Welcome back for the final post in this series about the neuroethology of whiskers! The goal of this post is to propose some research questions based on the information gathered in these last five weeks. As I was reading, a number of questions arose, so this post will work chronologically.
The first week, we looked at the general structure and function of whiskers in cats. One point of interest to me was that a cat’s skin temperature lowered during sympathetic stimulation of the whiskers, likely due to vasoconstriction (Nilsson 1972). This, along with the fact that the sensitive ring sinus of pinniped whiskers is a centimeter below the skin and surrounded by blubber, made me wonder at what temperatures cat vibrissae function optimally (Hyvarinen et al. 2009). Since whiskers are better suited to some vibrational frequencies, might they be better suited at certain temperatures (Williams and Kramer 2010)?. Are cats that live in extreme cold, such as lynxes, able to use their whiskers as well as say housecats?
In week two, we discussed vibrissae in rabbits and how they have two complete bodymap representations in their sensory cortex (Gould 1986). One source showed that lesioning the barrel cortex area in rabbits affected conditioned responses involving the whiskers, but it did not specify which of the two representations was lesioned (Galvez et al. 2007). My research question would be to see if rabbits can sense as well with just one of their two bodymap regions lesioned? This could suggest reasons as to why they might have two copies of their bodymap. If they can sense as well with just one, then the maps may be for redundancy in case of an injury. If they do not sense as well, it would be interesting to see which one seems more important, and further research could be done to determine how the two maps communicate with each other. This could be tested by lesioning SI in one group of rabbits and lesioning SII in another group of rabbits. Two control groups could have sham surgery with CSF injected into the same two brain regions, respectively. After a recovery period and short time without water, the rabbits would be blindfolded and complete a trial in a small room with water randomly placed somewhere inside. The amount of time in which they found the water, as well as the time from which they found the water until they properly found the nozzle to drink would be recorded. They would be blindfolded because vibrissae serve to enhance vision, and water would be used rather than food because it should not emit a smell that the rabbits would be able to detect regardless of treatment status.
In the next week, we talked about rodent vibrissae, which are quite well-understood. One area that did not seem to be explored in much depth was the fact that some follicles contained a second smaller vibrissa (Wineski 1983). I would like to look into the development of these secondary whiskers and determine if their function is to eventually replace the primary whisker when it falls out, as hypothesized by Wineski (1983). My questions would be: how do the secondary whiskers develop compared to the primary whiskers, and do they stimulate the same neurons over the same neural pathways as the primary whisker in the same follicle? To begin testing this, a group of rats could serve as the control and have a select whisker with a secondary whisker in the same follicle deflected while under anesthesia. During this procedure, several microelectrodes could be placed in the brain in the barrel region corresponding to that whisker and the firing patterns could be recorded. In another group of rats, the same primary whiskers used in the control group could be removed, and the smaller secondary whisker in that same follicle could be deflected to the same angle as the primary one had been. The same procedure with microelectrodes could be used to see if the same neurons fire in the same way for the primary and secondary vibrissae.
Then, we explored manatee vibrissae, which are unique in how they cover the whole body of the animals, how they are used for food manipulation, and how they have been studied (GB Bauer, interview, April 26,2019). Based on what is known about the morphology of pinniped whiskers, I would want to know how similar the morphology of an unrelated marine mammal’s whiskers is to see if there has been convergent evolution. Do manatee vibrissae have a tapered structure like that of pinnipeds (Williams and Kramer 2010)?
Finally, we discussed vibrissae in other aquatic animals, which have been studied rather differently than manatee vibrissae. Since pinnipeds have the longest vibrissae of any taxonomic group, it would be interesting to see how they would fair with whiskers of typical length (Ginter et al. 2012). How well would Antarctic fur seals be able to sense vibrations with whiskers trimmed to the length of an average pinniped whisker?
That wraps up our series on vibrissae across various mammalian species! Be sure to check out the posts from other authors on this blog about other neuroethology topics!
~Galvez R, Weible AP, Disterhoft JF. 2007. Cortical barrel lesions impair whisker-CS trace eyeblink conditioning. Learn Mem. 2007(14): 84-100.
~Ginter CC, DeWitt TJ, Fish FE, Marshall CD. 2012. Fused traditional and geometric morphometrics demonstrate pinniped whisker diversity. Plos one. 7(4): e34481.
~Gould HJ. 1986. Body surface maps in the somatosensory cortex of rabbit. J Comp Neurol. 243(1886): 207-233.
~Hyvarinen H, Palviainen A, Strandberg U, Holopainen IJ. 2009. Aquatic environment and differentiation of vibrissae: Comparison of sinus hair systems of ringed seal, otter and pole cat. Brain Behav Evol. 2009(74): 268-279.
~Nilsson BY. 1971. Effects of sympathetic stimulation on mechanoreceptors of cat vibrissae. Acta Physiol Scand. 1972(85): 390-397.
~Williams CM, Kramer CM. 2010. The advantages of a tapered whisker. Plos One. 5(1): e8806.
~Wineski LE. 1983. Movements of the cranial vibrissae in the Golden hamster (Mesocricetus auratus). J Zool Lond. 1983(200): 261-280.