Cortical networks for working memory and executive
functions sustain the conscious resting state in man
B. Mazoyer, L. Zago, E. Mellet, S. Bricogne, O. Etard, O. Houde ´, F. Crivello, M. Joliot, L. Petit and
Groupe d’Imagerie Neurofonctionnelle, UMR6095, CNRS, LEA, Universite ´ de Caen,
Universite ´ Paris 5, France
[Accepted 26 October 2000]
ABSTRACT: The cortical anatomy of the conscious resting state
(REST) was investigated using a meta-analysis of nine positron
emission tomography (PET) activation protocols that dealt with
different cognitive tasks but shared REST as a common control
state. During REST, subjects were in darkness and silence, and
were instructed to relax, refrain from moving, and avoid sys-
tematic thoughts. Each protocol contrasted REST to a different
cognitive task consisting either of language, mental imagery,
mental calculation, reasoning, finger movement, or spatial
working memory, using either auditory, visual or no stimulus
delivery, and requiring either vocal, motor or no output. A total
of 63 subjects and 370 spatially normalized PET scans were
entered in the meta-analysis. Conjunction analysis revealed a
network of brain areas jointly activated during conscious REST
as compared to the nine cognitive tasks, including the bilateral
angular gyrus, the left anterior precuneus and posterior cingu-
late cortex, the left medial frontal and anterior cingulate cortex,
the left superior and medial frontal sulcus, and the left inferior
frontal cortex. These results suggest that brain activity during
conscious REST is sustained by a large scale network of het-
eromodal associative parietal and frontal cortical areas, that
can be further hierarchically organized in an episodic working
memory parieto-frontal network, driven in part by emotions,
working under the supervision of an executive left prefrontal
network. © 2001 Elsevier Science Inc.
KEY WORDS: Consciousness, Working memory, Executive
functions, Resting state, Brain activation, PET.
A large part of our daily mental activities are internalized, id est
performed without external input or motor output, and not goal
directed. During this particular state of consciousness, that is not to
be confounded with arousal or perceptual consciousness, one is
monitoring both somesthesic and vegetative information, such as
sensations and body position, and experiencing association of free
thoughts that deal with the recollection of past experiences, inner
speech, mental images, emotions, planning of future activities, etc.
This mental state has been referred to as a Random Episodic Silent
Thinking (REST) state by previous authors , thereby emphasiz-
ing the unconstrained nature of this kind of thoughts, as opposed
to a more focused and constrained sort of episodic memory activity
when one is driven to search into his past history.
Despite the fact that assessing the exact mental content of a
subject during REST is by essence difficult and must rely on
introspection, which clearly constitutes a scientific limitation, there
is a considerable interest in the study of the neural bases of the
conscious resting state.
First, from a strict cognitive neuroscience point of view, it is
important to try to establish whether or not a network of brain
areas is specifically engaged during this mental state brain. If so,
this would provide a strong argument favoring the “computation-
al” nature of brain activity during REST  and, depending on the
locations of these areas, insights regarding the major cognitive
The answer to this question is also of primary importance for
cognitive neuroimaging experiments, because conscious rest has
been (and is still) widely used in the cognitive neuroimaging
community as a reference state to which better controlled cognitive
processes are contrasted. This is explicitly the case for positron
emission tomography (PET) or functional magnetic resonance
imaging (FMRI) experiments, in which local neural activity during
conscious rest serves as a baseline for assessing hemodynamic
variations during cognitive process execution. To some extent, it is
also implicitly the case for event-related electroencephalography
or magnetoencephalography experiments, because electrical/mag-
netic activity is generally compared to a baseline activity measured
over the several tens/hundreds of milliseconds that precede stim-
ulus presentation when the subject is in a state that resembles to
Although it is an ill-defined mental state, there are some good
reasons for using conscious rest as a reference state in cognitive
neuroimaging. First, it is applicable in all imaging experiments, as
opposed to high level cognitive control tasks that have been used
to test the involvement of a specific cognitive module, with the
potential drawback of masking joint activations in both the refer-
ence and the task of interest . As a matter of fact, differences
in the reference conditions have been put forward in order to try to
solve controversies regarding the putative brain network involved
in identical tasks . As such, the conscious resting state can
serve as a common reference both within and between laboratory
* Address for correspondence: Dr. Nathalie Tzourio-Mazoyer, Groupe d’Imagerie Neurofonctionnelle, GIP Cyceron, Bd Becquerel BP 5229, 14074 Caen
Cedex France. Fax: ?33-231-470-222; E-mail: firstname.lastname@example.org
Brain Research Bulletin, Vol. 54, No. 3, pp. 287–298, 2001
Copyright © 2001 Elsevier Science Inc.
Printed in the USA. All rights reserved
0361-9230/01/$–see front matter
experiments. Second, the conscious resting state does not rely on
a given sensory modality for stimulus delivery or on a specific kind
of behavioral output. Third, its variability both within and across
subjects has been shown to be of the same magnitude than any
other cognitive task .
