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Brain Research Bulletin 74 (2007) 387–396
Review
Self-awareness and the left inferior frontal gyrus: Inner speech
use during self-related processing
Alain Morin ∗, Jayson Michaud
Behavioral Sciences, Mount Royal College, 4825 Mount Royal Gate S.W., Calgary, Alberta, Canada T3E 6K6
Received 21 January 2007; received in revised form 4 May 2007; accepted 15 June 2007
Available online 5 July 2007
Abstract
To test the hypothesis of a participation of inner speech in self-referential activity we reviewed 59 studies measuring brain activity during
processing of self-information in the following self-domains: agency, self-recognition, emotions, personality traits, autobiographical memory,
preference judgments, and REST. The left inferior frontal gyrus (LIFG) has been shown to sustain inner speech use. We calculated the percentage
of studies reporting LIFG activity for each self-dimension. 55.9% of all studies reviewed identified LIFG (and presumably inner speech) activity
during self-awareness tasks. Furthermore, the LIFG was more frequently recruited during conceptual tasks (e.g., emotions, traits) than during
perceptual tasks (e.g., agency, self-recognition). This supports the view of a relative involvement of inner speech in self-reflective processes.
Crown Copyright © 2007 Published by Elsevier Inc. All rights reserved.
Keywords: Self-awareness; Self-referential activity; Inner speech; Left inferior frontal gyrus; Conceptual self-domains; Perceptual self-domains
Contents
1. Methods................................................................................................................ 388
2. Results and discussion ................................................................................................... 389
2.1. Overview ........................................................................................................ 389
2.2. Agency and self-recognition ....................................................................................... 390
2.3. Personality traits .................................................................................................. 390
2.4. Autobiographical memory ......................................................................................... 390
2.5. Emotions......................................................................................................... 391
2.6. Evaluative judgments .............................................................................................. 391
2.7. Rest ............................................................................................................. 392
3. Conclusion ............................................................................................................. 393
Conflicts of Interest ....................................................................................................... 393
Acknowledgements ..................................................................................................... 393
References ............................................................................................................. 393
Numerous studies looking into the neural basis of self-
referential activity have been conducted since the publication
of Craik et al.’s original paper in 1999. Convergent evidence
strongly suggests that the medial prefrontal cortex (MPFC) plays
an important role in self-related processes [43,44,86,87]. The
MPFC is also frequently activated during “Theory-of-Mind”
∗Corresponding author. Tel.: +1 403 440 7069; fax: +1 403 440 7027.
E-mail address: amorin@mtroyal.ca (A. Morin).
tasks [1,34,113], indicating that thinking about one’s own and
others’ mental states probably recruits the same neuroanatomi-
cal structures [22,23,79]. The neural representation of self also
includes the precuneus, anterior and posterior cingulate corti-
cles, right inferotemporal cortex, inferior and posterior parietal
corticles, basal ganglia, and insula [65].
Although the main focus of the aforementioned body of
work has consisted in identifying brain areas specifically acti-
vated during processing of self-information, current studies
are starting to examine underlying cognitive mechanisms that
0361-9230/$ – see front matter. Crown Copyright © 2007 Published by Elsevier Inc. All rights reserved.
doi:10.1016/j.brainresbull.2007.06.013
388 A. Morin, J. Michaud / Brain Research Bulletin 74 (2007) 387–396
mediate self-perception. That is, by looking at peripheral struc-
tures that are additionally recruited during self-awareness tasks,
researchers can infer what particular thought processes are
engaged as well (see [101,102]). To illustrate, retrieval of auto-
biographical information frequently activates occipital regions
(e.g., [36]); since these areas are known to support visuospa-
tial imagery [11], it has been suggested that one forms mental
images of the self in the past when accessing autobiographical
memories [39,123]. Thus mental imagery would represent one
cognitive process involved in self-awareness [80,81].
Language too has been linked to consciousness and
self-reflective activities [7,13,24,103,115,127]. Some have pro-
posed that inner speech in particular mediates self-awareness
[6,9,59,77,84,119]. Inner speech represents the activity of
talking to oneself in silence [134]. Related terms that
can be found in the literature are self-talk, subvocal/covert
speech, internal dialogue/monologue, subvocalization, utter-
ance, self-verbalization, auditory imagery, and self-statement.
