While the locations other senses such as sight and hearing are processed in the brain have long been known, the subjective nature of taste has made pinning down exactly where this sense is processed more difficult. Now researchers have finally homed in on the brain's "sweet spot," revealing the center responsible for processing different types of tastes.
"We have known that tastes activate the human brain for some time, but not where primary taste types such as sweet, sour, salty and bitter are distinguished," explains senior author on the new research, Adam Anderson.
The brain structure that processes our perception of taste is referred to as the gustatory cortex. We have long known that most neural taste processing activity occurs somewhere in the insular cortex, but taste turns out to be a remarkably complex sense. Different flavors seem to light up a huge variety of brain areas, triggering everything from taste preferences to prior food memories.
"One of the difficulties in prior work on the connection between the brain and taste specifically is that tastes come with strong associated hedonic responses, like sweet tastes good and bitter bad," says Anderson. "So we have not known if these taste regions are really dedicated to taste, but rather hedonics or palatability of taste."
The research utilized a new statistical analysis method in conjunction with detailed functional magnetic resonance imaging (fMRI) data to home in on exactly where the brain processes distinct tastes. It was revealed that this activity does indeed concentrate primarily in the insular cortex, but several other brain regions were also implicated in processing taste, including the frontal operculum, parietal operculum, and orbitofrontal cortex.
Instead of finding specific neuronal clusters that sense certain tastes, the research revealed a more complex system, with the same insular cortex region responding to different taste profiles. So, for example, there isn't exactly a single "sweet spot" in the brain solely responsible for processing sensations of sweetness, but rather it is the neural patterns of activity that determine whether the brain is sensing sweet or sour.
"While we identified a potential 'sweet' spot, its precise location differed across people and this same spot responded to other tastes, but with distinct patterns of activity," says Anderson. "To know what people are tasting, we have to take into account not only where in the insular is stimulated, but also how."
The research compellingly compliments a study from Columbia University last year that found profound connections between the parts of the brain that objectively measure tastes such as bitter or sweet, and the amygdala, the more emotional part of the brain that labels a taste with positive or negative value. In that study the researchers were able to artificially disrupt this amygdala connection and make a mouse respond to flavorless water as if it were either attractively sweet or unpleasantly bitter.
This latest study is just a small, new piece in the puzzle that is our massively complex brain, and it helps neuroscientists better understand how one of our most mysterious senses actually operates.
"That we have found a specific region in the insular that distinguishes primary tastes from each other as well as from subjective liking and disliking has provided strong evidence of where and how taste is represented in the human brain," says Anderson. "While we have long known the cortical areas for our external senses, we now have strong evidence for human gustatory cortex."
The new study was published in the journal Nature Communications.
Source: Cornell University