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Showing papers on "Receptive field published in 1998"


Journal ArticleDOI
13 Mar 1998-Science
TL;DR: It is demonstrated that episodic electrical stimulation of the nucleus basalis, paired with an auditory stimulus, results in a massive progressive reorganization of the primary auditory cortex in the adult rat, suggesting that input characteristics may be able to drive appropriate alterations of receptive fields independently of explicit knowledge of the task.
Abstract: Little is known about the mechanisms that allow the cortex to selectively improve the neural representations of behaviorally important stimuli while ignoring irrelevant stimuli. Diffuse neuromodulatory systems may facilitate cortical plasticity by acting as teachers to mark important stimuli. This study demonstrates that episodic electrical stimulation of the nucleus basalis, paired with an auditory stimulus, results in a massive progressive reorganization of the primary auditory cortex in the adult rat. Receptive field sizes can be narrowed, broadened, or left unaltered depending on specific parameters of the acoustic stimulus paired with nucleus basalis activation. This differential plasticity parallels the receptive field remodeling that results from different types of behavioral training. This result suggests that input characteristics may be able to drive appropriate alterations of receptive fields independently of explicit knowledge of the task. These findings also suggest that the basal forebrain plays an active instructional role in representational plasticity.

1,187 citations


Journal ArticleDOI
TL;DR: Properties of the receptive fields of simple cells in macaque cortex were compared with properties of independent component filters generated by independent component analysis on a large set of natural images: there is no match, however, in calculated and measured distributions for the peak of the spatial frequency response.
Abstract: Properties of the receptive fields of simple cells in macaque cortex were compared with properties of independent component filters generated by independent component analysis (ICA) on a large set of natural images. Histograms of spatial frequency bandwidth, orientation tuning bandwidth, aspect ratio and length of the receptive fields match well. This indicates that simple cells are well tuned to the expected statistics of natural stimuli. There is no match, however, in calculated and measured distributions for the peak of the spatial frequency response: the filters produced by ICA do not vary their spatial scale as much as simple cells do, but are fixed to scales close to the finest ones allowed by the sampling lattice. Possible ways to resolve this discrepancy are discussed.

1,134 citations


01 Jan 1998
TL;DR: The lateral intraparietal area (LIP) as mentioned in this paper has been shown to have visual responses to stimuli appearing abruptly at particular retinal locations (their receptive fields) and the visual representation in LIP is sparse, with only the most salient or behaviourally relevant objects being strongly represented.
Abstract: When natural scenes are viewed, a multitude of objects that are stable in their environments are brought in and out of view by eye movements. The posterior parietal cortex is crucial for the analysis of space, visual attention and movement 1 . Neurons in one of its subdivisions, the lateral intraparietal area (LIP), have visual responses to stimuli appearing abruptly at particular retinal locations (their receptive fields)2. We have tested the responses of LIP neurons to stimuli that entered their receptive field by saccades. Neurons had little or no response to stimuli brought into their receptive field by saccades, unless the stimuli were behaviourally significant. We established behavioural significance in two ways: either by making a stable stimulus task-relevant, or by taking advantage of the attentional attraction of an abruptly appearing stimulus. Our results show that under ordinary circumstances the entire visual world is only weakly represented in LIP. The visual representation in LIP is sparse, with only the most salient or behaviourally relevant objects being strongly represented.

1,007 citations


Journal ArticleDOI
29 Jan 1998-Nature
TL;DR: The lateral intraparietal area (LIP) as mentioned in this paper has been shown to have visual responses to stimuli appearing abruptly at particular retinal locations (referred to as receptive fields) and showed that the visual representation in LIP is sparse with only the most salient or behaviourally relevant objects being strongly represented.
Abstract: When natural scenes are viewed, a multitude of objects that are stable in their environments are brought in and out of view by eye movements. The posterior parietal cortex is crucial for the analysis of space, visual attention and movement. Neurons in one of its subdivisions, the lateral intraparietal area (LIP), have visual responses to stimuli appearing abruptly at particular retinal locations (their receptive fields). We have tested the responses of LIP neurons to stimuli that entered their receptive field by saccades. Neurons had little or no response to stimuli brought into their receptive field by saccades, unless the stimuli were behaviourally significant. We established behavioural significance in two ways: either by making a stable stimulus task-relevant, or by taking advantage of the attentional attraction of an abruptly appearing stimulus. Our results show that under ordinary circumstances the entire visual world is only weakly represented in LIP. The visual representation in LIP is sparse, with only the most salient or behaviourally relevant objects being strongly represented.

