Papers by juan-carlos letelier
arXiv (Cornell University), Mar 14, 2023
Journal of Comparative Neurology, 2018
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Scientific Reports, 2017
To what extent can the mammalian visual system be shaped by visual behavior? Here we analyze the ... more To what extent can the mammalian visual system be shaped by visual behavior? Here we analyze the shape of the visual fields, the densities and distribution of cells in the retinal ganglion-cell layer and the organization of the visual projections in two species of facultative non-strictly subterranean rodents, Spalacopus cyanus and Ctenomys talarum, aiming to compare these traits with those of phylogenetically closely related species possessing contrasting diurnal/nocturnal visual habits. S. cyanus shows a definite zone of frontal binocular overlap and a corresponding area centralis, but a highly reduced amount of ipsilateral retinal projections. The situation in C. talarum is more extreme as it lacks of a fronto-ventral area of binocular superposition, has no recognizable area centralis and shows no ipsilateral retinal projections except to the suprachiasmatic nucleus. In both species, the extension of the monocular visual field and of the dorsal region of binocular overlap as well...
Biological research, 1995
The self-organization of neurotopies where neural connections follow Hebbian dynamics is framed i... more The self-organization of neurotopies where neural connections follow Hebbian dynamics is framed in terms of linear operator theory. A general and exact equation describing the time evolution of the overall synaptic strength connecting two neural laminae is derived. This linear matricial equation, which is similar to the equations used to describe oscillating systems in physics, is modified by the introduction of non-linear terms, in order to capture self-organizing (or auto-organizing) processes. The behavior of a simple and small system, that contains a non-linearity that mimics a metabolic constraint, is analyzed by computer simulations. The emergence of a simple "order" (or degree of organization) in this low-dimensionality model system is discussed.
We introduce a new approach for Gaussianity testing using the envelope of a signal and its coeffi... more We introduce a new approach for Gaussianity testing using the envelope of a signal and its coefficient of variation. The envelope of a Gaussian signal follows the Rayleigh distribution, and given that the coefficient of variation of the Rayleigh distribution is invariant, the envelope of Gaussian noise's coefficient of variation is a universal constant and can be exploited as a discriminating statistic. The main application of this approach is to detect the Gaussianity of time series. However, the coefficient of variation of the envelope is also a measure of amplitude modulation patterns that captures the structure of the Fourier phase profile, making it a useful parameter to differentiate types of non-Gaussianity and for signal classification.
Journal of Neuroscience, 2006
Biological research, 1995
We propose that to understand the biological and neurophysiological processes that give rise to h... more We propose that to understand the biological and neurophysiological processes that give rise to human mental phenomena it is necessary to consider them as behavioral relational phenomena. In particular, we propose that: a) these phenomena take place in the relational manner of living that human language constitutes, and b) that they arise as recursive operations in such behavioral domain. Accordingly, we maintain that these phenomena do not take place in the brain, nor are they the result of a unique operation of the human brain, but arise with the participation of the brain as it generates the behavioral relational dynamics that constitutes language.
Magister en Biofísica MédicaLa clasificación de potenciales de acción generados por las neuronas ... more Magister en Biofísica MédicaLa clasificación de potenciales de acción generados por las neuronas es un problema complejo y recurrente en el análisis de datos neuroeléctricos. Los métodos de clasificación actuales se basan en escoger parámetros de clasificación que representen las características de cada espiga con un número reducido de coeficientes. Esta tesis propone utilizar los coeficientes de la transformada de wavelet discreta (DWT) como parámetros de clasificación. Los coeficientes DWT son ortogonales, de cómputo rápido y cuantifican componentes localizados de frecuencia. La eficiencia de la clasificación basada en coeficientes DWT ( wavelet-based spike classification WSC) de las espigas fue comparada con resultados obtenidos con coeficientes de análisis de componentes principales (PCA) y un método de reconocimiento de patrones publicado como método RFS ( reduced feature set ). En un tren de datos artificial ruidoso, el método WSC demostró mayor capacidad para discriminar entre espigas muy similares que los métodos PCA y RFS. Estos resultados fueron publicados en el Journal of Neuroscience Methods. También se mostró la utilidad del método WSC analizando trenes de espigas multiunitarios ruidosos registrados en tectum de paloma. Se discuten las ventajas del uso del método WSC sobre el PCA y el RFS. Se analiza la actual implementación del método WSC, y se proponen mejoras importantes, basándose en los avances más modernos de la adquisición y análisis de registros neuroeléctricos
Artificial Life IX, 2004
The work of Robert Rosen, related to metabolic networks called (MR) systems is reviewed and clari... more The work of Robert Rosen, related to metabolic networks called (MR) systems is reviewed and clarified. We study the algebraic formulation of (M,R) systems particularly the mapping , which encapsulates Rosen's solution to the problem of metabolic closure and infinite regress. We construct an arithmetical example of an (MR) system and also an (MR) system based on a three-step minimal metabolism.
