Minimal two-point discrimination in human tongue and palate

The distribution of minimal two-point discrimination values on the tongue and soft palate was investigated in normal subjects using electric stimulation. It was performed using square pulses of 0.35 ms duration, a rate 10 Hz, a voltage between 3.5 and 7.0 with an average of 4.09 using two silver-silver chloride electrodes (tip diameter, 0.4 mm), and a strain-guage device to control crimping pressure. The spatial threshold was 1.650 +/- 0.433 mm at the tongue tip and 2.650 +/- 0.856 mm and 1.675 +/- 0.269 mm on the anterior margin of each side of the tongue. The soft palate and lingual dorsum were almost completely insensitive. Electric stimulation is a convenient method of measuring two-point limen values.

[Objective examination of taste in man by measuring gustatory evoked potentials]

Taste is an indispensable sense as well as olfaction to spend a tasteful life. The objective method of examining taste has not yet been established. Previous attempts to get gustatory evoked potentials (GEPs) in men and animals failed by contaminating artifacts. Solving this problem, the following developments were done. 1) Avoiding tactile artifacts, the tongue was rinsed constantly with distilled water. 2) By recording and averaging the galvanic skin response (GSR) at the same time, its influence on GEPs was compensated. 3) For proper averaging by computer, conditions of precise onset, duration of stimulus, the shortest stimulus rise and fall times were fulfilled by magnetic valve system. The new gustometer is expected to be one of the standard objective methods of examining taste in clinical practice.

A new gustometer for computer evaluation of taste responses in men and animals

Many previous attempts to acquire gustatory evoked potentials (GEPs) in both men and animals could not satisfy strict requirements on purely unimodal stimulation free of contaminating artifacts. Therefore we developed an advanced new gustometer, based on our previous experience on olfactory evoked potentials, especially on magnetic valves as also used in our "Erlangen olfactometer". Several newly constructed magnetic valves were tested; the best one (MV3) enables us to fulfill the following indispensable conditions for proper averaging by computer: precise onset and duration of stimulus, and shortest possible stimulus rise and fall times. Tactile artifacts were avoided by constant rinsing of the tongue with neutral water, in which the taste stimulus was embedded without turbulences. By recording and averaging the galvanic skin response (GSR) at the same time, its influence on GEPs was compensated. To evaluate successfully objective correlates of taste sensation in man is believed to be of great basic and clinical importance.

[Smell and taste thresholds in older people]

The smell and taste ability of 105 persons at an age of 65 to 93 years was examined by adequate qualitative and semiquantitative chemical and electrogustometric methods. The basic levels of seniors were found above the levels of younger people. For the sense of smelling a significant connection of age and smell sensitivity could be measured. There was no difference between men and women using chemical test methods. With electrogustometry, however, women had a better taste sensitivity than men. At the age of 65 the taste levels are at a fix point. No higher levels could be realized in older persons. A significant reduction of smell ability was recognized in persons with reduction of cerebral blood flow and in smokers. The taste ability was disturbed in cases of diabetes, in persons using dental prostheses and selectively for "salty" in cases of hypertonia and "bitter" in smokers. Loss of taste was recognized in two women who used NaF-drugs, but also some other drugs were able to induce smell and taste alteration.

[The chemical senses of smell and taste in the course of life - changes of smell and taste perception]

Based on own experiments and on the results of other laboratories changes of olfactory and gustatory perception throughout the life span are discussed. Similar to other modalities gustatory and olfactory thresholds generally rise while age increases. Certain gustatory substances (amino acids), however, show a decrease of thresholds if 70 years old subjects are compared with 20 years old ones. Preference for certain odorants (strawberry, vanillin) are reported to increase in higher age (after initial higher peaks in young age).

[Clinical testing of impulse-gustometry as a new method of gustometry (author's transl)]

For the first time in clinical routine testings impulse-gustometry was used in comparison to normal chemical or electrogustometric methods. Loss of taste caused by tympanoplasty, radiation of tumors in head and neck and accompanying facial nerve palsies was tested. The exactly defined location of the stimulus is known advantage in electrogustometry. Impulse-gustometry, however, is able to stimulate different taste sensations like the chemical methods. The sensible sensation, therefore, is eliminated. The stimulating pulses ranged between 0,5 and 2,0 ms at frequencies of 10 to 300 cps. Like with Krarup's method in impulsegustometry there is not always a taste sensation.

[Decrease of latency of auditory evoked potentials in humans practicing transcendental meditation (author's transl]

Slow cortical auditory responses were recorded from humans practicing transcendental meditation. The potentials were computated according to Fig. 1, and the latencies of the positive peaks P1 and P2 and of the negative peaks N1 and N2 were measured as well as the areas of the on-effect FON, of the off-effect FOFF and of the DC-shift FDC during the stimulus duration. Latencies for most of the initial peaks during TM as well as during normal consciousness were significantly shorter than in a control group in a dozing state or during normal consciousness (Table 1 and Fig. 2). Certain differences were also found in regard to other parameters such as amplitudes and areas of the auditory evoked response.

Taste qualities elicited by electric stimulation of single human tongue papillae

Single human taste papillae in 5 young test subjects were electrically stimulated 84 times each with a silver wire (0.4 mm tip diameter) versus a 5 x 3.5 cm2 reference electrode on the left wrist of the subject. The electrical pulses were positive (54 papillae) or negative (45 papillae) of 0.5 msec duration and had a frequency of 50, 100, 200, 400, 600 or 800 Hertz. For control 45 papillae were merely touched by the electrode without current stimulation. Significant gustatory and tactile results (x2-test, P less than or equal to 0.05) signaled by the subjects were: a) on anodic stimulation 50 +/- 5% of the touched papillae gave overall taste responses, namely 22.2% sour, 3.8% bitter and 1.8% salty; the rest were mixed sensations. Sweet was not reported in these final experiments; b) on cathodic stimulation 42.2 +/- 5% of the papillae responded with taste, which again were reported as 22.2% sour, 2.2% salty, the rest mixed; c) on mere touching there were hardly any gustatory sensations reported. - These results indicate only a relative specifity for each single human taste papilla and its taste fibres.