974 citations


Journal ArticleDOI
TL;DR: A computational model of MT physiology, in which local image velocities are represented via the distribution of MT neuronal responses, which is performed in two stages, corresponding to neurons in cortical areas V1 and MT.

964 citations


Journal ArticleDOI
20 Aug 1998-Nature
TL;DR: It is shown that feedback connections facilitate responses to objects moving within the classical receptive field; enhance suppression evoked by background stimuli in the surrounding region; and have the strongest effects for stimuli of low salience.
Abstract: A single visual stimulus activates neurons in many different cortical areas. A major challenge in cortical physiology is to understand how the neural activity in these numerous active zones leads to a unified percept of the visual scene. The anatomical basis for these interactions is the dense network of connections that link the visual areas. Within this network, feedforward connections transmit signals from lower-order areas such as V1 or V2 to higher-order areas. In addition, there is a dense web of feedback connections which, despite their anatomical prominence1,2,3,4, remain functionally mysterious5,6,7,8. Here we show, using reversible inactivation of a higher-order area (monkey area V5/MT), that feedback connections serve to amplify and focus activity of neurons in lower-order areas, and that they are important in the differentiation of figure from ground, particularly in the case of stimuli of low visibility. More specifically, we show that feedback connections facilitate responses to objects moving within the classical receptive field; enhance suppression evoked by background stimuli in the surrounding region; and have the strongest effects for stimuli of low salience.

878 citations


Journal ArticleDOI
28 May 1998-Nature
TL;DR: It is proposed that nonlinear shunting inhibition may act during the initial stage of visual cortical processing, setting the balance between opponent ‘On’ and ‘Off’ responses in different locations of the visual receptive field.
Abstract: . Here we present a new approach to studying inhibition that is based on in vivo whole- cell voltage clamping. This technique allows the continuous measurement of conductance dynamics during visual activation. We show, in neurons of cat primary visual cortex, that the response to optimally orientated flashed bars can increase the somatic input conductance to more than three times that of the resting state. The short latency of the visually evoked peak of conductance, and its apparent reversal potential suggest a domi- nant contribution from g-aminobutyric acid ((GABA)A) receptor- mediated synapses. We propose that nonlinear shunting inhibi- tion may act during the initial stage of visual cortical processing, setting the balance between opponent 'On' and 'Off ' responses in different locations of the visual receptive field.

683 citations


Journal ArticleDOI
TL;DR: Whereas receptive field tuning properties reflect feedforward processing, modulations evoked by horizontal and feedback connections may reflect the integration of information that underlies perception.

611 citations


Journal ArticleDOI
05 Feb 1998-Nature
TL;DR: It is shown that neuronal facilitation preferentially occurs when a near-threshold stimulus inside the receptive field is flanked by higher-contrast, collinear elements located in surrounding regions of visual space.
Abstract: Neurons in the primary visual cortex are selective for the size, orientation and direction of motion of patterns falling within a restricted region of visual space known as the receptive field. The response to stimuli presented within the receptive field can be facilitated or suppressed by other stimuli falling outside the receptive field which, when presented in isolation, fail to activate the cell. Whether this interaction is facilitative or suppressive depends on the relative orientation of pattern elements inside and outside the receptive field. Here we show that neuronal facilitation preferentially occurs when a near-threshold stimulus inside the receptive field is flanked by higher-contrast, collinear elements located in surrounding regions of visual space. Collinear flanks and orthogonally oriented flanks, however, both act to reduce the response to high-contrast stimuli presented within the receptive field. The observed pattern of facilitation and suppression may be the cellular basis for the observation in humans that the detectability of an oriented pattern is enhanced by collinear flanking elements. Modulation of neuronal responses by stimuli falling outside their receptive fields may thus represent an early neural mechanism for encoding objects and enhancing their perceptual saliency.

