Do Lobsters have I-Functions?

gloudon's picture

                                                             Do Lobsters have I-Functions?


        Lobsters and crayfish are notorious for having simple nervous systems, and are therefore highly sought after in the world of neurobiology. So simple, they contain a clump of neurons in the rostral end that may not even constitute a brain. However elementary the scientific community may think these creatures are, their general movements and complex escape swimming responses lead me to believe that they are in fact complex enough to contain an I-function. Although most scientists are doubtful that some animals, especially simple crustaceans like lobsters, contain this complex choice enabling portion of the brain, I find it plausible that there is an I-function within this possibly non-existent brain.

             The three types of movement that I will address are responses to signals that travel through the ventral nerve cord. Within this cord, there is the lateral giant axon, the medial giant axon, and the non-giant axon. Each of the three unique movements is in response to signals that come from their respective axon within the ventral nerve cord. Stimulation at different points across the lobster’s body lead to signals traveling down different axons, and produce different movements (1).

             When the lobster is stimulated by a visual threat, the medial giant axon carries the signal up to the rostral end and down through the abdomen. The signal activates the motor neurons, which in turn contract the lobster’s abdominal muscles, sending the lobster directly backwards, away from the stimulus (1). However, when the lobster is stimulated tactilely along its abdomen, or generally from the telson end, the lateral giant axon carries the signal to the first three segments of the abdomen. This signal activates the motor neurons in the upper abdomen, which contracts the upper abdominal muscles. The contraction of only these upper abdominal muscles results in the lobster’s pinched position. Because the last three abdominal segments remain relaxed, the lower portion of the tail remains straight resulting in the lobster flipping over to face his predator (1,2).

             Signals that produce regular (non-escape) swimming originate in the subesophageal ganglia and are transmitted through non-giant axons. Unlike the escape swimming responses, this type of swimming does not require a visual or tactile stimulus but rather a decision by the lobster. This method of movement is used for non-emergency situations, unlike the two escape swimming techniques (1).

             The I-function is the part of the brain that allows us to make conscious decisions based on what we take in. Many creatures lack an I-function, and most scientists would probably argue that the lobster also lacks an I-function. "The I-function functions best with small numbers of variables, looks for clear and explicit relationships, and, in so doing, creates the capacity to conceive realities beyond those that follow directly from what has been experienced” (3). Further, “it creates a substantial capacity to make choices, not an absolute ‘free will’ but a quite significant (and nurturable) capability to be onself an agent of change, with regard both to the world and to oneself" (3). Perhaps this idea that the nervous system of the lobster is too elementary to contain an I-function comes from a lack of awareness about the complexity of lobster’s escape responses.

             The escape swimming response to a tactical stimulation, distributed by the lateral giant axon, does not lead me to believe that the lobster has an I-function. The lobster has no way to sense what is touching him when he cannot see the stimulus, so he has one reaction. One study compared lobster’s reactions to tactile response showed a much greater number of responses to taps (tactile stimuli) on the telson end compared to the rostral end (4). This result leads me to believe that escape responses to telson end taps occur more frequently because the lobster has no view of this threat, and further has no defensive appendages at the telson end, therefore making the escape swimming response more like a reflex. Although this escape response does not validate my theory that the lobster has an I-function, it does not negate it either. Escape swimming stimulated by a tactile response outside of the visual field of the lobster could only be an automatic (reflexive) response, just as screaming or jumping would be an automatic response of a human who had been startled from behind.

             However, the escape swimming response to visual stimulation distributed by the medial giant axon does lead me to believe that the lobster has an I-function. I believe this to be true because studies done on lobsters’ responses to visual stimuli are not 100% consistent. In some of the tests, lobsters confronted with threatening visual stimuli within their field of vision remained still – or chose to be still. Further, in the study comparing the number of responses to rostral versus telson taps, the lobsters responded just 4 times out of 30 taps to the rostral end as compared to 17 responses out of 30 taps on the telson end (4). To me, this validates the presence of the I-function because the lobsters were able to see and feel the threat, but they chose not to respond. The fact that they responded less frequently to the rostral tap and visual threat compared to the telson tap tells me that the lobster is confident in his ability to defend himself with his claws on the rostral end, and therefore chose not to escape. How could the lobster remain still if it was visually threatened in the absence of an I-function? In my opinion, lobsters that stood still during this test evaluated their environment, compared this threat to past threats, and deliberately chose to stay still. If their nervous systems were really as elementary as originally thought, the escape response would be a reflex, and would respond to the visually threatening stimulus during each and every encounter because they would have no choice otherwise (2).

              Signals that produce regular (non-escape) swimming originate in the subesophageal ganglia, are transmitted through non-giant axons, and give proof to the possibility that lobster’s have an I-function. One way to invalidate this possibility would be to prove that lobsters require stimuli to swim in any fashion. However, this type of casual swimming is unlike the escape swimming responses in that this type of swimming is not a reaction to visual or tactile stimuli (2). Rather, this type of swimming is the lobster’s choice. Activities such as scavenging for food, following another lobster, or looking for a new cave are self generated activities, thus resonating from the I-function (1).

              Based on the casual movements and escape swimming responses of lobsters, I find it conceivable that lobsters have an I-function. Though lobsters are known and loved by neurobiologists for their elementary nervous systems, perhaps it is because their nervous systems respond consistently to electricity in a dish, separately from their I-function’s control. I believe that the study presenting very few occurrences of escape swimming in response to visual and tactile stimulation at the rostral end proves that lobsters are making a conscience choice (4). Further, I believe that this study proves that they are able to process their ability to defend themselves on the rostral end with their claws and therefore choose not to escape, as opposed to their more frequent use of escapes swimming in response to stimulation on the telson end, where they lack defensive appendages.


Works Cited

(1)"Biotemp." The Lobster Conservancy. Web. 25 Mar. 2010. <>.


(2)Campos, Eric O. "Quick Forward Escape Swimming in the Stomatopod Crustacean Odontodactylus Havanensis." Berkeley McNair Research Journal 16 (2009): 2-12. 2009. Web. 25 Mar. 2010. <>.


(3)Grobstein, Paul. "The Brain's Images: Co-Constructing Reality and Self." Web Log post. Serendip. May 2002. Web. 25 Mar. 2010. <>.


(4)Newman, Phillip L., Douglas M. Neil, and Colin J. Chapman. "Escape Swimming in the Norway Lobster." Journal of Crustacean Biology 12.3 (1992): 342-53. JSTOR. Web. 25 Mar. 2010. <>.






Paul Grobstein's picture

I-functions in lobsters and ...

I agree that lobsters have different adaptive behaviors, and that their "choice" among behaviors is not entirely predictable given a complete knowledge of their inputs at any given time because, as in Pleurobranchea (discussed in class) and leechs, the output depends on internal activity and associated corollary discharge signals.  I also agree that lobsters and leeches probably have some randomness in that internal activity (cf Variability in brain function and behavior).  What I'm less sure is established by the observations described is that lobsters have consciousness in the sense of a "capacity to conceive realities beyond those that follow directly from what has been experienced" or "choice" in the sense humans conceive it, an exercise of "free will."   How does one know if lobsters "evaluated their environment, compared this threat to past threats, and deliberately chose to stay still"?  How would one know if any organism, humans included, "deliberately" chose to do something?    

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