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Our lab studies how animals generate rhythmic motor patterns such as walking, swimming, and flying. Nervous system rhythmicity also plays a role in some types of sensory processing and in attention. Understanding how the nervous system and body produce rhythms is thus important for understanding many central components of animal and human behavior. We perform our research in the experimentally advantageous and very well-studied lobster stomatogastric neuromuscular system, which produces the rhythmic swallowing, chewing, and filtering movements of the lobster stomach. The stomatogastric nervous system is anatomically segregated from the rest of the nervous system and continues to produce rhythmic outputs when removed from the lobster. Rhythmic motor pattern generation can therefore be studied in this preparation at all levels from individual neurons to neural networks to muscle response to movement.

We work on all these levels both experimentally and using computer modeling. Rhythms occur across time: they repeat with certain cycle periods, the movements that comprise them occur at characteristic times in the cycle period, and these movements last for characteristic durations. One aspect of our prior work concentrated on how neurons and networks deal with time^{1, 2, 5, 10, 12, 13, 21}. The neuron research showed that 1) isolated neuron intrinsic properties change as the temporal characteristics of their inputs change⁵, 2) individual neurons could thus "measure" parameters such as beat frequency, duty cycle, and duration in temporal patterns such as songs^{5, 10}, and 3) these abilities may result from slow membrane conductances^{10, 21}. The network research showed that different synaptic pathways play different roles in regulating network rhythmicity (serving to slow or speed the network)¹², that some pathways may be effective only in certain network conditions¹³, and characterized certain aspects of interactions between stomatogastric networks^{9, 11}. Our prior muscle work emphasized how dramatically muscles can alter their neural input, transforming, for instance, rhythmic motor neuron input into largely tonic muscle contractions^{3, 4} or even expressing the motor patterns of neurons that do not innervate the muscles^{6, 14}. We extended this work to identify some of the contractile, anatomical, and molecular mechanisms that underlie these transformations^{7, 8, 17, 23}. On the biomechanical level we have used high-resolution computed tomography (CT scans) of the lobster stomach to derive three-dimensional maps of its ossicles²². These data suggest that some stomach ossicles likely act as flexible, energy-storing elements. Predicting stomach movements thus likely requires not only knowing motor neuron output and muscle transformative properties, but also detailed, quantitative description of ossicle bending responses to force.

Our present research continues to combine experimental and computational techniques. Our neuron research revolves around using complicated, wide dynamic range driving of isolated neurons to distinguish among neuron types and to characterize neuron membrane conductance makeup¹⁸ (NIH support). Our muscle and biomechanics research is to continue measuring stomatogastric muscle, ossicle, and joint properties, and to use these and our CT data to build a computer model that predicts stomach movement and function in response to stomatogastric nervous system activity (NSF support).

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Selected Publications:

23. JB Thuma, SL Hooper (2010) Direct evidence that stomatogastric (Panulirus interruptus) muscle passive responses are not due to background actomyosin cross-bridges. J Comparative Physiology A 196:649-657.

22. KH Hobbs, SL Hooper (2009) High-resolution computed tomography of lobster (Panulirus interruptus) stomach: three dimensional coordinate-based map of ossicle shape and position, large inter- and intra-ossicle density variation, and lack of morphogically-specialized joints. J Morphology 270:1029-1041

21. SL Hooper, E Buchman, AL Weaver, JB Thuma, KH Hobbs (2009) Slow conductances could underlie intrinsic phase-maintaining properties of isolated lobster (Panulirus interruptus) pyloric neurons. J Neuroscience 29:1834-1845

20. JB Thuma, WE White, KH Hobbs, SL Hooper (2009) Pyloric neuron morphology in the stomatogastric ganglion of the lobster, Panulirus interruptus. Brain, Behavior, and Evolution 73:26-42

19. SL Hooper, JB Thuma, KH Hobbs (2008) Invertebrate muscles: thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle. Progress in Neurobiology 86:72-127

18. KH Hobbs, SL Hooper (2008) Using complicated, wide dynamic range, driving to develop models of single neurons in single recording sessions. J Neurophysiology 99:1871-1883

17. JB Thuma, PI Harness, TJ Koehnle, LG Morris, SL Hooper (2007) Muscle anatomy is a primary determinant of muscle relaxation dynamics in the lobster (Panulirus interruptus) stomatogastric system. J Comparative Physiology A 193:1101-1113

16. SL Hooper, JB Thuma (2005) Invertebrate muscles: muscle specific genes and proteins. Physiological Review 85:1001-1060

15. SL Hooper, RA DiCaprio (2004) Crustacean motor pattern generator networks. Neurosignals 13:50-69

14. JB Thuma, LG Morris, AL Weaver, SL Hooper (2003) Lobster (Panulirus interruptus) pyloric muscles express the motor patterns of three neural networks, only one of which innervates the muscles. J Neuroscience 23:8911-8920

13. AL Weaver, SL Hooper (2003) Relating network synaptic connectivity and network activity in the lobster (Panulirus interruptus) pyloric network. J Neurophysiology 90:2378-2386

12. AL Weaver, SL Hooper (2003) Follower neurons in lobster (Panulirus interruptus) pyloric network neurons that regulate pacemaker period in complementary ways. J Neurophysiology 89:1327-1338

11. JB Thuma, SL Hooper (2003) Quantification of cardiac sac network effects on a movement related parameter of pyloric network output in the lobster. J Neurophysiology 89:745-753

10. SL Hooper, E Buchman, KH Hobbs (2002) A computational role for slow conductances: single neuron models that measure duration. Nature Neuroscience 5:552-556

9. JB Thuma, SL Hooper (2002) Quantification of gastric mill network effects on a movement related parameter of pyloric network output in the lobster. J Neurophysiology 87:2372-2384

8. NJ Hoover, AL Weaver, PI Harness, SL Hooper (2002) Combinatorial and cross-fiber averaging transform muscle electrical responses with a large random component into deterministic contractions. J Neuroscience 22:1895-1904

7. LG Morris, SL Hooper (2001) Mechanisms underlying stabilization of temporally summated muscle contractions in the lobster (Panulirus) pyloric system. J Neurophysiology 85:254-268

6. LG Morris, JB Thuma, SL Hooper (2000) Muscles express motor patterns of non-innervating neural networks by filtering broad-band input. Nature Neuroscience 3:245-250

5. SL Hooper (1998) Transduction of temporal patterns by single neurons. Nature Neuroscience 1:720-726

4. LG Morris, SL Hooper (1998) Muscle response to changing neuronal input in the lobster (Panulirus interruptus) stomatogastric system: Slow muscle properties can transform rhythmic input into tonic output. J Neuroscience 18:3433-3442

3. LG Morris, SL Hooper (1997) Muscle response to changing neuronal input in the lobster (Panulirus interruptus) stomatogastric system: Spike number vs. spike frequency dependent domains. J Neuroscience 17:5956-5971

2. SL Hooper (1997) The pyloric pattern of the lobster (Panulirus interruptus) stomatogastric ganglion comprises two phase maintaining subsets. J Computational Neuroscience 4:207-219

1. SL Hooper (1997) Phase maintenance in the pyloric pattern of the lobster (Panulirus interruptus) stomatogastric ganglion. J Computational Neuroscience 4:191-206

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