Chem. Senses 38: 519–527, 2013
doi:10.1093/chemse/bjt022
Advance Access publication May 24, 2013
Changes in Fungiform Papillae Density During Development in Humans
Maryam Correa1, Ian Hutchinson1, David G. Laing1,2, and Anthony L. Jinks3
1
Children’s Food Research and Education Unit, Centre for Advanced Food Research,
College of Science and Technology and Environment, University of Western Sydney,
2
Locked Bag 1797, Penrith South, NSW 1797, Australia, School of Women’s and Children’s
Health, Faculty of Medicine, University of New South Wales, Level 3, Sydney Children’s
3
Hospital, High Street, Randwick, NSW 2031, Australia and School of Psychology and
Social Sciences, University of Western Sydney, Locked Bag 1797, Penrith South, NSW 1797,
Australia
Correspondence to be sent to: David G. Laing, School of Women’s and Children’s Health, Faculty of Medicine, University of New South
Wales, Level 3, Sydney Children’s Hospital, High Street, Randwick, NSW 2031, Australia. e-mail: [email protected]
Accepted April 24, 2013
Abstract
The anterior region of the human tongue ceases to grow by 8–10 years of age and the posterior region at 15–16 years. This
study was conducted with 30 adults and 85 children (7–12 year olds) to determine whether the cessation of growth in the
anterior tongue coincides with the stabilization of the number and distribution of fungiform papillae (FP) on this region of
the tongue. This is important for understanding when the human sense of taste becomes adult in function. This study also
aimed to determine whether a small subpopulation of papillae could be used to predict the total number of papillae. FP were
photographed and analyzed using a digital camera. The results indicated that the number of papillae stabilized at 9–10 years
of age, whereas the distribution and growth of papillae stabilized at 11–12 years of age. One subpopulation of papillae predicted the density of papillae on the whole anterior tongue of 7–10 year olds, whereas another was the best predictor for the
older children and adults. Overall, the population, size, and distribution of FP stabilized by 11–12 years of age, which is very
close to the age that cessation of growth of the anterior tongue occurs.
Key words: adults and children, gustatory development, papillae density predictors, tongue
Introduction
Fungiform papillae (FP) contain taste-sensing receptor cells,
which are accessible by tastants via pores in taste buds. They
are characteristically found on the tongue of mammals and
are visible to the eye on the dorsal surface. In humans, the
majority of FP are located on the most anterior area (Miller
and Reedy 1990a), which extends to about 2 cm from the
tongue tip (Temple et al. 2002). In contrast, they are only
sparsely distributed over the posterior area. Importantly, the
anterior tongue ceases to grow at 8–10 years of age, whereas
the posterior region continues to grow until 15–16 years of
age (Temple et al. 2002). A critical finding in the latter study
was that the area of the anterior tongue in 8–10 year olds
and adults is the same. Accordingly, this equivalence in size
allows direct comparison of papillae density in any part of
the anterior tongue of adults and children of this age. In
adults and children, FP density commonly varies across the
anterior tongue with the highest densities being recorded
near the tip (Miller 1986; Stein et al. 1994). However, there
can be wide differences between the distributions of papillae
of individual subjects with some having very high densities
near the tongue tip, whereas others exhibit more even
distributions of papillae across the anterior tongue (Miller
and Reedy 1990a). Furthermore, because 99% of papillae in
humans contain at least 1 taste bud (Segovia et al. 2002),
papillae density is related to taste sensitivity with subjects
who have higher numbers of papillae being more sensitive
to taste stimuli (Smith 1971; Stein et al. 1994; Delwiche
et al. 2001). Thus, because papillae density varies across the
tongue, sensitivity across the tongue also varies. A question
that has not been resolved is whether the densities of papillae
across the anterior tongue in children and adults are similar.
If differences in papillae distributions occur between
adults and children, they are also likely to affect
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520 M. Correa et al.
estimates of the total number of FP in the anterior
tongue. Previous estimates of the total number of papillae in adults have mostly been obtained by measuring the
number of papillae in a randomly selected single small
region and using this as an indicator of density on the
whole anterior tongue, for example, Tepper and Nurse
1997; Fast et al. 2002; Yackinous and Guinard 2002.
However, in none of these studies has the region chosen
been shown to be the best for predicting overall papillae density. More recently, Shahbake et al. (2005) used
a digital camera and the same software as described in
this study to show that 7/12 small regions across the
anterior tongue of adults were better predictors of the
total papillae numbers than the 2 areas previously used.
