51 research outputs found
A diagrammatic approach to study the information transfer in weakly non-linear channels
In a recent work we have introduced a novel approach to study the effect of
weak non-linearities in the transfer function on the information transmitted by
an analogue channel, by means of a perturbative diagrammatic expansion. We
extend here the analysis to all orders in perturbation theory, which allows us
to release any constraint concerning the magnitude of the expansion parameter
and to establish the rules to calculate easily the contribution at any order.
As an example we explicitly compute the information up to the second order in
the non-linearity, in presence of random gaussian connectivities and in the
limit when the output noise is not small. We analyze the first and second order
contributions to the mutual information as a function of the non-linearity and
of the number of output units. We believe that an extensive application of our
method via the analysis of the different contributions at distinct orders might
be able to fill a gap between well known analytical results obtained for linear
channels and the non trivial treatments which are required to study highly
non-linear channels.Comment: 17 pages, 3 figure
A replica free evaluation of the neuronal population information with mixed continuous and discrete stimuli: from the linear to the asymptotic regime
Recent studies have explored theoretically the ability of populations of
neurons to carry information about a set of stimuli, both in the case of purely
discrete or purely continuous stimuli, and in the case of multidimensional
continuous angular and discrete correlates, in presence of additional quenched
disorder in the distribution. An analytical expression for the mutual
information has been obtained in the limit of large noise by means of the
replica trick. Here we show that the same results can actually be obtained in
most cases without the use of replicas, by means of a much simpler expansion of
the logarithm. Fitting the theoretical model to real neuronal data, we show
that the introduction of correlations in the quenched disorder improves the
fit, suggesting a possible role of signal correlations-actually detected in
real data- in a redundant code. We show that even in the more difficult
analysis of the asymptotic regime, an explicit expression for the mutual
information can be obtained without resorting to the replica trick despite the
presence of quenched disorder, both with a gaussian and with a more realistic
thresholded-gaussian model. When the stimuli are mixed continuous and discrete,
we find that with both models the information seem to grow logarithmically to
infinity with the number of neurons and with the inverse of the noise, even
though the exact general dependence cannot be derived explicitly for the
thresholded gaussian model. In the large noise limit lower values of
information were obtained with the thresholded-gaussian model, for a fixed
value of the noise and of the population size. On the contrary, in the
asymptotic regime, with very low values of the noise, a lower information value
is obtained with the gaussian model.Comment: 34 pages, 5 figure
Replica symmetric evaluation of the information transfer in a two-layer network in presence of continuous+discrete stimuli
In a previous report we have evaluated analytically the mutual information
between the firing rates of N independent units and a set of multi-dimensional
continuous+discrete stimuli, for a finite population size and in the limit of
large noise. Here, we extend the analysis to the case of two interconnected
populations, where input units activate output ones via gaussian weights and a
threshold linear transfer function. We evaluate the information carried by a
population of M output units, again about continuous+discrete correlates. The
mutual information is evaluated solving saddle point equations under the
assumption of replica symmetry, a method which, by taking into account only the
term linear in N of the input information, is equivalent to assuming the noise
to be large. Within this limitation, we analyze the dependence of the
information on the ratio M/N, on the selectivity of the input units and on the
level of the output noise. We show analytically, and confirm numerically, that
in the limit of a linear transfer function and of a small ratio between output
and input noise, the output information approaches asymptotically the
information carried in input. Finally, we show that the information loss in
output does not depend much on the structure of the stimulus, whether purely
continuous, purely discrete or mixed, but only on the position of the threshold
nonlinearity, and on the ratio between input and output noise.Comment: 19 pages, 4 figure
A theoretical model of neuronal population coding of stimuli with both continuous and discrete dimensions
In a recent study the initial rise of the mutual information between the
firing rates of N neurons and a set of p discrete stimuli has been analytically
evaluated, under the assumption that neurons fire independently of one another
to each stimulus and that each conditional distribution of firing rates is
gaussian. Yet real stimuli or behavioural correlates are high-dimensional, with
both discrete and continuously varying features.Moreover, the gaussian
approximation implies negative firing rates, which is biologically implausible.
