Showing papers on "Receptive field published in 2012"

A neural circuit for spatial summation in visual cortex

Abstract: The response of cortical neurons to a sensory stimulus is modulated by the context. In the visual cortex, for example, stimulation of a pyramidal cell's receptive-field surround can attenuate the cell's response to a stimulus in the centre of its receptive field, a phenomenon called surround suppression. Whether cortical circuits contribute to surround suppression or whether the phenomenon is entirely relayed from earlier stages of visual processing is debated. Here we show that, in contrast to pyramidal cells, the response of somatostatin-expressing inhibitory neurons (SOMs) in the superficial layers of the mouse visual cortex increases with stimulation of the receptive-field surround. This difference results from the preferential excitation of SOMs by horizontal cortical axons. By perturbing the activity of SOMs, we show that these neurons contribute to pyramidal cells' surround suppression. These results establish a cortical circuit for surround suppression and attribute a particular function to a genetically defined type of inhibitory neuron.

The most numerous ganglion cell type of the mouse retina is a selective feature detector

Abstract: The retina reports the visual scene to the brain through many parallel channels, each carried by a distinct population of retinal ganglion cells. Among these, the population with the smallest and densest receptive fields encodes the neural image with highest resolution. In human retina, and those of cat and macaque, these high-resolution ganglion cells act as generic pixel encoders: They serve to represent many different visual inputs and convey a neural image of the scene downstream for further processing. Here we identify and analyze high-resolution ganglion cells in the mouse retina, using a transgenic line in which these cells, called “W3”, are labeled fluorescently. Counter to the expectation, these ganglion cells do not participate in encoding generic visual scenes, but remain silent during most common visual stimuli. A detailed study of their response properties showed that W3 cells pool rectified excitation from both On and Off bipolar cells, which makes them sensitive to local motion. However, they also receive unusually strong lateral inhibition, both pre- and postsynaptically, triggered by distant motion. As a result, the W3 cell can detect small moving objects down to the receptive field size of bipolar cells, but only if the background is featureless or stationary—an unusual condition. A survey of naturalistic stimuli shows that W3 cells may serve as alarm neurons for overhead predators.

Task reward structure shapes rapid receptive field plasticity in auditory cortex

Abstract: As sensory stimuli and behavioral demands change, the attentive brain quickly identifies task-relevant stimuli and associates them with appropriate motor responses. The effects of attention on sensory processing vary across task paradigms, suggesting that the brain may use multiple strategies and mechanisms to highlight attended stimuli and link them to motor action. To better understand factors that contribute to these variable effects, we studied sensory representations in primary auditory cortex (A1) during two instrumental tasks that shared the same auditory discrimination but required different behavioral responses, either approach or avoidance. In the approach task, ferrets were rewarded for licking a spout when they heard a target tone amid a sequence of reference noise sounds. In the avoidance task, they were punished unless they inhibited licking to the target. To explore how these changes in task reward structure influenced attention-driven rapid plasticity in A1, we measured changes in sensory neural responses during behavior. Responses to the target changed selectively during both tasks but did so with opposite sign. Despite the differences in sign, both effects were consistent with a general neural coding strategy that maximizes discriminability between sound classes. The dependence of the direction of plasticity on task suggests that representations in A1 change not only to sharpen representations of task-relevant stimuli but also to amplify responses to stimuli that signal aversive outcomes and lead to behavioral inhibition. Thus, top-down control of sensory processing can be shaped by task reward structure in addition to the required sensory discrimination.

Spatial profile of excitatory and inhibitory synaptic connectivity in mouse primary auditory cortex.

Abstract: The role of local cortical activity in shaping neuronal responses is controversial. Among other questions, it is unknown how the diverse response patterns reported in vivo—lateral inhibition in some cases, approximately balanced excitation and inhibition (co-tuning) in others—compare to the local spread of synaptic connectivity. Excitatory and inhibitory activity might cancel each other out, or, whether one outweighs the other, receptive field properties might be substantially affected. As a step toward addressing this question, we used multiple intracellular recording in mouse primary auditory cortical slices to map synaptic connectivity among excitatory pyramidal cells and the two broad classes of inhibitory cells, fast-spiking (FS) and non-FS cells in the principal input layer. Connection probability was distance-dependent; the spread of connectivity, parameterized by Gaussian fits to the data, was comparable for all cell types, ranging from 85 to 114 μm. With brief stimulus trains, unitary synapses formed by FS interneurons were stronger than other classes of synapses; synapse strength did not correlate with distance between cells. The physiological data were qualitatively consistent with predictions derived from anatomical reconstruction. We also analyzed the truncation of neuronal processes due to slicing; overall connectivity was reduced but the spatial pattern was unaffected. The comparable spatial patterns of connectivity and relatively strong excitatory-inhibitory interconnectivity are consistent with a theoretical model where either lateral inhibition or co-tuning can predominate, depending on the structure of the input.

