Physiology&Behavior, Vol. 47, pp. 1213-1219. ©Pergamon Press plc. 1990. Printed in the U.S.A.
0031-9384/90 $3.00 + .00
Variations in Human Taste Bud Density and Taste Intensity Perception I N G L I S J. M I L L E R , JR. A N D F R A N K E. R E E D Y , JR.
Department of Neurobiology and Anatomy, The Bowman Gray School of Medicine Wake Forest University, Winston-Salem, NC 27103 R e c e i v e d 15 January 1990
MILLER, I. J., JR. AND F. E. REEDY, JR. Variationsin humantaste bud density and taste intensityperception. PHYSIOL BEHAV 47(6) 1213-1219, 1990.--Some variations in human taste sensitivity may be due to different numbers of taste buds among subjects. Taste pores were counted on the tongue tips of 16 people with videomicroscopy, and the subjects were divided into two groups (N = 8) by the rank order of their taste bud densities. The "higher" density group averaged 374-+ 134 taste pores/cm 2, while the "lower" density group averaged 135 ___43 tp/cm 2. The higher density group had an average fungiform papilla density which was 1.8 times greater than the lower density group and an average of 1.5 times more taste pores/papilla. The subjects also rated the intensity for 4 suprathreshold concentrations of 5 taste stimuli placed on the same region of the tongue where taste pores were counted. The group with higher taste bud densities gave significantly higher average intensity ratings for sucrose (196%), NaCI (135%) and PROP (142%), but not for citric acid (118%) and quinine HC1 (110%) than the lower density group. Thus, the subjects with higher fungiform taste bud densities also reported some tastes as more intense than subjects with fewer fungiform taste buds. Taste bud density
Taste intensity
Individual variations
TASTE sensitivity and taste bud distribution vary among individuals. Thresholds for a taste stimulus differ by 1-2 log units of concentration among human subjects (5). Individual humans in a group yield unique profiles of thresholds for an array of taste stimuli (10). Magnitude estimates of suprathreshold taste intensifies for individual stimuli also differ among subjects, but the variation among individuals can be parceled into different constant factors times a power function of stimulus concentration (37). We reported that taste bud densities vary by 100-fold on the tips of human cadaver tongues (23,25), and these variations occurred for a range of subjects' ages (26). Genetics influences variations in taste sensitivity among humans (14) and fluid intake by animals. Avoidance of the bitter taste stimulus, sucrose octaacetate (SOA), differs among inbred strains of mice (12). One SOA-taster strain of mice, which avoids SOA at lower stimulus concentrations than nontasters, also has more taste buds in their vailate and foliate papillae than the nontasters (16,30). We hypothesize that variation in the number of taste buds among individuals may account for some differences in their taste perception. A relationship between taste sensitivity and the number of stimulated taste buds has been demonstrated by studies of human taste perception. Taste thresholds (19) and suprathreshold taste intensities produced by a constant concentration of stimulus (35) are related to the area and the number of fungiform papillae which are stimulated. A larger variety of perceptual qualities can be elicited from human fungiform papillae which have more taste buds present than from papillae with fewer taste buds (2). Differences among individuals in taste perception have not been related directly to quantification of their taste bud densities, perhaps because taste bud quantification has required destructive anatomical methods.
