neural coding refers to the processes by which external stimuli are translated into neural activity and represented in a manner that drives behavior. Research in this field aims to elucidate these processes by identif...
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neural coding refers to the processes by which external stimuli are translated into neural activity and represented in a manner that drives behavior. Research in this field aims to elucidate these processes by identifying the neural activity and mechanisms responsible for stimulus recognition and behavioral execution. This article provides a concise review of foundational studies and key concepts in neural coding, along with statistical formulations and recent advances in population coding research enabled by large-scale recordings.
Purpose: Observing the effects and roles of acupuncture on the morphology and neural coding damage of central amygdala (CeA) neurons in chronic inflammatory pain with depression (CIPD) mice and exploring the central n...
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Purpose: Observing the effects and roles of acupuncture on the morphology and neural coding damage of central amygdala (CeA) neurons in chronic inflammatory pain with depression (CIPD) mice and exploring the central nervous mechanism of acupuncture intervention in CIPD. Methods: A CIPD model was established by injecting Complete Freund's Adjuvant (CFA) into the left hind foot. Using paw withdrawal latency (PWLs), forced swimming, and open field tests, 40 mice with successfully replicated models were selected and randomly divided into a model group, acupuncture group, and sham acupuncture group, with 12 mice in each group. After treatment, Nissl staining was used to observe the morphology of CeA neurons and the number of Nissl bodies. In vivo multi-channel recordings measured the spontaneous firing frequency, waveform amplitude, inter-spike interval (ISI), and power spectral density (PSD) of CeA neurons. Results: The PWLs in the model and sham acupuncture groups were shortened, the activity time and distance in the central region were reduced, and the forced swimming immobility time increased. The arrangement of CeA neurons is sparse, neurons are damaged, and the number of Nissl bodies is reduced;CeA neurons exhibit abnormal changes in spatiotemporal patterns, with a decrease in spontaneous discharge frequency, discharge amplitude, PSD, and an increase in ISI. The acupuncture group showed prolonged PWLs, increased activity time and distance in the central region, and decreased immobility during forced swimming. The loss of CeA neurons decreased, the cells were arranged neatly, the nucleoli were evident, and the number of Nissl bodies increased. The damage to CeA neural coding was significantly improved, with increased spontaneous discharge frequency, discharge amplitude, PSD, and shortened ISI. Conclusion: Acupuncture may alleviate pain and depressive-like behaviors in CIPD mice and reduce neuronal damage, possibly through mechanisms related to improving the spatiote
We investigate the retrieval dynamics in a feature-based semantic memory model, in which the features are coded by neurons of the Hindmarsh-Rose type in the chaotic regime. We consider the retrieval process as consist...
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We investigate the retrieval dynamics in a feature-based semantic memory model, in which the features are coded by neurons of the Hindmarsh-Rose type in the chaotic regime. We consider the retrieval process as consisting of the synchronized firing activity of the neurons coding for the same memory pattern. The retrieval dynamics is investigated for multiple patterns, with particular attention to the case of overlapping memories. In this case, we hypothesize a dynamical nontransitive mechanism based on synchronization, that allows for a shared feature to participate in multiple memory representations. The problem of the choice of a cognitive plausible time-scale for the retrieval analysis is investigated by analyzing the information that can be inferred from finite-time analyses. Different types of indicators are proposed in order to evaluate the temporal dynamics of the neurons engaged in the retrieval process. We interpret the simulation results as suggestive of a role for chaotic dynamics in allowing for flexible composition of elementary meaningful units in memory representations. (c) 2006 Elsevier Ireland Ltd. All rights reserved.
Manual interactions with objects require precise and rapid feedback about contact events. These tactile signals are integrated with motor plans throughout the neuraxis to achieve dexterous object manipulation. To bett...