Inner speech serves various cognitive functions, among which
verbal rehearsal, planning, problem-solving, task switch-
ing, retrieval aid for task goals, and self-regulation (see
[26,42,76,78,83,104,117]). Therefore one can talk to oneself
about an unlimited number of things and for different reasons
(e.g., “I should take my umbrella with me since it will probably
rain”; “What is John’s phone number again?”). When one talks to
oneself about oneself, the function then is to gain access to infor-
mation about the self. For example, one can utter “I think I’m a
pretty punctual person” (thus assessing personality traits) or “I
remember spending a month at my brother’s place last summer”
(thus retrieving autobiographical material). Various theoretical
accounts of the role played by inner speech in self-referential
activity have been put forward; these are beyond the scope of
the present review (see [82,118]). Empirical evidence, although
indirect and limited, has also been reported: a positive and sig-
nificant correlation exists between frequency of self-focus and
use of inner speech [110,116]. Ojemann [90] observed that in
brain-damaged patients, conscious experience returns in parallel
with inner speech. Conversely, healthy volunteers report inner
speech inhibition when they transit from wakefulness to sleep
[106]. Recent work by Whitehouse et al. [130] identifies inner
speech deficits in autism, a condition in which self-awareness
and Theory of Mind abilities are known to be impaired.
The goal of this paper is to further explore the hypothe-
sis of an involvement of inner speech in the acquisition of
self-information. Below we review brain-imaging studies of
self-referential processing to determine if activation of areas
known to sustain inner speech activity is reported. We propose
that if such an activation is indeed frequently observed, one can
infer that inner speech most probably was used by participants
while working on self-awareness tasks. The left inferior frontal
gyrus (LIFG—e.g., Broadmann’s areas 44, 45, and 47; Broca’s
area; left ventrolateral PFC; left frontal operculum) has con-
sistently been identified as the neuroanatomical basis of inner
speech. That is, the LIFG reliably gets activated when partic-
ipants are asked to silently articulate sentences [74] or single
words [75]; furthermore, accidental destruction of the LIFG dis-
rupts inner speech [129]. Although it has been suggested that the
LIFG serves various additional functions (e.g., cognitive control,
working memory,selection among competing alternatives, inter-
preting actions of others—see [5,27,50,93,94]), its connection
to inner speech is well established [2,21,114]. It should also be
noted that the LIFG exhibits functional heterogeneity: its most
anterior part (BA 45) is involved in retrieval of words for their
meaning while its posterior part (BA 46/47) is specialized in
getting access to words through an articulatory code ([94]; also
see [102]).
Self-referential processing includes numerous self-
dimensions that can be organized along various lines. For
instance, Gillihan and Farah [37] developed a taxonomy of
self-domains where the physical self includes self-recognition
and agency, and the psychological self comprises personality
traits, autobiographical memory, and first-person perspec-
tive. Northoff et al. [87] instead suggest the following
self-dimensions: verbal, spatial, memory, emotional, facial,
social, and agency/ownership of movements. Based on our own
review of the literature, we classified self-aspects as follows:
agency (knowledge that one is the cause of one’s actions),
self-recognition, personality traits, autobiographical memory,
emotions (including interoception—i.e., awareness of bodily
states), and evaluative judgments (i.e., subjective choices and
preferences). We also reviewed studies of the resting state
(REST), which has been shown to coincide with introspective
awareness [41,131]. Our main prediction is that activation of the
LIFG (i.e., inner speech use) should be observed in a reasonable
number of studies (i.e., more than 50%) investigating the neural
correlates of self-related processes. We further hypothesize
apartial participation of inner speech during self-awareness
tasks, where the need to verbally label self-aspects should be
greater in conceptual self-domains (e.g., emotions, traits) than
in perceptual self-domains (e.g., agency, self-recognition). Per-
ceptual (or sensory) self-information refers to products of one’s
direct experience with oneself (e.g., the body) or environmental
stimuli (e.g., other persons, mirrors) that identify the self;
conceptual self-information designates data about the self that
is not available to immediate perceptual experience and that
somehow has to be mentally represented to be accessible to the
self. It seems plausible that not all forms of self-focus require
self-verbalization of the information to be assessed. Perceptual
self-aspects such as self-face recognition, because of the visual
and concrete nature of the information, can most likely be
captured without words. More conceptual self-dimensions such
as emotions and personality traits however, probably entail that
one talks to oneself about them (e.g., “I feel sad”, “I’m funny”)
to be fully brought to consciousness.