Hippocampal Place Fields Emerge upon Single-Cell Manipulation of Excitability During Behavior

Abstract: The origin of the spatial receptive fields of hippocampal place cells has not been established. A hippocampal CA1 pyramidal cell receives thousands of synaptic inputs, mostly from other spatially tuned neurons; however, how the postsynaptic neuron's cellular properties determine the response to these inputs during behavior is unknown. We discovered that, contrary to expectations from basic models of place cells and neuronal integration, a small, spatially uniform depolarization of the spatially untuned somatic membrane potential of a silent cell leads to the sudden and reversible emergence of a spatially tuned subthreshold response and place-field spiking. Such gating of inputs by postsynaptic neuronal excitability reveals a cellular mechanism for receptive field origin and may be critical for the formation of hippocampal memory representations.

Decorrelation and efficient coding by retinal ganglion cells.

Abstract: An influential theory of visual processing asserts that retinal center-surround receptive fields remove spatial correlations in the visual world, producing ganglion cell spike trains that are less redundant than the corresponding image pixels. For bright, high-contrast images, this decorrelation would enhance coding efficiency in optic nerve fibers of limited capacity. We tested the central prediction of the theory and found that the spike trains of retinal ganglion cells were indeed decorrelated compared with the visual input. However, most of the decorrelation was accomplished not by the receptive fields, but by nonlinear processing in the retina. We found that a steep response threshold enhanced efficient coding by noisy spike trains and that the effect of this nonlinearity was near optimal in both salamander and macaque retina. These results offer an explanation for the sparseness of retinal spike trains and highlight the importance of treating the full nonlinear character of neural codes.

Form and Function of the M4 Cell, an Intrinsically Photosensitive Retinal Ganglion Cell Type Contributing to Geniculocortical Vision

Abstract: The photopigment melanopsin confers photosensitivity upon a minority of retinal output neurons These intrinsically photosensitive retinal ganglion cells (ipRGCs) are more diverse than once believed, comprising five morphologically distinct types, M1 through M5 Here, in mouse retina, we provide the first in-depth characterization of M4 cells, including their structure, function, and central projections M4 cells apparently correspond to ON α cells of earlier reports, and are easily distinguished from other ipRGCs by their very large somata Their dendritic arbors are more radiate and highly branched than those of M1, M2, or M3 cells The melanopsin-based intrinsic photocurrents of M4 cells are smaller than those of M1 and M2 cells, presumably because melanopsin is more weakly expressed; we can detect it immunohistochemically only with strong amplification Like M2 cells, M4 cells exhibit robust, sustained, synaptically driven ON responses and dendritic stratification in the ON sublamina of the inner plexiform layer However, their stratification patterns are subtly different, with M4 dendrites positioned just distal to those of M2 cells and just proximal to the ON cholinergic band M4 receptive fields are large, with an ON center, antagonistic OFF surround and nonlinear spatial summation Their synaptically driven photoresponses lack direction selectivity and show higher ultraviolet sensitivity in the ventral retina than in the dorsal retina, echoing the topographic gradient in S- and M-cone opsin expression M4 cells are readily labeled by retrograde transport from the dorsal lateral geniculate nucleus and thus likely contribute to the pattern vision that persists in mice lacking functional rods and cones

Robustness of Cortical Topography across Fields, Laminae, Anesthetic States, and Neurophysiological Signal Types