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Manual interactions with objects require precise and rapid feedback about contact events. These tactile signals are integrated with motor plans throughout the neuraxis to achieve dexterous object manipulation. To better understand the role of somatosensory cortex in interactions with objects, we measured, using chronically implanted arrays of electrodes, the responses of populations of somatosensory neurons to skin indentations designed to simulate the initiation, maintenance, and termination of contact with an object. First, we find that the responses of somatosensory neurons to contact onset and offset dwarf their responses to maintenance of contact. Second, we show that these responses rapidly and reliably encode features of the simulated contact events-their timing, location, and strength-and can account for the animals' performance in an amplitude discrimination task. Third, we demonstrate that the spatiotemporal dynamics of the population response in cortex mirror those of the population response in the nerves. We conclude that the responses of populations of somatosensory neurons are well suited to encode contact transients and are consistent with a role of somatosensory cortex in signaling transitions between task subgoals.
How the brain processes temporal information embedded in sounds is a core question in auditory research. This article synthesizes recent studies from our laboratory regarding neural representations of time-varying sig...
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How the brain processes temporal information embedded in sounds is a core question in auditory research. This article synthesizes recent studies from our laboratory regarding neural representations of time-varying signals in auditory cortex and thalamus in awake marmoset monkeys. Findings from these studies show that 1) the primary auditory cortex (A1) uses a temporal representation to encode slowly varying acoustic signals and a firing rate-based representation to encode rapidly changing acoustic signals, 2) the dual temporal-rate representations in A1 represent a progressive transformation from the auditory thalamus, 3) firing rate-based representations in the form of monotonic rate-code are also found to encode slow temporal repetitions in the range of acoustic flutter in A1 and more prevalently in the cortical fields rostral to A1 in the core region of marmoset auditory cortex, suggesting further temporal-to-rate transformations in higher cortical areas. These findings indicate that the auditory cortex forms internal representations of temporal characteristics of sounds that are no longer faithful replicas of their acoustic structures. We suggest that such transformations are necessary for the auditory cortex to perform a wide range of functions including sound segmentation, object processing and multi-sensory integration. (c) 2008 IBRO. Published by Elsevier Ltd. All rights reserved.
Songbirds are a well-established animal model to study the neural basis of learning, perception and production of complex vocalizations. In this system, telencephalic neurons in HVC present a state-dependent, highly s...
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Songbirds are a well-established animal model to study the neural basis of learning, perception and production of complex vocalizations. In this system, telencephalic neurons in HVC present a state-dependent, highly selective response to auditory presentations of the bird's own song (BOS). This property provides an opportunity to study the neural code behind a complex motor behavior. In this work, we explore whether changes in the temporal structure of the sound envelope can drive changes in the neural responses of highly selective HVC units. We generated an envelope-modified BOS (MOD) by reversing each syllable's envelope but leaving the overall temporal structure of syllable spectra unchanged, which resulted in a subtle modification for each song syllable. We conducted in vivo electrophysiological recordings of HVC neurons in anaesthetized zebra finches (Taeniopygia guttata). Units analyzed presented a high BOS selectivity and lower response to MOD, but preserved the profile response shape. These results show that the temporal evolution of the sound envelope is being sensed by the avian song system and suggest that the biomechanical properties of the vocal apparatus could play a role in enhancing subtle sound differences.
A fundamental problem in neuroscience, to which Prof. Segundo has made seminal contributions, is to understand how action potentials represent events in the external world. The aim of this paper is to review the issue...
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A fundamental problem in neuroscience, to which Prof. Segundo has made seminal contributions, is to understand how action potentials represent events in the external world. The aim of this paper is to review the issue of neural coding in the context of the rodent whiskers, an increasingly popular model system. Key issues we consider are: the role of spike timing;mechanisms of spike timing;decoding and context-dependence. Significant insight has come from the development of rigorous, information theoretic frameworks for tackling these questions, in conjunction with suitably designed experiments. We review both the theory and experimental studies. In contrast to the classical view that neurons are noisy and unreliable, it is becoming clear that many neurons in the subcortical whisker pathway are remarkably reliable and, by virtue of spike timing with millisecond-precision, have high bandwidth for conveying sensory information. In this way, even small (similar to 200 neuron) subcortical modules are able to support the sensory processing underlying sophisticated whisker-dependent behaviours. Future work on neural coding in cortex will need to consider new findings that responses are highly dependent on context, including behavioural and internal states.