Establishing the age at which papillae densities in regions
on the anterior tongue stabilize would provide evidence
that full maturity has been achieved. With the discovery
that growth of the anterior tongue ceases at 8–10 years of
age, this can now be achieved. Thus, as indicated above, it
is now possible to compare equivalent tongue regions of
adults and children as regards their regional papillae densities. Accordingly, one of the major goal of this study is
to count the total number of FP in the anterior tongue
of adults and children in equivalent small regions. This
should provide the evidence necessary to demonstrate
at what age stabilization of papillae density occurs. The
advantage of being able to measure papillae density in a
small area to predict overall papillae numbers/densities is
that it would provide a rapid time-saving procedure for
monitoring taste loss and recovery in clinical conditions
that include lingual nerve section (Zuniga et al. 1997),
function during chemo- and radiotherapy in cancer treatment (Conger 1973), and administration of medications
that affect taste (Schiffman et al. 1998). Furthermore,
because papillae densities reflect taste sensitivity, the
ability to use a small area of the tongue to gain an insight
to the ability of a human to perceive tastes will be useful
in studies where the aim is to correlate objective anatomical data with subjective psychophysical measures such as
in classification of supertasters, tasters, and non-tasters
in studies using propthiouracil (PROP). Accordingly, a
goal of this study is to 1) determine whether the regions
that best predict overall papillae density in adults are
the same in children, and at what age this occurs and
2) determine whether the best predictors for children are
better than the 2 regions used previously by others with
adults. Such knowledge would also assist in defining the
age at which taste development on the tongue ceases. This
study consists of 3 parts. In Part 1, we describe when the
number and distribution of papillae stabilize and become
the same in children as in adults; in Part 2, we determine
whether a small region(s) of the anterior tongue can be
used to reliably predict the papillae density on the whole
anterior tongue of adults and children; and in Part 3, we
determine if the best predictor regions for children and
adults found here are better than those used by others
with adults.
Materials and methods
General
There were 115 participants (69 females and 46 males) comprising 30 adults aged 20–24 years (21.63 ± 0.95 [standard
error {SE}] years; 21 females and 9 males) and 85 children of
which 29 were 7–8 years old (7.78 ± 0.47 years; 17 females and
12 males), 23 were 9–10 years old (9.68 ± 0.51 years; 15 females
and 8 males) and 33 were 11–12 years old (11.60 ± 0.49 years;
16 females and 17 males). The adults were university students
who responded to poster advertisements around the campus and were examined in a university microscopy laboratory. The children were from local public schools and were
examined in a quiet room at their school. Written consent
was obtained from each adult and a parent of each child once
they had read an information sheet describing the purpose of
the study and details of how measurements would be conducted. Only subjects with obvious flu/colds/middle ear infections, or oral problems such as recent withdrawal of teeth,
which could have damaged the chorda tympani that innervates FP and possibly caused loss of papillae, were excluded.
Subjects within each age group were not fully matched for
gender for several reasons; 1) prior to the study, Temple
(1999) had found that the number of papillae in the anterior
tongue of matched female and male 8 year olds was the same;
2) Temple et al. (2002) found no gender differences as regards
the size/area of the anterior tongue of age-matched groups
of female and male 8–10 year olds, or in older children and
adults. All participants received compensation (movie tickets
and confectionary) at the conclusion of their participation.
The research was approved by the University of Western
Sydney Human Research Ethics Committee (Approval No.
HEC02/188) and conducted in accordance with the ethical
standards laid down in the 1984 Declaration of Helsinki.
Prior to commencing the photographing and counting of
papillae, subjects rinsed their mouth with deionized water
(Milli-Ro- Plus System, conductivity 0.9 µS), and their tongue
was dried with a filter paper by the experimenter. A piece of
filter paper (Whatman’s No. 1) that contained a blue food
dye (Robert’s Brilliant Blue FCF133) was placed on the
left side of the anterior tongue for 3 s (Figure 1). The area
stained was the most anterior 3–4 cm of the dorsal tongue.
This length was used because it adequately covered more
than 2 cm “demarcation line,” which defined the anterior and
posterior regions of the tongue in both adults and children
(Temple et al. 2002). On removal of the filter paper, the
tongue was dried with a clean filter paper. Head movement
during photography of the tongue was minimized by the
participant placing their arms on a table and holding their
head with their hands such that their chin protruded forward.