Abstract: Topographically organized maps of the sensory receptor epithelia are regarded as cornerstones of cortical organization as well as valuable readouts of diverse biological processes ranging from evolution to neural plasticity. However, maps are most often derived from multiunit activity recorded in the thalamic input layers of anesthetized animals using near-threshold stimuli. Less distinct topography has been described by studies that deviated from the formula above, which brings into question the generality of the principle. Here, we explicitly compared the strength of tonotopic organization at various depths within core and belt regions of the auditory cortex using electrophysiological measurements ranging from single units to delta-band local field potentials (LFP) in the awake and anesthetized mouse. Unit recordings in the middle cortical layers revealed a precise tonotopic organization in core, but not belt, regions of auditory cortex that was similarly robust in awake and anesthetized conditions. In core fields, tonotopy was degraded outside the middle layers or when LFP signals were substituted for unit activity, due to an increasing proportion of recording sites with irregular tuning for pure tones. However, restricting our analysis to clearly defined receptive fields revealed an equivalent tonotopic organization in all layers of the cortical column and for LFP activity ranging from gamma to theta bands. Thus, core fields represent a transition between topographically organized simple receptive field arrangements that extend throughout all layers of the cortical column and the emergence of nontonotopic representations outside the input layers that are further elaborated in the belt fields.

Gating and control of primary visual cortex by pulvinar

Abstract: The primary visual cortex (V1) receives its driving input from the eyes via the lateral geniculate nucleus (LGN) of the thalamus. The lateral pulvinar nucleus of the thalamus also projects to V1, but this input is not well understood. We manipulated lateral pulvinar neural activity in prosimian primates and assessed the effect on supra-granular layers of V1 that project to higher visual cortex. Reversibly inactivating lateral pulvinar prevented supra-granular V1 neurons from responding to visual stimulation. Reversible, focal excitation of lateral pulvinar receptive fields increased the visual responses in coincident V1 receptive fields fourfold and shifted partially overlapping V1 receptive fields toward the center of excitation. V1 responses to regions surrounding the excited lateral pulvinar receptive fields were suppressed. LGN responses were unaffected by these lateral pulvinar manipulations. Excitation of lateral pulvinar after LGN lesion activated supra-granular layer V1 neurons. Thus, lateral pulvinar is able to powerfully control and gate information outflow from V1.

The spatial structure of a nonlinear receptive field.

Abstract: The authors attempt to improve existing retinal models by incorporating measurements of the physiological properties and connectivity of only the primary excitatory circuitry of the retina. The resulting model predicts ganglion cell responses to a variety of spatial patterns and provides a direct correspondence between circuit connectivity and retinal output.

Mapping a complete neural population in the retina.

Abstract: Recording simultaneously from essentially all of the relevant neurons in a local circuit is crucial to understand how they collectively represent information. Here we show that the combination of a large, dense multielectrode array and a novel, mostly automated spike-sorting algorithm allowed us to record simultaneously from a highly overlapping population of >200 ganglion cells in the salamander retina. By combining these methods with labeling and imaging, we showed that up to 95% of the ganglion cells over the area of the array were recorded. By measuring the coverage of visual space by the receptive fields of the recorded cells, we concluded that our technique captured a neural population that forms an essentially complete representation of a region of visual space. This completeness allowed us to determine the spatial layout of different cell types as well as identify a novel group of ganglion cells that responded reliably to a set of naturalistic and artificial stimuli but had no measurable receptive field. Thus, our method allows unprecedented access to the complete neural representation of visual information, a crucial step for the understanding of population coding in sensory systems.

Switching Neuronal Inputs by Differential Modulations of Gamma-Band Phase-Coherence

Abstract: Receptive fields (RFs) of cortical sensory neurons increase in size along consecutive processing stages. When multiple stimuli are present in a large visual RF, a neuron typically responds to an attended stimulus as if only that stimulus were present. However, the mechanism by which a neuron selectively responds to a subset of its inputs while discarding all others is unknown. Here, we show that neurons can switch between subsets of their afferent inputs by highly specific modulations of interareal gamma-band phase-coherence (PC). We measured local field potentials, single- and multi-unit activity in two male macaque monkeys (Macaca mulatta) performing an attention task. Two small stimuli were placed on a screen; the stimuli were driving separate local V1 populations, while both were driving the same local V4 population. In each trial, we cued one of the two stimuli to be attended. We found that gamma-band PC of the local V4 population with multiple subpopulations of its V1 input was differentially modulated. It was high with the input subpopulation representing the attended stimulus, while simultaneously it was very low between the same V4 population and the other input-providing subpopulation representing the irrelevant stimulus. These differential modulations, which depend on stimulus relevance, were also found in the locking of spikes from V4 neurons to the gamma-band oscillations of the V1 input subpopulations. This rapid, highly specific interareal locking provides neurons with a powerful dynamic routing mechanism to select and process only the currently relevant signals.