Humans
A method for counting taste pores in fungiform papillae of living humans (27,29) and rabbits (24) has been developed which is innocuous and nondestructive. The taste pore is the portion of the taste bud which opens onto the surface of the tongue (1,17). It can be stained and identified by acidic dyes (7). Taste pores are located on the apical surfaces of human fungiform papillae, and individual papillae have from 0-20 taste pores. After methylene blue stain is applied to the tongue surface, images of the fungiform papillae and their taste pores are recorded and counted with videomicroscopy. A 14-fold variation in taste bud densities has been observed in healthy university students (29) with this method. The hypothesized relationship between the prevalence of taste buds and the sensitivity of taste perception among human subjects is examined here. Fungiform taste pores are quantified in a region of the tongue tips of young adult subjects, and taste intensity ratings are obtained for 5 stimuli over a range of concentrations applied to the same region. The subjects are divided, subsequently, into two groups with relatively higher and lower taste bud densities. Taste intensity ratings are compared across concentrations among the stimuli and subject groups. It is hypothesized that subjects with higher taste bud densities experience more intense taste perceptions (and report higher intensity ratings) than subjects with lower taste bud densities. METHOD Taste pores were counted in fungiform papillae of 16 living human subjects by staining the tongue surface with 0.5% methylene blue and by identifying papillae and taste pores with videomicroscopy (27,29) according to the method previously reported. A
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Wild dissecting microscope fitted with a video camera recorded the magnified images of the tongue surface. Images were stored on a video cassette recorder, and single-frame images were examined and documented with an image processor in a Macintosh II microcomputer. All fungiform papillae were mapped and counted on the most rostra1 2-3 cm of the tongue tip. Taste pores were counted on fungiform papillae in a subregion comprising about 1 cm 2 of tongue surface. The subjects were 16 university personnel comprised of 12 males and 4 females, ranging in age from 17-29 years. They were paid for participating in the experiment and gave their written consent. This procedure was reviewed and approved by the Human Subjects Committee of The Bowman Gray School of Medicine of Wake Forest University. Mapping of the tongue was conducted in one session lasting about one hour, and the taste testing procedure was conducted in a subsequent session lasting about one hour. Taste stimuli were applied with a cotton-tipped applicator to a small area of the tongue tip with the procedure of Bartoshuk et al. (4). Subjects were instructed to rinse their mouths with water before the application of each stimulus. The region of stimulation was the same as where taste pores were quantified, but the stimulus was not limited to the quantified papillae. Intensity ratings were made on a 10-point scale for water and 5 compounds in suprathreshold concentrations as follows: NaC1 (0.032-1.0 M), sucrose (0.032-1.0 M), 6-n-propyl-2 thiouracil (PROP) (0.0561.8 mM), quinine HC1 (0.030-1.0 mM), and citric acid (1.0-32 mM). The stimuli were made from reagent chemicals grade chemicals as follows: NaC1 (Fisher No. S-271), sucrose (Fisher No. S-5), 6-n-propyl-2 thiouracil (Sigma No. P-3755), citric acid (Fisher No. A-104), quinine hydrochloride (Sigma No. Q-1125). Solutes were dissolved and diluted in insipid, deionized water (Hydro Systems, resistance >5 MI~). Stimuli were presented in an increasing concentration series with water controls interspersed, and each series of stimuli was presented twice. Subjects were asked to mark a number between 1 and 9 for each trial which corresponded to the relative intensity of the taste perception. The instructions to the subject were: Mark '0' if the stimulus application tastes like water; mark '1' if the stimulus tastes 'weak'; and mark '9' if the stimulus tastes 'strong.' They also chose one of the following words: sweet, salty, bitter, sour or other to describe the taste quality. Intensity ratings were averaged within subjects for the two presentations and across subjects in each group at each stimulus concentration. After completion of both taste pore quantification and taste intensity testing, the 16 subjects were ranked in increasing order by taste pore density. The subjects were divided into two groups (N = 8), which were arbitrarily designated "higher" and "lower" taste pore density groups. Taste pore densities (one-way ANOVA) and taste intensity ratings (two-way ANOVA: concentration, group) were averaged for each group and compared by ANOVA. Variances for the intensity ratings were parceled as follows: Total df= 63; within taste bud density groups, df= 7; among concentrations, df= 3; among taste bud density groups, df= 1; interaction: concentration x density group, df= 1; error df= 56. RESULTS
Fungiforrn Papilla and Taste Pore Quantification Figure 1A shows a region of the human tongue near the margin of the tongue tip containing an array of fungiform papillae (F) and filiform papillae (f). Methylene blue has been applied to the tongue surface, so that regions with higher affinity for the dye stained dark and regions with less affinity for the dye stained light. Tips of filiform papillae stained dark, and the dorsal surfaces of fungiform papillae stained light, except for taste pores. The taste
