Objective evaluation of taste with 122-channel biomagnetometer SQUID

Professor PHOTIOS A.ANNINOS, Assistant Professor ATHANASIA KOTINI, Associate Professor GEORGIOS KEKES*, PhD student PAVLOS PAVLIDIS**

Lab of Medical Physics, Medical School, Democritus Univ. of Thrace, University Campus, Alex/polis, 68100,Greece

*Aristotle University of Thessaloniki, Dir. of 2nd.ENT Clinic Papageorgiou Hospital, Greece

**Aristotle University of Thessaloniki, Medical School, Greece

Abstract: The aim of this study was to evaluate the taste and the way that it is connected with the central nervous system (CNS) using a 122-channel SQUID biomagnetometer. Case report: A 27-years-old male healthy volunteer was referred to our department and his magnetoencephalography (MEG) was evaluated in three different states: physiological condition; with a sweet taste; with a salt taste. There was a differentiation in the spatial distribution of the frequencies over his head in all the states after the application of Fast Fourier Transform in his MEG data. This report provides novel insights into the evaluation of taste with the MEG systems and encourages more studies to be conducted.

Keywords: MEG, 122-channel, taste, Frequency domain, Fourier transform

1.Introduction

Physiology of tasteAs it is known the basic taste sensations are sweet, salty, sour and bitter, though some researchers identify a fifth sensation, which is named after the Japanese word umami. The sensory organ of taste are the taste buds which can be identified in foliate papillae, vallate papillae and fungiform papillae. Taste buds can be also found on the tonsil, the esophageal orifice, hard palate, epiglotis, the anterior faucial pillar and the buccal mucosa. Saliva is also very important for taste because it allows the dilution of the chemical substances and the fine gustatory cells are bathed in it. Taste is a very common sensation, which takes place when chemical substances cause depolarization of the taste receptor cells, which bare located in the taste buds in the oral cavity. Gustatory information is transferred to the central nervous system through the facial nerve (chorda tympani), the vagus nerve and the glossopharyngeal nerve. In specific, the anterior half of the tongue is innervated by the chorda tympani, the posterior third of the tongue is innervated by the glossopharyngeal

nerve. Above these nerve fibers, the stimuli can be transferred from a number of general sensory fibers of the trigeminal nerve and lay in the lingual epithelium. It is obvious that the boundary between the area supplied by the lingual nerve and the chorda tympani cannot be easily discriminated. We must mention the participation of olfaction in the initiation of taste senses. This gustatory olfaction is caused by the pass of the olfactory substances of the foods through the olfactory cleft when someone expires during mastication. Obviously olfaction can cause the initiation of taste stimuli and appetite, but can also cause the depression of it.

Taste transductionThe main role of the taste receptors is to transform the chemical signals into changes of the potential of the membrane the intracellular concentration of calcium ions. These mechanisms have a great variety in number and pathways in every type of neuron.

Taste disorders

The disorders of taste are very common and can be caused by many factors such as: Lesions at the mucosa, taste buds and

impairment of the cranial nerves can cause taste disorders.

Oral inflammation and mucositis can impair taste sensation.

Malignancies and tumors of head and neck cause inability to appreciate flavours.

Endocrine disorders also are involved in taste and olfactory disorders. Diabetes mellitus and hypothyroidism lead to changes of taste sensitivity.

Drug toxicity caused by substances such as acetylsalic acid, biguanidune, carbamazepine, levodopa, ethambutal gold, penicillamine and lithium. Drugs damage the sensory endings or the peripheral nerves.

Other causes are hereditary disorders (aplasia of the taste buds), consumption of alcohol, radiotherapy and chemotherapy, lack of copper and vitamin A.

Evaluation of taste Taste is evaluated with two methods: the chemical gustometry and Electrogustometry. According to the first method the clinical doctor applies substances, which represent the four taste qualities of sweet, salty, sour and bitter in different concentrations in order to determine the lowest concentration that can be recognised.When Electrogustometry is used, then the clinical doctor uses electric current to stimulate the taste receptors. An anode current is used ranging between 2 and 8 mA. This method is, in addition to

chemical gustometry, quantitive and not qualitative. It is necessary to evaluate the function of the chorda tympani (1-6).

2. CASE REPORTA 27-years-old male healthy volunteer was referred to our department and his magnetoencephalography (MEG) was evaluated in the following three states: physiological condition; after he ate sweet; after he ate salt. Biomagnetic measurements were performed using a whole-head Neuromag 122-channel MEG system in a magnetically shielded room of low magnetic noise with broadband (f>10Hz) gradient noise 5fT/ (cm Hz) for the 95% of the channels and max noise 10fT/ (cm Hz), a broadband (1Hz<f<10Hz) gradient noise 15fT/ (cm Hz) for the 95% of the channels and max noise 20fT (cm Hz) (7, 8). The spontaneous MEG recordings were obtained with a sampling frequency of 256Hz and filtered with cut – off frequencies between 0.3 to 40Hz. The time taken for each recording was 5 min. There was a differentiation in the spatial distribution of the frequencies over his head in the three states after the application of Fast Fourier Transform in his MEG data (Figs 1-3).

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Figure 1. The frequency distribution of each channel over the scalp in the physiological condition

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Figure 2. The frequency distribution of each channel over the scalp with a sweet taste

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Figure 3. The frequency distribution of each channel over the scalp with a salt taste

3.CONCLUSIONSThe lack of new methods, which can be used to evaluate taste, forced the authors to use the 122-channel biomagnetometer SQUID. Our results provide useful insights into the connection of taste with the CNS encouraging more studies to be conducted.

Reference

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