Studies on the cortical anatomy of the resting state have been
first relying on the observation of the regional pattern of the
glucose metabolic rate (rCMRGlu) or regional cerebral blood flow
(rCBF) [14,42,55]. These studies revealed brain areas of higher or
lower metabolic/hemodynamic activity, provided figures of their
local variability, but did not allow to uncover a specific network of
brain areas involved during the resting state. A recent PET exper-
iment compared rCMRGlu maps in healthy volunteers at REST to
that of patients in a vegetative state , showing a widely
distributed network of brain areas having higher neural activity
during REST. A recent FMRI experiment has focused on the issue
of the neural bases of the resting state, contrasting REST to
auditory perceptual or semantic tasks . A left hemisphere pari-
eto-frontal network was found of equal activity during REST and
the semantic task, but of reduced activity during the perceptual
task, leading the authors to propose that mental activity during
REST was of “conceptual processing” nature.
However, this claim remains to be formally demonstrated be-
cause it relied on simple contrast analysis (REST vs. tone, REST
vs. semantic, etc.), concerned task involving the sole auditory
modality, with possible unwanted interference of attentional pro-
cess due to scanner noise, and was based on a somewhat limited
sample size, which raises a sensitivity issue. One way of alleviat-
ing these limits could be through a meta-analysis of activation
protocols in which a REST condition was used. The idea of using
a meta-analysis to uncover process common to different tasks has
been proposed and previously exploited by others [63–66]. In their
approach, Shulman et al. reanalyzed a set of 9 PET experiments
contrasting passive vs. active visual tasks, using activation map
averaging in order to uncover processes that generalize across
tasks. This approach has the potential drawback that it could reveal
activation that would not necessarily be common to all protocols
but rather driven by the strongest ones, with possibly reduced
activity in some others. Actually, conjunction analysis appears as
the optimal statistical approach of choice when trying to identify
joint activations across protocols .
The present study was designed to alleviate some of the con-
cerns raised by previous studies dealing with the neural bases of
the conscious resting state. It combines the intrinsic power of
meta-analysis, the specificity of conjunction analysis, and a variety
of cognitive tasks to be contrasted to REST. Accordingly, a set of
nine PET activation protocols performed in our laboratory over the
past 3 years, all including REST as a control task, have been
reanalyzed using conjunction analysis, searching for joint activa-
tion during REST as compared to a variety of cognitive tasks,
including different stimulus presentation modalities, cognitive pro-
cesses, and behavioral outputs.
MATERIALS AND METHODS
Sixty-three young healthy male volunteers participated to the
study (22.0 ? 2.0 years, mean ? SD). All were right-handed as
assessed by the Edinburgh questionnaire (88.1 ? 13.7; range,
50–100) and were free of brain abnormalities as assessed on their
T1-weighted 3D MRI scan. All subjects gave their informed con-
sent. The study was approved by the Basse-Normandie Ethic
Each of the 63 subjects participated in one and only one of nine
different activation protocols (see Table 1). Each protocol con-
sisted of repeated cerebral blood flow mapping with PET during a
series of cognitive tasks, including a resting state condition.
Resting state condition. The resting state condition, which we
will refer to as REST in the following, was common to all
protocols. During this condition, the subject was placed in the PET
camera, a dark curtain entirely covering the camera tunnel and
turning it into a black chamber (Fig. 1), thereby ensuring total
darkness. During REST, luminance in the black chamber was
measured at 0 ? 1 Lux (Testo 545 Luxmeter; CORAME, Epron,
France). Noise in the black chamber, was reduced to that of the
cooling system and measured at 53.0 ? 1.5 dB (Testo 815 Sonom-
eter; CORAME). Before each REST acquisition, subjects were
instructed to “keep their eyes closed, to relax, to refrain from
moving, and to avoid any structured mental activity such as count-
ing, rehearsing, etc.” These instructions were given 30 s before
water infusion and repeated before each REST scan.
DESCRIPTION OF THE NINE POSITRON EMISSION TOMOGRAPHY ACTIVATION PROTOCOLS INCLUDED IN THE META-ANALYSIS
Protocol*Stimulus TaskResponse Subjects Pairs Scans
1. Visual motor  VIS 5 ? 4 grid ? fixation point cell
VIS Object/animal drawing
VIS Digit pair
AUD Abstract sentence
AUD Abstract word pair
AUD Object name
Press cursor if a corner cell has been litMOT6 1836
2. Verb generation 
3. Mental calculation 
4. Language 
5. Language 
6. Language 
7. Mental imagery 
Generate semantically related verb
Mental multiplication; say product
Listen; press cursor on second word
Generate object mental image; press cursor
when it is vivid
Move objects with cursor so as to
invalidate the rule
Move right index (self-paced)
8. Perceptual matching  VIS Colored geometric figures ? logical
MOT8 24 48
9. Motor 
MOT8 24 48
* In all protocols, conscious resting states served as a reference to the cognitive task.
VIS, visual; AUD, auditory; MOT, motor; VOC, vocal; numbers in square brackets refer to individual protocol publications in reference list.