pores appeared as dark spots, 25-60 Ixm in diameter. Examples of single fungiform papillae are shown which contain 3 taste pores (Fig. 1B, arrow) and 6 taste pores (Fig. IC, arrow), respectively. Each taste pore corresponds to a single taste bud. Total fungiform papilla density on the tongue tip ranged among subjects from 22.1 to 74.3 papillae/cm2 with a mean of 43.8 --- 15.8 pap/cm 2 (s.d., N = 16). An average of 57 ± 18 pap/subject (s.d., N = 1 6 ) was studied for taste pores, and a mean of 5 2 -+ 17 pap/subject (s.d., N = 16) (91%) contained taste pores. Fungiform papillae containing taste pores are referred to as gustatory papillae. The number of taste pores/papilla ranged from 0-26 within subjects with a mean of 4.56-+ 1.71 taste pores/gustatory papilla (s.d., N = 1 6 ) and 4.26-+ 1.85 (s.d., N = 1 6 ) taste pores/total fungiform papillae (including those without pores). The percentage of fungiform papillae which lacked taste pores averaged 8.8 -+ 8.6 (s.d., N = 16) percent with a range among subjects from 0% to 35%. The density of taste pores in the sampled region of the tongue tip ranged from 36 to 582 taste pores/cm 2 among subjects with a mean of 254± 156 taste pores/cm 2 (s.d., N = 16). At the conclusion of the experiments, subjects were ordered by rank according to the taste pore densities on their tongue tips. The ranked subjects were divided into two groups (N = 8) so that taste intensity responses could be compared for groups with "higher" and "lower" taste pore densities (Fig. 2). The higher taste pore density group had a mean of 374---134 (s.d., N = 8 ) taste pores/cm 2 (range: 212-582 taste pores/cm2), and the group with lower taste pore densities had a mean of 135-+43 (s.d., N--8) taste pores/cm 2 (range: 36-173). The distributions of taste pore densities for the higher and lower density groups, which did not overlap, are shown in Fig. 2. Differences among the "higher" and "lower" density groups in the prevalence of taste buds on the front of the tongue are found in two factors: the relative abundance of fungiform papillae, and the relative numbers of taste buds on each papilla. Fungiform papilla density averaged 54.8 _+ 14.6 pap/cm 2 (s.d., N = 8, range 33.1-74.3) on the higher density subjects, while the lower density subjects averaged 32.8-+ 6.6 pap/cm 2 (s.d., N = 8, range 22.138.9). The density of fungiform papillae differed significantly between the two groups [ANOVA, F( 1,15 ) = 15.2, p
0031-9384/90 $3.00 + .00
Variations in Human Taste Bud Density and Taste Intensity Perception I N G L I S J. M I L L E R , JR. A N D F R A N K E. R E E D Y , JR.
Department of Neurobiology and Anatomy, The Bowman Gray School of Medicine Wake Forest University, Winston-Salem, NC 27103 R e c e i v e d 15 January 1990
MILLER, I. J., JR. AND F. E. REEDY, JR. Variationsin humantaste bud density and taste intensityperception. PHYSIOL BEHAV 47(6) 1213-1219, 1990.--Some variations in human taste sensitivity may be due to different numbers of taste buds among subjects. Taste pores were counted on the tongue tips of 16 people with videomicroscopy, and the subjects were divided into two groups (N = 8) by the rank order of their taste bud densities. The "higher" density group averaged 374-+ 134 taste pores/cm 2, while the "lower" density group averaged 135 ___43 tp/cm 2. The higher density group had an average fungiform papilla density which was 1.8 times greater than the lower density group and an average of 1.5 times more taste pores/papilla. The subjects also rated the intensity for 4 suprathreshold concentrations of 5 taste stimuli placed on the same region of the tongue where taste pores were counted. The group with higher taste bud densities gave significantly higher average intensity ratings for sucrose (196%), NaCI (135%) and PROP (142%), but not for citric acid (118%) and quinine HC1 (110%) than the lower density group. Thus, the subjects with higher fungiform taste bud densities also reported some tastes as more intense than subjects with fewer fungiform taste buds. Taste bud density
Taste intensity
Individual variations
TASTE sensitivity and taste bud distribution vary among individuals. Thresholds for a taste stimulus differ by 1-2 log units of concentration among human subjects (5). Individual humans in a group yield unique profiles of thresholds for an array of taste stimuli (10). Magnitude estimates of suprathreshold taste intensifies for individual stimuli also differ among subjects, but the variation among individuals can be parceled into different constant factors times a power function of stimulus concentration (37). We reported that taste bud densities vary by 100-fold on the tips of human cadaver tongues (23,25), and these variations occurred for a range of subjects' ages (26). Genetics influences variations in taste sensitivity among humans (14) and fluid intake by animals. Avoidance of the bitter taste stimulus, sucrose octaacetate (SOA), differs among inbred strains of mice (12). One SOA-taster strain of mice, which avoids SOA at lower stimulus concentrations than nontasters, also has more taste buds in their vailate and foliate papillae than the nontasters (16,30). We hypothesize that variation in the number of taste buds among individuals may account for some differences in their taste perception. A relationship between taste sensitivity and the number of stimulated taste buds has been demonstrated by studies of human taste perception. Taste thresholds (19) and suprathreshold taste intensities produced by a constant concentration of stimulus (35) are related to the area and the number of fungiform papillae which are stimulated. A larger variety of perceptual qualities can be elicited from human fungiform papillae which have more taste buds present than from papillae with fewer taste buds (2). Differences among individuals in taste perception have not been related directly to quantification of their taste bud densities, perhaps because taste bud quantification has required destructive anatomical methods.