Here, we generalize the analysis to the case where the stimulus or behavioural
correlate has both a discrete and a continuous dimension. In the case of large
noise we evaluate the mutual information up to the quadratic approximation as a
function of population size. Then we consider a more realistic distribution of
firing rates, truncated at zero, and we prove that the resulting correction,
with respect to the gaussian firing rates, can be expressed simply as a
renormalization of the noise parameter. Finally, we demonstrate the effect of
averaging the distribution across the discrete dimension, evaluating the mutual
information only with respect to the continuously varying correlate.Comment: 20 pages, 10 figure
Predictors of Early Thrombotic Events in Adult Patients with Acute Myeloid Leukemia: A Real-World Experience
Information regarding the incidence and the prognostic impact of thrombotic events (TE) in non-promyelocytic acute myeloid leukemia (AML) is sparse. Although several risk factors associated with an increased risk of TE development have been recognized, we still lack universally approved guidelines for identification and management of these complications. We retrospectively analyzed 300 consecutive patients with newly diagnosed AML. Reporting the incidence of venous TE (VTE) and arterial TE (ATE) was the primary endpoint. Secondarily, we evaluated baseline patient- and disease-related characteristics with a possible influence of VTE-occurrence probability. Finally, we evaluated the impact of TE on survival. Overall, the VTE incidence was 12.3% and ATE incidence was 2.3%. We identified three independent predictors associated with early-VTE: comorbidities (p = 0.006), platelets count >50x10e9/L (p = 0.006), and a previous history of VTE (p = 0.003). Assigning 1 point to each variable, we observed an overall cumulative incidence of VTE of 18.4% in the high-risk group
(>2 points) versus 6.4% in the low-risk group (0–1 point), log-rank = 0.002. Overall, ATE, but not VTE, was associated with poor prognosis (p < 0.001). In conclusion, TE incidence in AML patients is not negligible. We proposed an early-VTE risk score that could be useful for a proper management of VTE prophylaxis
Understanding Factors Associated With Psychomotor Subtypes of Delirium in Older Inpatients With Dementia
Population coding of continuous+discrete stimuli: experimental evidence and theoretical modelling
Análisis del grado de implementación de las TIC en la práctica docente del profesorado de las especialidades técnico-profesionales de la Academia Politécnica Naval de Chile
his document is part of the implementation of the PMI Performance Agreement
FPN whose main objective is "To promote the professional technical training imparted in the
Naval Polytechnic Academy (APN) of Chile, through the improvement of teaching, access to
information and the development of quality assurance mechanisms that tend to curricular innovation
". his paper presents the analysis of the degree of implementation of ICT in teaching
practice of teachers in the area of Sea People. Among the most outstanding results is a low level
of integration of ICT in the teaching and learning process, a consequence of a basic instrumental
management of ICT and a little update regarding participatory active methodological strategies. he conclusion drawn from the analysis carried out is that for ICTs not to be kept out of the teaching
and learning process it is essential, together with an improvement in their use and application,
to train in methodological teaching and innovation of the teaching staf.Este documento es parte de la implementación del PMI FPN 1501, cuyo objetivo
principal es "Promover la capacitación técnica profesional impartida en la Academia Politécnica
Naval (APN) de Chile, mediante la mejora de la enseñanza, el acceso a la información y el desarrollo
de mecanismos de calidad aseguramiento que tiende a la innovación curricular ". Este
trabajo presenta el análisis del grado de implementación de las TIC en la práctica docente del
profesorado del área de Gente de Mar. Entre los resultados más destacados se evidencia un bajo
nivel de integración de las TIC en el proceso de enseñanza y aprendizaje, consecuencia de un básico
manejo instrumental de las TIC y una poca actualización respecto a estrategia metodológica
activo participativa. La conclusión que se extrae del análisis realizado es que para que las TIC no
se mantengan al margen del proceso de enseñanza y aprendizaje es fundamental, junto a un perfeccionamiento
en su uso y aplicación, una formación en didáctica e innovación metodológicas
del profesorado
- …