Burst Firing is a Neural Code in an Insect Auditory System

Various classes of neurons alternate between high-frequency discharges and silent intervals. This phenomenon is called burst firing. To analyze burst activity in an insect system, grasshopper auditory receptor neurons were recorded in vivo for several distinct stimulus types. The experimental data show that both burst probability and burst characteristics are strongly influenced by temporal modulations of the acoustic stimulus. The tendency to burst, hence, is not only determined by cell-intrinsic processes, but also by their interaction with the stimulus time course. We study this interaction quantitatively and observe that bursts containing a certain number of spikes occur shortly after stimulus deflections of specific intensity and duration. Our findings suggest a sparse neural code where information about the stimulus is represented by the number of spikes per burst, irrespective of the detailed interspike-interval structure within a burst. This compact representation cannot be interpreted as a firing-rate code. An information-theoretical analysis reveals that the number of spikes per burst reliably conveys information about the amplitude and duration of sound transients, whereas their time of occurrence is reflected by the burst onset time. The investigated neurons encode almost half of the total transmitted information in burst activity

Ashing techniques in the determination of macronutrient contents in carrot root samples (Daucus carota L.)

Con el objeto de determinar la metodología más adecuada para la mineralización de muestras de raíz de zanahoria (Daucus carota L) se emplearon 5 técnicas por vía seca, que se compararon con el método estándar (vía húmeda). El ensayo se condujo bajo un diseño en bloques completos aleatorizados con 5 repeticiones. No se encontraron diferencias significativas en la evaluación de P y Ca, con respecto a los valores del método estándar, pero sí en la evaluación del contenido de K, calcinando a temperaturas inferiores a 550 ºC, y en la determinación de Na a 600 ºC. Se calcularon los coeficientes de correlación entre los elementos estudiados y el contenido de cenizas, encontrándose correlación altamente significativa en la mayoría de los casos. Los resultados obtenidos mostraron que las técnicas de mineralización probadas fueron efectivas para la determinación simultánea de los elementos minerales.To choose a suitable method for the digestion of carrot root samples (Daucus carota L.) five dry ashing techniques were used and compared with the standard wet ashing method. The analysis of the data was based on a randomized complete block design, with five replications. No significant differences with the standard method for P and Ca determination were found but in K evaluation, employing the dry ashing technique at a temperature lower than 550 oC, and in Na evaluation at 600 oC significant differences were obtained. Correlation coefficients between the elements studied and ash content were assessed, and a significant correlation in most cases was found. The results obtained showed that ashing techniques employed were effective.Facultad de Ciencias Agrarias y Forestale

Ashing techniques in the determination of macronutrient contents in carrot root samples (Daucus carota L.)

Con el objeto de determinar la metodología más adecuada para la mineralización de muestras de raíz de zanahoria (Daucus carota L) se emplearon 5 técnicas por vía seca, que se compararon con el método estándar (vía húmeda). El ensayo se condujo bajo un diseño en bloques completos aleatorizados con 5 repeticiones. No se encontraron diferencias significativas en la evaluación de P y Ca, con respecto a los valores del método estándar, pero sí en la evaluación del contenido de K, calcinando a temperaturas inferiores a 550 ºC, y en la determinación de Na a 600 ºC. Se calcularon los coeficientes de correlación entre los elementos estudiados y el contenido de cenizas, encontrándose correlación altamente significativa en la mayoría de los casos. Los resultados obtenidos mostraron que las técnicas de mineralización probadas fueron efectivas para la determinación simultánea de los elementos minerales.To choose a suitable method for the digestion of carrot root samples (Daucus carota L.) five dry ashing techniques were used and compared with the standard wet ashing method. The analysis of the data was based on a randomized complete block design, with five replications. No significant differences with the standard method for P and Ca determination were found but in K evaluation, employing the dry ashing technique at a temperature lower than 550 oC, and in Na evaluation at 600 oC significant differences were obtained. Correlation coefficients between the elements studied and ash content were assessed, and a significant correlation in most cases was found. The results obtained showed that ashing techniques employed were effective.Facultad de Ciencias Agrarias y Forestale

The information transmitted by spike patterns in single neurons

Spike patterns have been reported to encode sensory information in several brain areas. Here we assess the role of specific patterns in the neural code, by comparing the amount of information transmitted with different choices of the readout neural alphabet. This allows us to rank several alternative alphabets depending on the amount of information that can be extracted from them. One can thereby identify the specific patterns that constitute the most prominent ingredients of the code. We finally discuss the interplay of categorical and temporal information in the amount of synergy or redundancy in the neural code.Comment: To be published in Journal of Physiology Paris 200

ESTUDIOS DE VARIABILIDAD GENÉTICA EN MAÍZ PISINGALLO (Zea mays L. var. Everta) PARA ASOCIAR VALORES DE MEJORA A MARCADORES MOLECULARES

El objetivo de este trabajo fue evaluar la variabilidad genética de la población de mejoramiento de maíz pisingallo mediante el uso de marcadores moleculares (SNP) e información fenotípica de los caracteres arriba mencionados (expansión y K10), tanto en líneas como híbridos. La información molecular (SNPs) se usará para conocer las distancias genéticas entre los diferentes genotipos y en un futuro asociar marcadores moleculares a ambos caractere