Modeling center-surround configurations in population receptive fields using fMRI.

Abstract: Antagonistic center-surround configurations are a central organizational principle of our visual system. In visual cortex, stimulation outside the classical receptive field can decrease neural activity and also decrease functional Magnetic Resonance Imaging (fMRI) signal amplitudes. Decreased fMRI amplitudes below baseline-0% contrast-are often referred to as "negative" responses. Using neural model-based fMRI data analyses, we can estimate the region of visual space to which each cortical location responds, i.e., the population receptive field (pRF). Current models of the pRF do not account for a center-surround organization or negative fMRI responses. Here, we extend the pRF model by adding surround suppression. Where the conventional model uses a circular symmetric Gaussian function to describe the pRF, the new model uses a circular symmetric difference-of-Gaussians (DoG) function. The DoG model allows the pRF analysis to capture fMRI signals below baseline and surround suppression. Comparing the fits of the models, an increased variance explained is found for the DoG model. This improvement was predominantly present in V1/2/3 and decreased in later visual areas. The improvement of the fits was particularly striking in the parts of the fMRI signal below baseline. Estimates for the surround size of the pRF show an increase with eccentricity and over visual areas V1/2/3. For the suppression index, which is based on the ratio between the volumes of both Gaussians, we show a decrease over visual areas V1 and V2. Using non-invasive fMRI techniques, this method gives the possibility to examine assumptions about center-surround receptive fields in human subjects.

Computing with Neural Synchrony

Abstract: Neurons communicate primarily with spikes, but most theories of neural computation are based on firing rates. Yet, many experimental observations suggest that the temporal coordination of spikes plays a role in sensory processing. Among potential spike-based codes, synchrony appears as a good candidate because neural firing and plasticity are sensitive to fine input correlations. However, it is unclear what role synchrony may play in neural computation, and what functional advantage it may provide. With a theoretical approach, I show that the computational interest of neural synchrony appears when neurons have heterogeneous properties. In this context, the relationship between stimuli and neural synchrony is captured by the concept of synchrony receptive field, the set of stimuli which induce synchronous responses in a group of neurons. In a heterogeneous neural population, it appears that synchrony patterns represent structure or sensory invariants in stimuli, which can then be detected by postsynaptic neurons. The required neural circuitry can spontaneously emerge with spike-timing-dependent plasticity. Using examples in different sensory modalities, I show that this allows simple neural circuits to extract relevant information from realistic sensory stimuli, for example to identify a fluctuating odor in the presence of distractors. This theory of synchrony-based computation shows that relative spike timing may indeed have computational relevance, and suggests new types of neural network models for sensory processing with appealing computational properties.

Pruriceptive spinothalamic tract neurons: physiological properties and projection targets in the primate

Abstract: Itch of peripheral origin requires information transfer from the spinal cord to the brain for perception. Here, primate spinothalamic tract (STT) neurons from lumbar spinal cord were functionally characterized by in vivo electrophysiology to determine the role of these cells in the transmission of pruriceptive information. One hundred eleven STT neurons were identified by antidromic stimulation and then recorded while histamine and cowhage (a nonhistaminergic pruritogen) were sequentially applied to the cutaneous receptive field of each cell. Twenty percent of STT neurons responded to histamine, 13% responded to cowhage, and 2% responded to both. All pruriceptive STT neurons were mechanically sensitive and additionally responded to heat, intradermal capsaicin, or both. STT neurons located in the superficial dorsal horn responded with greater discharge and longer duration to pruritogens than STT neurons located in the deep dorsal horn. Pruriceptive STT neurons discharged in a bursting pattern in response to the activating pruritogen and to capsaicin. Microantidromic mapping was used to determine the zone of termination for pruriceptive STT axons within the thalamus. Axons from histamine-responsive and cowhage-responsive STT neurons terminated in several thalamic nuclei including the ventral posterior lateral, ventral posterior inferior, and posterior nuclei. Axons from cowhage-responsive neurons were additionally found to terminate in the suprageniculate and medial geniculate nuclei. Histamine-responsive STT neurons were sensitized to gentle stroking of the receptive field after the response to histamine, suggesting a spinal mechanism for alloknesis. The results show that pruriceptive information is encoded by polymodal STT neurons in histaminergic or nonhistaminergic pathways and transmitted to the ventrobasal complex and posterior thalamus in primates.