1. Methods
English-language articles published prior to September 2006 were identified
from searches using PubMed, Scirus, Cogprints, and PsycINFO.1The reference
1Keywords used were: agency, autobiographical memory, brain, emotions,
fMRI, functional magnetic resonance imaging, intentions, interoceptive aware-
ness, introspection, neural correlates, PET, positron emission tomography,
personality traits, preference judgments, reflective self-awareness, resting state,
A. Morin, J. Michaud / Brain Research Bulletin 74 (2007) 387–396 389
section of each paper was examined for additional studies. Review articles (e.g.
[87,37,63]) were also carefully scrutinized. Inclusion criteria for selection of
articles were all studies measuring brain activity using hemodynamic methods
(PET and fMRI) during self-related tasks tapping into the seven aforementioned
self-domains. Exclusion criteria were: (a) Theory-of-Mind studies—these will
be examined in an independent project; (b) electrophysiological studies using
event-related potentials or EEG (e.g. [58,91]), as well as Transcranial Magnetic
Stimulation studies (e.g. [72]); (c) studies of clinical populations, including split-
brain patients (e.g. [126,128]); and (d) studies not reporting all areas of activation
(e.g. [19]). Some articles were also excluded because the tasks used, although
self-related, did not involve genuine introspection. To illustrate, in Heinzel et
al.’s report [45], participants were simply asked to view erotic and non-erotic
emotional pictures while brain activity was assessed, as opposed to rate (i.e.,
focus, introspect on) their sexual arousal levels. Two other studies that were
discarded on that basis are Kampe et al. [49] and Ochsner et al. [89].
By using this selection process, 59 articles were analyzed in order to iden-
tify the reported frequency of LIFG activation. Control conditions (i.e., non-self
tasks) were not examined because our main focus consisted in calculating LIFG
(and inner speech) involvement during self-tasks exclusively. Such a participa-
tion of the LIFG during non-self tasks does indeed occur (e.g., [17]), which is
not surprising since (as mentioned previously) inner speech is known to serve
many cognitive functions other than the one explored here—processing of self-
information. Control tasks (e.g., encoding nonsemantic information, making
decisions about statements of factual knowledge) often rely on these additional
functions of inner speech.
2. Results and discussion
2.1. Overview
Fig. 1 presents the percentage of studies in which LIFG activ-
ity for each self-domain examined here was observed. Overall,
33 of the 59 studies (55.9%) reported LIFG activity during self-
awareness tasks. This activity most likely reflects inner speech
use, as opposed to other potential LIFG functions, namely, cog-
nitive control (the ability to orchestrate thoughts and actions in
accordance with internal goals), working memory (temporar-
ily storing and manipulating information), selection among
competing alternatives (choosing among competing sources
of information to guide response—e.g., classifying pictures
according to one of many different attributes), and interpreting
others’ actions (e.g., hand and mouth movements). We argue
that none of the self-referential tasks described below engage
these functions. Our finding, to the extent that one equates LIFG
activation with inner speech use, supports the hypothesis of an
inner speech involvement in some self-referential processing.
Had we observed a very low percentage of LIFG recruitment
during self-related tasks (e.g., 10%), obviously the aforemen-
tioned hypothesis would need to be rejected or significantly
qualified; on the other hand, finding a very high percentage (e.g.,
90%) was not expected given the likelihood that other compet-
ing processes (e.g., imagery) underlie self-reflection, and that
some forms of self-awareness (e.g., agency) most probably do
not require cognition (see below).
Many studies across self-domains employed identical tasks.
For instance, four of the seven self-recognition tasks consisted in
judging if faces presented on a screen were self or other; 7 of the
self, self-awareness, self-reference, self-inferential processing, self-related pro-
cessing, self-reflection, self-recognition.
Fig. 1. Percentage of studies in which LIFG activity was observed as a function
of self-domains.
