European Journal of Neuroscience, Vol. 14, pp. 887±892, 2001

ã Federation of European Neuroscience Societies

SHORT COMMUNICATION
Temporal characterization of memory retrieval processes:
an fMRI study of the `tip of the tongue' phenomenon
Hideyuki Kikyo,1 Kenichi Ohki1 and Kensuke Sekihara2
1

Department of Physiology, The University of Tokyo School of Medicine, 7±3-1 Hongo, Bunkyo-ku, Tokyo 113±0033, Japan
Mind Articulation Project, ICORP, Japan Science and Technology Corporation, Bunkyo-ku, Tokyo 113±0034, Japan

2

Keywords: human, multiple regression analysis, proper name, random-effects models, retrieval success

Abstract`Tip of the tongue' (TOT) is a natural phenomenon in which people cannot retrieve a target word immediately, even though they
feel con®dent that they know the target. This provides us an opportunity to understand the human memory system, because
cognitive components of memory retrieval such as retrieval effort and successful retrieval are temporally dissociated from eachother during the TOT states. The purpose of the present study was to reveal the neural correlates of the cognitive components of
the retrieval process by separating cognitive phases of the TOT phenomenon using event-related functional magnetic resonanceimaging with multiple regression analysis. We demonstrated that the left dorsolateral prefrontal cortex (DLPFC) and anterior
cingulate cortex were activated at the time of successful retrieval, and the left DLPFC also showed activation when the subjects
successfully retrieved the target names as compared to when they gave up. This result suggests that the left DLPFC is speci®cto the successful retrieval process. During the TOT state, a number of regions were activated, and this suggests that widelydistributed brain regions are engaged when people make a hard effort to retrieve a proper name in the TOT state. Our new
approach employing temporal resolution of the TOT phenomenon may contribute to the understanding of the mechanisms of thehuman memory system.

Introduction
People often experience dif®culty in retrieving a proper name, though
they can vividly remember the face and clothes of the person inquestion. They have con®dence that they know the target name, andsometimes can access the ®rst letter of the missing name, often with afeeling of being just within reach of retrieving it (i.e. feeling of
imminence). This is known as the `tip of the tongue' (TOT) state(James, 1893; Burke et al., 1988). In ordinary life, TOT states occur
sporadically, which makes it dif®cult to study TOT in the laboratory.
Brown & McNeill (1966) ®rst succeeded in studying TOT undercontrolled conditions using rare words. In the TOT states, people
cannot retrieve a target word immediately, despite a hard effort at
retrieval. The recovery of the missing target often occurs later. In thisTOT phenomenon, a cognitive component such as successful
retrieval is temporally dissociated with retrieval effort. We thought
therefore that the TOT phenomenon would give us a good opportunity to examine the components of the retrieval processes.
Investigating the neural correlates of memory retrieval processes
has been one of the fundamental themes among neuroimaging
studies. Previous block-designed functional magnetic resonanceimaging (fMRI) and positron emission tomography studies attempted
to distinguish between retrieval effort and success (Kapur et al.,
1995; Nyberg et al., 1995; Rugg et al., 1996; Buckner et al., 1998b;
Wagner et al., 1998), but the interpretation of the results has been
debated. Recent event-related fMRI studies reported that frontal andparietal regions were important for retrieval success (Henson et al.,
1999; Konishi et al., 2000; McDermott et al., 2000). Those studies
identi®ed regions associated with retrieval success by comparing
between trials with and without retrieval success. Their method ofcomparison is, however, based on the assumption that cognitive
components other than retrieval success, such as retrieval effort, werebalanced between the two trials compared (Konishi et al., 2000).
The purpose of the present study is to determine the neuralcorrelates for components of the retrieval processes by temporally
separating the cognitive phases of the TOT phenomenon. Based on
the method of Brown & McNeill (1966), we developed a TOT taskwith proper names that appeared in a major Japanese newspaper andwere controlled in frequency. The task successfully induced TOTstates in a high percentage of cases. For data analysis, we ®rst sorted
fMRI data according to the subjects' responses. Second, we
temporally separated the cognitive phases of the TOT phenomenon
with multiple regression analysis (Worsley & Friston, 1995; Courtney
et al., 1997). This became possible because the retrieval effort and theretrieval success are temporally separated from each other in the TOT
phenomenon. Finally, we compared the activities related to successful retrieval and giving up of retrieval with random-effects models(Holmes & Friston, 1998).