605 citations


Journal ArticleDOI
29 May 1998-Science
TL;DR: Data suggest that the cortex decomposes an auditory scene into component parts using a feature-processing system reminiscent of that used for the cortical decomposition of visual images.
Abstract: The brain's cerebral cortex decomposes visual images into information about oriented edges, direction and velocity information, and color. How does the cortex decompose perceived sounds? A reverse correlation technique demonstrates that neurons in the primary auditory cortex of the awake primate have complex patterns of sound-feature selectivity that indicate sensitivity to stimulus edges in frequency or in time, stimulus transitions in frequency or intensity, and feature conjunctions. This allows the creation of classes of stimuli matched to the processing characteristics of auditory cortical neurons. Stimuli designed for a particular neuron's preferred feature pattern can drive that neuron with higher sustained firing rates than have typically been recorded with simple stimuli. These data suggest that the cortex decomposes an auditory scene into component parts using a feature-processing system reminiscent of that used for the cortical decomposition of visual images.

465 citations


Journal ArticleDOI
TL;DR: The model demonstrates that fundamental response properties of cortical layer 4 can be explained by circuitry expected to develop under correlation-based rules of synaptic plasticity, and shows how such circuitry allows the cortex to distinguish stimulus intensity from stimulus form.
Abstract: The origin of orientation selectivity in visual cortical responses is a central problem for understanding cerebral cortical circuitry. In cats, many experiments suggest that orientation selectivity arises from the arrangement of lateral geniculate nucleus (LGN) afferents to layer 4 simple cells. However, this explanation is not sufficient to account for the contrast invariance of orientation tuning. To understand contrast invariance, we first characterize the input to cat simple cells generated by the oriented arrangement of LGN afferents. We demonstrate that it has two components: a spatial-phase-specific component (i.e., one that depends on receptive field spatial phase), which is tuned for orientation, and a phase-nonspecific component, which is untuned. Both components grow with contrast. Second, we show that a correlation-based intracortical circuit, in which connectivity between cell pairs is determined by the correlation of their LGN inputs, is sufficient to achieve well tuned, contrast-invariant orientation tuning. This circuit generates both spatially opponent, "antiphase" inhibition ("push-pull"), and spatially matched, "same-phase" excitation. The inhibition, if sufficiently strong, suppresses the untuned input component and sharpens responses to the tuned component at all contrasts. The excitation amplifies tuned responses. This circuit agrees with experimental evidence showing spatial opponency between, and similar orientation tuning of, the excitatory and inhibitory inputs received by a simple cell. Orientation tuning is primarily input driven, accounting for the observed invariance of tuning width after removal of intracortical synaptic input, as well as for the dependence of orientation tuning on stimulus spatial frequency. The model differs from previous push-pull models in requiring dominant rather than balanced inhibition and in predicting that a population of layer 4 inhibitory neurons should respond in a contrast-dependent manner to stimuli of all orientations, although their tuning width may be similar to that of excitatory neurons. The model demonstrates that fundamental response properties of cortical layer 4 can be explained by circuitry expected to develop under correlation-based rules of synaptic plasticity, and shows how such circuitry allows the cortex to distinguish stimulus intensity from stimulus form.

Journal ArticleDOI
TL;DR: It is shown that performing independent component analysis (ICA) on video sequences of natural scenes produces results with qualitatively similar spatio-temporal properties, contrary to earlier ICA results on static images, which gave only filters at the finest possible spatial scale.
Abstract: Simple cells in the primary visual cortex process incoming visual information with receptive fields localized in space and time, bandpass in spatial and temporal frequency, tuned in orientation, and commonly selective for the direction of movement. It is shown that performing independent component analysis (ICA) on video sequences of natural scenes produces results with qualitatively similar spatio-temporal properties. Whereas the independent components of video resemble moving edges or bars, the independent component filters, i.e. the analogues of receptive fields, resemble moving sinusoids windowed by steady Gaussian envelopes. Contrary to earlier ICA results on static images, which gave only filters at the finest possible spatial scale, the spatio-temporal analysis yields filters at a range of spatial and temporal scales. Filters centred at low spatial frequencies are generally tuned to faster movement than those at high spatial frequencies.

