Flexible and accurate inference and learning for deep generative models

We introduce a new approach to learning in hierarchical latent-variable generative models called the "distributed distributional code Helmholtz machine", which emphasises flexibility and accuracy in the inferential process. In common with the original Helmholtz machine and later variational autoencoder algorithms (but unlike adverserial methods) our approach learns an explicit inference or "recognition" model to approximate the posterior distribution over the latent variables. Unlike in these earlier methods, the posterior representation is not limited to a narrow tractable parameterised form (nor is it represented by samples). To train the generative and recognition models we develop an extended wake-sleep algorithm inspired by the original Helmholtz Machine. This makes it possible to learn hierarchical latent models with both discrete and continuous variables, where an accurate posterior representation is essential. We demonstrate that the new algorithm outperforms current state-of-the-art methods on synthetic, natural image patch and the MNIST data sets

Neural networks with small-world topology are optimal for encoding based on spatiotemporal patterns of spikes

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Scale-free statistics of neuronal assemblies predict learning performance

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Septal projections to the nucleus incertus in the rat: Bidirectional pathways for modulation of hippocampal function

Projections from the nucleus incertus (NI) to the septum have been implicated in the modulation of hippocampal theta rhythm. In this study we describe a previously uncharacterized projection from the septum to the NI, which may provide feedback modulation of the ascending circuitry. Fluorogold injections into the NI resulted in retrograde labeling in the septum that was concentrated in the horizontal diagonal band and areas of the posterior septum including the septofimbrial and triangular septal nuclei. Double-immunofluorescent staining indicated that the majority of NI-projecting septal neurons were calretinin-positive and some were parvalbumin-, calbindin-, or glutamic acid decarboxylase (GAD)−67-positive. Choline acetyltransferase-positive neurons were Fluorogold-negative. Injection of anterograde tracers into medial septum, or triangular septal and septofimbrial nuclei, revealed fibers descending to the supramammillary nucleus, median raphe, and the NI. These anterogradely labeled varicosities displayed synaptophysin immunoreactivity, indicating septal inputs form synapses on NI neurons. Anterograde tracer also colocalized with GAD-67-positive puncta in labeled fibers, which in some cases made close synaptic contact with GAD-67-labeled NI neurons. These data provide evidence for the existence of an inhibitory descending projection from medial and posterior septum to the NI that provides a "feedback loop" to modulate the comparatively more dense ascending NI projections to medial septum and hippocampus. Neural processes and associated behaviors activated or modulated by changes in hippocampal theta rhythm may depend on reciprocal connections between ascending and descending pathways rather than on unidirectional regulation via the medial septum.Grant sponsors: Fundación Alicia Koplowitz Fellowship (to A.M.S.P.), CAPES-Brasil Bex - 4494/09-1 (to F.N.S.) and 4496/09-4 (to C.W.P.) and Fapitec edital #01/08 (to F.N.S.), FIS-isciiiPI10/01399 (to J.S.), National Health and Medical Research Council of Australia - 520299 (to S.M.), 509246, 1005985, and 1005988 (to A.L.G.), the Florey Foundation (to S.M., A.L.G.), Besen Family Foundation (to A.L.G.) and a NEUREN project, FP7-PEOPLE-IRSES PIRSES-GA-2012-318997 (to A.L.G., F.E.O.-B.)

Comparative local analysis of metabolites, lipids and proteins in intact fish tissues by LAESI mass spectrometry

Direct mass spectrometric analysis of animal tissues is an emerging field enabled by recent developments in ambient ion sources. Label-free in situ analysis of metabolites, lipids, and peptides/proteins from intact tissues in whole fish specimens of different gender and age were performed by laser ablation electrospray ionization (LAESI) mass spectrometry (MS). Hypertrophied glandular tissue (gill gland) of adult male Aphyocharax anisitsi (bloodfin tetra) was compared with gill tissues in females of the same species. Comparison of a large number of sample-specific ions was aided by a multivariate statistical method based on orthogonal projections to latent structures discriminant analysis. More than 200 different ions were detected in the mass spectra corresponding to primary metabolites, hormones, lipids and peptides/proteins. The gill tissues of the sexually mature males exhibited multiply charged ions in the 6+ to 10+ charge states corresponding to a protein with a molecular weight of 11 380 Da. This protein was present only in the mature male gill glands but absent in the corresponding area of the female and immature male specimens. An additional nine proteins were detected by LAESI-MS in both the male and female gill tissues