Relative spike time coding and STDP-based orientation selectivity in the early visual system in natural continuous and saccadic vision: a computational model

Abstract: We have built a phenomenological spiking model of the cat early visual system comprising the retina, the Lateral Geniculate Nucleus (LGN) and V1's layer 4, and established four main results (1) When exposed to videos that reproduce with high fidelity what a cat experiences under natural conditions, adjacent Retinal Ganglion Cells (RGCs) have spike-time correlations at a short timescale (~30 ms), despite neuronal noise and possible jitter accumulation. (2) In accordance with recent experimental findings, the LGN filters out some noise. It thus increases the spike reliability and temporal precision, the sparsity, and, importantly, further decreases down to ~15 ms adjacent cells' correlation timescale. (3) Downstream simple cells in V1's layer 4, if equipped with Spike Timing-Dependent Plasticity (STDP), may detect these fine-scale cross-correlations, and thus connect principally to ON- and OFF-centre cells with Receptive Fields (RF) aligned in the visual space, and thereby become orientation selective, in accordance with Hubel and Wiesel (Journal of Physiology 160:106---154, 1962) classic model. Up to this point we dealt with continuous vision, and there was no absolute time reference such as a stimulus onset, yet information was encoded and decoded in the relative spike times. (4) We then simulated saccades to a static image and benchmarked relative spike time coding and time-to-first spike coding w.r.t. to saccade landing in the context of orientation representation. In both the retina and the LGN, relative spike times are more precise, less affected by pre-landing history and global contrast than absolute ones, and lead to robust contrast invariant orientation representations in V1.

Topographic Maps within Brodmann's Area 5 of Macaque Monkeys

Abstract: Brodmann's area 5 has traditionally included the rostral bank of the intraparietal sulcus (IPS) as well as posterior portions of the postcentral gyrus and medial wall. However, different portions of this large architectonic zone may serve different functions related to reaching and grasping behaviors. The current study used multiunit recording techniques in anesthetized macaque monkeys to survey a large extent of the rostral bank of the IPS so that hundreds of recording sites could be used to determine the functional subdivisions and topographic organization of cortical areas in this region. We identified a lateral area on the rostral IPS that we term area 5L. Area 5L contains neurons with receptive fields on mostly the shoulder, forelimb, and digits, with no apparent representation of other body parts. Thus, there is a large magnification of the forelimb. Receptive fields for neurons in this region often contain multiple joints of the forelimb or multiple digits, which results in imprecise topography or fractures in map organization. Our results provide the first overall topographic map of area 5L obtained in individual macaque monkeys and suggest that this region is distinct from more medial portions of the IPS.

The influence of surround suppression on adaptation effects in primary visual cortex

Abstract: Adaptation, the prolonged presentation of stimuli, has been used to probe mechanisms of visual processing in physiological, imaging, and perceptual studies. Previous neurophysiological studies have measured adaptation effects by using stimuli tailored to evoke robust responses in individual neurons. This approach provides an incomplete view of how an adapter alters the representation of sensory stimuli by a population of neurons with diverse functional properties. We implanted microelectrode arrays in primary visual cortex (V1) of macaque monkeys and measured orientation tuning and contrast sensitivity in populations of neurons before and after prolonged adaptation. Whereas previous studies in V1 have reported that adaptation causes stimulus-specific suppression of responsivity and repulsive shifts in tuning preference, we have found that adaptation can also lead to response facilitation and shifts in tuning toward the adapter. To explain this range of effects, we have proposed and tested a simple model that employs stimulus-specific suppression in both the receptive field and the spatial surround. The predicted effects on tuning depend on the relative drive provided by the adapter to these two receptive field components. Our data reveal that adaptation can have a much richer repertoire of effects on neuronal responsivity and tuning than previously considered and suggest an intimate mechanistic relationship between spatial and temporal contextual effects.