14 personality trait tasks asked participants to decide if adjec-
tive traits were self-descriptive. It remains unclear why, using
similar experimental tasks, some studies did find the target acti-
vation (e.g., [53,54]) while others did not (e.g., [31,122]). The
only detectable difference between identical tasks was the time
taken for image acquisition. One possibility might be that very
short tasks (e.g., milliseconds) did not provide participants with
enough time to genuinely self-reflect, whereas longer ones (e.g.,
minutes) did. That is, very short tasks might actually be seen
as recognition tasks not entailing much introspection (and thus
inner speech use). To test this idea, all studies specifying time
taken for image acquisition during self-awareness tasks were
divided into two groups: those reporting LIFG activity (n= 30)
and those not reporting LIFG activity (n= 24). The studies were
further divided into those with time taken for image acqui-
sition above the median duration (Mdn = 4000 ms) and those
below. A chi-squared analysis revealed no statistically signifi-
cant relationship between time and the detection of LIFG activity
(χ2(1) = 0.087, p= 0.768) (Fig. 1).2
Also consistent with our view, access to more conceptual self-
information was linked to increased LIFG activation. 68.1% of
all studies employing conceptual self-tasks (n= 44; i.e., REST,
evaluating one’s personality traits, emotions and judgments, and
accessing one’s autobiographical memory) reported LIFG activ-
ity, whereas only 20% of studies using perceptual self-tasks
(n= 15; i.e., sense of agency and face/voice self-recognition)
identified such activation. This difference was statistically sig-
nificant (χ2(1) = 11.363, p= .001). This corroborates the notion
ofadifferential involvement of inner speech across subtypes of
self-processing, where perceptual self-aspects (e.g., one’s face)
can be brought to conscious awareness without words, whereas
2We also analyzed the median split by combining the median observations
with the observations above the median and by combining the median observa-
tions with the observations below the median. In no case did the results approach
statistical significance (lowest p= 0.483). In addition, we conducted a t-test com-
paring the recording durations of observations with/without LIFG activity, even
though the distribution of recording durations is non-normal. This comparison
also failed to reach significance (t(54) = −1.04, p= 0.301). A Mann–Whitney
U-test on the same data also failed to reach significance (p= 0.397).
390 A. Morin, J. Michaud / Brain Research Bulletin 74 (2007) 387–396
conceptual self-dimensions (e.g., one’s current emotional state)
most probably necessitate verbalization.
2.2. Agency and self-recognition
All Tables included below specify (1) the authors of individ-
ual articles, (2) the hemodynamic method used, (3) the self-task
used, (4) the time required for image acquisition, and (5) LIFG
activation—or not. Table 1 presents 15 studies that measured
brain activity during agency tasks (e.g., deciding if one is respon-
sible for the movement of one’s hand) and self-recognition tasks
(e.g., judging if a face seen on a screen is one’s own or that
of another person). In accordance with the discussion above
on perceptual and conceptual self-domains, only one agency
study out of seven (14.3%) reported LIFG activity. Two out of
eight self-recognition studies (25%) showed a LIFG recruitment.
The view that self-(face) recognition unlikely necessitates verbal
labeling (i.e., inner speech use) is illustrated by Sugiura et al.’s
observation [122] that “... covert naming often accompanies
recognition of a familiar face, but rarely occurs during visual
self-recognition” (p. 147).
2.3. Personality traits
Table 2 presents 14 studies that measured brain activity during
personality trait tasks. In their review paper, Ochsner et al. [88]
(p. 798) noted frequent left inferior PFC activation in many self-
referential studies that included trait tasks. In our sample, 50%
of the studies (seven out of 14) reported LIFG activation. Fossati
et al.’s study [32] was excluded because in reporting their results,
the “Self” and “Others” conditions were combined. Most tasks
consisted in asking participants to judge if an adjective trait is
self-descriptive. As indicated earlier, one can postulate that such
a task will activate inner speech use—e.g., the presentation of the
adjective “good-looking”, for instance, could very well initiate
the following internal verbal comment: “Yes, I’m rather attrac-
tive” or “Well, it varies, I have ‘bad hair’ days”. Note that in Kjaer
et al.’s study [56] participants were explicitly invited to silently
think about their personality traits and physical appearance for
2 min: unsurprisingly, LIFG was reported.