288 MAZOYER ET AL.
Upon completion of the PET study, subjects had to answer a
detailed questionnaire in order to assess the content of their mental
activity during the REST conditions. In the questionnaire, the
subjects were asked to subjectively describe the nature of their
mental activity, particularly with respect to the presence of mental
images, inner speech, memory reminiscences, and somesthesic
Cognitive tasks. Nine different cognitive tasks, one for each
protocol, were contrasted to the REST condition: visuomotor, verb
generation, mental calculation, listening to language stimuli (three
protocols), visual mental imagery, perceptual matching, and self-
paced movement (see Table 1). Stimuli were delivered to the
subjects using either the visual or the auditory modality (four
protocols each), while responses required finger movement (five
protocols) or vocalization (two protocols, see Table 2). Auditory
stimuli were recorded on digital tapes and binaurally delivered
using earphones, while visual stimuli were presented on computer
screen, placed inside the black chamber, that the subject could
view thanks to a mirror attached to the head holder. Responses
were recorded via using either a computer device or a microphone.
Characteristics of the nine cognitive tasks used in the present
study have been published elsewhere in some form (see references
below) and will only be sketched here.
FIG. 1. Experimental setup for positron emission tomography (PET) experiments. Black curtains are attached to
the front and rear of the PET camera ensuring total darkness during the conscious resting state condition
(luminance in the camera tunnel 0 ? 1 Lux). The black chamber at the PET camera rear can accommodate a PC
for visual stimulus delivery.
NUMBER OF POSITRON EMISSION TOMOGRAPHY ACTIVATION
PROTOCOLS PER STIMULUS/RESPONSE TYPES
NEURAL BASES OF THE CONSCIOUS RESTING STATE289
In the visuomotor task (#1) , subjects were presented a 4 ?
5 grid on a computer screen, including a fixation point at its center
on which they were to keep their gaze. Grid cells were succes-
sively and randomly lit for 1 s; the subject had to press a button
whenever a corner has been lit.
The visual language task (#2)  consisted in the presentation
of black line drawings of objects (73%) or animals (27%), on a
white computer screen, at a rate of 0.25 Hz. Subjects were re-
quested to generate aloud a verb semantically related to the dis-
played object/animal drawing.
The calculation task (#3)  consisted in simple arithmetic
facts. The subjects had to overtly name the result of the mental
multiplication of pairs of digits presented on a computer screen at
an average rate of 1.25 Hz.
The auditory language tasks consisted in listening to either (1)
abstract word pairs presented at a rate of 0.12 Hz (#4) , (2)
abstract word definitions (#5)  consisting in short sentences
lasting 6 s and followed by a 2-s silent delay, or (3) 2-minute long
factual stories (#6) . In all three tasks, subjects were asked to
attentively but passively listen to the stimuli that were given in the
subject’s mother tongue.
The mental imagery task (#7)  consisted of generating and
maintaining a vivid visual mental image of an object upon hearing
its name. Objects’ names were delivered through earphones at a
0.1 Hz rate.
During the perceptual matching task (#8) , subjects were
presented with 12 colored geometric shapes on a computer screen,
and a logical conditional rule such as, for example, “If there is not
a red square on the left, then there is a yellow circle on the right”.
The task was to move, using the computer mouse, two of the
shapes in a two-part box drawn on the screen so as to falsify the
Finally, the motor task (#9)  consisted in self-paced right
index flexion and extension that were performed at an average rate
of 0.75 Hz.
PET Data Acquisition
The same experimental apparatus and design was used for all
PET studies. The subject head was positioned in the PET camera
field of view, immobilization being ensured by means of a custom
head holder attached to the camera bed. rCBF was monitored using
PET and oxygen 15 labeled water bolus injection in the left basilic
vein. For each rCBF measurement, a single 90-s scan was acquired
using an ECAT HR? PET camera (SIEMENS, Erlangen, Ger-
many) with septa retracted (3D mode), starting at the arrival of the
15O labeled water. Each scan was reconstructed with a 0.5 mm?1
cut-off frequency Hanning filter, including correction for attenua-
tion (using an acquired 130 Mevents 2D transmission scan), ran-
doms and scatter. The time between two PET measurements was
rCBF images were spatially normalized using the SPM package
(SPM96 version, ) to the Montreal Neurological Institute
(MNI) template, and filtered using a 12-mm Gaussian filter leading
to a final image smoothness of 12.1 ? 13.6 ? 15.1 mm3. Raw
counts volumes were proportionally normalized to 50 ml/min per
The REST condition was compared to the set of the nine other
cognitive tasks using a conjunction analysis  as implemented
in the SPM package (SPM99 version), searching for brain areas
jointly activated or deactivated during REST as compared to the
nine cognitive tasks. Depending on the protocol, two or three
replicates of both the cognitive task and the REST condition were
available for each of the 63 subjects, leading to a total of 185 pairs
of REST/TASK scans (see Table 1). A multigroup conjunction
analysis was performed using SPM99, with a significance level set
at 0.05 corrected for multiple comparisons.