The participants extended their tongue and held it steady with
Changes in Fungiform Papillae Density 521
their lips while 3–7 images of the 2-cm anterior stained area
were captured with the camera. Images were taken at different
angles to ensure that all of the 2-cm stained area was visible
in the images captured. A 10 × 3 mm wide piece of filter paper
placed on the right side of the anterior tongue provided a
scale to calculate the magnification of each image (Figure 1).
Images were recorded with a Nikon Coolpix 4500 (4.0
megapixels) camera with a macro light attachment (Macro
Cool-light SL-1). The digital images were downloaded to a
computer (Toshiba Satellite Pro 6100) and analyzed using
a “zoom” option in the Adobe Photoshop 7.0 program
(Shahbake et al. 2005). The best image of the 2-cm anterior
tongue from an individual was the image that was used for
counting papillae in each part of the study. Accordingly, the
data collected in the 3 parts were from the same subjects and
images were recorded at this one and only photography session. The magnification used for the image analysis ranged
between ×14.12 and ×23.73 (mean = ×18.43).
FP were identified as mostly mushroom-shaped and elevated structures (Miller 1995; Segovia et al. 2002; Shahbake
et al. 2005). Some papillae were flat and short with little
elevation, others were double papillae. In addition, FP were
readily distinguished from filiform papillae by their very light
staining with the food dye compared with the latter papillae,
which stained dark (Miller and Reedy 1990b).
Part 1
Aims
Determine 1) whether the number of FP in the whole anterior tongue differs for adults and children and 2) whether FP
density in two 1 cm wide regions of the anterior tongue is
different and change throughout childhood.
Materials and methods
Prior to image analysis, the midline of the tongue and
each of the 2 most anterior centimeters of the stained area
were “marked” using the horizontal and vertical “guide”
option in the “view” menu of Adobe Photoshop resulting
in two 1-cm horizontal bands (Figure 1). Because the area
of the anterior tongue was the same in adults and children
(Temple et al. 2002), the software adjusted the 2 bands to be
equivalent for all subjects. In essence, the software provided
a “virtual template” that adjusted the size of the bands to be
equivalent across subjects. The number of FP in each 1-cm
region were identified and counted using the “zoom” option
in the “view” menu of Adobe Photoshop. All images were
coded with a 4-digit number and randomized before analysis
so that the identity of the participants and their age groups
were unknown to the experimenter.
Results and discussion
For data analysis, the participants were divided into 4 age
groups: 7–8, 9–10, 11–12 years, and adults, and for each participant, the number of FP in each 1-cm region and total
number of papillae in the anterior tongue were determined
(Table 1).
Total number of FP
A 2 × 4 (gender × group) analysis of variance (ANOVA) was
performed amongst all age groups to determine if there were
significant differences in the total number of FP in the anterior tongue. This indicated that there was a significant difference between age groups (F[3,107] = 3.238, P = 0.025; Table 1).
Post-hoc Tukey Least Squares Difference-paired comparison tests (P < 0.05) indicated that 7–8 year olds had significantly more papillae than adults (P = 0.01), and there were
no significant differences between any other groups. This is
an important finding because it indicates the total number of
FP in humans stabilized during childhood at 9–10 years of
age. The ANOVA also indicated that there was no significant
gender differences (F[1,107] = 0.033, P = 0.855; Table 1) and no
gender × group interactions (F[7,107] = 0.974, P = 0.408).
Figure 1 Analysis of FP density. (A) Image of the tongue showing the most anterior stained area on the left side divided into two 1-cm intervals as in Part
1 and 8 smaller areas as in Part 2. On the right side is the 1-cm scale. (B) A diagram of the tongue showing the numbering sequence of the 8 small areas.
522 M. Correa et al.
Table 1 Mean number of FP in the anterior tongue and in two 1-cm regions for different age groups
Group
Total FP
counts ± (SE)
FP range
First cm FP
counts ± (SE)
Second cm FP
counts ± (SE)
Total FP M/F ± (SE)
Male
Female
7–8 years
162.24 ± 3.74
116–195
109.93 ± 2.63
52.31 ± 2.90
159.08 ± 6.41
164.47 ± 4.59
9–10 years
146.09 ± 4.69
75–186
93.87 ± 3.09
52.22 ± 2.43
140.07 ± 5.21
157.38 ± 8.33
11–12 years
150.79 ± 5.27
85–217
93.39 ± 4.24
57.40 ± 2.81
149.71 ± 6.27
151.94 ± 8.81
Adults
140.20 ± 5.50
93–222
91.30 ± 4.07
48.90 ± 3.01
134.11 ± 8.25
141.95 ± 7.11
Regional analysis
Two 2 × 4 (gender × group) between-participants ANOVAs
were performed to determine if there were significant differences 1) in the FP density of the age groups within the first and
second 1-cm regions of the anterior tongue and 2) between
females and males of all groups within these regions.