The topology of connections between rat prefrontal, motor and sensory cortices

The connections of prefrontal cortex (PFC) were investigated in the rat brain to determine the order and location of input and output connections to motor and somatosensory cortex. Retrograde (100 nl Fluoro-Gold) and anterograde (100 nl Biotinylated Dextran Amines, BDA; Fluorescein and Texas Red) neuronanatomical tracers were injected into the subdivisions of the PFC (prelimbic, ventral orbital, ventrolateral orbital, dorsolateral orbital) and their projections studied. We found clear evidence for organized input projections from the motor and somatosensory cortices to the PFC, with distinct areas of motor and cingulate cortex projecting in an ordered arrangement to the subdivisions of PFC. As injection location of retrograde tracer was moved from medial to lateral in PFC, we observed an ordered arrangement of projections occurring in sensory-motor cortex. There was a significant effect of retrograde injection location on the position of labelled cells occurring in sensory-motor cortex (dorsoventral, anterior-posterior and mediolateral axes p < 0.001). The arrangement of output projections from PFC also displayed a significant ordered projection to sensory-motor cortex (dorsoventral p < 0.001, anterior-posterior p = 0.002 and mediolateral axes p < 0.001)

Differences in anatomical connections across distinct areas in the rodent prefrontal cortex

Prefrontal cortex (PFC) network structure is implicated in a number of complex higher-order functions and with a range of neurological disorders. It is therefore vital to our understanding of PFC function to gain an understanding of its underlying anatomical connectivity. Here, we injected Fluoro-Gold and Fluoro-Ruby into the same sites throughout rat PFC. Tracer injections were applied to two coronal levels within the PFC (anterior +4.7mm to bregma and posterior +3.7mm to bregma). Within each coronal level, tracers were deposited at sites separated by approximately 1mm and located parallel to the medial and orbital surface of the cortex. We found that both Fluoro-Gold and Fluoro-Ruby injections produced prominent labelling in temporal and sensory-motor cortex. Fluoro-Gold produced retrograde labelling and Fluoro-Ruby largely produced anterograde labelling. Analysis of the location of these connections within temporal and sensory-motor cortex revealed a consistent topology (as the sequence of injections was followed mediolaterally along the orbital surface of each coronal level). At the anterior coronal level, injections produced a similar topology to that seen in central PFC in earlier studies from our laboratory (i.e. comparing equivalently located injections employing the same tracer), this was particularly prominent within temporal cortex. However, at the posterior coronal level this pattern of connections differed significantly, revealing higher levels of reciprocity, in both temporal cortex and sensory-motor cortex. Our findings indicate changes in the relative organization of connections arising from posterior in comparison to anterior regions of PFC, which may provide a basis to determine how complex processes are organized

Practice Makes Imperfect: Restorative Effects of Sleep on Motor Learning

Emerging evidence suggests that sleep plays a key role in procedural learning, particularly in the continued development of motor skill learning following initial acquisition. We argue that a detailed examination of the time course of performance across sleep on the finger-tapping task, established as the paradigm for studying the effect of sleep on motor learning, will help distinguish a restorative role of sleep in motor skill learning from a proactive one. Healthy subjects rehearsed for 12 trials and, following a night of sleep, were tested. Early training rapidly improved speed as well as accuracy on pre-sleep training. Additional rehearsal caused a marked slow-down in further improvement or partial reversal in performance to observed levels below theoretical upper limits derived on the basis of early pre-sleep rehearsal. This decrement in learning efficacy does not occur always, but if and only if it does, overnight sleep has an effect in fully or partly restoring the efficacy and actual performance to the optimal theoretically achieveable level. Our findings re-interpret the sleep-dependent memory enhancement in motor learning reported in the literature as a restoration of fatigued circuitry specialized for the skill. In providing restitution to the fatigued brain, sleep eliminates the rehearsal-induced synaptic fatigue of the circuitry specialized for the task and restores the benefit of early pre-sleep rehearsal. The present findings lend support to the notion that latent sleep-dependent enhancement of performance is a behavioral expression of the brain's restitution in sleep