Anatomical localization of activation/deactivation foci was per-
formed using anatomical landmarks of the single subject MRI
normalized to MNI template provided by SPM; in order to com-
pare our results with that of previous studies, each focus was also
assigned a Brodmann’s area (BA) number based on its stereotactic
coordinates and the Talairach atlas . Conjunction maps ob-
served in the present study were compared to that of a previously
published similar meta-analysis  and to two other studies
dealing with the conscious resting state [7,40], using the Euclidian
distance between corresponding foci in the Talairach space as an
index of similarity.
Among the 63 subjects that were included in the study, 41
properly answered the questionnaire dealing with their REST
condition mental activity. Overall, a majority of subjects (56%)
reported that mental events were partly dealing with autobio-
graphic reminiscences, either recent or ancient, consisting of fa-
miliar faces, scenes, dialogs, stories, melodies, etc.
Inner speech and mental images were the most frequently
reported types of mental events during REST. Ranking the occur-
rence of such events on a three-level scale (Absent, Rare, Fre-
quent; Table 3), we found that mental images (respectively inner
speech) occurred in 83% (respectively 73%) of the subjects. How-
ever, there was no association between the occurrences of these
two types of events (?2? 4.16, p ? 0.38, df ? 4) meaning that
subjects did not engage systematically in one type of mental
activity during the REST condition. No systematic difference was
observed between the groups of subjects of the various protocols
regarding the occurrence of mental events during REST, although
there was a much larger proportion of subjects reporting frequent
mental imagery activity during REST in the group of subjects of
the perceptual matching protocol (87%) as compared to the other
groups (23%) (p ? 0.001, chi-square test). Finally, some subjects
reported discomfort or light pain in the back of their head (58%) or
in their left arm (22%).
Conjunction Analysis of PET Data
Brain areas jointly “activated” during REST as compared to
the nine cognitive tasks. As shown in Table 4 and Fig. 2, a network
OBSERVED OCCURRENCES OF REPORTED MENTAL IMAGERY AND
INNER SPEECH MENTAL ACTIVITIES DURING THE CONSCIOUS
RESTING CONDITION IN 41 SUBJECTS
?2? 4.16, df ? 4, p ? 0.38.
290MAZOYER ET AL.
of brain areas, mainly localized in the left hemisphere, was found
jointly activated during REST. The larger activation focus was
found in the left posterior cingulate cortex (BA 30 and 31),
extending caudally to the anterior precuneus (BA 7) and paracen-
tral lobule (BA 5). In addition, bilateral activations were found at
the junction of the middle occipital gyrus and the angular gyrus
(BA 19 and 39). Foci of activations were also detected in the right
post-central gyrus (BA 2), at the level of the hand/arm represen-
All other foci of activation were found in the left frontal lobe,
including the upper parts of the superior and middle frontal gyrus
(BA 6/8), the median superior frontal (BA 10) and anterior cin-
gulate (BA 32) cortex, the inferior frontal gyrus (BA 45/46), the
lower parts of the superior and middle frontal gyrus (BA 10/11).
FIG. 2. Three-dimensional renderings of statistical parametric conjunction maps showing brain areas of
higher normalized cerebral flow during conscious resting state than in any of the nine cognitive tasks included
in the protocol. Left: front view, Right: rear view. Conjunction maps were generated at a 0.001 statistical
(uncorrected for multiple comparisons) for display purposes.
ACTIVATION CLUSTERS DURING CONSCIOUS RESTING STATE* AS COMPARED TO THE NINE TASKS INCLUDED IN THE META-ANALYSIS
L superior occipital/angular
L superior occipital
R superior occipital/angular
L posterior cingulate
L paracentral lobule/anterior precuneus
L paracentral lobule
L posterior cingulate
L superior frontal sulcus
L superior frontal
L middle frontal
L middle frontal
L inferior frontal (triangularis)
L median superior frontal
L anterior cingulate
L anterior cingulate
L anterior cingulate
L middle frontal sulcus
L orbital superior frontal
L superior frontal
R rolando sulcus
* p ? 0.05 corrected for multiple comparisons.
L, left; R, right; BA, Brodmann’s area; x, y, z stereotactic coordinates; k ? activation cluster size in voxels.
NEURAL BASES OF THE CONSCIOUS RESTING STATE291
Figures 3 and 4 demonstrates the consistency of these activations
across the different protocols, although in two areas, namely the
median superior frontal and anterior cingulate gyrus, four tasks
induced more variations as compared to REST than the five others.
Interestingly, these four tasks share visual stimulus presentation as
a common feature.
Brain areas jointly “deactivated” during REST as compared to
the nine cognitive tasks. As shown in Table 5 and Fig. 4, we found
only a restricted set of brain areas with lower NrCBF during
REST, all located in the lobule VI (according to ) of both
cerebellum hemispheres and the vermis. Note again on Fig. 4 that
the amplitude of cerebellar deactivation during REST varied be-
tween protocols, the largest ones being observed during the same
four tasks involving visual stimulus presentation.