Topographic Distribution, Frequency, and Intensity Dependence of Stimulus-Specific Adaptation in the Inferior Colliculus of the Rat

Abstract: The ability to detect unexpected sounds within the environment is an important function of the auditory system, as a rapid response may be required for the organism to survive. Previous studies found a decreased response to repetitive stimuli (standard), but an increased response to rare or less frequent sounds (deviant) in individual neurons in the inferior colliculus (IC) and at higher levels. This phenomenon, known as stimulus-specific adaptation (SSA) has been suggested to underpin change detection. Currently, it is not known how SSA varies within a single neuron receptive field, i.e., it is unclear whether SSA is a unique property of the neuron or a feature that is frequency and/or intensity dependent. In the present experiments, we used the common SSA index (CSI) to quantify and compare the degree of SSA under different stimulation conditions in the IC of the rat. We calculated the CSI at different intensities and frequencies for each individual IC neuron to map the neuronal CSI within the receptive field. Our data show that high SSA is biased toward the high-frequency and low-intensity regions of the receptive field. We also find that SSA is better represented in the earliest portions of the response, and there is a positive correlation between the width of the frequency response area of the neuron and the maximum level of SSA. The present data suggest that SSA in the IC is not mediated by the intrinsic membrane properties of the neurons and instead might be related to an excitatory and/or inhibitory input segregation.

Strong Recurrent Networks Compute the Orientation Tuning of Surround Modulation in the Primate Primary Visual Cortex

Abstract: In macaque primary visual cortex (V1), neuronal responses to stimuli inside the receptive field (RF) are modulated by stimuli in the RF surround. This modulation is orientation specific. Previous studies suggested that, for some cells, this specificity may not be fixed but changes with the stimulus orientation presented to the RF. We demonstrate, in recording studies, that this tuning behavior is instead highly prevalent in V1 and, in theoretical work, that it arises only if V1 operates in a regime of strong local recurrence. Strongest surround suppression occurs when the stimuli in the RF and the surround are iso-oriented, and strongest facilitation when the stimuli are cross-oriented. This is the case even when the RF is suboptimally activated by a stimulus of nonpreferred orientation but only if this stimulus can activate the cell when presented alone. This tuning behavior emerges from the interaction of lateral inhibition (via the surround pathways), which is tuned to the preferred orientation of the RF, with weakly tuned, but strong, local recurrent connections, causing maximal withdrawal of recurrent excitation at the feedforward input orientation. Thus, horizontal and feedback modulation of strong recurrent circuits allows the tuning of contextual effects to change with changing feedforward inputs.

Sparse codes for speech predict spectrotemporal receptive fields in the inferior colliculus.

Abstract: We have developed a sparse mathematical representation of speech that minimizes the number of active model neurons needed to represent typical speech sounds. The model learns several well-known acoustic features of speech such as harmonic stacks, formants, onsets and terminations, but we also find more exotic structures in the spectrogram representation of sound such as localized checkerboard patterns and frequency-modulated excitatory subregions flanked by suppressive sidebands. Moreover, several of these novel features resemble neuronal receptive fields reported in the Inferior Colliculus (IC), as well as auditory thalamus and cortex, and our model neurons exhibit the same tradeoff in spectrotemporal resolution as has been observed in IC. To our knowledge, this is the first demonstration that receptive fields of neurons in the ascending mammalian auditory pathway beyond the auditory nerve can be predicted based on coding principles and the statistical properties of recorded sounds.

The role of starburst amacrine cells in visual signal processing.

Abstract: Starburst amacrine cells (SBACs) within the adult mammalian retina provide the critical inhibition that underlies the receptive field properties of direction-selective ganglion cells (DSGCs). The SBACs generate direction-selective output of GABA that differentially inhibits the DSGCs. We review the biophysical mechanisms that produce directional GABA release from SBACs and test a network model that predicts the effects of reciprocal inhibition between adjacent SBACs. The results of the model simulations suggest that reciprocal inhibitory connections between closely spaced SBACs should be spatially selective, while connections between more widely spaced cells could be indiscriminate. SBACs were initially identified as cholinergic neurons and were subsequently shown to contain release both acetylcholine and GABA. While the role of the GABAergic transmission is well established, the role of the cholinergic transmission remains unclear.

