A neuromorphic model of olfactory processing and sparse coding in the Drosophila larva brain

Animal nervous systems are highly efficient in processing sensory input. The neuromorphic computing paradigm aims at the hardware implementation of neural network computations to support novel solutions for building brain-inspired computing systems. Here, we take inspiration from sensory processing in the nervous system of the fruit fly larva. With its strongly limited computational resources of <200 neurons and <1.000 synapses the larval olfactory pathway employs fundamental computations to transform broadly tuned receptor input at the periphery into an energy efficient sparse code in the central brain. We show how this approach allows us to achieve sparse coding and increased separability of stimulus patterns in a spiking neural network, validated with both software simulation and hardware emulation on mixed-signal real-time neuromorphic hardware. We verify that feedback inhibition is the central motif to support sparseness in the spatial domain, across the neuron population, while the combination of spike frequency adaptation and feedback inhibition determines sparseness in the temporal domain. Our experiments demonstrate that such small, biologically realistic neural networks, efficiently implemented on neuromorphic hardware, can achieve parallel processing and efficient encoding of sensory input at full temporal resolution

Functional Properties of Cortical Feedback Projections to the Olfactory Bulb

SummarySensory perception is not a simple feed-forward process, and higher brain areas can actively modulate information processing in “lower” areas. We used optogenetic methods to examine how cortical feedback projections affect circuits in the first olfactory processing stage, the olfactory bulb. Selective activation of back projections from the anterior olfactory nucleus/cortex (AON) revealed functional glutamatergic synaptic connections on several types of bulbar interneurons. Unexpectedly, AON axons also directly depolarized mitral cells (MCs), enough to elicit spikes reliably in a time window of a few milliseconds. MCs received strong disynaptic inhibition, a third of which arises in the glomerular layer. Activating feedback axons in vivo suppressed spontaneous as well as odor-evoked activity of MCs, sometimes preceded by a temporally precise increase in firing probability. Our study indicates that cortical feedback can shape the activity of bulbar output neurons by enabling precisely timed spikes and enforcing broad inhibition to suppress background activity

High-frequency neural oscillations and visual processing deficits in schizophrenia

Visual information is fundamental to how we understand our environment, make predictions, and interact with others. Recent research has underscored the importance of visuo-perceptual dysfunctions for cognitive deficits and pathophysiological processes in schizophrenia. In the current paper, we review evidence for the relevance of high frequency (beta/gamma) oscillations towards visuo-perceptual dysfunctions in schizophrenia. In the first part of the paper, we examine the relationship between beta/gamma band oscillations and visual processing during normal brain functioning. We then summarize EEG/MEG-studies which demonstrate reduced amplitude and synchrony of high-frequency activity during visual stimulation in schizophrenia. In the final part of the paper, we identify neurobiological correlates as well as offer perspectives for future research to stimulate further inquiry into the role of high-frequency oscillations in visual processing impairments in the disorder

Morpho-physiological analysis of interneuronal populations in the rat piriform cortex before and after kindling induced epilepsy

The piriform cortex (PC) is involved in olfactory sensory processing, associative learning tasks and is highly seizurogenic. Understanding how interneurons participate in these behaviours, especially their contribution in epileptogenic mechanisms, is hampered by an incomplete understanding of their functional and morphological diversity. The hypothesis in this work is that kindling-induced epilepsy alters the firing properties of PC interneuronal populations. Altered/impaired interneuronal firing could lead to abnormal processing in the PC and epileptogenesis. Therefore it was important to first identify and describe interneuronal morpho-functional properties in the unkindled brain and then to assess the electrophysiological parameters following kindling. Based on interneuronal calcium-binding protein content, immunohistochemical analysis of PC showed that the four distinct interneuronal populations (calretinin, calbindin, parvalbumin, and parvalbumin/calbindin containing interneurons) had distinct layer localizations, preferred dendritic arborization patterns and specific innervations onto interneurons and pyramidal cells. Whole cell patch-clamp recordings of PC interneuronal populations indicated a large heterogeneity of firing patterns that could be classified into five main patterns ranging from non-adapting very high frequency (NAvHF) to various degrees of spiking adaptation: adapting high frequency (AHF), adapting low frequency (ALF), strongly adapting low frequency (sALF), and weakly adapting low frequency (wALF). This high firing variability in the PC suggests that different interneuronal populations might have distinct functional means to control and regulate the olfactory network processing, memory coding and/or generation of oscillatory activities. However, after kindling, NAvHF and wALF firing patterns were absent. These changes were correlated to an increased K+ current in multipolar cells. This result was confirmed by quantitative real time polymerase chain reaction (QPCR) and immunohistochemistry studies indicating an increased expression of a voltage-gated potassium channel Kv1.6 after kindling. Thus, kindling-induced alteration of interneuronal firing properties, especially the absence of NAvHF firing behaviour, might reduce the efficacy of inhibition on the pyramidal cells leading to increased disinhibition and/or altered oscillatory activities in the PC. Overall, this work provides a morpho-functional analysis of PC interneuronal populations indicating a high complexity of innervation and firing behaviours. It also shows for the first time that kindling induces alterations of interneuronal firing patterns that might be responsible for epileptogenesis in this area

