title: Two Distinct Stimulus Frequencies Delivered Simultaneously at Low Intensity Generate Robust Locomotor Patterns.
abstract: OBJECTIVE
  Explore the primary characteristics of afferent noisy stimuli, which optimally activate locomotor patterns at low intensity.
  
  
  METHODS
  Intracellular and extracellular electrophysiological traces were derived from single motoneurons and from ventral roots, respectively. From these recordings, we obtained noisy stimulating protocols, delivered to a dorsal root (DR) of an isolated neonatal rat spinal cord, while recording fictive locomotion (FL) from ventral roots.
  
  
  RESULTS
  We decreased complexity of efficient noisy stimulating protocols down to single cell spikes. Then, we identified four main components within the power spectrum of these signals and used them to construct a basic multifrequency protocol of rectangular impulses, able to induce FL. Further disassembling generated the minimum stimulation paradigm that activated FL, which consisted of a pair of 35 and 172 Hz frequency pulse trains, strongly effective at low intensity when delivered either jointly to one lumbosacral DR or as single simultaneous trains to two distinct DRs. This simplified pulse schedule always activated a locomotor rhythm, even when delivered for a very short time (500 ms). One prerequisite for the two-frequency protocol to activate FL at low intensity when applied to sacrocaudal afferents was the ability to induce ascending volleys of greater amplitude.
  
  
  CONCLUSIONS
  Multifrequency protocols can support future studies in defining the most effective characteristics for electrical stimulation to reactivate stepping following motor injury.
authors.affiliation: Neuroscience Area, International School for Advanced Studies (SISSA), Trieste, TS, Italy.|SPINAL (Spinal Person Injury Neurorehabilitation Applied Laboratory), Istituto di Medicina Fisica e Riabilitazione (IMFR), Udine, UD, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Dose
authors.affiliation: Neuroscience Area, International School for Advanced Studies (SISSA), Trieste, TS, Italy.|SPINAL (Spinal Person Injury Neurorehabilitation Applied Laboratory), Istituto di Medicina Fisica e Riabilitazione (IMFR), Udine, UD, Italy.
authors.forename: Giuliano
authors.initials: G
authors.lastname: Taccola
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D055592:Biophysical Phenomena / Q000502:physiology*; D001703:Biophysics; D004558:Electric Stimulation; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008124:Locomotion / Q000187:drug effects / Q000502:physiology*; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D016202:N-Methylaspartate / Q000494:pharmacology; D009415:Nerve Net; D018408:Patch-Clamp Techniques; D051381:Rats; D012701:Serotonin / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology*
chemical_list: D018690:Excitatory Amino Acid Agonists; D012701:Serotonin; D016202:N-Methylaspartate
keywords: Spinal cord; central pattern generators; fictive locomotion; frequency; train of pulses