Ayesha Azeem ‘23
The gustatory system is the sensory system that allows humans to perceive the sense of taste, or flavor. Humans are able to perceive different flavors via the taste receptors on taste buds, which can be found on the upper surface of the tongue as well as on the epiglottis. Taste perception depends on the chemical characteristics of the stimulus, as well as its hedonic value – its pleasantness or aversiveness. Hedonic value can be determined by one’s life experiences and may change over time if associated with bad memories. A powerful memory can be formed when a taste is associated with gastrointestinal pain in a process known as conditioned taste aversion (CTA). Dr. Arianna Maffei, a professor in the Department of Neurobiology and Behavior, led a Stony Brook University study in which she and other researchers conditioned rats to experience taste aversion sugar water, something they would usually enjoy, by creating gastric malaise after consumption.
The researchers fed female and male rats 0.1 M sucrose water and then immediately gave an injection of lithium chloride (LiCl), causing gastrointestinal distress in the rats. The researchers held two conditioning sessions to ensure the aversive memory was solidified. There was also a control condition in which the animals received the LiCl injection the night before they received the sucrose water. The researchers found that before the injection, the rats found the taste of the sugar water to be pleasurable and drank more of it in comparison to the baseline water provided. On the second conditioning day, the rats decreased their consumption of sucrose, holding a strong preference for the baseline water instead.
While the areas of the brain involved in taste aversion learning – the basolateral amygdala and the gustatory cortex in the insular cortex – have been known for quite some time, little is known about how these areas work together during learning processes. Professor Maffei and the other researchers found that CTA learning decreases the strength of the synaptic connections between the basolateral amygdala and the gustatory cortex, leading to a reduced activation of the gustatory cortex neurons. The study provides the first evidence that proves that learned taste aversion depends on the long-term reduction in the connections between the taste and threat sensors of the brain and implies that reducing the activity between two areas of the brain can affect the way animals learn other behaviors.
 M.S. Haley, et al., LTD at amygdalocortical synapses as a novel mechanism for hedonic learning. eLife (2020). doi: 10.7554/eLife.55175.
 Image retrieved from: https://upload.wikimedia.org/wikipedia/commons/6/6c/1402_The_Tongue.jpg