在螯蝦(Procambarus clarkii)的神經網路裡，有些特定刺激會產生特定行為，並不需要經過大腦思考。若兩種刺激引發的行為不能同時執行，螯蝦最後只會出現一種行為，神經網路要如何協調呢？在這篇論文裡面，我們利用螯蝦對於光線和碰觸兩種刺激，引發兩種不能同時執行的行為反應，來討論協調機制。
螯蝦突然暴露在明亮的環境，會步行後退(backward walking)，但是尾扇被碰觸則會引起步行前進。根據我們的觀察，光線和碰觸這兩種刺激同時給予，通常導致螯蝦前進，這和純粹碰觸尾扇造成的行為相同。
將螯蝦去除視覺之後，螯蝦仍然擁有避光行為，其感光能力是來自尾端的一對感光細胞(caudal photoreceptor)，簡稱CPR。它的感光部分位在腹部最後一個神經節，當黑暗中突然受到光線刺激時，CPR會產生高頻神經衝動，最後造成螯蝦產生後退行為，這一連串動作通常是蜷曲腹部收起尾節，並一路倒退步行到陰影內。而CPR也會接受機械感受神經元(mechanoreceptor neuron，簡稱MRN) 調控，MRN是螯蝦用來感受水流及碰觸的偵測器。利用電生理技術量測CPR的神經衝動頻率，我們的實驗結果支持，尾扇周圍水流的刺激經由MRN，可以壓抑光所誘發的CPR高頻神經衝動，可能進而阻止CPR誘發的後退行為。
更進一步研究，支持MRN透過乙醯膽鹼調控CPR的神經衝動頻率；活化尼古丁類(nicotinic)和毒蕈膽鹼類(muscarinic)兩種乙醯膽鹼受器，都可以壓抑光誘發CPR所產生高頻神經衝動。

For crayfish (Procambarus clarkii), the brain is not necessary for some specific behaviors elicited by certain external stimuli. How do the neural network coordinate and/or integrate with two stimuli which evoke incompatible behaviors? In this study, we will investigate the possible regulatory mechanism by examining the incompatible behaviors elicited by light and touch .

Crayfish walks backward when abruptly exposed to light but moves forward when its tail fan is stimulated by mechanical stimulation. Based on our observation, if light and touch were given simultaneously, crayfishes usually moved forward, which is in line with the behavior caused by simply touching the tail fan.

Crayfish still have photonegative behavior while deprived of vision. Its photosensitivity comes from a pair of caudal photoreceptors (CPR). The light sensor of CPR is at the last abdominal ganglion. CPR will produce high-frequency impulses when suddenly exposed to light in the dark and then lead the crayfish to walk backward to the shadow. The backward walking is usually accompanied by the abdominal and tail flexion. CPR will also be regulated by mechanoreceptor neuron (MRN), which senses mechanical stimulation such as water flow and touch.

We measure the spike rates by the electrophysiological technique. Our results supported that the mechanical stimulation on the tail fan can inhibit the high-frequency impulses evoked by CPR via MRN. It implies that mechanical stimulation on the tail suppresses the CPR-induced backward walking by MRN inhibiting CPR.

Another research suggested that MRN could regulate the spike rates of CPR by acetylcholine. Activating nicotinic and muscarinic acetylcholine receptors could also depress the light-evoked high frequency impulses of CPR.