Neuronal inputs and outputs of aging and longevity.

An animal's survival strongly depends on its ability to maintain homeostasis in response to the changing quality of its external and internal environment. This is achieved through intracellular and intercellular communication within and among different tissues. One of the organ systems that plays a major role in this communication and the maintenance of homeostasis is the nervous system. Here we highlight different aspects of the neuronal inputs and outputs of pathways that affect aging and longevity. Accordingly, we discuss how sensory inputs influence homeostasis and lifespan through the modulation of different types of neuronal signals, which reflects the complexity of the environmental cues that affect physiology. We also describe feedback, compensatory, and feed-forward mechanisms in these longevity-modulating pathways that are necessary for homeostasis. Finally, we consider the temporal requirements for these neuronal processes and the potential role of natural genetic variation in shaping the neurobiology of aging

VOLTAGE-SENSITIVE DYE IMAGING OF RAT PIRIFORM CORTEX BEFORE AND AFTER KINDLING

To determine the role of inhibitory cells in the propagation of activity in the rat piriform cortex (PC) before and after kindling, we used voltage-sensitive dye imaging technique to follow the membrane potential changes in three layers of the PC after stimulating the lateral olfactory tract (LOT) with beta and gamma frequencies. Stimulation of LOT was followed by propagation of excitatory (in layer II) and inhibitory responses (in layer III) through the PC. Decreasing the inhibition by applying gabazine, a GABAa- receptor antagonist, decreased the inhibitory responses and increased the excitatory responses in the control rats; however, it did not affect the excitatory and inhibitory responses in the kindled rats. Furthermore, cutting the slice below the layer II decreased the both responses. Thus, we concluded that disinhibition of layer III intemeurons is necessary for principle cells firing and kindling can result in seizures by increasing disinhibition in layer III of PC

Role of the AMPA receptor auxiliary subunit CKAMP44 in the olfactory bulb

The olfactory bulb is the first processing station of olfactory information. Mitral and tufted cells, which are the output neurons of the olfactory bulb, receive input from olfactory sensory neurons. The activity of the output neurons is controlled by inhibitory periglomerular and granule cells. Periglomerular cells also receive excitatory input from olfactory sensory neurons and provide feedforward inhibition. Little is known about how AMPA receptor number and function in synapses of periglomerular cells is controlled. It is also not well understood how changes in AMPA receptor number of periglomerular cells affect the olfactory bulb network. Here I show with fluorescence in situ hybridization that the AMPA receptor auxiliary protein CKAMP44 is expressed at high levels in periglomerular cells, but not or only at low levels in other neurons of the olfactory bulb. With ex vivo slice electrophysiology I found that deletion of CKAMP44 decreases AMPA receptor-mediated currents in periglomerular cells. This in turn reduces the inhibition from periglomerular cells onto mitral cells and increases mitral cell activity upon olfactory sensory neuron activation. Data from a computational model of olfactory bulb neuron activity corroborate these findings and indicate that feedforward inhibition from periglomerular cells reduces mitral cell activity in particular during weak or intermediate excitation from olfactory sensory neurons. Behavior experiments showed that the function of the olfactory bulb, at least concerning the differentiation of odors, is not affected by decreased periglomerular cell excitability. Whether other odor functions (e.g. detection threshold) and in vivo network activity is affected remains to be investigated