Journal
JOURNAL OF NEUROSCIENCE
Volume 24, Issue 22, Pages 5269-5282Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.5626-03.2004
Keywords
drive; EMG (electromyogram); hindbrain; hindlimb (leg); limb; motor; reflex; pattern generation; force-field; primitive; premotor drive; unit burst
Categories
Funding
- NINDS NIH HHS [R01 NS040412-03, R01 NS040412-04, NS40412, R01 NS040412] Funding Source: Medline
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Spinal cord modularity impacts on our understanding of reflexes, development, descending systems in normal motor control, and recovery from injury. We used independent component analysis and best-basis or matching pursuit wavepacket analysis to extract the composition and temporal structure of bursts in hindlimb muscles of frogs. These techniques make minimal a priori assumptions about drive and motor pattern structure. We compared premotor drive and burst structures in spinal frogs with less reduced frogs with a fuller repertoire of locomotory, kicking, and scratching behaviors. Six multimuscle drives explain most of the variance of motor patterns (similar to80%). Each extracted drive was activated with pulses at a single time scale or common duration (similar to275 msec) burst structure. The data show that complex behaviors in brainstem frogs arise as a result of focusing drives to smaller core groups of muscles. Brainstem drives were subsets of the muscle groups from spinal frogs. The 275 msec burst duration was preserved across all behaviors and was most precise in brainstem frogs. These data support a modular decomposition of frog behaviors into a small collection of unit burst generators and associated muscle drives in spinal cord. Our data also show that the modular organization of drives seen in isolated spinal cord is fine-tuned by descending controls to enable a fuller movement repertoire. The unit burst generators and their associated muscle synergies extracted here link the biomechanical primitives, described earlier in the frog, rat, and cat, and to the elements of pattern generation examined in fictive preparations.
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