We all know it's rude to stick your tongue out. But some creatures don't just stick it out, they hurl it out at any tasty passing morsel. One creature that hunts with its tongue is the Imperial Cave Salamander, extending it up to 80% of its body length by squeezing down on the tongue's folding cartilaginous skeleton. Over short distances, the animal controls its tongue's extension with coordinated contractions of the protractor and retractor muscles. However, over longer ranges the protractor muscles hurl the tongue, complete with skeleton, out of the mouth. How the tiny animals launch their articulated tongues fascinates Stephen Deban. Could they vary the muscular activity that launches the tongue depending on the range the tongue must cover? Deban and his colleague, Ursula Dicke, were keen to find how the complex protractor muscle is activated during short- and long-range launches. Placing tiny electrodes along the surface of the subarcualis rectus protactor muscles,Deban and Dicke recorded electromyograms (EMGs) as the salamanders took aim and fired ().
Fortunately, working with the tiny ballistics experts was straightforward;the salamanders were `very cooperative for amphibians' says Deban. But preparing the tiny implants to record the muscle's EMGs was far trickier. `It took a few months of experimentation' Deban remembers before he and Dicke were ready to begin recording EMGs from five hungry animals.
Placing a cricket close to the salamander's mouth and monitoring the subarcualis rectus's electrical activity as it squeezed the tongue out, Deban admits he was surprised when he noticed that the muscle's activation pattern originated at the back of the muscle, and moved forward sequentially. However,this activation pattern changed entirely as Deban moved the crickets further away. Over long-range ballistic launches, the same electrodes recorded simultaneous activity from the muscle's surface as the salamander fired its tongue.
But would the salamanders switch rapidly from the short-range launch pattern to the ballistic launch pattern when the cricket was placed beyond a certain range? Or would the transition happen more gently as the cricket target moved further away? Deban and Dicke monitored the amphibian's EMGs as they fired their tongues over distances ranging from 0–5 cm and realised that the EMG pattern changed gradually and lasted longer as their tongues extended over greater distances. The salamanders were modulating their muscular activity.
The team also compared EMG patterns from successful launches that hit the cricket with launches that missed and realised that not only was the modulation unrelated to the animal's ability to hit its target, but the amphibian had no control over its tongue's trajectory once fired. Deban explains that this is a `feedforward mechanism in which the movement is completed once it is initiated, with no further input from the senses'.
Having begun to unravel the mysteries of the salamander's intriguing subarcualis rectus muscles, Deban is keen to learn more about the salamander's ballistic launch mechanism. Meanwhile, salamanders keep on sticking their tongues out, regardless of social mores.