2.4. Autobiographical memory
Table 3 reports 12 studies that measured brain activity dur-
ing autobiographical memory tasks (e.g., remembering past
personal experiences). Several articles were excluded (e.g.,
[8,20,10,85]), because episodic memory (recollection of past
events), as opposed to autobiographical memory (recollection
of past personal events), was tested. As noted before, autobio-
graphical tasks typically recruit brain areas that are active when
participants manipulate mental images. But the notion that lan-
guage is also simultaneously used to access autobiographical
memory has been discussed in the literature (see [15], pp. 10–11;
[111]). Gilboa et al. [36] observe that “Both types of studies
[autobiographical and episodic memory studies] report ventro-
lateral activations (BA 44/47) bilaterally” (p. 1341). Nolde et
al. [85] suggest greater LPFC activation (which includes the
LIFG) during more complex autobiographical remembering. In
our sample, 9 studies out of 12 (75%) reported a recruitment of
the LIFG. In phenomenological terms, one can propose that par-
ticipants remembering a past personal experience often engaged
in self-talk—e.g., “Yes, I remember that trip to South America,
it was very pleasant and exciting, my wife and kids were with
me...”, etc.
Table 1
Agency and self-recognition studies
Paper Imaging Self-task Time LIFG (BA)
Agency
Farrer and Frith [29] PET Driving a circle along a T-shaped path, either by oneself (agency)
or by the experimenter (other)
5s NO
Farrer et al. [28] PET Providing accurate/inaccurate visual feedback to participants
performing hand movements
70 s NO
Leube et al. [60] fMRI See above 2 s NO
Leube et al. [61] fMRI Deciding if there is a temporal delay between hand movements
and visual feedback of those movements
3s NO
McGuire et al. [73] PET Providing accurate/inaccurate auditory feedback while reading
aloud
250 ms NO
Ruby and Decety [105] PET Imagining self vs. other movements 5 s NO
Wraga et al. [132] fMRI Imagining rotating one’s body about a sphere until one’s eyes line
up behind the horizontal line of a prompt
500 ms 47 (but 45
deactivated)
Self-recognition
Kircher et al. [54] fMRI Judging if faces are self or other 3 s 45
Kircher et al. [55] fMRI See above 3 s 45
Perrin et al. [95] PET (and ERPs) Passively listening to one’s first name, unfamiliar names, and
common first names
600 ms NO
Platek et al. [99] fMRI Judging if faces are self or other 20 s NO
Platek et al. [100] fMRI Judging if faces are self or other (known/unknown persons) 775 ms NO
Sugiura et al. [121] PET Judging if faces are self or other Unspecified NO
Sugiura et al. [122] fMRI See above 11 s NO
Uddin et al. [128] fMRI Deciding if faces presented are composites of oneself or others 2 s NO
A. Morin, J. Michaud / Brain Research Bulletin 74 (2007) 387–396 391
Table 2
Personality trait studies
Paper Imaging Self-task Time LIFG (BA)
Blackwood et al. [4] fMRI Judging if various ambiguous self-referent elements (traits,
activities and emotions) are self-descriptive (Yes/No)
7.5 s NO
Craik et al. [17] PET Judging if adjective traits are self-descriptive (Likert scale) 4 s 47
Fossati et al. [31] fMRI Judging if adjective traits are self-descriptive (Yes/No) 5 s NO
Johnson et al. [47] fMRI Judging if adjective traits, abilities and attitudes are
self-descriptive (Yes/No)
4s NO
Kelly et al. [53] fMRI Judging if adjective traits are self-descriptive (Yes/No) 2 s 47
Kircher et al. [54] fMRI Judging if adjective traits and physical characteristics are
self-descriptive (Likert scale)
3s 44
Kjaer et al. [56] PET Silently thinking about one’s traits and physical appearance 2 ms 45/47 (physical appearance
only)
Lieberman et al. [64] fMRI Judging if adjective traits are self-descriptive in high/low
experience domains (Yes/No)
3 s 44 (nonschematics only)
Lou et al. [66] PET Judging if adjective traits are self-descriptive (Yes/No) Unspecified 47
Macrae et al. [67] fMRI See above 750 ms Near 44/45/47
Ochsner et al. [88] fMRI See above 2.2 s NO
Schmitz et al. [108] fMRI See above 4 s NO
Schmitz et al. [109] fMRI See above 4 s NO
Zhang et al. [133] fMRI Judging if adjective traits are self-descriptive (Likert scale) 3 s NO
2.5. Emotions
Table 4 reports nine studies that measured brain activity dur-
ing emotion tasks (e.g., evaluating one’s emotional response to
an auditory or visual stimulus). 77.8% of the studies (seven out of
nine) detected LIFG activation. As Ochsner et al. [89] put it, “...
the MPFC and the inferior lateral PFC might work in concert to
mediate interference between, and select the appropriate, seman-
tic description of emotional states” (p. 1750; emphasis added).