Journal ArticleDOI
TL;DR: The results suggest that intracortical inhibition is the dominant, and perhaps sole, mechanism of suppression in the simple receptive field, and the inhibitory influences operated within a wide dynamic range.
Abstract: Simple cells in the visual cortex respond to the precise position of oriented contours (Hubel and Wiesel, 1962) This sensitivity reflects the structure of the simple receptive field, which exhibits two sorts of antagonism between on and off inputs First, simple receptive fields are divided into adjacent on and off subregions; second, within each subregion, stimuli of the reverse contrast evoke responses of the opposite sign: push–pull (Hubel and Wiesel, 1962;Palmer and Davis, 1981; Jones and Palmer, 1987; Ferster, 1988) We have made whole-cell patch recordings from cat area 17 during visual stimulation to examine the generation and integration of excitation (push) and suppression (pull) in the simple receptive field The temporal structure of the push reflected the pattern of thalamic inputs, as judged by comparing the intracellular cortical responses to extracellular recordings made in the lateral geniculate nucleus Two mechanisms have been advanced to account for the pull–withdrawal of thalamic drive and active, intracortical inhibition (Hubel and Wiesel, 1962; Heggelund, 1986; Ferster, 1988) Our results suggest that intracortical inhibition is the dominant, and perhaps sole, mechanism of suppression The inhibitory influences operated within a wide dynamic range When inhibition was strong, the membrane conductance could be doubled or tripled Furthermore, if a stimulus confined to one subregion was enlarged so that it extended into the next, the sign of response often changed from depolarizing to hyperpolarizing In other instances, the inhibition modulated neuronal output subtly, by elevating spike threshold or altering firing rate at a given membrane voltage

Journal ArticleDOI
TL;DR: It is demonstrated that subthreshold receptive fields are on average large, and the spatio-temporal dynamics of these receptive fields vary as a function of position within the receptive field and strength of excitatory input.
Abstract: Moore, Christopher I. and Sacha B. Nelson. Spatio-temporal subthreshold receptive fields in the vibrissa representation of rat primary somatosensory cortex. J. Neurophysiol. 80: 2882–2892, 1998. Wh...

Journal ArticleDOI
TL;DR: Multi-unit activity was recorded with implanted electrodes from primary visual cortex of awake, fixating monkeys viewing textured displays in which figure and ground regions were segregated by differences in either orientation or motion and the modulatory activity is functionally distinct from the RF properties.
Abstract: By means of their small receptive fields (RFs), neurons in primary visual cortex perform highly localized analyses of the visual scene, far removed from our normal unified experience of vision. Local image elements coded by the RF are put into more global context, however, by means of modulation of the responses of the V1 neurons. Contextual modulation has been shown to follow closely the perceptual interpretation of the scene as a whole. This would suggest that some aspects of contextual modulation can be recorded only in awake and perceiving animals. In this study, multi-unit activity was recorded with implanted electrodes from primary visual cortex of awake, fixating monkeys viewing textured displays in which figure and ground regions were segregated by differences in either orientation or motion. Contextual modulation was isolated from local RF processing, by keeping RF stimulation identical across trials while sampling responses for various positions of the RF relative to figure and ground. Contextual modulation was observed to unfold spatially and temporally in a way that closely resembles the figure-ground percept. When recording was repeated, but with the animals anesthetized, the figure-ground related modulatory activity was selectively suppressed. RF tuning properties, however, remained unaffected. The results show that the modulatory activity is functionally distinct from the RF properties. V1 thus hosts distinct regimes of activity that are mediated by separate mechanisms and that depend differentially on the animal being awake or anesthetized.

Journal ArticleDOI
TL;DR: Krapp et al. as discussed by the authors studied the structure and receptive field organization of optic flow processing interneurons in the fly and found that the receptive field of the interneuron is more receptive than that of the optic flow.
Abstract: Krapp, Holger G., Barbel Hengstenberg, and Roland Hengstenberg. Dendritic structure and receptive-field organization of optic flow processing interneurons in the fly. J. Neurophysiol. 79: 1902–1917...

