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Closed Access item Phantom reflexes: Muscle contractions at a frequency not physically present in the input stimuli

Authors:Manjarrez, Elías
Balenzuela, Pablo
García-Ojalvo, Jordi
Vázquez, E. E.
Martínez, Lourdes
Flores, Amira
Mirasso, Claudio R.
Keywords:Coincidence, Ghost resonance, Missing fundamental illusion, Monosynaptic reflex, Facilitation, Motoneurons
Issue Date:1-Jan-2007
Citation:BioSystems 90, 379-388 (2007)
Abstract:In the motor system, the periodic stimulation of one Ia-afferent input produces reflex muscle contractions at the input frequency. However, we observed that when two Ia monosynaptic reflex-afferent inputs are involved the periodic muscle contractions may occur at a frequency physically not present in the afferent inputs even when these inputs are sub-threshold. How can the muscles respond with such phantom reflex contractions at a frequency physically absent in the sub-threshold Ia-afferent input stimuli? Here we provide an explanation for this phenomenon in the cat spinal cord, that we termed “ghost motor response”. We recorded monosynaptic reflexes in the L7 ventral root, intracellular potentials in the motoneurons, and the associated muscular contractions elicited by stimulation of the lateral and medial gastrocnemius nerves. By stimulating with periodic pulses of sub-threshold intensities and distinct frequencies of 2 and 3 Hz the lateral and medial gastrocnemius nerves, respectively, we observed monosynaptic responses and phantom reflex muscle contractions occurring at the fundamental frequency (1 Hz), which was absent in the input stimuli. Thus we observed a reflex ghost motor response at a frequency not physically present in the inputs. We additionally studied the inharmonic case for sub-threshold stimuli and observed muscular contractions occurring at much lower frequencies, which were also conspicuously absent in the inputs. This is the first experimental evidence of a phantom reflex response in the nervous system. The observed behavior was modeled by numerical simulations of a pool of neurons subjected to two different input pulses.
Description:Final full-text version of the paper available at: http://dx.doi.org/10.1016/j.biosystems.2006.10.002.
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