Humans
A method for counting taste pores in fungiform papillae of living humans (27,29) and rabbits (24) has been developed which is innocuous and nondestructive. The taste pore is the portion of the taste bud which opens onto the surface of the tongue (1,17). It can be stained and identified by acidic dyes (7). Taste pores are located on the apical surfaces of human fungiform papillae, and individual papillae have from 0-20 taste pores. After methylene blue stain is applied to the tongue surface, images of the fungiform papillae and their taste pores are recorded and counted with videomicroscopy. A 14-fold variation in taste bud densities has been observed in healthy university students (29) with this method. The hypothesized relationship between the prevalence of taste buds and the sensitivity of taste perception among human subjects is examined here. Fungiform taste pores are quantified in a region of the tongue tips of young adult subjects, and taste intensity ratings are obtained for 5 stimuli over a range of concentrations applied to the same region. The subjects are divided, subsequently, into two groups with relatively higher and lower taste bud densities. Taste intensity ratings are compared across concentrations among the stimuli and subject groups. It is hypothesized that subjects with higher taste bud densities experience more intense taste perceptions (and report higher intensity ratings) than subjects with lower taste bud densities. METHOD Taste pores were counted in fungiform papillae of 16 living human subjects by staining the tongue surface with 0.5% methylene blue and by identifying papillae and taste pores with videomicroscopy (27,29) according to the method previously reported. A
1213
1214
MILLER AND REEDY
Wild dissecting microscope fitted with a video camera recorded the magnified images of the tongue surface. Images were stored on a video cassette recorder, and single-frame images were examined and documented with an image processor in a Macintosh II microcomputer. All fungiform papillae were mapped and counted on the most rostra1 2-3 cm of the tongue tip. Taste pores were counted on fungiform papillae in a subregion comprising about 1 cm 2 of tongue surface. The subjects were 16 university personnel comprised of 12 males and 4 females, ranging in age from 17-29 years. They were paid for participating in the experiment and gave their written consent. This procedure was reviewed and approved by the Human Subjects Committee of The Bowman Gray School of Medicine of Wake Forest University. Mapping of the tongue was conducted in one session lasting about one hour, and the taste testing procedure was conducted in a subsequent session lasting about one hour. Taste stimuli were applied with a cotton-tipped applicator to a small area of the tongue tip with the procedure of Bartoshuk et al. (4). Subjects were instructed to rinse their mouths with water before the application of each stimulus. The region of stimulation was the same as where taste pores were quantified, but the stimulus was not limited to the quantified papillae. Intensity ratings were made on a 10-point scale for water and 5 compounds in suprathreshold concentrations as follows: NaC1 (0.032-1.0 M), sucrose (0.032-1.0 M), 6-n-propyl-2 thiouracil (PROP) (0.0561.8 mM), quinine HC1 (0.030-1.0 mM), and citric acid (1.0-32 mM). The stimuli were made from reagent chemicals grade chemicals as follows: NaC1 (Fisher No. S-271), sucrose (Fisher No. S-5), 6-n-propyl-2 thiouracil (Sigma No. P-3755), citric acid (Fisher No. A-104), quinine hydrochloride (Sigma No. Q-1125). Solutes were dissolved and diluted in insipid, deionized water (Hydro Systems, resistance >5 MI~). Stimuli were presented in an increasing concentration series with water controls interspersed, and each series of stimuli was presented twice. Subjects were asked to mark a number between 1 and 9 for each trial which corresponded to the relative intensity of the taste perception. The instructions to the subject were: Mark '0' if the