Journal ArticleDOI
TL;DR: Results indicate that PF neurons can simultaneously convey precise location and object information and thus may play a role in constructing a unified representation of a visual scene.
Abstract: Many prefrontal (PF) neurons convey information about both an object's identity (what) and its location (where). To explore how they represent conjunctions of what and where, we explored the receptive fields of their mnemonic activity (i.e., their "memory fields") by requiring monkeys to remember both an object and its location at many positions throughout a wide portion of central vision. Many PF neurons conveyed object information and had highly localized memory fields that emphasized the contralateral, but not necessarily foveal, visual field. These results indicate that PF neurons can simultaneously convey precise location and object information and thus may play a role in constructing a unified representation of a visual scene.

Journal ArticleDOI
TL;DR: It is demonstrated that layer IV simple cells and layer II and III complex cells show correlated firing consistent with monosynaptic connections, and as expected from the hierarchical model, all connections were in the direction from the simple cell to the complex cell.
Abstract: In the cat primary visual cortex, neurons are classified into the two main categories of simple cells and complex cells based on their response properties. According to the hierarchical model, complex receptive fields derive from convergent inputs of simple cells with similar orientation preferences. This model received strong support from anatomical studies showing that many complex cells lie within the range of layer IV simple-cell axons but outside the range of most thalamic axons. Physiological evidence for the model, however, has remained elusive. Here we demonstrate that layer IV simple cells and layer II and III complex cells show correlated firing consistent with monosynaptic connections. As expected from the hierarchical model, all connections were in the direction from the simple cell to the complex cell, most frequently between cells with similar orientation preferences.

Journal ArticleDOI
TL;DR: In this paper, the role of correlated firing among neurons in visual coding was examined using an information-theoretic analysis, and the average increase in information was approximately 20% for strongly correlated pairs.
Abstract: Correlated firing among neurons is widespread in the nervous system. Precisely correlated spiking, occurring on a millisecond time scale, has recently been observed among neurons in the lateral geniculate nucleus with overlapping receptive fields. We have used an information-theoretic analysis to examine the role of these correlations in visual coding. Considerably more information can be extracted from two cells if temporal correlations between them are considered. The percentage increase in information depends on the degree of correlation; the average increase is approximately 20% for strongly correlated pairs. Thus, precise temporal correlation could be used as an additional information channel from thalamus to visual cortex.

Journal ArticleDOI
TL;DR: Receptive field plasticity develops in several tasks, one-tone and two-tone discriminative classical and instrumental conditioning (habituation produces a frequency-specific decrease in the receptive field), suggesting it as a general process for representing the acquired meaning of a signal stimulus.

Journal ArticleDOI
TL;DR: This study shows the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception and explains the activity of bimodal neurons in premotor and parietal cortex of macaque.
Abstract: Current interpretations of extinction suggest that the disorder is due to an unbalanced competition between ipsilesional and contralesional representations of space. The question addressed in this study is whether the competition between left and right representations of space in one sensory modality (i.e., touch) can be reduced or exacerbated by the activation of an intact spatial representation in a different modality that is functionally linked to the damaged representation (i.e., vision). This hypothesis was tested in 10 right-hemisphere lesioned patients who suffered from reliable tactile extinction. We found that a visual stimulus presented near the patient's ipsilesional hand (i.e., visual peripersonal space) inhibited the processing of a tactile stimulus delivered on the contralesional hand (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). It was also found that a visual stimulus presented near the contralesional hand improved the detection of a tactile stimulus applied to the same hand. In striking contrast, less modulatory effects of vision on touch perception were observed when a visual stimulus was presented far from the space immediately around the patient's hand (i.e., extrapersonal space). This study clearly demonstrates the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand and corresponding visual receptive fields in the space immediately adjacent to the tactile fields.