The ANOVA indicated that for the most anterior 1-cm
region (tongue tip), the number of papillae differed between
the groups (F[3,107] = 5.282, P = 0.002). Post-hoc Tukey tests
(P = 0.05) showed that 7–8 year olds had significantly more
papillae than the 3 older groups and the latter groups had
similar numbers of papillae. As regards gender, there were
no significant differences between females and males within
each age group (F[1,107] = 0.021, P = 0.885). Interestingly, there
was a significant gender × group interaction (F[7,107] = 2.993,
P = 0.007). Accordingly, an interaction graph was constructed
to investigate where these differences appear. This showed that
with males, FP density decreased from 7–8 year olds to adults,
whereas with females, there was a density decrease from 7–8
to 9–10 years, where it remained stable through to adulthood.
As regards the second 1-cm region, a 2 × 4 (gender × group)
ANOVA indicated that there were no significant differences
between the papillae numbers of the groups (F[3,107] = 1.288,
P = 0.282), or between females and males (F[1,107] = 0.249,
P = 0.619), and there were no significant interactions
(F[7,107] = 0.804, P = 0.586). In brief, because 7–8 year olds
had more papillae on the most anterior 1-cm region than the
other age groups but had similar numbers to the other groups
in the second more posterior 1-cm region, it can be concluded
that papillae numbers stabilize at 9–10 years of age.
Another feature of the papillae was a variation in their
shape with age. In the youngest group, papillae were identified as small and round structures. In 9–10 year olds, the
papillae were noticeably larger in size, whereas in 11–12 year
olds and adults, many papillae were irregular in shape,
which was similar to previous findings from this laboratory
(Segovia et al. 2002). The increase in size with age is in agreement with the finding that adult papillae have significantly
larger diameters than those of 8–9 year olds (Segovia et al.
2002). Thus, although the number of papillae stabilizes by
9–10 years of age, changes in the shape and size of the papillae continue until 11–12 years.
Adults and children were also observed to have 2 qualitatively different distribution patterns of FP across the 2-cm
anterior tongue region. The patterns were recorded by “marking” each fungiform papilla with a dot and the tongue midline and 2-cm region were “marked” to enhance consistency
of regions between subjects. The “markings” were superimposed on each image. One pattern had clusters of closely
packed FP at the tip of the tongue with a sharply decreasing
number toward the posterior tongue. A second pattern had
no clusters, and the papillae were distributed approximately
evenly over the anterior 2 cm of the tongue. No other type
of distribution was discerned and there appeared to be no
gender-related differences in the patterns of papillae distribution. The finding of variations in the distributions of FP is
not new and has been reported for adults (Miller and Reedy
1990a) and both adults and 8 year olds (Stein et al. 1994).
In summary, only the 7–8-year-old group had more papillae than adults, and this difference was due to the youngest
group having more papillae in the 1-cm region nearest the
tongue tip. The shape and size of papillae were smaller and
more regular in 7–10 year olds than in 11–12 year olds and
adults. From these data, it can be concluded that the number of papillae stabilizes by 9–10 years of age, whereas the
growth and shape of papillae stabilizes by 11–12 years. In
none of the measures was there a gender difference.
Part 2
Aims
Determine 1) whether there is a subpopulation(s) of FP on
the anterior tongue whose density is a reliable predictor of
the total number of papillae and 2) whether the location of
the subpopulation (s) is dependent on age.
These questions were of interest for several reasons. First,
in Part1, papillae were counted in 2 relatively large regions
of the anterior tongue and the time required to count the
papillae in all the subjects was considerable. Accordingly,
it was important to determine if a smaller regional
subpopulation(s) of papillae would prove to be a suitable
predictor of overall papillae density. The data should also
show when the papillae density across the anterior tongue
stabilizes signaling maturation of the peripheral gustatory
system. To achieve a more fine-grained analysis, the two
1-cm anterior regions described in Part 1 were divided
into 8 smaller regions (Figure 1). Also, because it had been
shown that for adults the best predictor of total papillae
Changes in Fungiform Papillae Density 523
numbers was a subpopulation located in the second 1-cm
region (Shahbake et al. 2005), another goal was to expand
this finding to determine if the same result was obtained for
children of different ages. This was of particular interest
because in Part 1, it had been shown that papillae numbers
varied with age with changes being observed in the most
anterior 1-cm region for 7–8 year olds.
