Medial temporal lobe structures participate differentially in consolidation of safe and aversive taste memories

De la Cruz, V., Rodriguez-Ortiz, C. J., Balderas, I., & Bermudez-Rattoni, F. (2008). Medial temporal lobe structures participate differentially in consolidation of safe and aversive taste memories. European Journal of Neuroscience, 28(7), 1377-1381. doi:10.1111/j.1460-9568.2008.06432.x. Retrived from EBSCO.

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            In Chapter 14, the specific processes involved in different types of learning and memory are the focus. There are two types of association learning that we discuss: classical (or Pavlovian) conditioning and operant conditioning. Classical conditioning involves the pairing of a neutral stimulus and an unconditioned stimulus to elicit a conditioned response. This type of learning occurs without conscious awareness and is a reflexive behavior.  This type of association learning is so reflexive, in fact, that we do not even realize it has occurred after the fact either – we may react to a conditioned stimulus and be unable to explain why we have done so. We have all had an experience in which a certain food has caused a terrible upset stomach or that awful situation when your digestive system just refuses to accept the food and must get it out somehow (you know what I mean). From that time on, we avoid that food like the black plague, refusing to even try variations of the food in some cases. This learned taste aversion is by the very process that was previously explained: classical conditioning. The question arises, though: what biological processes underlie this type of learning? Evolutionary psychologists point to the importance of learning from taste of objects for survival. Truthfully, learning nor memory can be linked to a localized area in the brain; different types of learning and different types of memory occur in different areas, and most often have interactions from other areas as well. Even though this is the case, researchers attempt to find neurological correlates with classically conditioned behaviors. For example, De la Cruz, Rodriguez-Ortiz, Balderas, & Bermudez-Rattoni (2008) examined medial temporal lobe structures and their role in taste memories. As we learned from Chapter 14, the medial temporal lobe plays a key role in the consolidation of implicit memories, which are precisely the type of memories involved in classical conditioning (due to their reflexive nature). The investigators used a population of rats to study their brain activity. Specifically, they looked into the perirhinal cortex, the dorsal hippocampus, the basolateral nucleus of the amygdala, and the central nucleus of the amygdala. Instead of simply looking at learned taste aversions, they also examined safe taste memories – memories of foods that are safe to eat (from a survival standpoint). They injected the protein synthesis inhibitor anisomycin into the rats to study these areas. They found different specific areas are responsible for the protein synthesis to stabilize taste aversions than those that are responsible in learning which tastes are “safe.” The realized that the central nucleus of the amygdala, is required in taste aversion, but interestingly the basolateral nucleus is not. Contrary to what they expected to see, the perirhinal cortex and the hippocampus where required for safe taste memories. Researchers suggest these differences in locations are dependent upon the consequences associated with tastes (i.e. sickness or no response).