Receptive field atlas and related CNN models

In this paper we demonstrate the potential of the cellular nonlinear/neural network paradigm (CNN) that of the analogic cellular computer architecture (called CNN Universal Machine | CNN-UM) in modeling different parts and aspects of the nervous system. The structure of the living sensory systems and the CNN share a lot of features in common: local interconnections ("receptive field architecture"), nonlinear and delayed synapses for the processing tasks, the potentiality of feedback and using the advantages of both the analog and logic signal-processing mode. The results of more than ten years of cooperative work of many engineers and neurobiologists have been collected in an atlas: what we present here is a kind of selection from these studies emphasizing the exibility of the CNN computing: visual, tactile and auditory modalities are concerned

Functional mechanisms of stimulus-specific adaptation in neurons of the auditory thalamus and its cortical modulation

[ES] Nuestra hipótesis general de trabajo es que la detección de la novedad es un principio básico de organización funcional del sistema auditivo y que el potencial de disparidad (MMN) y las neuronas detectoras de sonidos novedosos son expresiones distintas pero, correlacionadas, de la activación de este sistema detector de la novedad. El conocimiento sobre los mecanismos neurológicos implicados en la detección de la novedad en el sistema auditivo pasa por establecer las posibles relaciones funcionales entre estas neuronas y el potencial de disparidad (MMN). Para ello, es fundamental caracterizar la naturaleza de las respuestas de estas mismas neuronas en los diferentes niveles de la vía auditiva. Puesto que desconocemos en gran medida los detalles de este tipo de adaptación en el cuerpo geniculado medial y que los estudios existentes son en gran medida discutibles (Anderson et al., 2009; Ulanovsky et al., 2003; Yu et al., 2009), pensamos que es necesario un estudio detallado de caracterización fisiológica de la adaptación específica al estímulo en este centro talámico.[EN] Our general hypothesis is that the work of novelty detection is a basic principle of functional organization of the auditory system and the potential for disparity (MMN) and the novel sound detector neurons are different expressions, but correlated, activation of this novelty detection system. Knowledge about the neural mechanisms involved in novelty detection in the auditory system involves establishing the possible functional relationships between these neurons and the potential for disparity (MLM). To do this, it is essential to characterize the nature of the responses of these same neurons at different levels of the auditory pathway. Since the largely unknown details of this type of adaptation in the medial geniculate body and that existing studies are largely debatable (Anderson et al., 2009; Ulanovsky et al., 2003, Yu et al., 2009) we think that we need a detailed study of the physiological characterization of specific adaptation thalamic stimulation in the center

Stimulus-specific adaptation and deviance detection in the inferior colliculus

[EN] Deviancy detection in the continuous flow of sensory information into the central nervous system is of vital importance for animals. The task requires neuronal mechanisms that allow for an efficient representation of the environment by removing statistically redundant signals. Recently, the neuronal principles of auditory deviance detection have been approached by studying the phenomenon of stimulus-specific adaptation (SSA). SSA is a reduction in the responsiveness of a neuron to a common or repetitive sound while the neuron remains highly sensitive to rare sounds (Ulanovsky et al., 2003). This phenomenon could enhance the saliency of unexpected, deviant stimuli against a background of repetitive signals. SSA shares many similarities with the evoked potential known as the “mismatch negativity,” (MMN) and it has been linked to cognitive process such as auditory memory and scene analysis (Winkler et al., 2009) as well as to behavioral habituation (Netser et al., 2011). Neurons exhibiting SSA can be found at several levels of the auditory pathway, from the inferior colliculus (IC) up to the auditory cortex (AC). In this review, we offer an account of the state-of-the art of SSA studies in the IC with the aim of contributing to the growing interest in the single-neuron electrophysiology of auditory deviance detection. The dependence of neuronal SSA on various stimulus features, e.g., probability of the deviant stimulus and repetition rate, and the roles of the AC and inhibition in shaping SSA at the level of the IC are addressed

Processing Submillisecond Timing Differences in a Model Electrosensory System

Perception of sensory cues requires peripheral encoding followed by extraction of behaviorally relevant signal components by central neurons. Some sensory systems can detect temporal information with submillisecond accuracy, despite these signals occurring faster than the approximately 1 ms timescale of neuronal firing. In sound localization, the best studied example of this phenomenon, there are at least two distinct mechanisms for detecting submillisecond timing differences, indicating that multiple solutions to this fundamental problem exist. I investigated mechanisms for processing submillisecond timing differences by studying electrosensory processing in a time coding expert, mormyrid weakly electric fish, which can detect submillisecond differences in the duration of electric signals. First, I measured responses of peripheral receptors to stimuli of different durations. I found that each unit responded preferentially to longer stimuli, but with response thresholds that varied among units within the behaviorally relevant range of durations. This variability establishes a population code operating at near threshold intensities in which the number and identity of responding receptors represents duration. At higher stimulus intensities all units respond independent of duration, rendering the population code obsolete. Importantly, peripheral receptors respond either to the start or end of a signal. Thus, stimulus duration is also represented by a temporal code, as a difference in spike times between receptors. Next, I investigated the central mechanism for detection of submillisecond spike time differences by recording from time comparator neurons (Small Cells) in the midbrain. Recording from Small Cells is challenging because their somas are small and relatively inaccessible. I therefore designed a novel method using retrograde labeling to directly visualize and record from Small Cells in vivo. I showed that patterns of duration tuning vary among Small Cells due to a combination of blanking inhibition corresponding to one edge of a stimulus and variably delayed excitation corresponding to one or both edges of a stimulus. Other circuits that detect submillisecond timing differences rely either on precisely-timed inhibition or delay-line coincidence detection. I demonstrate a novel mechanism by which mormyrids combine delay-line coincidence detection with precisely-timed blanking inhibition to establish diverse patterns of duration tuning among a population of time comparators