Of all the self-domains examined here, awareness of one’s emo-
tional experiences most likely requires inner speech. We suggest
that one needs to verbally label one’s current emotions in order
to accurately identify them [82]. In a typical experiment assess-
ing one’s emotional reaction to a set of pictures, it is conceivable
that participants covertly verbalized “That one feels warm, nice
colors” or “No. Too much repetition, boring”.
2.6. Evaluative judgments
Table 5 presents five studies that measured brain activity
during evaluative judgment tasks (e.g., judging if one likes or
dislikes various food items). Such tasks are self-referential in
nature because one first has to assess one’s own preferences in
order to produce a judgment. Here too it is reasonable to assume
that evaluative judgment tasks depend on inner speech. As John-
son et al. [48] suggest in their own study, “The finding in the
inferior frontal gyrus, left more than right on both the subjec-
tive [evaluative judgments] tasks relative to the [control tasks],
Table 3
Autobiography studies
Paper Imaging Self-task Time LIFG (BA)
Cabeza et al. [12] fMRI Remembering if sets of pictures where taken by participants or by others 15 s 47
Conway et al. [16] PET Generating AM following the presentation of cue words 5 s 44/45/47
Fink et al. [30] PET Listening to and visualizing personal and non-personal AM Unspecified NO
Gilboa et al. [36] fMRI Remembering the entire context (emotional, physical, cognitive) of
recent/remote personal episodes depicted in photographs of self
30 s 47
Levine et al. [62] fMRI Listening to verbal descriptions of AM Unspecified 45/47
Maguire and Mummery [69] PET Indicating if read statements representing past personal episodes (collected
earlier to scan) were participants’ own AM (Yes/No)
4s NO
Maguire et al. [70] fMRI See above 4 s NO
Maguire and Frith [68] fMRI See above 8 s 47
Piefke et al. [97] fMRI Remembering positive/negative and old/recent past personal events 30 s LIFG (BA
unspecified)
Piolino et al. [98] PET Verbally instructing participants to mentally relive personal episodes in
details
45 s 47
Ryan et al. [107] fMRI Remembering past old/recent personal events following the presentation of
cues
20 s 47
Steinvorth et al. [120] fMRI Mentally re-experiencing autobiographical memories (AM) following the
presentation of cue words formulated by family members; participants
were asked to confirm retrieval
8 s 44/45 (remote
AM only)
392 A. Morin, J. Michaud / Brain Research Bulletin 74 (2007) 387–396
Table 4
Emotion studies
Paper Imaging Self-task Time LIFG (BA)
Critchley et al. [18] fMRI Perceiving (or not) a feedback delay of one’s heartbeat
(Interoception)
100 ms LIFG (BA unspecified)
Goldberg et al. [38] fMRI Evaluating up to what point images and music produce an
emotional experience (High/Low)
12 s LIFG (BA unspecified)
Gusnard et al. [41] fMRI Evaluating one’s emotional responses to pictures (positive,
negative or neutral)
4100 ms LIFG (BA unspecified)
Jackson et al. [46] fMRI Imagining various levels of pain by viewing normal and
distorted limbs
3 s LIFG (BA unspecified)
Lane et al. [57] PET Evaluating one’s emotional responses to pictures (positive,
negative or neutral)
500 ms 44/45
Ochsner et al. [89] fMRI Evaluating one’s emotional responses to pictures (Likert scale) 3.5s 45
Phan et al. [96] fMRI Indicating up to what point participants emotionally associated
with pictures (Likert scale)
5s NO
Takahashi et al. [124] fMRI Judging if guilt and embarrassment are present in short
sentences (Likert scale)
4 s 47 (embarrassment only)
Taylor et al. [125] PET Rating aversive and nonaversive pictures (Likert scale) 2.8s NO
Table 5
Evaluative judgment studies
Paper Imaging Self-task Time LIFG (BA)
Johnson et al. [48] fMRI Choosing which color one prefers 4 s LIFG (BA unspecified)
Paulus and Frank [92] fMRI Determine which one of two items (e.g., drinks) one
prefers
8s NO
Seger et al. [112] fMRI Judging if one likes or dislikes food 2500 ms NO
Zysset et al. [135] fMRI Making evaluative judgments of people (e.g., Bush
is a good president) (Yes/No)
6 s 45/47
Zysset et al. [136] fMRI See above 6 s LIFG (BA unspecified)
may reflect a verbal reasoning strategy during those conditions
that may not have been employed during the [control] condi-
tion” (p. 1990; emphasis added). In our sample, three studies
out of five (60%) reported LIFG activation. For example, a par-
ticipant asked to select which of two drinks he or she prefers
may covertly verbalize “The first one is too sweet—I prefer the
second drink”.