Comparison with other studies dealing with the conscious
resting state. As shown in Table 6, a good agreement was observed
with the results reported in the FMRI study of REST by Binder et
al. . Congruent foci of activation were found at the level of the
posterior cingulate cortex, angular gyrus, left anterior cingulate,
dorsolateral prefrontal, and orbitofrontal cortex. Most discrepan-
cies came from the absence of detection in the FMRI study of foci
reported in our study at the level of both the median frontal cortex,
the inferior frontal sulcus, and right rolandic cortex. In addition,
angular gyrus activations were found more symmetrical in the
present study than in the FMRI study, while the parahippocampal
focus found in the Binder et al. study did not have a counterpart in
ours. Finally, there was no report of hemodynamic variations in the
cerebellum during REST in the FMRI study, which could be
explained by the limited axial field of view of the FMRI acquisi-
Laurey et al.’s results were also in remarkable agreement with
ours at the level of the posterior cingulate, left occipito-parietal,
and left dorsolateral prefrontal . However, additional increased
glucose metabolism during REST as compared to the vegetative
state were also described in the right prefrontal cortex, and bilat-
erally in the temporal cortex. It is worth noticing that the REST
activation conjunction map obtained at a less stringent threshold
(0.001 uncorrected) shows a right dorsolateral prefrontal focus
consistent with that of Laurey et al. study (see Fig. 2).
Comparison with Shulman et al. meta-analysis. Table 7 sum-
marizes the comparison between our meta-analysis and that of
Shulman et al. Overall, a good agreement was observed in terms of
number and location of activation foci found either during REST
(present study) or visual passive tasks . Posterior cingulate, left
and right occipito-parietal, left frontal, anterior cingulate, and
cerebellar foci found in the two studies were within twice the
FIG. 3. Histograms of the variations across conditions of normalized cerebral flow activation during
conscious resting state as compared to the cognitive tasks in some selected areas. Images were generated
by fusion of axial sections of the Montreal Neurological Institute brain magnetic resonance imaging
template and of the conjunction volume at the same level. Task number on histogram horizontal axis refers
to task number in Table 1.
292 MAZOYER ET AL.
resolution of the conjunction maps, id est 25 mm. A few discrep-
ancies were found at the level of a second focus in the left parietal
cortex that was found to lie in a lower and more posterior location
in our study (D ? 42 mm), and for the right postcentral focus that
was not found in Shulman et al.’s study, while left and right
temporal foci were found in Shulman et al.’s study but not in ours.
There also was agreement between the foci of cerebellar deac-
tivations during REST observed in the present study and the foci
of cerebellar deactivations observed in the passive minus active
contrast of Shulman et al. study.
The present meta-analysis uncovered a parieto-frontal network
of brain areas that was more active during the resting condition
than during a variety of cognitive tasks, independent of the mo-
dality in which the stimuli were delivered, of the type of cognitive
activity, and of behavioral output. In the following we will, (1)
argue that this network sustains processes active during REST
rather than reflects deactivation processes common to all tasks, (2)
discuss the similarities between this network and the one active
during passive visual tasks, (3) address the issue of how it may
reflect high level cognitive processes active during REST, such as
working memory and executive functions.
A Network of Brain Areas Sustaining Cognitive Processes Active
As previously emphasized, there are two general frameworks
for interpreting positive increase of hemodynamic activity ob-
served in a task difference map, say A minus B, namely either as
increased neural activity generated by processes active during A,
or as reduced neural activity generated by processes active during
B [7,66]. In the context of the present study, several arguments can
be put forward that favor the first type of interpretation, namely
that it is active processes during REST that cause increased he-
modynamic activity in the network of areas described above.
First, the deliberate choice of a variety of cognitive tasks to be
contrasted to REST ensures that these cognitive tasks share only a
very limited set of cognitive processes. With this respect, the
findings by Binder et al.  provide additional examples of cog-
nitive tasks whose contrast with REST leads to a remarkably
similar cortical network of higher hemodynamic activity during
REST. In order to explain higher hemodynamic activity observed
FIG. 4. Histograms of the variations across conditions of normalized cerebral flow activation during conscious resting state
as compared to the cognitive tasks in some selected areas. Image was generated by fusion of a midline sagittal section of the
Montreal Neurological Institute brain magnetic resonance imaging template and of the conjunction volume. Task number on
histogram horizontal axis refers to task number in Table 1. Note the similar pattern of across task variations in the median
superior frontal sulcus, anterior cingulate gyrus, and cerebellar vermis.
DEACTIVATION CLUSTERS DURING CONSCIOUS RESTING STATE* COMPARED TO THE NINE TASKS INCLUDED IN THE META-ANALYSIS
L Cerebellar hemisphere lobule VI
R Cerebellar hemisphere lobule VI
Cerebellar vermis lobule VI
Cerebellar vermis lobule VI
* p ? 0.05 corrected for multiple comparisons.
L, left; R, right; x, y, z stereotactic coordinates; k ? activation cluster size in voxels.
