parietal cor-
tical activations when leptin supplementation is discontinued.
Along with reductions in self-reports of hunger, leptin treat-
ment produced significantly greater brain activation in the
middle, superior, and medial frontal gyri and cerebellum in
the contrast high-calorie ? low-calorie. The role of the PFC in
the intentional control of behavior (18) and the inhibition of
inappropriate behavioral responses (19) has been well estab-
lished, thereby supporting the link between satiety (13–15, 20)
and successful dieting (21) with increased activity in the PFC.
Greater activation of the PFC during leptin supplementation
may involve enhancement of satiety or activation of inhibitory
processes, in line with the general belief that high calorie foods
are unhealthy and should be avoided.
Although the cerebellum has not traditionally been linked
with eating behavior, it is thought to play a role in reinforcement
(22) and drug craving (23). The cerebellum contains leptin
receptors (9), and participants studied here exhibited evidence
of cerebellar plasticity in response to leptin replacement (6).
With leptin supplementation, the cerebellum showed enhanced
activation (in the contrast high-calorie ? low-calorie stimuli). In
healthy adults, high-calorie foods elicit greater activation of the
cerebellum in an analogous contrast (11), but cerebellar perfu-
sion reportedly decreases with satiety (13, 15). Further study is
needed to clarify the role of leptin in modulating cerebellar
The results of this study are limited inasmuch as genetic leptin
deficiency is extremely rare, and elevated plasma leptin usually
accompanies obesity, indicating leptin resistance (24). However,
in clinical trials, high-dose leptin administration can produce
moderate weight loss in some obese patients (25). Because
evolution pressured the development of redundant systems to
prevent negative energy balance, the therapeutic use of leptin is
Table 3. Greater activation while leptin-deficient in high-calorie >
low-calorie contrast at t > 3.45 with P < 0.001 uncorrected
and extent > 10 voxels
(x y z)
Insula, left 20
Limbic lobe, right
Parahippocampal gyrus, left
Parietal postcentral gyrus, right
Parietal supramarginal gyrus, left
Temporal fusiform gyrus, left
Occipital precuneus, right
Images are SPM T maps of significantly greater BOLD response during leptin
supplementation (vs. 33 days after discontinuation) for the contrast of high-
calorie ? low-calorie stimuli. Left image (x ? 0) shows largest significant
clusters in the medial frontal gyrus (MFG): left MFG extent ? 102, t ? 4.70, z
score ? 4.70, peak voxel at ?2 32 ?12; right MFG extent ? 202, t ? 4.69, z
score ? 4.58, peak voxel at 10 56 12. Right image (x ? 14) shows the largest
significant cluster in the right cerebellum: extent ? 379, t ? 5.39, z score ?
5.38, peak voxel at 16 ?84 ?24. Images are in neurologic orientation, dis-
played on the SPM5 EPI template. Coordinates are in MNI space, contrast
comparisons at P ? 0.001 uncorrected.
Leptin supplementation enhanced activation in PFC and cerebellum.
Table 2. BMI of subjects at time of fMRI scans
leptin supplementation. Images are SPM T maps of significant BOLD signal
change greater when leptin supplementation was discontinued (vs. during
supplementation) for the contrast high-calorie ? low-calorie stimuli. Left
image (z ? 29) shows a significant cluster in the region of the left parietal
supramarginal gyrus: extent ? 52 voxels, t ? 4.06, z score ? 4.05, peak voxel
bilaterally in the insula. Left insula: extent ? 20 voxels, t ? 3.9, z score ? 3.89,
peak voxel at 48 0 0. Images are in neurologic orientation, displayed on the
Greater activation in parietal cortex and insula in the absence of
Baicy et al.
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likely limited to certain forms of obesity or combination thera-
pies. Despite these limitations, elucidating the mechanisms by
which leptin alters brain function in congenital leptin deficiency
can provide understanding of normal leptin physiology and may
ultimately help identify new targets for the treatment of obesity
and related metabolic disorders. We show here that leptin
reduces brain activation in regions linked to hunger (insula,
linked to inhibition and satiety (prefrontal cortex), suggesting
possible therapeutic targets for human obesity.
Research Subjects. Three adults from a Turkish family gave
written informed consent and were admitted to the General
Clinical Research Center at the University of California Los
Angeles (UCLA) for study, under approval of the UCLA
Institutional Review Board. There was a baseline adjustment
of leptin replacement therapy. The participants were allowed to
was not restricted.
A detailed description of the treatment procedure (4) and a
microanalysis of eating behavior for the first 15 weeks of
treatment (5) have been published. Briefly, the subjects received
daily (between 1800 and 2000 h) s.c. injections of recombinant
methionyl human leptin (provided by Amgen, Thousand Oaks,
CA) at low physiological doses (0.002–0.040 mg/kg) for the
duration of the study. The dose was chosen to achieve physio-
logical leptin concentrations and was administered in the
evening to model the normal circadian variations in endogenous
leptin. As subjects lost weight, the dose was reduced to avoid
excessive weight loss. Along with BMI, leptin dose has remained
stable, at low physiological replacement levels, for several years,
indicating that there is no resistance to exogenous leptin sup-
plementation in these patients.