Journal ArticleDOI
TL;DR: The findings indicate that area 3b neurons act as local spatiotemporal filters that are maximally excited by the presence of particular stimulus features, suggesting that form and texture perception are based on high-level representations and that area3b is an intermediate stage in the processes leading to these representations.
Abstract: We investigated the two-dimensional structure of area 3b neuronal receptive fields (RFs) in three alert monkeys. Three hundred thirty neurons with RFs on the distal fingerpads were studied with scanned, random dot stimuli. Each neuron was stimulated continuously for 14 min, yielding 20,000 response data points. Excitatory and inhibitory components of each RF were determined with a modified linear regression algorithm. Analyses assessing goodness-of-fit, repeatability, and generality of the RFs were developed. Two hundred forty-seven neurons yielded highly repeatable RF estimates, and most RFs accounted for a large fraction of the explainable response of each neuron. Although the area 3b RF structures appeared to be continuously distributed, certain structural generalities were apparent. Most RFs (94%) contained a single, central region of excitation and one or more regions of inhibition located on one, two, three, or all four sides of the excitatory center. The shape, area, and strength of excitatory and inhibitory RF regions ranged widely. Half the RFs contained almost evenly balanced excitation and inhibition. The findings indicate that area 3b neurons act as local spatiotemporal filters that are maximally excited by the presence of particular stimulus features. We believe that form and texture perception are based on high-level representations and that area 3b is an intermediate stage in the processes leading to these representations. Two possibilities are considered: (1) that these high-level representations are basically somatotopic and that area 3b neurons amplify some features and suppress others, or (2) that these representations are highly transformed and that area 3b effects a step in the transformation.

Journal ArticleDOI
TL;DR: This work supports the notion that receptive field integration is the result of local processing within small groups of neurons rather than in single neurons, and construction of self-contained modules that capture nonlinear local circuit interactions are constructed.
Abstract: Integration of inputs by cortical neurons provides the basis for the complex information processing performed in the cerebral cortex. Here, we have examined how primary visual cortical neurons integrate classical and nonclassical receptive field inputs. The effect of nonclassical receptive field stimuli and, correspondingly, of long-range intracortical inputs is known to be context-dependent: the same long-range stimulus can either facilitate or suppress responses, depending on the level of local activation. By constructing a large-scale model of primary visual cortex, we demonstrate that this effect can be understood in terms of the local cortical circuitry. Each receptive field position contributes both excitatory and inhibitory inputs; however, the inhibitory inputs have greater influence when overall receptive field drive is greater. This mechanism also explains contrast-dependent modulations within the classical receptive field, which similarly switch between excitatory and inhibitory. In order to simplify analysis and to explain the fundamental mechanisms of the model, self-contained modules that capture nonlinear local circuit interactions are constructed. This work supports the notion that receptive field integration is the result of local processing within small groups of neurons rather than in single neurons.

Journal ArticleDOI
29 Oct 1998-Nature
TL;DR: This work proposes that the sparse, S-opponent signal in the lateral geniculate nucleus is amplified in area V1, possibly through recurrent excitatory networks, and results in a delayed, sluggish cortical S-cone signal which is then integrated with L/M-opp opponent signals to rotate the lateralgeniculated nucleus chromatic axes.
Abstract: The ability to distinguish colour from intensity variations is a difficult computational problem for the visual system because each of the three cone photoreceptor types absorb all wavelengths of light, although their peak sensitivities are at relatively short (S cones), medium (M cones), or long (L cones) wavelengths The first stage in colour processing is the comparison of the outputs of different cone types by spectrally opponent neurons in the retina and upstream in the lateral geniculate nucleus Some neurons receive opponent inputs from L and M cones, whereas others receive input from S cones opposed by combined signals from L and M cones Here we report how the outputs of the L/M- and S-opponent geniculate cell types are combined in time at the next stage of colour processing, in the macaque primary visual cortex (V1) Some V1 neurons respond to a single chromatic region, with either a short (68-95 ms) or a longer (96-135 ms) latency, whereas others respond to two chromatic regions with a difference in latency of 20-30 ms Across all types, short latency responses are mostly evoked by L/M-opponent inputs whereas longer latency responses are evoked mostly by S-opponent inputs Furthermore, neurons with late S-cone inputs exhibit dynamic changes in the sharpness of their chromatic tuning over time We propose that the sparse, S-opponent signal in the lateral geniculate nucleus is amplified in area V1, possibly through recurrent excitatory networks This results in a delayed, sluggish cortical S-cone signal which is then integrated with L/M-opponent signals to rotate the lateral geniculate nucleus chromatic axes