espanolEntrevista realizada por un sociologo y cineasta a un especialista en la neurobiologia de ... more espanolEntrevista realizada por un sociologo y cineasta a un especialista en la neurobiologia de la percepcion visual, la que busca construir transdiciplinariamente una descripcion sobre los problemas de la cognicion y percepcion del 3D. En ella el entrevistador remite al arte y los desafios de la tecnologia 3D y su audiencia, mientras que las respuestas son planteadas desde el punto de vista de lo que la neurociencia puede aportar al arte. EnglishInterview by a sociologist and filmmaker to a specialist in the neurobiology of visual perception, looking in transdisciplinary form build a description of the problems of cognition and perception of 3D. Here the interviewer refers to the art and challenges of 3D technology and its audience, while responses are raised from the point of view of what neuroscience can contribute to art.
From the many attempts to produce a conceptual framework for the organization of living systems, ... more From the many attempts to produce a conceptual framework for the organization of living systems, the notions of (M,R) systems and Autopoiesis stand out for their rigor, their presupposition of the circularity of metabolism, and the new epistemologies that they imply. From their inceptions, these two notions have been essentially disconnected because each has defined its own language and tools. Here we demonstrate the existence of a deep conceptual link between (M,R) systems and Autopoietic systems. But in order to prove such connection we will have to explain with detail the conceptual framework of both models. The case of (M,R) systems is rather difficult as its structure was never explained in detail by Rosen. We will give our understanding of Rosen model (see Organizational invariance and metabolic closure: analysis in terms of (M,R) systems. Journal of Theoretical Biology 238 (4): 949-961. (2006)). Also the history of the notion of Autopoietic systems (created by Humberto Matura...
European Journal of Anaesthesiology, 2014
Soft Computing …, 2002
... Computing with Autopoietic and (M, R) System Juan Carlos Letelier, Gonzalo Mann, Jorge Mpodoz... more ... Computing with Autopoietic and (M, R) System Juan Carlos Letelier, Gonzalo Mann, Jorge Mpodozis and Jorge Soto-Andrade Departamento de ... Instead of having a replication map DQ APs have an iteration map that defines the internal dynamics through a recursive procedure. ...
There are deep underlying similarities between Rosen's (M,R) systems as a definition of life and ... more There are deep underlying similarities between Rosen's (M,R) systems as a definition of life and the RAF sets (Reflexive Autocatalytic systems generated by a Food source) introduced by Hordijk and Steel as a way of analyzing autocatalytic sets of reactions. Using RAF concepts we have systematically explored the set of possible small idealized metabolic networks, searching for instances of (M,R) systems. This exhaustive search has shown that the central requirement of Rosen's framework, unicity of , becomes harder and harder to obtain as the network grows in size. In addition, we give an expression for operators , and in terms of RAF sets.
The origin of the human alpha rhythm has been a matter of debate since Lord Adrian attributed it ... more The origin of the human alpha rhythm has been a matter of debate since Lord Adrian attributed it to synchronous neural populations in the occipital cortex. While some authors have pointed out the Gaussian characteristics of the alpha rhythm, their results have been repeatedly disregarded in favor of Adrian’s interpretation; even though the first EEG Gaussianity reports can be traced back to the origins of EEG. Here we revisit this problem using the envelope analysis — a method that relies on the fact that the coefficient of variation of the envelope (CVE) for continuous-time zero-mean Gaussian white noise (as well as for any filtered sub-band) is equal to , thus making the CVE a fingerprint for Gaussianity. As a consequence, any significant deviation from Gaussianity is linked to synchronous neural dynamics. Low-CVE signals come from phase-locking dynamics, while mid-CVE signals constitute Gaussian noise. High-CVE signals have been linked to unsteady dynamics in populations of nonli...
NeuroImage, May 2, 2018
Traditionally, EEG is understood as originating from the synchronous activation of neuronal popul... more Traditionally, EEG is understood as originating from the synchronous activation of neuronal populations that generate rhythmic oscillations in specific frequency bands. Recently, new neuronal dynamics regimes have been identified (e.g. neuronal avalanches) characterized by irregular or arrhythmic activity. In addition, it is starting to be acknowledged that broadband properties of EEG spectrum (following a 1/f law) are tightly linked to brain function. Nevertheless, there is still no theoretical framework accommodating the coexistence of these two EEG phenomenologies: rhythmic/narrowband and arrhythmic/broadband. To address this problem, we present a new framework for EEG analysis based on the relation between the Gaussianity and the envelope of a given signal. EEG Gaussianity is a relevant assessment because if EEG emerges from the superposition of uncorrelated sources, it should exhibit properties of a Gaussian process, otherwise, as in the case of neural synchronization, deviatio...
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Papers by juan-carlos letelier