2.7. Rest
Table 6 reports four studies that measured brain activity dur-
ing REST. Note that Laufs et al.’s experiment [58] was not
included because results are reported in terms of correlations
between fMRI activity and power in EEG bands. Greicius et
al.’s study [40] was also discarded because results are presented
in terms of functional connectivity. In a typical resting state
condition participants are simply requested to stay still and do
nothing. Although the resting state has repeatedly been used
as a control condition in neuroimaging experiments, Gusnard
et al. [41] recently proposed that REST actually represents
a particularly active state in which participants think about
their current, past, or future goals, emotions, needs, behav-
ior, physiological sensations, etc. As such, REST consists of
an introspective state that recruits most brain sites that have
also been shown to be active during self-referential tasks. In
our sample, all studies found LIFG activation. Binder et al.
[3] explicitly measured inner speech use in their study and
observed that “...conscious resting subjects frequently experi-
ence thoughts (consisting variously of mental images, auditory
verbal images, ‘ideas,’ and other similar phenomena) that are
relatively unrelated to external perceptual events. In the pilot
study conducted here, subjects reported such phenomena at the
conclusion of a 15- to 24-s period of rest on 62.8% of queries
...” (p. 85; emphasis added). Mazoyer et al. [71] and Frans-
son [33] also report inner speech use by participants in their
experiments.
Table 6
REST studies
Paper Imaging Self-task Time LIFG (BA)
Binder et al. [3] fMRI Resting still with eyes closed 3 s 45
Christoff et al. [14] fMIR Unspecified 16 s 46
Fransson [33] fMRI Resting still with eyes closed 10 m 47
Mazoyer et al. [71] PET See above Unspecified 45/46
A. Morin, J. Michaud / Brain Research Bulletin 74 (2007) 387–396 393
3. Conclusion
The notion that language, and more specifically inner speech,
are an integral part of self-referential activities is both intu-
itively appealing and largely accepted in the literature (but see
[51], p. xxiii). Empirical evidence nonetheless is sparse, and
the present review provides additional (albeit indirect) support
to this hypothesis. 55.9% of the 59 studies we examined found
LIFG activity during various self-awareness tasks. We suggest
that this activity most likely consists in the use of introspec-
tive inner speech by the participants. Clearly this represents
a tentative inference that requires further corroboration given
the fact that the observed LIFG activity may reflect the use
of other processes. To the extent that LIFG activity signifies
inner speech use, our review further qualifies the hypothesis by
suggesting that inner speech is increasingly recruited as self-
information to be assessed becomes less perceptual and more
conceptual—hence, a differential involvement of inner speech
across self-domains. One persistent debate in the study of self-
awareness is the neuroanatomical localization of self-processes.
Three main views have been proposed so far: self-awareness is
mainly located (1) in the right prefrontal lobe [52], (2) in the left
hemisphere exclusively [35], and (3) in a widespread fashion
throughout the brain [127,37]. The present review strongly sug-
gests that the left prefrontal lobe plays a role in self-awareness
and thus favors the last two views.
While most current brain-imaging experiments aim at iden-
tifying the exact sites correlated to self-related activities, our
novel approach rather looks at tangential activations—the LIFG
in the present case—in order to isolate the underlying cogni-
tive processes implicated in self-awareness. We believe that this
method should be extended to include other peripheral brain
regions (e.g., occipital regions) activated during various addi-
tional self-domains (e.g., intentions), as well as to other complex
social cognitive activities—e.g., Theory-of-Mind.
Conflicts of Interest
None.
Acknowledgements
We would like to thank Petra Kamstra, James Taylor, and Gen
Thurlow for their constructive comments on earlier versions of
this paper.
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