David Shenk discussed how John C. Crabbe's experiment with mice proved to the world that even slight environmental changes could radically change a mouse's reaction to alcohol and cocaine. In order to minimize extraneous variables and to really narrow down on slight environmental factors, "he conducted the exact same study at the same time in three different locations" (128). Crabbe went through specific procedures to ensure that the mice had "identical genetic strains, identical food, identical bedding, identical cages, identical light schedule, etc." (129). Even with all these controls put into play, "invisible factors" (129) managed to influence the behavior of these mice. Using the GxE equation and information about this experiment, explain how it is possible for such results to occur in spite of the measures taken to control certain variables. What internal processes influenced the mice to have different reactions to alcohol and cocaine?
(Kalista Noegroho, Kalista.dara@gmail.com)
As Shenk explains, researchers did everything they could think of to control the environment the animals were exposed to in addition to their genes. However, the varied results could be based on a number of factors supported by the GxE model.
ReplyDeleteAlthough the scientists controlled as many potential variables as possible, there are factors which they themselves are unconscious of or unable to control. If different scientists were performing the experiment in each location, the scent given off by the scientist handling the mice would be different and scent has been shown to greatly impact mice behavior. For instance, the scent of "cat saliva, rat urine, or snake skin essence" picked up by a mouse vomeronasal organ has been shown to cause mice to cower as though a predator were present even if the mice have never come into contact with the predator itself (http://news.sciencemag.org/sciencenow/2010/05/the-scent-that-makes-mice-run-sc.html). Should a scientist involved in one of the three locations have given off a natural, unconscious scent that the electrical signals transmitted to the mice brains from the chemoreceptors picking up on the smell interpreted as threatening or caused the mice to experience some other form or stimulation, their behaviors would have been altered. Even if the scientists interacting with the mice were kept the same at each of the three locations, the scientist interacting with the mice would potentially unconsciously carry scents from the outside location on them self which the mice would experience when handled. It is also possible a scientist was giving off certain pheromones, a form of chemical communication common in mammals and insects, in one location based on their personal feelings or experiences there that the mice could have experienced and reacted to.
Tactile communication is another potential variable researchers may not have thoroughly controlled for at each location. If there was a variation in the scientists that handled the mice at each location or even a variation in the psychological response to each location of the scientists handling the mice were they kept consistent that would translate into variation of how the mice were being handled and for how long. For example, if at one location the scientist handling the mice is inexperienced or nervous to be handling the mice, their sympathetic nervous system may be activated to produce epinephrine which can cause increased muscle tension and shaking, and such jerky movements could in turn cause nervousness and nervous activity in the mice (http://wiki.answers.com/Q/Can_adrenalin_cause_shaking_of_the_hands). In addition, perhaps a scientist who has remained constant in all the locations is particularly agitated or unhappy in one of the three locations and this is reflected in his handling of the mice by perhaps treating them more roughly or carelessly. The "invisible factors" Shenk describes are likely the result of either what humans cannot detect or control.
These potential variables acting on the mice at the different locations support Shenk's GxE theory because although the mice are genetically identical and given identical doses of identical drugs in identical cages with identical food and water and light exposure, certain unconscious environmental variables have stimulated the mice, turning on and off different genes that they may all possess however not all experience the activation of, at each location and have led to varied behavioral results.
Kate White (kw2020@gmail.com)