Data Acquisition. Each subject participated in three scanning
sessions. The first session was conducted 57 months after the
initial start of leptin replacement, which was then discontinued
for 33 days before the second test session. To distinguish
responses to leptin replacement from possible effects of task
repetition, treatment was resumed for 14 days before the third
test session. Participants received a standard breakfast that
consisted of 20% of daily calories of an isocaloric weight-
maintaining diet (according to the Mayo Clinic nomogram: 55%
carbohydrates, 20% protein, 25% fat) 3 h before fMRI, with no
Neuroimaging data were collected on a 3 T MRI scanner
(Allegra, Siemens). Using a T2*-weighted gradient-recalled
echoplanar imager (EPI), with blood oxygen level-dependent
(BOLD) contrast (repetition time, 1,500 ms; echo time, 30; flip
angle, 70; slice thickness, 4 mm with a 1-mm interslice interval;
matrix, 64 ? 64; in-plane resolution, 3.12 mm2). A set of 240
images of each axial slice through the brain was acquired.
Using a block design, three sets of visual stimuli were pre-
sented once in each of two runs per test session. All stimuli were
high-quality, full color photographs. Images of high-calorie
foods (e.g., fried chicken, cheeseburgers, pizza), low-calorie
foods (e.g., strawberries, salad), and brick walls (neutral condi-
tion) were presented. Each block lasted 30 sec, during which two
photographs from the same set were presented consecutively for
9 s each, and a rating scale (‘‘1’’ minimum to ‘‘7’’ maximum) was
then presented for 12 s along with the expression ‘‘Aciktim?’’
(which means ‘‘I am hungry?’’ in Turkish). The participants were
instructed to provide their ratings by pressing a button, with the
number of presses indicating their score of how hungry the
images made them feel.
Table 4. Greater activation with leptin supplement in high
calorie > low calorie contrast at t > 3.45 with P < 0.001
uncorrected and extent > 10 voxels
(x y z)
Medial frontal gyrus, left102
Medial frontal gyrus, right
Middle frontal gyrus, right
Superior frontal gyrus, left
Frontal lobe, right
Cingulate gyrus, left
high-calorie ? low-calorie stimuli. Each subject showed greater activation in
the insula but less activation in the right cerebellum and prefrontal cortex
(medial frontal gyrus, MFG) when no leptin supplementation (center), com-
pared with test sessions when supplemental leptin was administered (left
Region of interest analysis by subject by fMRI scan for the contrast
www.pnas.org?cgi?doi?10.1073?pnas.0706481104Baicy et al.
Data Analysis. Ratings of hunger were analyzed in separate
analyses of variance for each of the three subjects, with stimulus
type (high-calorie food, low-calorie food, neutral) and scan
session [first (57-month supplementation), second (supplemen-
tation discontinued 33 days), third (supplementation resumed 2
weeks)] as independent variables. Data from the individual test
sessions were compared by using Fisher’s least significant dif-
ferences post hoc tests. BMI was assessed by using paired
samples t test.
Imaging data were analyzed by using Statistical Parametric
Mapping (SPM5, Welcome Department of Cognitive Neurol-
ogy, London, U.K.). Treating the data for each subject sepa-
rately, all of the images from the functional scans were aligned
to the first functional image collected in the first test session.
They were then corrected for motion, coregistered, spatially
normalized to the EPI template from SPM5, and then smoothed
with a 6-mm full-width half-maximal Gaussian filter. A 128-s
high-pass temporal filter was used, and individual movement
parameters were applied as a multiple regressor. Data were
analyzed by using the general linear model with model time
courses constructed for each condition by convolving each block
with the canonical hemodynamic response function.
A fixed effects group analysis included all of the functional
scans in one general linear model. To determine whether the
food-related stimuli were salient and our scanning paradigm
valid for the population studied, SPM (T) maps were made of the
contrast high-calorie ? neutral, collapsing data across test
sessions and subjects. Then SPM (T) maps were made of the
contrast high-calorie ? low-calorie in conditions of leptin sup-
plementation and discontinuation. We selected this contrast
because pictures of high-calorie foods elicit higher reward value,
have greater motivational salience, and induce stronger emo-
tional memories than pictures of low-calorie foods (11). We
reasoned, therefore, that the possible differences observed
would reflect leptin effects on conditioned responses to stimuli
related to high-calorie food, rather than responses to complex
visual stimuli in general. One-sample t tests were used to identify
regions where BOLD signal change (with task condition) dif-
fered with leptin status. A voxel-level height threshold of P ?
0.001 (uncorrected) was used to identify significant stimulus-
related activity in a whole brain analysis.
Clusters of activation, significant at a voxel level threshold of
t ? 3.45 and having an extent ?10 voxels, were extracted using
the ‘‘volumes’’ option in SPM5. The Montreal Neurological
Institute (MNI) coordinates of the peak voxels in each cluster
were transformed to those of the atlas of Talairach and Tour-
noux (mni2tal.m matlab program by Matthew Brett), and the
associated brain regions were labeled by using the Talairach
Daemon Client (Peter Kochunov and Angela Uecker, http://
To confirm that the findings represented those of the entire
group and both long-term stabilization (57-month) and sub-
acute supplementation (2 weeks), we analyzed data from
significant activation clusters, selected on the basis of prior
imaging studies (10, 11). These clusters were regions of interest
from which mean % signal change was extracted (for each
subject and test session) with the SPM5-compatible tool
This work was supported in part by National Institutes of Health (NIH)
Grants DA022539 and DA020726 (to E.D.L.), RR016996, DK058851,
and GM061394 (to J.L.), and RR017365 and DK063240 (to M.-L.W.)
Center (NIH Grant RR00865 to G. S. Levy). K.B. has been supported
by NIH Training Grants GM08042 and DA021961. During the course of
this study, Amgen, Inc., graciously provided leptin; Amylin, Inc., now
provides leptin to these patients. Neither Amgen, Inc., nor Amylin, Inc.,
contributed to the design, analysis, or writing of this study.
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