stimulus application tastes like water; mark '1' if the stimulus tastes 'weak'; and mark '9' if the stimulus tastes 'strong.' They also chose one of the following words: sweet, salty, bitter, sour or other to describe the taste quality. Intensity ratings were averaged within subjects for the two presentations and across subjects in each group at each stimulus concentration. After completion of both taste pore quantification and taste intensity testing, the 16 subjects were ranked in increasing order by taste pore density. The subjects were divided into two groups (N = 8), which were arbitrarily designated "higher" and "lower" taste pore density groups. Taste pore densities (one-way ANOVA) and taste intensity ratings (two-way ANOVA: concentration, group) were averaged for each group and compared by ANOVA. Variances for the intensity ratings were parceled as follows: Total df= 63; within taste bud density groups, df= 7; among concentrations, df= 3; among taste bud density groups, df= 1; interaction: concentration x density group, df= 1; error df= 56. RESULTS
Fungiforrn Papilla and Taste Pore Quantification Figure 1A shows a region of the human tongue near the margin of the tongue tip containing an array of fungiform papillae (F) and filiform papillae (f). Methylene blue has been applied to the tongue surface, so that regions with higher affinity for the dye stained dark and regions with less affinity for the dye stained light. Tips of filiform papillae stained dark, and the dorsal surfaces of fungiform papillae stained light, except for taste pores. The taste
pores appeared as dark spots, 25-60 Ixm in diameter. Examples of single fungiform papillae are shown which contain 3 taste pores (Fig. 1B, arrow) and 6 taste pores (Fig. IC, arrow), respectively. Each taste pore corresponds to a single taste bud. Total fungiform papilla density on the tongue tip ranged among subjects from 22.1 to 74.3 papillae/cm2 with a mean of 43.8 --- 15.8 pap/cm 2 (s.d., N = 16). An average of 57 ± 18 pap/subject (s.d., N = 1 6 ) was studied for taste pores, and a mean of 5 2 -+ 17 pap/subject (s.d., N = 16) (91%) contained taste pores. Fungiform papillae containing taste pores are referred to as gustatory papillae. The number of taste pores/papilla ranged from 0-26 within subjects with a mean of 4.56-+ 1.71 taste pores/gustatory papilla (s.d., N = 1 6 ) and 4.26-+ 1.85 (s.d., N = 1 6 ) taste pores/total fungiform papillae (including those without pores). The percentage of fungiform papillae which lacked taste pores averaged 8.8 -+ 8.6 (s.d., N = 16) percent with a range among subjects from 0% to 35%. The density of taste pores in the sampled region of the tongue tip ranged from 36 to 582 taste pores/cm 2 among subjects with a mean of 254± 156 taste pores/cm 2 (s.d., N = 16). At the conclusion of the experiments, subjects were ordered by rank according to the taste pore densities on their tongue tips. The ranked subjects were divided into two groups (N = 8) so that taste intensity responses could be compared for groups with "higher" and "lower" taste pore densities (Fig. 2). The higher taste pore density group had a mean of 374---134 (s.d., N = 8 ) taste pores/cm 2 (range: 212-582 taste pores/cm2), and the group with lower taste pore densities had a mean of 135-+43 (s.d., N--8) taste pores/cm 2 (range: 36-173). The distributions of taste pore densities for the higher and lower density groups, which did not overlap, are shown in Fig. 2. Differences among the "higher" and "lower" density groups in the prevalence of taste buds on the front of the tongue are found in two factors: the relative abundance of fungiform papillae, and the relative numbers of taste buds on each papilla. Fungiform papilla density averaged 54.8 _+ 14.6 pap/cm 2 (s.d., N = 8, range 33.1-74.3) on the higher density subjects, while the lower density subjects averaged 32.8-+ 6.6 pap/cm 2 (s.d., N = 8, range 22.138.9). The density of fungiform papillae differed significantly between the two groups [ANOVA, F( 1,15 ) = 15.2, p