Correspondence: Dr Hideyuki Kikyo, as above.
E-mail: kikyo@m.u-tokyo.ac.jp

Subjects

Received 2 March 2001, revised 10 July 2001, accepted 11 July 2001

Materials and methods
Fourteen volunteers (12 males and 2 females, aged 20±35 years)
participated in the experiment. They had all received college- or888 H. Kikyo et al.
graduate-level education, and were strongly right-handed (Edinburgh
Inventory scores of all subjects were 100; Old®eld, 1971). We
excluded ®ve subjects' data from analysis due to poor behaviouralperformance (proportion of correct responses < 50%) or excessive
head motion. Written informed consent was obtained from eachsubject in accordance with the declaration of Helsinki, and theprotocol was approved by the University of Tokyo School of
Medicine.

Who*

Cognitive
Phase

Retrieval

Questions to identify a speci®c person's name were crafted toeffectively induce prolonged memory retrieval. First, we collected
proper names from the Asahi newspaper database (http://www.asahi.com/information/webdb.html), names which appeared fewer than
1000 times from 1985 to 1999. The collected names included thenames of company founders, scientists, politicians etc. Then wecreated questions based on the newspaper articles. Finally, we
selected the questions that induced TOT phenomena with a highfrequency in pilot studies with another group of subjects, whose age
and educational background matched the scanned subjects. In theexperimental scans, the questions were presented in Japanese andsubtended less than » 5° of visual angle. A question was presented for
2 s using LabVIEW software (National Instrument, Inc., Austin, TX,
USA) and a colour LCD projector (Sharp 2000, Osaka, Japan).
Subjects were required to respond by pressing buttons made of optical®bres.

Hit-onThe subjects were required to retrieve the target name as quickly andaccurately as possible. When they retrieved the target name, they
were required to press button 1 with their right hand. After 8±10 sfrom the button press, the correct answer was presented and theyreported whether their answer was correct or not by pressing the
button again (Fig. 1). When they did not know or gave up retrieving
the target, they were required to press button 2, also with the righthand. During retrieval, they were instructed to ®xate on a central
point on the screen. The durations of the retrieval phase were variable
for each trial, and the intertrial interval was 10±12 s. The total
number of questions differed among subjects because the length ofeach trial depended on the subject's responses.
MRI procedures
Functional images were obtained with a 1.5 T scanner system(Hitachi, Tokyo, Japan) and gradient echo echo-planar imaging withBOLD contrasts [TR 2 s, TE 20 ms (half scan), ¯ip angle 90°,
3 3 3 mm2 in-plane resolution, 8 slices, 7 mm thickness]. One
session consisted of 59 scans for each slice, lasted 119 s, and a totalof 24 sessions per subject were obtained. To maintain the same head
position, we used cushions which were designed for each subject. We
also took structural images every four runs to check for head
movement based on anatomical landmarks, and rejected data with
> 3 mm of movement in any direction. The range of the scans wasaround z = 4±60 mm in the coordinates of Talairach and Tournoux(1988), avoiding susceptibility artifacts of the nasal sinuses. For eachsubject, conventional T1-weighted structural images were collected
to provide anatomic information.
Data analysis
After discarding the initial ®ve volumes of each session to avoid thenonequilibrium effects of magnetization, functional images wererealigned with AIR software (Woods et al., 1992) to compensate thehead movement, and spatially smoothed with a Gaussian ®lter (6 mm

ButtonPress*

ButtonPress

Question

Materials

TOT task

Masa
Ibuk ruaesta'SO blishedNY'?

After retrieval
2 sec

1 sec
Variable Duration

8 - 10 sec

TOT Time
FIG. 1. A schematic representation of a `tip of the tongue' (TOT) task andcontrasts used for multiple regression analysis. In the TOT task, a question
was presented for 2 s and a subject was required to retrieve the target nameas quickly and accurately as possible. When they retrieved the target, they
responded by a button press, and the answer was veri®ed later also by
button pressing. We de®ned the following four cognitive phases for a trialthat induced a successful but prolonged retrieval: `Question', `Retrieval',`Hit-on' and `After-retrieval'. We applied four contrasts for each phase.
Multiple regression analysis was performed with those contrasts convolved
with the haemodynamic response function.