Probing Real Sensory Worlds of Receivers with Unsupervised Clustering

The task of an organism to extract information about the external environment from sensory signals is based entirely on the analysis of ongoing afferent spike activity provided by the sense organs. We investigate the processing of auditory stimuli by an acoustic interneuron of insects. In contrast to most previous work we do this by using stimuli and neurophysiological recordings directly in the nocturnal tropical rainforest, where the insect communicates. Different from typical recordings in sound proof laboratories, strong environmental noise from multiple sound sources interferes with the perception of acoustic signals in these realistic scenarios. We apply a recently developed unsupervised machine learning algorithm based on probabilistic inference to find frequently occurring firing patterns in the response of the acoustic interneuron. We can thus ask how much information the central nervous system of the receiver can extract from bursts without ever being told which type and which variants of bursts are characteristic for particular stimuli. Our results show that the reliability of burst coding in the time domain is so high that identical stimuli lead to extremely similar spike pattern responses, even for different preparations on different dates, and even if one of the preparations is recorded outdoors and the other one in the sound proof lab. Simultaneous recordings in two preparations exposed to the same acoustic environment reveal that characteristics of burst patterns are largely preserved among individuals of the same species. Our study shows that burst coding can provide a reliable mechanism for acoustic insects to classify and discriminate signals under very noisy real-world conditions. This gives new insights into the neural mechanisms potentially used by bushcrickets to discriminate conspecific songs from sounds of predators in similar carrier frequency bands

The Cercal Organ May Provide Singing Tettigoniids a Backup Sensory System for the Detection of Eavesdropping Bats

Conspicuous signals, such as the calling songs of tettigoniids, are intended to attract mates but may also unintentionally attract predators. Among them bats that listen to prey-generated sounds constitute a predation pressure for many acoustically communicating insects as well as frogs. As an adaptation to protect against bat predation many insect species evolved auditory sensitivity to bat-emitted echolocation signals. Recently, the European mouse-eared bat species Myotis myotis and M. blythii oxygnathus were found to eavesdrop on calling songs of the tettigoniid Tettigonia cantans. These gleaning bats emit rather faint echolocation signals when approaching prey and singing insects may have difficulty detecting acoustic predator-related signals. The aim of this study was to determine (1) if loud self-generated sound produced by European tettigoniids impairs the detection of pulsed ultrasound and (2) if wind-sensors on the cercal organ function as a sensory backup system for bat detection in tettigoniids. We addressed these questions by combining a behavioral approach to study the response of two European tettigoniid species to pulsed ultrasound, together with an electrophysiological approach to record the activity of wind-sensitive interneurons during real attacks of the European mouse-eared bat species Myotis myotis. Results showed that singing T. cantans males did not respond to sequences of ultrasound pulses, whereas singing T. viridissima did respond with predominantly brief song pauses when ultrasound pulses fell into silent intervals or were coincident with the production of soft hemi-syllables. This result, however, strongly depended on ambient temperature with a lower probability for song interruption observable at 21°C compared to 28°C. Using extracellular recordings, dorsal giant interneurons of tettigoniids were shown to fire regular bursts in response to attacking bats. Between the first response of wind-sensitive interneurons and contact, a mean time lag of 860 ms was found. This time interval corresponds to a bat-to-prey distance of ca. 72 cm. This result demonstrates the efficiency of the cercal system of tettigoniids in detecting attacking bats and suggests this sensory system to be particularly valuable for singing insects that are targeted by eavesdropping bats

Bursts and Isolated Spikes Code for Opposite Movement Directions in Midbrain Electrosensory Neurons

Directional selectivity, in which neurons respond strongly to an object moving in a given direction but weakly or not at all to the same object moving in the opposite direction, is a crucial computation that is thought to provide a neural correlate of motion perception. However, directional selectivity has been traditionally quantified by using the full spike train, which does not take into account particular action potential patterns. We investigated how different action potential patterns, namely bursts (i.e. packets of action potentials followed by quiescence) and isolated spikes, contribute to movement direction coding in a mathematical model of midbrain electrosensory neurons. We found that bursts and isolated spikes could be selectively elicited when the same object moved in opposite directions. In particular, it was possible to find parameter values for which our model neuron did not display directional selectivity when the full spike train was considered but displayed strong directional selectivity when bursts or isolated spikes were instead considered. Further analysis of our model revealed that an intrinsic burst mechanism based on subthreshold T-type calcium channels was not required to observe parameter regimes for which bursts and isolated spikes code for opposite movement directions. However, this burst mechanism enhanced the range of parameter values for which such regimes were observed. Experimental recordings from midbrain neurons confirmed our modeling prediction that bursts and isolated spikes can indeed code for opposite movement directions. Finally, we quantified the performance of a plausible neural circuit and found that it could respond more or less selectively to isolated spikes for a wide range of parameter values when compared with an interspike interval threshold. Our results thus show for the first time that different action potential patterns can differentially encode movement and that traditional measures of directional selectivity need to be revised in such cases