NEURAL BASES OF THE CONSCIOUS RESTING STATE293
in a conjunction of REST minus task contrast, a cognitive process
common to all tasks but REST should generate decreased neural
activity during the task. Transmodal inhibition due to focal atten-
tion could be one such process and there have been multiple
reports in the literature of deactivations in auditory or somato-
sensory areas during visual tasks [28,53,64], or in the associative
visual cortex during somato-sensory tasks . However,
transmodal inhibition effects seem to be restricted to primary
cortices and thus cannot be at the origin of the network of joint
activations observed during REST because, with the exception of
the right rolandic area, this network includes no primary or uni-
modal associative areas. Regarding the right rolandic area activa-
tion during REST, one can hypothetize that subjects were likely to
pay more attention to external somato-sensory inputs during REST
than during stimulus-response driven tasks. Recalling that all our
subjects had a catheter for water infusion in their left arm, one can
reasonably postulate that increased rCBF during REST in the right
postcentral region could be due to a shift of attention away from
this somato-sensory input. However, one could also argue that it is
an active attentional process during REST that causes this rCBF
increase, as it has also been shown that focal attention on periph-
eral somatosensory stimulation enhances activity in the corre-
sponding cortex .
Second, use of a conjunction analysis to pool activation maps
across protocols guarantees that when increased, rCBF is increased
in all REST minus task comparisons, whereas averaging maps
across protocols, as was performed in a similar meta-analysis ,
could reveal activation during REST that would not necessarily be
common to all protocols but rather driven by the strongest ones,
with possibly reduced activity during REST in some others (see,
e.g., Figs. 2–5 of ).
Third, the network active at REST observed in the present
study remarkably overlaps the network of areas of reduced metab-
olism during the vegetative state (VS, ) as compared to a
conscious resting condition in normal volunteers. Considering that
VS is by definition a disorder of consciousness, that affects both
external and self awareness, this finding strongly supports the
proposal that the network active at REST found in the present
study closely reflects cognitive process at work during REST, such
as the free generation, association, and monitoring of conscious
thoughts. In the same vein, a recent study on propofol induced loss
of consciousness in humans demonstrated that it was associated
with reduction of neural activity in a subset of areas belonging to
the network active at REST of the present study, namely the
bilateral parieto-occipital junction, precuneus, posterior cingulate,
and left orbitofrontal cortex .
A Common Network of Brains Areas Active During REST and
We observed striking similarities between the network of brain
areas of higher blood flow during REST of the present study and
the network of areas reported to be activated during passive visual
conditions as compared to active ones , a finding which has
been also reported by others . Indeed, despite several method-
ological differences between the two meta-analyses (sample size,
spatial normalization and statistical procedure) the only major
mismatch between the two networks concerned temporal cortex
foci found in the meta-analysis of passive minus active visual
COMPARISON OF ACTIVATION FOCI OBSERVED DURING CONSCIOUS RESTING STATE (REST) IN THE PRESENT STUDY WITH: (1) FOCI OF
DECREASED METABOLISM DURING VEGETATIVE STATE AS COMPARED TO REST IN HEALTHY CONTROLS (LEFT COLUMNS , (2) FOCI OF
FUNCTIONAL MAGNETIC RESONANCE IMAGING SIGNAL ACTIVATION DURING REST AS COMPARED TO TONE LISTENING (RIGHT COLUMNS, )
Laurey et al. Study
D (mm) Present Study
D (mm) Binder et al. Study
?2, ?40, 368.0 L31/7
?8, ?36, 42
?6, ?50, 26 6.5
?9, ?55, 24
9, ?53, 23
?43, ?70, 26 L39/19
?50, ?62, 30
?64, ?34, 36
?52, ?74, 18
46, ?68, 26
24, ?34, 64
?44, 24, 42
?36, 14, 40
?32, 26, 56
?16, 56, 26
?56, 34, 0
?32, 22, 42
?24, 24, 52
?4, 58, 12
?46, 48, 0
0, 38, ?2
?46, 36, 18
?26, 36, ?10
?20, 30, 44
?9, 34, ?7
?51, 26, 14
?26, 28, ?8
?28, 56, 2023.7
14, 38, 52
46, 32, 30
30, 52, 24
42, 12, 54
?66, ?44, ?6
?62, ?60, ?8
48, ?56, 16
?26, ?35, ?12
Foci are identified by their stereotactic coordinates and Brodmann area number according to the Talairach atlas. Cells in grey indicate mismatch between
the studies. D, euclidian distance between corresponding foci in the Talairach space, L, left; R, right.
294 MAZOYER ET AL.
conditions. This discrepancy could be due to enhanced visual
attention during active visual tasks generating transmodal inhibi-
tion in the auditory cortex .
In their discussion, Shulman et al.  could not settle between
alternative interpretations of their results, namely whether higher
blood flow during passive visual tasks as compared to active visual
tasks were due to active processes during the passive tasks or to
common inhibitory processes during the active tasks. The similar-
ities between the passive visual conditions and REST networks
favors the first interpretation and leads to postulate that this net-
work sustains cognitive processes that are active during both the
passive visual tasks and REST. Among possible candidates, Shul-
man et al. proposed that unconstrained verbal thought, monitoring
of the external environment, body image, and emotional state
could be at work during passive visual conditions: all these pro-
cesses are likely to be also at work during the REST conditions as
implemented both in the present study and in the Binder et al.
FMRI study .