full width, half-maximum). Signal intensity was normalized withintrial to remove baseline ¯uctuation, and temporal high frequency
noise was removed (cut off 4 s). To compensate for the different
sampling timings of different slices, voxel values were interpolated ina time series.
We analysed the trials in which prolonged retrieval was induced,that is, when it took > 6 s until the subjects responded that they had
retrieved the targets (Hit-on trials) or that they had given up (Give-up
trials). In this study, we used multiple regression analysis todifferentiate transient from sustained activity. We de®ned four
cognitive phases for a Hit-on trial: `Question', `Retrieval', `Hit-on'
and `After-retrieval' phases. The phases were de®ned as follows: (i)the Question phase extended for 2 s during presentation of a question;(ii) the Retrieval phase followed the Question phase, and continued
until 1 s before the subjects' responses signifying target retrieval; (iii)the Hit-on phase extended for 1 s just before the subjects' responses;
and (iv) the After-retrieval phase was de®ned as following the Hit-on
phase until the presentation of a correct answer. The contrast
corresponding to each cognitive phase (Fig. 1) was convolved withthe modelled haemodynamic response function to create theregressor. In the Give-up trials, we used another set of four regressors
in the same way as in the Hit-on trials, and we termed the phasecorresponding to the Hit-on phase in the Hit-on trials as the Give-up
phase. We de®ned the After-retrieval phase so that the haemodynamic responses of the Hit-on phase were not contaminated by thoseof phase after the button press. A multiple regression analysis basedon the general linear model (Worsley & Friston, 1995; Courtney et al.,1997) was performed for the Hit-on and Give-up trials, by in-house
software programmed with MATLAB (MathWorks, Natick, MA,
USA).
Group analysis was performed between the Hit-on and Give-up
phases (Fig. 2) based on random-effects models (Holmes & Friston,1998). The functional images were smoothed with a Gaussian ®lter ofã 2001 Federation of European Neuroscience Societies, European Journal of Neuroscience, 14, 887±892

Neuroimaging study of `tip of the tongue' phenomenon

889

TABLE 1. Activated regions in each phase of the Hit-on trials
Coordinates
Phase
Region (Brodmann Area)

R/L

N

Volume
(cm3)

R
L
L
L

6
8
9
7

1.1 6 0.6
1.1 6 0.6
2.6 6 0.8
3.2 6 0.8

38
±35
±46
±60

16
20
4
±30

34
32
26
12

Anterior cingulate cortex (BA 32/24)
Precentral gyrus/Postcentral gyrus (BA 4/3/1/2)

L
R
L
R
L
L
R
L
R
L
R
L
R
L
R
L
R/L
L

8
6
5
5
5
9
6
6
7
8
6
6
6
6
7
8
8
7

2.3 6 0.9
3.5 6 0.8
2.6 6 1.1
2.3 6 0.4
2.1 6 0.7
2.0 6 1.1
3.0 6 0.9
3.1 6 1.3
1.0 6 0.5
1.4 6 0.5
1.6 6 0.8
1.2 6 1.0
1.5 6 0.5
1.5 6 0.5
1.7 6 0.5
2.0 6 0.6
2.2 6 0.7
2.2 6 1.2

±38
34
±36
30
±34
±43
40
±37
30
±35
37
±30
40
±35
55
±50
3
±35

18
30
26
50
48
4
21
18
±10
±5
±59
±65
±38
±35
±35
±26
25
±20

32
32
35
8
10
24
11
11
55
50
46
42
38
40
10
12
36
49

Hit-on phase
Dorsolateral prefrontal cortex (BA 9/44/6)
Anterior cingulate cortex (BA 32/24)
Middle frontal gyrus (BA 9)
Lateral parietal cortex (BA 7)
Precentral gyrus/Postcentral gyrus (BA 4/3/1/2)

L
R/L
R
L
L

6
6
5
5
5

2.0 6 0.9
1.5 6 0.4
1.2 6 0.2
1.8 6 0.6
1.8 6 0.8

±40
0.3
34
±34
±38

22
20
32
±65
±22

35
31
35
44
48

Question phase
Dorsolateral prefrontal cortex (BA 9/44/6)
Inferior frontal gyrus (BA 44/6)
Superior temporal gyrus (BA 22/42)
Retrieval phase
Dorsolateral prefrontal cortex (BA 9/44/6)
Middle frontal gyrus (BA 9)
Middle frontal gyrus (BA 10)
Inferior frontal gyrus (BA 44/6)
Inferior frontal gyrus (BA 45/47)/insula
Premotor cortex (BA 6)
Lateral parietal cortex (BA 7)
Supramarginal gyrus (BA 40/39)
Superior temporal gyrus (BA 22/42)

x

y

z

Activated regions in each phase of the Hit-on trials detected in more than ®ve subjects. N, the number of subjects whose corresponding regions showed activation;
R, right; L, left. Stereotaxic coordinates of each region were averaged among the subjects according to the atlas of Talairach and Tournoux (1988), and theapproximate Brodmann areas are based on the atlas coordinates. All volumes are indicated as mean 6 SD.