Sensory Coding in the Mammalian Nervous System

Abstract: I: Introduction.- 1: Assumptions.- 2: Methods.- Critique.- Design.- Electrical recording.- Probes.- Experimental animals.- Stimulation.- 3: Signalling in the Nervous System.- Neurons.- The nerve impulses: Physical nature.- The nerve impulses: Conduction in myelinated and nonmyelinated fibers.- Generator potentials and receptor potentials.- Transmission between neurons.- II: The First-Order Code.- 4: Variables of the Sensory Code.- The diversity of stimuli and of sensory signalling.- The coding of quality.- Intensity.- Input-output functions of individual afferent fibers.- Input-output functions of populations.- Time.- Velocity: Receptor adaptation.- The coding of size, shape, and location.- 5: Direct Contact with the World.- The skin as a sense organ.- The so-called 'sensory spots', and the specificity of cutaneous afferents.- Corpuscles of Pacini.- Partially and slowly adapting mechanoreceptors.- Receptors of hair follicles.- Temperature receptors.- Temperature sensitivity of other receptors.- Pain.- The shape of things touched.- 6: The Inner Senses.- Proprioception 1: Feedback signals of movement.- Proprioception 2: Sense organs of joints.- Visceral receptors.- Receptor cells sought within the brain.- 7: The External Chemical Senses.- Taste: The stimuli.- Taste: The receptors.- Taste: The code.- The receptors and their nerves.- Smell.- The common problem of the codes of taste and of smell.- Common chemical sense, and how it relates to pain.- 8: The Inner Ear.- The transducers.- Semicircular canals.- The utricle.- The saccule.- The sound stimulus.- The cochlea.- Cochlear potentials and the stimulation of the receptors.- Analysis of frequencies.- The neural code.- Alternatives to the Bekesy/Davis/Tasaki/Whitfield model: The pulse-frequency code.- Alternatives to Davis' 'carbon microphone' model.- Some loose ends in auditory theory.- 9: The Photoreceptors of the Retina.- The receptors.- Visual pigments.- The stimulation of photoreceptors.- Photoreceptor potentials.- Three receptors to see so many tints, hues and shades.- III: Coding in the Center.- 10: Approaches to Brain Function.- Lessons learned from electrical recording and from ablations of the brain.- Firing patterns of central neurons.- 11: Sensory Synaptic Cascades.- Place and identity of relay sites.- Transmission and transformation at relay synapses.- How and where active processing.- Amplifiers, attenuators, and linear operators.- Lateral inhibition: The enhancement of contrast.- Self-inhibition and automatic gain control.- Relationships of transformations in the domains of time and space.- Changes of the rules of coding: Abstractions and invariances. Transcriptions?.- Parallel channels, redundancy, and the possible significance of fiber size.- The cortex: Blueprint and performance.- The cortex: On topographic representation.- 12: Central Coding in the Somatic Senses.- One system, two, or several?.- A paradox resolved?.- Neurons in somatic relays: 'Lemniscal' and 'anterolateral' types.- Input from the face.- Neurons of the nuclei of the dorsal columns.- Neurons of the ventrobasal region of the thalamus.- Cells of the first somatic receiving area (S I) of the cerebral cortex.- Neurons of the dorsal horns of the spinal cord.- Connections of the dorsal horns with the brain.- More on Melzack and Wall: Support.- Even more on Melzack and Wall: Doubts.- The posterior group of nuclei of the thalamus.- Spinothalamic contribution to the ventrobasal thalamus.- Coding for skin temperature by thalamic neurons.- Skin temperature and neurons in the somatic cortex.- 13: The Central Code of Hearing.- Components of the central auditory system.- Centrifugal control in the auditory system.- Tonotopic organization.- Discharges of cells in the auditory pathway.- Nural correlates of directional hearing.- 14: The Central Code of Sight.- The organization of the retina.- What excites ganglion cells: Shape of the receptive fields.- Colored stimuli: Effects on ganglion cells and on cells of the lateral geniculate nucleus.- Retinal ganglion cells: Adaptation to light and to darkness.- Synaptic mechanisms of the retina.- Detectors of movement and of direction.- Beyond the retina.- The visual thalamus: The lateral geniculate.- Neurons of the visual cortex.- Blueprints for the cortex: In series processing or parallel channels?.- Seeing in depth.- Visual function of the roof of the midbrain.- 15: The Central Code of the Chemical Senses.- Neurons in the central pathway of taste.- The olfactory bulb.- IV: Postscript.- In praise of redundancy.- The hierarchies of input revisited.- Relevancies and irrelevancies for sensory physiology in psychophysics and in information theory.- Last words.- V: Literature.- Key Titles.- Works of historic importance and works concerned with history.- Brain theory.- Psychology of sensation and perception.- Coding and information theory.- Sensory physiology (general works).- Sensory receptors.- Somatic senses.- Chemical senses.- Hearing.- Vision.- References.- Name Index.