A Network Sustaining Working Memory and Executive
Functions During REST
Actually, based on the introspective questionnaires of our sub-
jects regarding the content of their mind during REST, one must
admit that processes at work during REST go well beyond uncon-
strained verbal thoughts, but also include generation and manipu-
lation of mental images, reminiscence of past experiences based on
episodic memory, and making plans. Moreover, in order to follow
the instructions of the REST condition (see Materials and Methods
section), subjects had to recruit inhibitory process in order both to
refrain from moving and to avoid structured mental activities,
especially those related to the cognitive task of the protocol they
participated in. All these cognitive processes are components of
working memory and executive systems, known to be sustained by
high-order associative heteromodal and paralimbic areas [25,46].
As a matter of fact, the network active during REST as well as
during passive visual conditions exclusively includes such corti-
ces. The high-order nature of these areas led previous authors to
consider “conceptual processing” as the main cognitive process at
work during REST, and more specifically semantic processing .
This interpretation was based on the observation that, when com-
pared to the same tone matching task, REST and a semantic task
elicited hemodynamic activity increases of similar amplitudes in a
common network of brain areas. However, the present study shows
that hemodynamic activity in this network is more active during
REST than during several tasks included in the conjunction anal-
ysis that did require semantic processing. This apparent discrep-
ancy between the two studies could be due to a lack of sensitivity
of the FMRI study, which could be due either to a limited sample
size or to a threshold effect, and led us to propose an alternative
interpretation of our findings. Before proceeding to this, and es-
pecially to a tentative segregation of the network activated at
REST in separate sub-networks sustaining different cognitive
components, it seems worthwhile to emphasize that such an inter-
pretation will be largely putative both because of the ill controlled
nature of the REST state and of the observational nature of the
experimental design. However, the large corpus of cognitive neu-
roimaging data that is available today allows one to use inductive
reasoning for observational data interpretation.
Within this framework, it is noteworthy that retrosplenial areas,
namely the posterior cingulate cortex and precuneus, are known to
be involved in episodic memory  (for review see [13,59]), a
cognitive function that has psychological commonality with REST
as emphasized by others . Retrosplenial activations have indeed
been reported in a large variety of episodic memory tasks, would
they be based on explicit visual material [22,58], requesting the
retrieval of material including a visual memory component [3,21,
50,54,69], based on verbal material [1,2,4,9,27,32,68], or irrespec-
tive of the imagery content of the material to be retrieved .
COMPARISON OF ACTIVATION AND DEACTIVATION FOCI OBSERVED IN SHULMAN’S METANALYSIS  AND IN THE PRESENT STUDY
Shulman et al.  Study
D (mm)Present Study
Activation foci during control state
?5, ?49, 40
?53, ?39, 42
?45, ?67, 36
45, ?57, 34
?8, ?36, 42
?52, ?74, 18
?40, ?82, 34
46, ?68, 26
24, ?34, 64
?32, 22, 42
?18, 40, 48
?27, 27, 40
?11, 41, 42
5, 49, 36
?15, 55, 26
?19, 57, 8
?1, 47, ?4
?33, 45, ?6
?4, 58, 12
?4, 58, 12
?4, ?46, ?4
?46, 48, 0
?46, 36, 18
0, 38, ?2 12. L32
Deactivations foci during control state (cerebellum)
L lobule VI
Vermis lobule VI
R lobule VI
3, 31, ?10
?49, ?19, ?18
21, ?9, ?18
?23, ?61, ?14
?3, ?69, ?8
33, ?63, ?18
L lobule VI
Vermis lobule VI
R lobule VI
?28, ?52, ?30
0, ?70, ?14
16, ?62, ?26
Foci are identified by their stereotactic coordinates and Brodmann area number according to the Talairach atlas. Cells in grey indicate mismatch between
the 2 studies. D, euclidian distance in the Talairach space between corresponding foci; L, left; R, right.
NEURAL BASES OF THE CONSCIOUS RESTING STATE295
Actually, the analysis of the REST questionnaires shows that the
subjects of the present study preferentially reported autobiographic
episodes. With this respect, it is worth noticing that the recall of
autobiographic episodic memory, that includes a greater emotional
content than non-autobiographic retrieval, has been reported to
induce larger activation of the posterior cingulate cortex . In
addition, a recent review of the neuroimaging literature has
stressed the involvement of the retrosplenial regions in emotional
processing and provided strong arguments for a specific role of the
posterior cingulate (BA 30) as a mediator of the interaction be-
tween emotion and episodic memory . The hypothesis that the
posterior cingulate is implicated in salient emotion monitoring is
further supported by the fact that other regions dealing in emo-
tional processing are activated during REST, in particular the
orbital frontal cortex.
Regarding the precuneus, one should emphasize that it is its
most anterior part that was found activated during REST. An
antero-posterior functional segregation within the precuneus has
already been suggested by Buckner et al. , who reported
deactivation of its anterior portion during various cognitive tasks
when compared to REST or passive conditions, whereas the pos-
terior precuneus had been repeatedly reported as involved in
conscious effortful recollection of episodes . The present study
confirms the activation during REST of the anterior precuneus and,
given its anatomical and functional proximity with the posterior
precuneus and posterior cingulate, leads us to postulate that it
could be part of a network specifically involved in the free willed
recall, as opposed to constraint or effortful recall, of episodic
memory items present during REST.