In contrast to the visual system, the auditory system has longer subcortical pathways and more spiking synapses between the peripheral receptors and the cortex. This unique organization reflects the needs of the audit...
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In contrast to the visual system, the auditory system has longer subcortical pathways and more spiking synapses between the peripheral receptors and the cortex. This unique organization reflects the needs of the auditory system to extract behaviorally relevant information from a complex acoustic environment using strategies different from those used by other sensory systems. The neural representations of acoustic information in auditory cortex can be characterized by three types: (1) isomorphic (faithful) representations of acoustic structures;(2) non-isomorphic transformations of acoustic features and (3) transformations from acoustical to perceptual dimensions. The challenge facing auditory neurophysiologists is to understand the nature of the latter two transformations. In this article, I will review recent Studies front our laboratory regarding temporal discharge patterns in auditory cortex of awake marmosets and cortical representations of time-varying signals. Findings from these studies show that (1) firing patterns of neurons in auditory cortex are dependent on stimulus optimality and context and (2) the auditory cortex forms internal representations of sounds that are no longer faithful replicas of their acoustic structures. (c) 2007 Published by Elsevier B.V.
There is increasing evidence, both electrophysiological and behavioral, that bitter and sweet stimuli drive parallel pathways in the gustatory brainstem. Here we report two lines of investigation that suggest signific...
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There is increasing evidence, both electrophysiological and behavioral, that bitter and sweet stimuli drive parallel pathways in the gustatory brainstem. Here we report two lines of investigation that suggest significant interactions among these parallel systems. First, responses recorded from single cells in the hamster's parabrachial nuclei (PbN) show that quinine hydrochloride (QHCl) produces a substantial suppression (> 40%) of the responses of PbN cells to sucrose. Sucrose stimulation has a reciprocal suppressive effect on the response to QHCl. These results imply that aversive and appetitive stimuli produce mutual inhibition in the gustatory system;studies of the chorda tympani nerve response suggest that this inhibition likely arises within the brainstem. A second line of investigation, using both an in vitro brainstem slice preparation and in vivo pharmacological manipulations of cells in the hamster NST, has demonstrated an inhbitory network within the rostral NST that plays a role in the modulation of taste activity. Patch-clamp and extracellular recording studies in vitro show that cells within the rostral central subdivision of the NST are inhibited by gamma-aminobutyric acid (GABA);this mediation is largely through the GABA(A) receptor subtype. Here we show that responses to taste stimulation recorded extracellularly from NST cells in vivo can be inhibited by local microinjections of GABA;this inhibition is blocked by the GABA(A) receptor antagonist bicuculline methiodide. Responses to sucrose are significantly more inhibited than those to NaCl or KCl. These combined lines of evidence show that appetitive and aversive stimuli activate mutually inhibitory systems within the brainstem and suggest that the basis for this interaction is a GABAergic inhibitory network within the NST. Further studies are underway to evaluate this hypothesis.
We examine the responses of single neurons and pairs of neurons, simultaneously recorded with a single tetrode in the primary visual cortex of the anesthetized macaque monkey, to transient presentations of stationary ...
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We examine the responses of single neurons and pairs of neurons, simultaneously recorded with a single tetrode in the primary visual cortex of the anesthetized macaque monkey, to transient presentations of stationary gratings of varying spatial phase. Such simultaneously recorded neurons tended to have similar tuning to the phase of the grating. To determine the response features that reliably discriminate these stimuli, we use the metric-space approach extended to pairs of neurons. We find that paying attention to the times of individual spikes, at a resolution of similar to30 ms, and keeping track of which neuron fires which spike rather than just the summed local activity contribute substantially to phase coding. The contribution is both quantitative (increasing the fidelity of phase coding) and qualitative (enabling a 2-dimensional "response space" that corresponds to the spatial phase cycle). We use a novel approach, the extraction of "temporal profiles" from the metric space analysis, to interpret and compare temporal coding across neurons. Temporal profiles were remarkably consistent across a large subset of neurons. This consistency indicates that simple mechanisms (e.g., comparing the size of the transient and sustained components of the response) allow the temporal contribution to phase coding to be decoded.
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