Table 3 Predictor models of total FP on the anterior tongue
Group (year)
Model
R2
7–8
1: y = (2.281A1 + 60.850)
0.44
2: y = (2.259A1 + 2.048A5 + 31.878)
0.56
3: y = (2.009A1 + 2.990A5 + 1.904A7 + 7.429)
0.69
1: y = (1.701A1 + 84.563)
0.45
9–10
Materials and methods
Each of the two 1-cm regions on the anterior tongue was
divided into 4 smaller areas using the “grid” option in the
“view” menu of Adobe Photoshop (Figure 1). These 8 areas
were numbered in a manner where Areas from 1 to 4 were in
the most anterior 1-cm region, and Areas from 5 to 8 were in
the second region. Papillae were counted in each of the 8 areas,
which were then compared with the total number of papillae
in the 2-cm anterior tongue region. The length and width of
each small area were measured based on the 1-cm scale. This
allowed the area of each of the 8 areas to be calculated and the
density of papillae per cm2 to be determined (Table 2).
Results and discussion
For each of the 4 age groups, a stepwise multiple regression
analysis (SPSS 12.0.1) was used to identify which Area(s) best
predicted the total number of papillae in the 2-cm anterior
tongue region, and for each of the 8 areas, the best 3 predictor
models were calculated (Table 3). The models were based on
the equation y = bA1 + bA2 + bA3 + … + Constant, where b
was the coefficient calculated from the regression analysis, Ax
represented the number of the Area, and the constant was calculated from the regression analysis. As shown in Table 3, Area
1 was the best predictor of total FP density for 7–8 (R2 = 0.44)
and 9–10 (R2 = 0.45) year olds, respectively, with Area 5 the
best predictor for 11–12 year olds (R2 = 0.52) and adults
(R2 = 0.46). Table 3 also indicated that including 1 and 2 other
Table 2 Mean FP density (papillae/cm2 ± SE) in 8 regional subpopulations
and Areas X and Y on the anterior tongue
Area
7–8 years
9–10 years
11–12 years
Adult
1
120.95 ± 9.11
113.69 ± 9.12
115.44 ± 6.53
118.79 ± 13.33
2
76.48 ± 8.02
79.23 ± 5.86
74.40 ± 5.86
68.30 ± 13.73
3
64.78 ± 4.19
62.57 ± 6.52
60.29 ± 3.67
52.47 ± 4.28
4
64.75 ± 3.68
65.33 ± 4.82
60.44 ± 3.61
61.39 ± 8.53
5
32.72 ± 2.17
32.75 ± 2.80
34.40 ± 2.58
36.15 ± 6.24
6
38.71 ± 3.67
37.38 ± 3.02
33.12 ± 2.88
43.30 ± 10.97
7
30.36 ± 3.10
27.23 ± 3.64
26.40 ± 2.81
21.82 ± 4.75
8
32.35 ± 2.46
34.16 ± 3.40
23.40 ± 2.33
18.44 ± 2.46
X
139.05 ± 4.32
138.11 ± 5.75
135.49 ± 5.43
133.95 ± 4.04
Y
64.16 ± 2.61
62.44 ± 2.73
59.49 ± 3.05
59.43 ± 2.26
11–12
Adults
2: y = (1.779A1 + 2.422A5 + 50.787)
0.62
3: y = (1.806A1 + 1.916A5 + 2.210A7 + 9.959)
0.71
1: y = (3.067A5 + 100.215)
0.52
2: y = (2.522A5 + 2.516A4 + 58.28)
0.72
3: y = (2.123A5 + 2.477A4 + 2.141A2 + 25.932)
0.81
1: y = (3.190A5 + 92.569)
0.46
2: y = (2.195A5 + 0.865A1 + 61.313)
0.60
3: y = (2.894A5 + 0.638A1 + 1.203A2 + 48.321)
0.69
areas in the calculations increased predictability. For example,
in the case of 7–8 year olds, predictability increased from 0.44
to 0.56 when Area 5 was included, and for adults, predictability increased from 0.46 to 0.60 when Area 1 was included. The
data were also analyzed by including data from all age groups,
and this indicated that the best overall predictor was Area 1
2
(R = 0.33). Inclusion of Area 5 in the calculations increased
2
R to 0.51. As expected from previous studies (Miller 1986;
Miller and Reedy 1990a; Stein et al. 1994; Segovia et al. 2002;
Shahbake et al. 2005), for all age groups, the number of papillae per area decreased in the anterior to posterior direction.