In the same vein, activations located at the junction between the
angular and the middle occipital gyri have been described, to our
knowledge, only during the REST condition as compared to pic-
ture  and verbal  recall tasks. These cortical areas, which are
different but in the vicinity of occipital areas involved during
visual mental imagery [43,44,58], are singular in that they do not
belong to the unimodal associative cortex, such as those involved
in visual mental imagery, but rather to the high-order heteromodal
associative cortex [47,51]. Together with the anterior precuneus,
they appear to constitute a network specific for the recall and
maintenance of multimodal thoughts, such as mental images, inner
speech, etc., from episodic and long term memory through free
association, under the control of the prefrontal network of regions
evidenced in the present study.
As a matter of fact, working memory load from long term
memory and manipulation of thoughts are known to be sustained
by hierarchically organized and reverberating fronto-parietal re-
ciprocal connections . During REST, we observed a high
hierarchical level network constituted with left prefrontal, bilateral
angular gyri, and retrosplenial regions. The claim that this set of
areas does constitute a network is supported by neuroanatomical
studies in the rhesus monkey that have shown long fibers projec-
tion from the prefrontal cortex to the posterior cingulate cortex, as
well as reciprocal connections through the occipito-frontal fascic-
ulus between the parieto-occipital junction (corresponding to the
angular gyrus in humans) and the prefrontal cortices . Within
this large scale cortical network, heteromodal dorsolateral and
paralimbic medial prefrontal cortices co-activation corresponds to
the integration of mental events and to the monitoring of emotions
and motivational resources , the orbital frontal region being, in
particular, known to be devoted to emotional and motivational
Meanwhile, recent data from neuroimaging studies have dem-
onstrated that, although it seems difficult to dissociate the working
memory from the manipulation of data in working memory ,
the left middle and inferior frontal gyrus are in charge of manip-
ulation and inhibition of material held on line [15,16,56]. In
particular, the left inferior frontal gyrus, together with the anterior
cingulate, has been reported to be specifically implicated in the
inhibitory control of interference during go-no go tasks [36,37,49],
working memory tasks [17,31] and reasoning tasks. The im-
plication of an inhibitory control network is related, as stated
above, to the inhibition of movements, and of mental activities
related to the cognitive task of the protocol they participated in, as
it was explicitly stated by the REST condition instructions.
Finally, the leftward asymmetry of prefrontal activations found
during REST can be brought together with a recent model for
episodic memory retrieval, the “generate-recognize” model, as-
signing specialization for recall to the left prefrontal cortex (BA
45, 46), and for recognition to its right hemisphere homologue
[12,60]. This model is consistent with the results of the present
study, because, in absence of external stimuli, the generation
process dominates the episodic memory recollection during REST.
Joint Deactivations During REST
A final point of discussion on the results of the present study
concerns the joint deactivations observed in both cerebellar hemi-
spheres. Considering the variety of tasks used in our meta-analysis
and the absence of cerebellar hypometabolism during both the
vegetative state  and propofol induced loss of consciousness
, the most likely explanation for joint cerebellar deactivations
in REST minus task contrasts is that they reflect common pro-
cesses active during the tasks.
Based on the results of a recent study, a first candidate could be
internal timing because it appears to be associated with cerebellar
activations at locations very close to that of the present study .
However, although one may consider that internal timing is an
intrinsic component of cognitive activity, explicit instruction of
timing was not given to the subjects but in the finger movement
Another candidate could be the executive component proper to
each task because it has been demonstrated that cerebellar hemi-
spheres are concerned with executive language, visuospatial, or
mnemonic functions . In particular, the protocols showing the
larger activations during the tasks as compared to REST are those
containing a major memory component (see Fig. 4): recall for the
verb generation and the arithmetical facts tasks, maintenance of the
rule in working memory for the visuomotor and perceptual match-
However, it should be underlined that these protocols also share
visual stimulus presentation as a common feature that requires
both coordination of the voluntary eye movements and spatial
attention, two processes that are under the control of a network
including the lateral zone of the cerebellum to which belongs the
lobule VI .
The conscious resting state in humans is sustained by a large
scale network of heteromodal associative parietal and frontal cor-
tical areas, that can be further hierarchically organized in an
episodic working memory parieto-frontal network, driven in part
by emotions, working under the supervision of an executive pre-
frontal network. The bilateral angular gyrus and the anterior pre-
cuneus, parts of the parieto-frontal sub-network, appears to be
specifically involved during REST and may reflect the recall and
maintenance of multimodal thoughts through free association
which characterizes this mental state.
296 MAZOYER ET AL.
The authors are indebted to the Cyceron Cyclotron (P. Lochon, O.
Tirel) and PET camera staff (V. Beaudoin, G. Perchey) for their invaluable
help in acquiring the PET activation studies. The authors would also like
to thank A. Mazard for her help in some of data acquisition. Parts of this
work have been supported by grants from the GIS Sciences de la Cogni-
This work has been presented in part at the 5th International Confer-
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