( /p> In the most telling experiments ...)How taste response is hard-wired into the brain

In the most telling experiments, the researchers engineered flies so that the hot pepper compound capsaicin would selectively switch-on either the sweet-detecting Gr5a neurons or the bitter-detecting Gr66a neurons. Normal flies do not respond to the hot pepper taste.

The researchers found that flies engineered to recognize capsaicin on the sweet-tasting neurons were attracted to the chemical, while those that recognized it as a bitter taste avoided it.

"In this paper, we demonstrate that these taste cells selectively recognize different taste modalities, such that there is functional segregation of taste qualities in the periphery and at the first relay in the brain," concluded the researchers. "Moreover, we show that activation of these different taste neurons is sufficient to elicit different taste behaviors. Thus, activity of the sensory neuron, rather than the receptor, is the arbiter of taste behavior.

Our studies argue that animals distinguish different tastes by activation of dedicated neural circuits that dictate behavioral outputs," they wrote.