It is concluded that the FP density of the whole anterior tongue
can be predicted from 1 or at most 2 small areas on the tongue,
with different areas being better predictors depending on the
age of subjects. Because the best predictor area for 11–12-yearold children is the same as for adults, it can be concluded that
the distribution of papillae stabilizes at 11–12 years of age.
Part 3
Aim
Determine whether the papillae density in a 6-mm diameter
circular area (0.28 cm2) on the anterior tongue is 1) a reliable
predictor of the total number of papillae on the anterior
tongue in adults and children, and 2) that it is a more reliable
predictor than either of the 2 predictors, that is, Areas 1 and
5, found in Part 2.
This study was conducted as an advance on earlier studies with adults that used the papillae density of a randomly
selected small circular area of the anterior tongue to estimate density of the whole anterior tongue (Tepper and
Nurse 1997; Fast et al. 2002; Yackinous and Guinard 2002).
However, only 1 study (Shahbake et al. 2005) determined the
reliability of the procedure, which was found to provide a
modest but statistically significant estimate.
524 M. Correa et al.
Materials and methods
FP density was quantified in two 6-mm diameter circular
areas designated Area X and Area Y (Figure 2.). The figure
shows these 2 areas superimposed on the stained anterior
tongue. Area X included Area 1, which was the best indicator of anterior tongue papillae density for 7–8 and 9–10 year
olds, and a small part of Area 3. Area Y encompassed Area
5, which was the best predictor of overall papillae density for
11–12 year olds and adults, and part of Area 7. Area X was
similar to that used to measure papillae density in adults by
Tepper and Nurse (1997), Yackinous and Guinard (2002),
Fast et al. (2002), and Shahbake et al. (2005).
Results and discussion
The FP density for Area X was 139.05 ± 4.32 (SE),
138.11 ± 5.72, 135.49 ± 5.43, and 133.95 ± 4.04 papillae/cm2 for
7–8, 9–10, 11–12 year olds, and adults, respectively (Table 2).
Lower densities were found in Area Y for all age groups.
These were 64.16 ± 2.61, 62.44 ± 2.73, 59.49 ± 3.05, and
59.43 ± 2.26 papillae/cm2 for 7–8 year olds to adults, respectively. Importantly, the densities for adults found here were
similar to those reported. Thus, the density here for Area X
was 133.95 papillae/cm2 compared with 99.5 and 141 by Fast
et al. (2002) and Yackinous and Guinard (2002), respectively.
Pearson’s correlation analyses showed there were significant correlations between the total FP counts on the anterior tongue and both Areas X (R2 = 0.24, P < 0.001) and
Y (R2 = 0.11, P < 0.001) when the data from all subjects
were combined. Both correlations are poorer than that for
Area 1 (R2 = 0.33) when all subjects were included in the
analysis. In addition, a 2 × 4 (gender × group) ANOVA indicated there was no significant difference in papillae density
between groups in Area X (F[1, 107] = 0.783, P = 0.860) and
there were no significant gender differences (F[1,107] = 0.783,
P = 0.378) within the groups or gender × group interactions.
As regards Area Y, papillae densities were not different
across groups (F[3,107] = 0.594, P = 0.620 and there were no
significant gender differences within groups (F[1, 107] = 0.216,
Figure 2 Image of tongue showing the locations of Areas X and Y.
P = 0.643), but there was a significant gender × group interaction (F[4,139] = 1.10, P = 0.044). The interaction plot showed
there were similar trends for females and males with a gradual decrease from 7–8 year olds to adults.
In summary, the 2 regions selected by others to predict the
total papillae density of the anterior tongue gave statistically
significant results for both adults and children. However, the
correlations for Areas X (R2 = 0.24) and Y (R2 = 0.18) were
lower than when the predictor was Area 1 (R2 = 0.33), which
was the best predictor area when the data from all subjects
were combined. However, the most reliable correlations for
each age group were recorded when Area 1 was used for 7–8
(R2 = 0.44) and 9–10 (0.45) year olds and Area 5 for 11–12
(R2 = 0.52) year olds and adults (R2 =0.46). In every instance,
a lower correlation was obtained for each age group when
either Area X or Y was used as the predictor area.
General discussion
The study had 3 major aims, all of which were achieved. The
first was to determine at what age the number of papillae
stabilized. The results of Part 1 indicated the number became
constant by 9–10 years of age. The second was to determine
whether there is a location on the tongue where the papillae
density can be used to predict the overall papillae density of
the anterior tongue. Again, a clear outcome was achieved with
the data of Part 2 indicating that there are 2 locations, which
are dependent on age. Third, it was shown in Part 3 that the
method used by earlier workers for estimating overall papillae
density on the anterior tongue produced reliable results, but
these were less reliable than the 2 subpopulations of papillae
that were found here to be the best for particular age groups.