Beall, S.P., Langley, D.J., and Edwards, D.H. (1990). Inhibition of escape tailflip in crayfish during backward walking and the defense posture. J Exp Biol 152, 577-582.
Bristol, A.S., and Carew, T.J. (2005). Differential role of inhibition in habituation of two independent afferent pathways to a common motor output. Learn Mem 12, 52-60.
Calabrese, R. (1976b). Crayfish mechanoreceptive interneurons. II. Bilateral interactions and inhibition. J comp Physiol 105, 103-114.
Cattaert, D., Araque, A., Buno, W., and Clarac, F. (1994). Nicotinic and muscarinic activation of motoneurons in the crayfish locomotor network. J Neurophysiol 72, 1622-1633.
Cattaert, D., Pearlstein, E., and Clarac, F. (1995). Cholinergic control of the walking network in the crayfish Procambarus clarkii. J Physiol Paris 89, 209-220.
Crandall, K.A., and Cronin, T.W. (1997). The molecular evolution of visual pigments of freshwater crayfishes (Decapoda: Cambaridae). J Mol Evol 45, 524-534.
Crisp, K.M., and Mesce, K.A. (2003). To swim or not to swim: regional effects of serotonin, octopamine and amine mixtures in the medicinal leech. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 189, 461-470.
Croll, R.P., Kovac, M.P., Davis, W.J., and Matera, E.M. (1985). Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. III. Role fo the paracerebral neurons and other identified brain neurons. J Neurosci 5, 64-71.
Edwards, D.H., Heitler, W.J., and Krasne, F.B. (1999). Fifty years of a command neuron: the neurobiology of escape behavior in the crayfish. Trends Neurosci 22, 153-161.
Edwards, D.H., Jr. (1984). Crayfish extraretinal photoreception. I. Behavioral and motorneuronal responses to abdominal illumination. J Exp Biol 109, 291-306.
Fiorillo, C.D., and Williams, J.T. (2000). Cholinergic inhibition of ventral midbrain dopamine neurons. J Neurosci 20, 7855-7860.
Flood, P.M., and Wilkens, L.A. (1978). Directional Sensitivity in a Crayfish Mechanoreceptive Interneurone: Analysis by Root Ablation. J Exp Biol 77, 89-106.
Friesen, W.O., and Kristan, W.B. (2007). Leech locomotion: swimming, crawling, and decisions. Curr Opin Neurobiol 17, 704-711.
Galeano, C., and Chow, K.L. (1971). Response of caudal photoreceptor of crayfish to continuous and intermittent photic stimulation. Can J Physiol Pharmacol 49, 699-706.
Glantz, R.M. (1974). Habituation of the motion detectors of the crayfish optic nerve: their relationship to the visually evoked defense reflex. J Neurobiol 5, 489-510.
Gulledge, A.T., and Stuart, G.J. (2005). Cholinergic inhibition of neocortical pyramidal neurons. J Neurosci 25, 10308-10320.
Hafner, G.S., Martin, R.L., and Tokarski, T.R. (2003). Photopigment gene expression and rhabdom formation in the crayfish (Procambarus clarkii). Cell Tissue Res 311, 99-105.
Hermann, H.T., and Olsen, R.E. (1968). Afferent stochastic modulation of crayfish caudal photoreceptor units. J Gen Physiol 51, 534-551.
Hermann, H.T., and Skiles, M.S. (1969). Cholinergic inhibition of the crayfish caudal photoreceptor. Comp Biochem Physiol 31, 575-588.
Kehoe, J. (1972). Three acetylcholine receptors in Aplysia neurones. J Physiol 225, 115-146.
Kelly, T.M., and Chapple, W.D. (1990). Kinematic analysis of the defense response in crayfish. J Neurophysiol 64, 64-76.
Kennedy, D. (1963). Physiology of photoreceptor neurons in the abdominal nerve cord of the crayfish. J Gen Physiol 46, 551-572.
Krasne, F.B., and Lee, S.C. (1988). Response-dedicated trigger neurons as control points for behavioral actions: selective inhibition of lateral giant command neurons during feeding in crayfish. J Neurosci 8, 3703-3712.
Kruszewska, B., and Larimer, J.L. (1993). Specific second messengers activate the caudal photoreceptor of crayfish. Brain Res 618, 32-40.
Larimer, J.L., Trevino, D.L., and Ashby, E.A. (1966). A comparison of spectral sensitivities of caudal photoreceptors of epigeal and cavernicolous crayfish. Comp Biochem Physiol 19, 409-415.
Marzelli, G.A., and Wilkens, L.A. (1976). Central inhibitory fibers in the crayfish abdomen: effects on a sensory interneuron. Amer Zool 16, 178.
Mittmann, T., and Alzheimer, C. (1998). Muscarinic inhibition of persistent Na+ current in rat neocortical pyramidal neurons. J Neurophysiol 79, 1579-1582.
Nagayama, T., Takahata, M., and Hisada, M. (1986). Behavioral transition of crayfish avoidance reaction in response to uropod stimulation. Exp Biol 46, 75-82.
Pei, X., and Moss, F. (1996). Detecting low dimensional dynamics in biological experiments. Int J Neural Syst 7, 429-435.
Pei, X., Wilkens, L.A., and Moss, F. (1996). Light enhances hydrodynamic signaling in the multimodal caudal photoreceptor interneurons of the crayfish. J Neurophysiol 76, 3002-3011.
Saideman, S.R., Blitz, D.M., and Nusbaum, M.P. (2007). Convergent motor patterns from divergent circuits. J Neurosci 27, 6664-6674.
Simon, T.W., and Edwards, D.H. (1990). Light-evoked walking in crayfish: Behavioral and neuronal responses triggered by the caudal photoreceptor J Comp Physiol A 166, 745-755.
Stein, P.S. (1978). Motor systems, with specific reference to the control of locomotion. Annu Rev Neurosci 1, 61-81.
Tsai, L.Y., and Yeh, S.R. (2008). Modulatory effects of acetylcholine on crayfish lateral giant escape command neurons. 國立清華大學博士論文.
Welsh, J.H. (1934). The caudal photoreceptor and responses of the crayfish to light. J Cell Comp Physiol 4, 379– 388.
Wilkens, L., and Douglass, J. (1994). A Stimulus Paradigm for Analysis of near-Field Hydrodynamic Sensitivity in Crustaceans. J Exp Biol 189, 263-272.
Wilkens, L.A. (1988). The crayfish caudal photoreceptor: advances and questions after the first half century. Comp Biochem Physiol C 91, 61-68.
Wilkens, L.A., and Larimer, J.L. (1972). The CNS photoreceptor of crayfish: morphology and synaptic activity. J Comp Physiol 80, 389-407.
Yeh, S.R., Yang, J.W., Lee, Y.T., and Tsai, L.Y. (2008). Static magnetic field expose enhances neurotransmission in crayfish nervous system. Int J Radiat Biol 84, 561-567.
楊正維 (2002). 靜磁場對於螯蝦逃跑迴路神經的影響. 國立清華大學碩士論文.