12 mm, linearly transformed into the Talairach & Tournoux (1988)
space with translation, rotation and stretching in the three dimensions
with in-house software on MATLAB, and second-level inferenceswere performed. We delineated activated regions with ®ve or more
contiguous voxels above P < 0.001 (uncorrected) (Buckner et al.,1998a). The time course of the activated regions determined as above
was calculated by averaging magnetic resonance signals in theactivated voxels with a lower threshold (P < 0.005, uncorrected) in
the grouped data. To ensure the validity of our multiple regression
model, we also calculated ®tted response functions (Courtney et al.,1997) by multiplying each regressor coef®cient with the time seriesof the corresponding regressor, and by summing up the total
contribution from the regressors.
For single-subject analysis, we regarded the activated regions as®ve or more contiguous voxels above P < 0.001 (Fig. 3). We
identi®ed the regions among subjects based on anatomical landmarks(Grachev et al., 1999), and the locations of activated regions among
subjects were within 15 mm of each other. The respective peaks ofthese regions were indicated based on the coordinates of Talairach &Tournoux (1988).

Results
Behavioural results
The number of questions for each subject was 72.0 6 8.1 (mean
6 SD). The numbers of Hit-on and Give-up trials were 21.7 6 4.1

and 13.8 6 8.6, respectively. The mean response latency (TOT timein Fig. 1) was 10.5 6 1.7 s in the Hit-on trials and 12.6 6 3.3 s in
the Give-up trials. The percentage of correct in Hit-on trials, which
was the ratio of the number of correctly answered Hit-on trials to thesum of correctly and wrongly answered Hit-on trials, was75.0 6 14.0%. After the functional scan sessions, subjects very
often reported that they experienced a feeling of imminence in the
Hit-on trials, which is one of the characteristic features of the TOT
state (Brown, 1991).
FMRI results
First, we applied multiple regression analysis with random-effects
models to the fMRI data from nine subjects. The left dorsolateralprefrontal cortex (DLPFC; ±40, 25, 33) and anterior cingulate cortex(ACC; ±1, 25, 34) showed activation (P < 0.001) in the Hit-on phaseof the Hit-on trials (Fig. 2A), whilst neither region showed activation(P > 0.1) in the Give-up phase of the Give-up trials (Fig. 2B).
Moreover, the left DLPFC (±45, 18, 32) showed activation(P < 0.001) when it was compared between Hit-on and Give-up
phases. In this comparison, the ACC was subthreshold at P < 0.001,
but some activity was observed at P < 0.005 (Fig. 2C).
The time courses of the regions are shown in Fig. 2D and E. Theirmagnetic resonance signals were already elevated before the time of
response (0 s) and transiently increased, time-locked with the
response that the subjects had retrieved the targets.

ã 2001 Federation of European Neuroscience Societies, European Journal of Neuroscience, 14, 887±892

890 H. Kikyo et al.

ã 2001 Federation of European Neuroscience Societies, European Journal of Neuroscience, 14, 887±892

Neuroimaging study of `tip of the tongue' phenomenon
We also con®rmed in the single-subject analyses that the tworegions showed activation (P < 0.001) in six out of nine subjects
during the Hit-on phase (upper part of Fig. 3), but did not show
activation in the Give-up phase even at a lower threshold (P > 0.01)(lower part of Fig. 3). In the single-subject analyses, we identi®ed
activations in the right prefrontal, left parietal and left motor/sensory
regions during the Hit-on phase in ®ve subjects (Table 1), but these
activations were subthreshold in the random-effects analysis.
Figure 2F showed the results of group analysis during the Retrieval
phase in the Hit-on trials. Bilateral activations were found in the
DLPFC [Brodmann area (BA) 9/44/6], inferior frontal gyrus (BA 45/
47/insula), supmarginal gyrus (BA 40/39) and superior temporalgyrus (BA 22/42), as well as supplementary motor area (BA 6) and
ACC. We also observed left side activation in the inferior frontal
gyrus (BA 44/6) and motor/sensory area (BA 4/3/1/2). Regions inwhich more than ®ve subjects showed activation during the Question,
Retrieval and Hit-on phase are listed in Table 1.

