RESUMEN
The information transmission properties of ensembles of MSs and the effect of the gamma system on these properties were studied. Three converging lines of research were taken: (1) the development of information theoretic estimation tools, and the formulation of an "operational" interpretation for the information rate; (2) animal experiments in which the mutual information rate was estimated and the effect of the gamma system was quantified; (3) simulation of a muscle spindle model with gamma activation in order to corroborate the results of the animal experiments. The main hypothesis was that the gamma system will enhance information theoretic measures that quantify the quality of the sensory neural channel comprised from an ensemble of primary muscle spindle afferents. A random stimulus was applied to a muscle in the hind limb of a cat, while spike trains from several primary MS afferents were recorded simultaneously. The stimulus was administered twice, with an operative and a disconnected gamma system. The mutual information rate between the stimulus and spike trains, as well as other information theoretic measures, was estimated. The information rate of ensembles of MSs increased with increasing ensemble size. However, with an operative gamma system the "ensemble effect" was much higher. In addition, the ensemble effect was influenced by the stimulus spectrum. A muscle spindle population model with gamma activation was simulated with stimuli that were identical to that of the animal experiments. The simulation results supported the experimental results and corroborated the main hypothesis. The results indicate that the gamma system has an important role in enhancing information transmission from ensembles of MSs to the spinal cord.
Asunto(s)
Potenciales de Acción/fisiología , Neuronas Motoras gamma/fisiología , Husos Musculares/fisiología , Músculo Esquelético/inervación , Neuronas Aferentes/fisiología , Reflejo de Estiramiento/fisiología , Algoritmos , Animales , Gatos , Estimulación Eléctrica , Modelos Neurológicos , Músculo Esquelético/fisiología , Conducción Nerviosa/fisiología , Médula Espinal/citología , Médula Espinal/fisiología , Raíces Nerviosas Espinales/fisiología , Transmisión Sináptica/fisiologíaRESUMEN
The information transmission properties of single, de-efferented primary muscle-spindle afferents from the hind limb of the cat were investigated. The gastrocnemius medialis muscle was stretched randomly while recording spike trains from several muscle-spindle afferents in the dorsal root. Two classes of input stimuli were used: (i) Gaussian noise with band-limited flat spectrum, and (ii) Gaussian noise with a more "naturalistic" 1/f(n) spectrum. The "reconstruction" method was used to calculate a lower bound to the information rate (in bits per second) between the muscle spindles and the spinal cord. Results show that in response to the flat-spectrum input, primary muscle-spindle afferents transfer information mainly about high frequencies, carrying 2.12 bits/spike. In response to naturalistic-spectrum inputs, primary muscle-spindle afferents transfer information about both low and high frequencies, with "spiking efficiency" increasing to 2.67 bits/spike. A simple muscle-spindle simulation model was analyzed with the same method, emphasizing the important part played by the intrafusal fiber mechanical properties in information transmission.
Asunto(s)
Vías Aferentes/fisiología , Husos Musculares/fisiología , Músculo Esquelético/inervación , Neuronas Aferentes/fisiología , Potenciales de Acción/fisiología , Vías Aferentes/citología , Animales , Gatos , Estimulación Eléctrica , Mecanotransducción Celular/fisiología , Modelos Neurológicos , Neuronas Motoras gamma/fisiología , Contracción Muscular/fisiología , Husos Musculares/citología , Músculo Esquelético/fisiología , Neuronas Aferentes/citología , Distribución Normal , Raíces Nerviosas Espinales/citología , Raíces Nerviosas Espinales/fisiologíaRESUMEN
The information transmission properties of single, deefferented, primary muscle spindle afferents (MSAs) from the hind limb of the cat were investigated. Random stretches were delivered to the gastrocnemius medialis muscle, while recording spike trains from several MSAs near the dorsal root. Two classes of input stimuli were used: Gaussian noise with band-limited flat spectrum, and Gaussian noise with a more "naturalistic" 1/fn spectrum. The "reconstruction" method was used to calculate a lower bound to the information rate (in bit/ sec) delivered from MSAs to the spinal cord. Results show that in response to flat spectrum primary MSAs transfer information mainly about high frequencies, carrying 1.97 bits per spike. In response to naturalistic spectrum MSAs transfer information about both low and high frequencies, with "spiking efficiency" increasing to 2.99 bits per spike. A simple muscle spindle model was simulated, exemplifying the part of the intrafusal fiber mechanical properties in information transmission.