Mechanisms of Odor-Tracking: Multiple Sensors for Enhanced Perception and Behavior

Early in evolution, the ability to sense and respond to changing environments must have provided a critical survival advantage to living organisms. From bacteria and worms to flies and vertebrates, sophisticated mechanisms have evolved to enhance odor detection and localization. Here, we review several modes of chemotaxis. We further consider the relevance of a striking and recurrent motif in the organization of invertebrate and vertebrate sensory systems, namely the existence of two symmetrical olfactory sensors. By combining our current knowledge about the olfactory circuits of larval and adult Drosophila, we examine the molecular and neural mechanisms underlying robust olfactory perception and extend these analyses to recent behavioral studies addressing the relevance and function of bilateral olfactory input for gradient detection. Finally, using a comparative theoretical approach based on Braitenberg's vehicles, we speculate about the relationships between anatomy, circuit architecture and stereotypical orientation behaviors

Decoding the Brain: Neural Representation and the Limits of Multivariate Pattern Analysis in Cognitive Neuroscience

Since its introduction, multivariate pattern analysis (MVPA), or “neural decoding”, has transformed the field of cognitive neuroscience. Underlying its influence is a crucial inference, which we call the Decoder’s Dictum: if information can be decoded from patterns of neural activity, then this provides strong evidence about what information those patterns represent. Although the Dictum is a widely held and well-motivated principle in decoding research, it has received scant philosophical attention. We critically evaluate the Dictum, arguing that it is false: decodability is a poor guide for revealing the content of neural representations. However, we also suggest how the Dictum can be improved on, in order to better justify inferences about neural representation using MVPA

Peripheral and Central Mechanisms of Temporal Pattern Recognition

Encoding information into the timing patterns of action potentials, or spikes, is a strategy used broadly in neural circuits. This type of coding scheme requires downstream neurons to be sensitive to the temporal patterns of presynaptic inputs. Indeed, neurons with temporal filtering properties have been found in a wide range of sensory pathways. However, how such response properties arise was previously not well understood. The goal of my dissertation research has been to elucidate how temporal filtering by single neurons contributes to the behavioral ability to recognize timing patterns in communication signals. I have addressed this question using mormyrid weakly electric fish, which vary the time intervals between successive electric pulses to communicate. Fish detect these signals with sensory receptors in their skin. In the majority of species, these receptors fire a single spike in response to each electric pulse. Spiking receptors faithfully encode the interpulse intervals in communication signals into interspike intervals, which are then decoded by interval-selective midbrain neurons. Using in vivo intracellular recordings from awake fish during sensory stimulation, I found that short-term depression and temporal summation play important roles in establishing single-neuron interval selectivity. Moreover, the combination of short-term depression and temporal summation in the circuit resulted in greater diversity of interval tuning properties across the population of neurons, which would increase the population’s ability to detect temporally patterned communication signals. Indeed, I found that the responses of single interval-selective neurons were sensitive to subtle variation in the timing patterns of a specific communication display produced by different individuals. A subset of mormyrid species has sensory receptors that produce spontaneously oscillating potentials. How the electrosensory system of these species established sensitivity to temporally patterned communication signals was completely unknown. Using in vivo extracellular recordings, I demonstrated that these receptors encode sensory stimuli into phase resets, which is the first clear instance of information coding by oscillatory phase reset. Furthermore, the ongoing oscillations conferred enhanced sensitivity to fast temporal patterns that are only found in the communication signals of a large group of fish. Behavioral playback experiments provided further support for the hypothesis that oscillating receptors are specialized for detecting communication signals produced by a group of conspecifics, which is a novel role for a sensory receptor. These findings demonstrate that temporal pattern sensitivity, which was previously thought to be a central processing problem, can also arise from peripheral filtering through a novel oscillatory phase reset mechanism

Engineering derivatives from biological systems for advanced aerospace applications

The present study consisted of a literature survey, a survey of researchers, and a workshop on bionics. These tasks produced an extensive annotated bibliography of bionics research (282 citations), a directory of bionics researchers, and a workshop report on specific bionics research topics applicable to space technology. These deliverables are included as Appendix A, Appendix B, and Section 5.0, respectively. To provide organization to this highly interdisciplinary field and to serve as a guide for interested researchers, we have also prepared a taxonomy or classification of the various subelements of natural engineering systems. Finally, we have synthesized the results of the various components of this study into a discussion of the most promising opportunities for accelerated research, seeking solutions which apply engineering principles from natural systems to advanced aerospace problems. A discussion of opportunities within the areas of materials, structures, sensors, information processing, robotics, autonomous systems, life support systems, and aeronautics is given. Following the conclusions are six discipline summaries that highlight the potential benefits of research in these areas for NASA's space technology programs