|
|
 |
|
| Thomas C. Pritchard |
 |
Dept. Behavioral Sci, Pennsylvania State University, Hershey, USA
|
Presentation: |
| 2002-10-10, 10:00-10:30 |
|
| Gustatory system. |
|
|
| Despite the fact that taste has been recognized since antiquity as one of the five senses, we know the least about its organization in the brain and how it analyzes taste information. One issue that has resisted the efforts of the medical and scientific communities is the location(s) in the cerebral cortex where gustatory information is processed. During the first half of the 20th century the medical community believed that taste, like its chemosensory cousin smell, was processed within the temporal lobe. By the middle of the 20th century, several clinical studies suggested that taste information was processed within the postcentral gyrus, close to the areas where tactile and thermal information from the tongue, mouth, and face is represented. The technological improvements of the last half century that have transformed society also have revolutionized medical research. Armed with the ability to record the electrical and metabolic activity of the brain in both the clinic and the laboratory, we now know that taste information is processed by neurons located in the insula, one of the older tenants of the cortical mantle. Over the millennia the insula has been buried by the more proliferative frontal cortex, and thus, cannot be seen from the outside of the brain. Despite the fact that the road to the insula was tortuous and that its role in taste took a long time to secure, there is little doubt that the true location of primary gustatory cortex has now been identified. Anatomical studies have shown that the insula receives projections from the subcortical taste relay in the thalamus. Electrophysiological studies have shown that individual neurons in the insula respond when sapid stimuli are applied to the tongue. Modern imaging techniques such functional magnetic imaging resonance (fMRI) and positron emission tomography (PET) have shown that neural activity in the insula increases following gustatory stimulation. Clinical studies have shown that taste deficits are common in patients who have stroke- or tumor-induced damage to the insula. Knowing the location of primary taste cortex is an important step toward the long term goal of understanding how the brain processes taste information. Perception of taste, just like smell, sight, touch, and hearing, is a complicated process that we are just beginning to understand. In general terms, it is believed that the reflexive aspects of acceptance and rejection of potential foods are managed by subcortical taste areas while more sophisticated aspects of taste processing are performed by primary taste cortex or by areas that receive projections from the insula. For example, we believe that naming of tastes and foods is performed within the language areas in the temporal and parietal cortices and that the insula is a critical component in that circuit. The orbitofrontal cortex, which also receives projections from the insula, may play an important role in flavor perception. Flavor is a more complicated percept than taste because it also includes the sensations of smell, touch, temperature, sight, and even pain. Some taste-responsive neurons within the orbitofrontal cortex also respond to these other sensory modalities. In a related vein, the orbitofrontal cortex has been implicated in feeding by data showing that the responsiveness of taste neurons there decreases as satiety is reached over the course of a meal. |
|
|
 |
|
|
|
