Comparative study of extracellular recording methods for analysis of afferent sensory information: Empirical modeling, data analysis and interpretation.

BACKGROUND: Physiological studies of sensorial systems often require the acquisition and processing of data extracted from their multiple components to evaluate how the neural information changes in relation to the environment changes. In this work, a comparative study about methodological aspects of two electrophysiological approaches is described. NEW METHOD: Extracellular recordings from deep vibrissal nerves were obtained by using a customized microelectrode Utah array during passive mechanical stimulation of rat´s whiskers. These recordings were compared with those obtained with bipolar electrodes. We also propose here a simplified empirical model of the electrophysiological activity obtained from a bundle of myelinated nerve fibers. RESULTS: The peripheral activity of the vibrissal system was characterized through the temporal and spectral features obtained with both recording methods. The empirical model not only allows the correlation between anatomical structures and functional features, but also allows to predict changes in the CAPs morphology when the arrangement and the geometry of the electrodes changes. COMPARISON WITH EXISTING METHOD(S): This study compares two extracellular recording methods based on analysis techniques, empirical modeling and data processing of vibrissal sensory information. CONCLUSIONS: This comparative study reveals a close relationship between the electrophysiological techniques and the processing methods necessary to extract sensory information. This relationship is the result of maximizing the extraction of information from recordings of sensory activity.

Time-frequency analysis of neuronal populations with instantaneous resolution based on noise-assisted multivariate empirical mode decomposition.

BACKGROUND: Linear analysis has classically provided powerful tools for understanding the behavior of neural populations, but the neuron responses to real-world stimulation are nonlinear under some conditions, and many neuronal components demonstrate strong nonlinear behavior. In spite of this, temporal and frequency dynamics of neural populations to sensory stimulation have been usually analyzed with linear approaches. NEW METHOD: In this paper, we propose the use of Noise-Assisted Multivariate Empirical Mode Decomposition (NA-MEMD), a data-driven template-free algorithm, plus the Hilbert transform as a suitable tool for analyzing population oscillatory dynamics in a multi-dimensional space with instantaneous frequency (IF) resolution. RESULTS: The proposed approach was able to extract oscillatory information of neurophysiological data of deep vibrissal nerve and visual cortex multiunit recordings that were not evidenced using linear approaches with fixed bases such as the Fourier analysis. COMPARISON WITH EXISTING METHODS: Texture discrimination analysis performance was increased when Noise-Assisted Multivariate Empirical Mode plus Hilbert transform was implemented, compared to linear techniques. Cortical oscillatory population activity was analyzed with precise time-frequency resolution. Similarly, NA-MEMD provided increased time-frequency resolution of cortical oscillatory population activity. CONCLUSIONS: Noise-Assisted Multivariate Empirical Mode Decomposition plus Hilbert transform is an improved method to analyze neuronal population oscillatory dynamics overcoming linear and stationary assumptions of classical methods.

Effects of soy milk as a dietary complement during the natural aging process.

INTRODUCTION: Oxidative stress is one mechanism that could contribute to the acceleration of aging and age-related diseases. On the other hand, because of their antioxidative qualities soybean derived foods could have beneficial effects on the aging process. OBJECTIVES: The aim of our work was to study the effects of a diet supplemented with soy milk on certain biological features of aging in rats. METHODS: Male Wistar rats of 3 to 18 months of age, were assigned to one of two diets: 1) Experimental Group, commercial rat formula and soy milk; 2) Control Group, commercial rat formula and water. Every three months both lipid profile and lipid peroxidation were determined and neuronal cells of hippocampus were counted in control and experimental rats. RESULTS: The soy milk diet significantly improved the plasmatic lipid profile, decreasing serum cholesterol (total as well as LDL) and serum triglycerides, HDL-cholesterol was significatively higher in experimental animals. The LDL/HDL ratio was thus significantly lowered. The soy diet also produced decreased values of lipid peroxidation in brain, liver and kidney. These effects were significant after 6 to 9 months. The experimental animals lost fewer hippocampal neurons than the controls. Finally at 18 months of age, a greater number of surviving animals in experimental group with respect to the control one was observed. CONCLUSIONS: 1) soy intake could have beneficial effects as a complement of normal diet, but not as a replacement for animal proteins and 2) these effects are the result of a very long period (almost lifelong) of consumption of this diet.

Blockage of vibrissae afferents: I. Motor effects.

In the past, it has been proposed that the rat vibrissae play an important role in other hand, postural abnormalities, muscle tone decreases and hypomotility after sensory organ destructions were proposed as evidence supporting the "level setting" or "tonic" hypothesis. This hypothesis postulates that afferent activity, besides its well know transductive functions, sets the excitability state of the central nervous system. We thought the vibrissal system to be a good model to dissect these two postulated roles because vibrissae trimming would annul the transductive function without affecting the integrity of nerve activity. Thus we compare the effects of trimming the whiskers with blocking the vibrissal afferent nerves on two types of motor behavior: activity in an open field and walking over a rope connecting two elevated platforms. We found that only vibrissal afferent blockage (both nerve section and local anaesthesia) produced severe failures in the motor performances studied. These effects could not be fully explained by the abolition of the vibrissae as a sensory modality because cutting the whiskers did not significantly affect the motor performance. These data are discussed in reference to a tonic or general excitatory function of sensory inputs upon the central nervous system.