This study is the first to demonstrate that the FP density
on the human tongue reaches adult numbers by mid-childhood. The results are in agreement with 2 earlier studies of
papillae numbers that had shown papillae density decreased
from childhood to adulthood. One study found that density
decreased from 0–10 year olds to adults aged 50–60 years
(Moses et al. 1967) and the other study showed that 8–9 year
olds had significantly higher papillae densities than adults
(Segovia et al. 2002). However, neither indicated at what
age papillae density stabilized. Importantly, the most striking feature in both studies was that the number of papillae
decreased from childhood to adulthood, as was reported for
circumvallate papillae (Arey et al. 1935).
The mean number of FP found in the anterior tongue
of adults in this study was 140.20 ± 5.50 (SE) and is similar to the number reported by Miller and Reedy (1990a)
using video microscopy. Comparison of the adult papillae number (140.20) with the number found for 7–8 year
olds (162.24 ± 3.74) indicates that the children had ~13.6%
more papillae, which is a statistically significant difference.
Analysis of the papillae numbers in each of the two 1-cm
regions indicated the difference was primarily due to the
Changes in Fungiform Papillae Density 525
greater number of papillae in the most anterior region of
7–8-year-old tongues (Table 1). The finding that there were
no changes in the numbers of papillae in the first 1-cm
region in children aged above 7–8 years and no changes in
the second 1-cm region with any of the age groups indicates
that stabilization of papillae numbers in the anterior tongue
had occurred by 9–10 years of age. Importantly, stabilization of papillae numbers by 9–10 years of age coincides with
completion of the growth of the “taste-sensitive” area of the
anterior tongue (Temple et al. 2002).
Another feature of the papillae that indicated changes in
papillae density occurs until mid-childhood was their shape
and size. As indicated in Part 1, papillae of 7–8 year olds were
identified as small round structures; in 9–10 year olds, they
were larger in size, whereas in 11–12 year olds and adults,
they were irregular in shape. These results are in agreement
with the report that 8–9 year olds have rounder and smaller
papillae than adults, and adults have papillae that differ
in shape more than in children (Segovia et al. 2002). The
changes in size and shape also suggest that development of
the structure of papillae is complete at 11–12 years of age.
The imaging procedure described in Part B that was used
to accurately divide the anterior tongue into 8 regions, which
were equivalent in size across subjects, produced data that
for the first time provided a reliable method for predicting the papillae density of the whole anterior tongue from
the density of a small regional subpopulation of papillae.
Importantly, the data indicated that the location of the
regional subpopulation that best predicted overall papillae
density was dependent on age. Thus, the density of papillae in Area 1 at the tongue tip was the best predictor of the
density of papillae in the whole anterior tongue for children
aged 7–8 and 9–10 years, whereas Area 5 in the second 1-cm
region was the best predictor for 11–12 year olds and adults
(Table 3). Given that a reduction in the number of papillae occurs in the most anterior 1-cm region in the youngest
age groups and stabilizes in number with 11–12 year olds
and adults, it is not surprising that different locations are
more reliable for predicting the overall papillae density of
the anterior tongue of different age groups. The finding that
Area 5 is the best area to use for predicting total papillae
density in 11–12 year olds and adults also indicates that stabilization of the distribution of papillae occurs by the age
of 11–12 years. Taken together with the findings that 1) the
size and shape of papillae stabilizes at the age of 11–12 years
and 2) adults and 8–9 year olds have a similar number of
taste pores per papilla (Segovia et al. 2002), the data provide
strong evidence that the peripheral gustatory system is fully
functional by 11–12 years of age.
Although the data from the 8 regional subpopulations of
papillae indicated which subpopulations should be used for
predicting overall papillae densities on the anterior tongue,
examination of larger areas, namely, Areas X and Y used by
other workers, was also found to be predictors of papillae
density. However, these latter 2 areas produced less reliable
densities than indicated by the R2 values for Areas 1 and 5
for particular age groups. The lower predictability of Area
X appears to be due to the inclusion of part of Area 3 in
the papillae counts, which was not one of the Areas found
to be a predictor for any of the age groups in the 3 models
described in Table 3. Similarly, the R2 values for Area Y were
lower than found for Area 5 for 11–12 year olds (0.52 vs.