Discussion
We investigated the neural correlates of the retrieval processes by
separating the cognitive phases of the `tip of the tongue' (TOT)
phenomenon. The fMRI data were analysed based on the randomeffects models with multiple regression methods. We demonstrated
that the left DLPFC and ACC were activated at the time of successful
retrieval, and neither region showed activation in the Give-up phasein the Give-up trials. Especially, the left DLPFC showed activation

891

when the subjects successfully retrieved the target names ascompared to when they gave up.
Previous event-related fMRI studies (Henson et al., 1999; Konishi
et al., 2000; McDermott et al., 2000) reported that the frontal andparietal regions were important for retrieval success. The left DLPFC
activation found in our study (±45, 18, 32) is close to the region
reported by Henson et al. (1999) and Konishi et al. (2000).
However, we should be careful in interpreting the results, because
there are four major differences between these three previous studies
and ours. (i) Previous studies detected regions responsible for
retrieval success by comparing between trials with and without
retrieval success in event-related fMRI. This comparison is based on
the assumption that other cognitive components, such as retrieval
effort, were balanced between trials with and without retrieval
success (Konishi et al., 2000). In contrast, the method used in thisstudy separated cognitive states within-trial by exploiting the
temporal resolution of the TOT phenomenon without such anassumption. (ii) Previous studies used recognition tasks in episodic
memory, whilst the TOT task required recall from semantic memory.
(iii) The TOT task required subjects to retrieve targets from several
years ago, whilst the recognition tasks required retrieval from at mosta few hours previously. (iv) Previous studies compared between hit(correct recognition of a target encoded previously) and correct
rejection (correct recognition of a target not encoded previously)
trials, whilst we compared between Hit-on and Give-up phases.
Despite these differences, the left DLPFC was commonly detected inassociation with retrieval success, suggesting that the region isimportant regardless of the type of memory.

FIG. 3. Activation in the left dorsolateral prefrontal cortex (blue arrows) and anterior cingulate cortex (green arrows) of each subject during the Hit-on phase(upper panel) and the Give-up phase (lower panel). The right side of the images corresponds to the right side of the brain, and the stereotaxic coordinates
based on the atlas of Talairach and Tournoux (1988) are indicated below. Both regions showed activation (P < 0.001) in six out of nine subjects, whilst there
were no activations in these regions during the Give-up phase even at a lower threshold (P < 0.01).

FIG. 2. Statistical maps of grouped analysis during the Hit-on and Give-up phases. (A) Hit-on phase. (B) Give-up phase. (C) Hit-on phase vs. Give-up phase.
The stereotaxic coordinates based on the atlas of Talairach and Tournoux (1988) are indicated below. (D and E) Time courses in (D) the left dorsolateralprefrontal cortex and (E) the anterior cingulate cortex. The red solid lines indicate the percentage changes of magnetic resonance signals as compared withthe signals at the presentation of a question. The time point zero (0 s) was at the subjects' responses that they successfully retrieved the target or gave up.
The red broken lines show the corresponding ®tted response functions. Blue solid lines indicate the signal changes in the Give-up trials and blue broken lines
represent their ®tted functions. (F) The statistical maps of group analysis in the Retrieval phase in the Hit-on trials.
ã 2001 Federation of European Neuroscience Societies, European Journal of Neuroscience, 14, 887±892

892 H. Kikyo et al.
We demonstrated that a number of regions were activated in the
Retrieval phase, including all the retrieval mode sites (Lepage et al.,2000), which were previously reported for episodic retrieval and/or
working memory (Wagner, 1999; Smith & Jonides, 1999). Above all,the left prefrontal regions were continuously activated from dorsal toventral, it is consistent with the notion that these regions serve as
rehearsal circuits (Smith & Jonides, 1999). The left superior temporal
cortex has been discussed in relation to the phonological processing(Demonet et al., 1992). These results support the idea that the regions
might play a phonological role in the TOT states (James & Burke
2000), and the activations were emphasized in comparison with therecognition tasks, because the TOT task required longer and hardereffort of recall than did recognition tasks. We observed activations in
the middle frontal gyrus (BA 10) in the single-subject analysis during
the Retrieval phase, but not in the group analysis. We suppose this isbecause the distortion due to susceptibility artifacts caused dif®culties
in the transformation among subjects. These results suggest thatwidely distributed brain regions are engaged when people make ahard effort to retrieve a proper name in the TOT states.

Acknowledgements
We are grateful to Prof. Y Miyashita for his encouragement. We thank Dr
Konishi and Dr S. T. Hayashi for valuable comments on the manuscript.

Abbreviations
ACC, anterior cingulate cortex; BA, Brodmann area; DLPFC, dorsolateralprefrontal cortex; fMRI, functional magnetic resonance imaging; TOT, `tip of
the tongue'.

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ã 2001 Federation of European Neuroscience Societies, European Journal of Neuroscience, 14, 887±892