The tongue as an excitable medium

Abstract

Geographic tongue (GT) is a medical condition affecting approximately 2% of the population, whereby the papillae covering the upper part of the tongue are lost due to a slowly expanding inflammation. The resultant dynamical appearance of the tongue has striking similarities with well known out-of-equilibrium phenomena observed in excitable media, such as forest fires, cardiac dynamics, chemically driven reaction-diffusion systems and morphogenesis in multicellular organisms. Here we identify GT as a novel example of excitable media dynamics and explore the evolution of the condition from a dynamical systems perspective. We focus on two characteristic aspects of GT in particular: anisotropic expansion of lesions and re-entry of the inflammation into recovering regions. Our investigation sheds light on the evolution of the inflammation and suggests a practical way to classify the severity of the condition, based on the characteristic patterns observed in GT patients.Some of the most important organs in the human body incorporate microscopic coupled elements possessing a property of excitability. The resultant network usually performs a specific function, crucial for the successful operation of the organ. Under certain conditions, however, this excitable medium can experience unwanted and in some instances harmful dynamics. Probably the most well known example is the heart muscle [1][2][3][4][5], which under normal conditions contracts periodically due to the propagation of electrical waves resulting in blood being pumped to the different parts of the body. Irregular heart rhythm (cardiac arrhythmias) caused either by abnormal initiation of impulses [4] or due to the occurrence of spiral waves [2, 3] may be life-threatening. Yet another example is the cerebral cortex, which under normal conditions is responsible for important functions such as conciseness and memory, but may experience dangerous electrophysiological waves (i.e., spreading depression waves [6,7] ). Further examples of biological excitable systems include intercellular calcium waves in Xenopus laevi oocytes [8] and morphogenesis in multicellular Dictyostelium discoideum (see e.g., [9]).The human tongue is vital for tasting, mastication and speech. With respect to the former function, a thin layer (epithelium) consisting of four types of tiny hair-like protrusions (papillae) covers the upper part of the tongue (see figure 1(a)). Taste buds are located on three of the four papillae. The medical condition of geographic tongue (GT) [10][11][12][13][14][15][16][17][18][19] (also known as benign migratory glossitis) is associated with the gradual loss of the fourth papilla, called filiform papilla. A filiform papilla hair is approximately 250 μm long and 35 μm in diameter [20]. Filiform papillae are mainly distributed in the anterior two-thirds (oral part) of the tongue and do not contain taste buds. GT has been investigated within the medical community for several decades, with the main focus being on the clinical, histological and epidemiological characte...

Geographic Tongue: The Waging Wanderlust of the Oral Cavity – A Case Report

“…They observed different evolutionary phases between "a healed (rest) state, a highly inflamed (excited) state, and a healing (recovering state)". They narrowed down different patterns of geographic tongue under 3 types -Oblate pattern, Wavy 1D pattern and a ring shaped concentric pattern [9]. Our case clearly resembles the wavy 1D pattern.…”

Benign Migratory Glossitis in Toddlers: Report of Two Cases and Review

“…However, spiral patterns, which result due to inhomogeneity in the medium or due to external intervention in other excitable media, tend to be continuous, self-sustaining and will linger for a longer duration of time. 19…”

“…Three patterns: oblate, spiral and wavy 1D pattern of the geographical tongue along with the evolution have been described by Seiden and Curland. 19 Most common sites are lateral margins and the tip of the tongue followed by dorsal and ventral surfaces. However, extra lingual sites including labial mucosa, buccal mucosa, the gingival surfaces, floor of the mouth, soft palate and uvula have also been described.…”

Laplace-based modeling of fiber orientation in the tongue

“…The spatial distribution of fiber orientations is part of the tongue’s mechanical makeup through structure and constitutive behavior (Kajee et al 2013; Harandi et al 2017). The distribution is also involved in electrical propagation across the organ and wave excitation on its surface (Seiden and Curland 2015). Therefore, accurate fiber distribution modeling should be included in computational models to improve the agreement with experimental observations.…”