0.28) and adults (0.46 vs. 0.13) because part of Area 7 was
included in the papillae counts, and this area was not found
to be a significant predictor for these age groups. In brief, the
results indicated Areas 1 and 5 were better predictors than
Areas X and Y for particular age groups.
In none of the above measures of papillae density, or the
best predictor regions, was there a significant gender effect.
Absence of a gender effect has been reported in a number
of studies on tongue growth (Temple et al. 2002), taste bud
density (Miller 1988; Zuniga et al. 1993), and taste buds per
papilla (Arvidson 1979) and appears to be a robust finding
as regards anatomical features of the human peripheral gustatory system.
As mentioned above, an important finding of this study was
that taste-sensing papillae on the anterior tongue decrease
in number during mid-childhood and plateau at about
9–10 years of age. This loss of papillae, which would include
loss of taste buds and cells within the papillae, parallels other
developmental phenomena in mammalian gustation and
other sensory systems. For example, 8–9 year olds have a
greater density of taste pores than adults (Segovia et al. 2002),
and the number of taste buds in FP in sheep innervated by
a single chorda tympani neuron increases in perinatal sheep
as compared with fetal sheep and then decreases through
postnatal development (Mistretta et al. 1988; Nagai et al.
1988). In olfaction, there is a large loss of granule cells, the
major interneurons in the mouse olfactory bulb, during the
first 2 postnatal weeks, after which the number of granule cells
and their synapse formation with mitral and other granule
cells stabilizes (Hinds and Hinds 1976). As regards behavior
although newborn humans respond with adult-like facial
expressions to sweet, sour, and bitter tastants, psychophysical
data indicate humans do not respond to the taste of salt
(sodium chloride) similarly to adults until about 2 years of age
(Beauchamp et al. 1986). Furthermore, at 8–9 years of age,
male humans appear to have a poorer sensitivity for sweet,
salt, and sour stimuli (James et al. 1997) and a poorer ability
to perceive the constituents of taste mixtures (Oram et al.
2001). Thus, even though 8–9 year olds have more papillae
and more taste buds than adults, these latter data suggest that
neural maturation is not complete at this age.
Loss of FP during childhood may also affect somatosensory
perception on the tongue. FP receive both taste (chorda tympani) and somatosensory (lingual nerve) afferents. Although
the gustatory afferents distribute into taste buds to synapse
with taste cells, somatosensory afferents distribute around the
taste buds but terminate predominantly in the apex of papillae.
It has been reported that humans with fewer papillae tend to
526 M. Correa et al.
have poorer spatial acuity (touch) than those who have significantly more papillae (Essick et al. 2003). For example, humans
classified as supertasters because of their ability to taste the
bitter substance PROP at very low concentrations have significantly higher numbers of papillae and superior spatial acuity
than those classified as poor PROP tasters. Because 8–9 year
olds have a similar number of taste buds per papilla as adults
but a greater number of papillae (Segovia et al. 2002), it would
be expected that the loss of papilla they experience would be
accompanied by a decrease in their spatial acuity. Such a proposal suggests that children up to mid-childhood would be
expected to have a superior spatial acuity ability to adults. In
addition, because the somatosensory afferents respond to
chemical irritants, it is possible that children would be more
sensitive than adults to “hot” tasting food ingredients such as
chilli, mustard, and curries or “cooling” sensations as occurs
with mints. As yet, these 2 proposals have not been tested.
Conclusion
In conclusion, this investigation has shown that children up to
mid-childhood have a greater number of FP than adults and
that their papillae are smaller and more uniform in shape. The
difference in papillae numbers between adults and 7–8-year-old
children appears to be confined to the most anterior region of
the tongue and it is at a location within this region (Area 1) that
a subpopulation was found that was the best predictor of the
overall number of papillae on the anterior tongue of children
up to 10 years of age. The finding that a different subpopulation of papillae (Area 5) was a better predictor for 11–12 year
olds and adults is yet another feature of the data that indicates
the organization of papillae and related neural connections in
children continues until 11–12 years of age. Importantly, the
subpopulations of papillae found for predicting overall papillae
density are smaller than those reported providing a more rapid
procedure for measuring overall papillae numbers. Finally, the
cessation of papillae loss by 9–10 years of age coincides with
the cessation of growth of the anterior tongue (Temple et al.
2002), suggesting that the gross anatomical development of the
anterior tongue in humans is achieved by mid-childhood.
Funding
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Acknowledgements
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The authors wish to thank the university students and the children
and staff of participating schools for their assistance and cooperation.
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