Detecting vibration source for the orientation behavior of sand scorpions
© Jeong and Kim; licensee BioMed Central Ltd. 2012
Published: 16 July 2012
Sand scorpions can locate their prey through their vibration sensitivity. They have their tactile sense organs on their legs to detect vibration reaching their body. They show an orientation behavior towards their prey when there is any vibration signal generated by prey movement. How they respond to the vibration source is an open question. It is believed that stimulus-locked neuron firings from the sensor organs on each leg are processed and the brain system of sand scorpions has sensory projections from the sense organs. It is known that eight command neurons in the brain interact each other with triad inhibitions [1, 2]. Then a population coding of the neuron activity determines the direction of vibration source .
In our experiments, sensory activations depending on Rayleigh wave are measured with microphone sensors and a population coding of command neuron activities with triad inhibitions are applied to the time course of vibration sensor readings. The approach can estimate the direction of vibration source. Unlike the direction, the distance to a vibration source is not clearly measured in our experiments. The distance estimation seems to be involved with the intensity of vibration signals or the time difference between the P-wave and the Rayleigh wave. The time difference roughly guides the distance in the experiments, but it does not provide accurate results. It suggests that sand scorpions might focus on estimating the direction of the vibration source caused by a prey rather than accurately calculate how far away from their body a prey is. The distance accuracy may be achieved within small distances.
Sand scorpions can orient towards their prey with high accuracy when there is any prey movement. We assume a circular array of directionally sensitive neurons with inhibition mechanism to explain the orientation behavior, receiving sensory signals of vibration as pointed out by other researchers [1, 2]. What type of inhibition mechanism is available, how they detect the distance of a vibration source, or whether they can sense or use both the sound wave and surface wave is an open question. We need further study on these subjects. More sophisticated measurements and experiments of vibration signals might explain those questions partly.
This work was supported by the NRF (National Research Foundation) grant funded by the Ministry of Education, Science and Technology in South Korea (No. 2012-0005677).
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