Quality-specific taste changes in multiple sclerosis

Neurolocalization of taste disorders

Neurolocalization of taste disorders requires a knowledge of the functional anatomy involved in mediating taste information from the peripheral mucosal surfaces through numerous peripheral cranial nerves to complex subcortical and cortical brain regions. Our understanding of this functional anatomy has advanced in recent years. Taste is an experience that is both innate and learned, and the "taste" experience involves the integration of information from other sensory modalities, such as olfaction and somatosensation. Normal taste perception is influenced by different neurophysiologic states, which involve endocrine function, emotions, and even attitudes and expectations toward eating. At its core, the normal effective ability to taste is a reflection of the proper function of many organ systems within the body and may be considered a marker for good health. Clinical taste disorders, on the other hand, involve the dysfunction of the normal neural taste pathways and/or aberrant influences on multisensory integration and cortical taste processing. The number of disease processes, which can adversely affect taste, are numerous and quite varied in their presentation. There may be contributory involvement of other organ systems within the body, and the appropriate management of taste disorders often requires a multidisciplinary approach to fully understand the disorder. Depending on the underlying cause, taste disorders can be effectively managed when identified. Treatments may include correcting underlying metabolic disturbances, eliminating infections, changing offending medications, replenishing nutritional deficiencies, operating on structural impairments, calming autoimmune processes, and even stabilizing electrochemical interactions.

Taste dysfunction in multiple sclerosis

Empirical studies of taste function in multiple sclerosis (MS) are rare. Moreover, a detailed assessment of whether quantitative measures of taste function correlate with the punctate and patchy myelin-related lesions found throughout the CNS of MS patients has not been made. We administered a 96-trial test of sweet (sucrose), sour (citric acid), bitter (caffeine) and salty (NaCl) taste perception to the left and right anterior (CN VII) and posterior (CN IX) tongue regions of 73 MS patients and 73 matched controls. The number and volume of lesions were assessed using quantitative MRI in 52 brain regions of 63 of the MS patients. Taste identification scores were significantly lower in the MS patients for sucrose (p = 0.0002), citric acid (p = 0.0001), caffeine (p = 0.0372) and NaCl (p = 0.0004) and were present in both anterior and posterior tongue regions. The percent of MS patients with identification scores falling below the 5th percentile of controls was 15.07 % for caffeine, 21.9 % for citric acid, 24.66 % for sucrose, and 31.50 % for NaCl. Such scores were inversely correlated with lesion volumes in the temporal, medial frontal, and superior frontal lobes, and with the number of lesions in the left and right superior frontal lobes, right anterior cingulate gyrus, and left parietal operculum. Regardless of the subject group, women outperformed men on the taste measures. These findings indicate that a sizable number of MS patients exhibit taste deficits that are associated with MS-related lesions throughout the brain.

Gustation

Much has been discovered over the last few decades about the anatomy and physiology of the human taste system, most notably its receptor mechanisms and intermodal factors that influence its function. While the taste system works in concert with the olfactory, somatosensory, auditory, and visual sensory systems to establish the overall gestalt of flavor, its primary specialization is to ensure that the organism obtains energy, maintains proper electrolyte balance, and avoids ingestion of toxic substances. Despite its focus on inborn functions, taste-like its sister sense of smell-is remarkably malleable, reflecting the need to adapt to changing circumstances and general nutrient availability. It is now widely appreciated that taste dysfunction is common in many diseases and disorders, and is a frequent side effect of a number of medications. This interdisciplinary review examines salient aspects of the human gustatory system, including its anatomy, physiology, and pathophysiology. WIREs Cogn Sci 2012, 3:29-46. doi: 10.1002/wcs.156 For further resources related to this article, please visit the WIREs website.

The application of d.c. electrical stimulation in evoking and recording gustatory brain potentials

Evidence exists which supports the hypothesis that electrical stimulation of appropriate parameters can fulfil the fundamental requirements for an effective evoked potential taste stimulus. Nevertheless, it had previously been considered that electrical taste stimulation is inadequate for evoking gustatory brain potentials. Consequently, the majority of the earlier attempts to record gustatory evoked potentials (GEPs) reported in the literature have employed chemical stimulus techniques. The design of an electrical taste stimulator and its interface to an evoked potential recording unit is described. The first human brain potentials recorded with this system are presented, among which are those attributable to taste pathway activation. Following future work to unequivocally confirm that taste evoked brain potentials are achievable with this system, it has potential to become a clinically valuable tool.

Evoked taste thresholds in a normal population and the application of electrogustometry to trigeminal nerve disease

No standardised method for taste threshold measurement is available and therefore comparison between clinical studies is difficult. An electrogustometer was evaluated in normal subjects. No sex difference in taste threshold was noted; however, there was a significant elevation in detection threshold with age and smoking. Electrogustometric values both in patients before and after surgery for trigeminal neuralgia and in patients with trigeminal sensory neuropathy were determined. Many patients with trigeminal nerve disorders had abnormal electrogustometric detection thresholds suggesting that there is possibly an accessory taste pathway through the trigeminal nerve, although in some individuals the site of lesion may be in the brain stem. Electrogustometry is a convenient method for clinically assessing taste.

Rank order scaling in taste evaluation

A scoring system developed for comparing taste in two groups of individuals, patients with multiple sclerosis and a normal control group is described. The scoring system was extended to evaluate taste in renal patients paired by age and sex with controls. The results of the two comparisons are given. The scoring system can be used very flexibly in statistical comparison among groups and generated easily using a FORTRAN computer program. The use of this scoring system is compared with an alternative method which uses psychophysical functions.