Journal ArticleDOI
12 Nov 1998-Nature
TL;DR: It is shown experimentally that the shape of receptive fields in the primary visual cortex of anaesthetized cats undergoes significant modifications, which are correlated with the general state of the brain as assessed by electroencephalography: receptive fields are wider during synchronized states and smaller during non-synchronized states.
Abstract: To extract important information from the environment on a useful timescale, the visual system must be able to adapt rapidly to constantly changing scenes. This requires dynamic control of visual resolution, possibly at the level of the responses of single neurons. Individual cells in the visual cortex respond to light stimuli on particular locations (receptive fields) on the retina, and the structure of these receptive fields can change in different contexts. Here we show experimentally that the shape of receptive fields in the primary visual cortex of anaesthetized cats undergoes significant modifications, which are correlated with the general state of the brain as assessed by electroencephalography: receptive fields are wider during synchronized states and smaller during non-synchronized states. We also show that cortical receptive fields shrink over time when stimulated with flashing light spots. Finally, by using a network model we account for the changing size of the cortical receptive fields by dynamically rescaling the levels of excitation and inhibition in the visual thalamus and cortex. The observed dynamic changes in the sizes of the cortical receptive field could be a reflection of a process that adapts the spatial resolution within the primary visual pathway to different states of excitability.

Journal ArticleDOI
TL;DR: This finding demonstrates a dramatic 'top-down' influence of cortex on receptive field size in the somatosensory thalamus and indicates that changes in 'higher-order' areas of the brain can trigger extensive changes in the receptive field characteristics of neurons located earlier in the processing pathway.
Abstract: The influence of cortical feedback on receptive field organization in the thalamus was assessed in the primate somatosensory system. Chronic and acute suppression of neuronal activity in primary somatosensory cortex resulted in a striking enlargement of receptive fields in the ventroposterior thalamus. This finding demonstrates a dramatic 'top-down' influence of cortex on receptive field size in the somatosensory thalamus. In addition, this result has important implications for studies of adult neuronal plasticity because it indicates that changes in 'higher-order' areas of the brain can trigger extensive changes in the receptive field characteristics of neurons located earlier in the processing pathway.

Journal ArticleDOI
26 Nov 1998-Nature
TL;DR: It is concluded that synchronin V1 does not reflect the binding of features that leads to texture segregation, and there is no systematic relationship between the synchrony of firing of pairs of neurons and the perceptual organization of the scene.
Abstract: The visual environment is perceived as an organized whole of objects and their surroundings. In many visual cortical areas, however, neurons are typically activated when a stimulus is presented over a very limited portion of the visual field, the receptive field of that neuron. To bridge the gap between this piecewise neuronal analysis and our global visual percepts, it has been postulated that neurons representing elements of the same object fire in synchrony to represent the perceptual organization of a scene. Experiments with stimuli such as moving bars or gratings have provided evidence for this hypothesis. We have further tested this by presenting monkeys with various textured scenes consisting of a figure on a background, and recorded neuronal activity in the primary visual cortex (area V1). Our results show no systematic relationship between the synchrony of firing of pairs of neurons and the perceptual organization of the scene. Instead, pairs of recording sites representing elements of the same figure most commonly showed equal amounts of synchrony between them as did pairs of which one site represented the figure and the other the background. We conclude that synchrony in V1 does not reflect the binding of features that leads to texture segregation.

Journal ArticleDOI
TL;DR: Adenylyl cyclase type I (Adcy1) is identified as the gene disrupted in brl mutant mice by fine mapping of proximal chromosome 11, enzyme assay, mutation analysis and examination of mice homozygous for a targeted disruption of Adcy1.
Abstract: The somatosensory (SI) cortex of mice displays a patterned, nonuniform distribution of neurons in layer IV called the 'barrelfield' (ref 1) Thalamocortical afferents (TCAs) that terminate in layer IV are segregated such that each barrel, a readily visible cylindrical array of neurons surrounding a cell-sparse center, represents a distinct receptive field TCA arbors are confined to the barrel hollow and synapse on barrel-wall neurons whose dendrites are oriented toward the center of the barrel Mice homozygous for the barrelless (brl) mutation, which occurred spontaneously in ICR stock at Universite de Lausanne (Switzerland), fail to develop this patterned distribution of neurons, but still display normal topological organization of the SI cortex Despite the absence of barrels and the overlapping zones of TCA arborization, the size of individual whisker representations, as judged by 2-deoxyglucose uptake, is similar to that of wild-type mice We identified adenylyl cyclase type I (Adcy1) as the gene disrupted in brl mutant mice by fine mapping of proximal chromosome 11, enzyme assay, mutation analysis and examination of mice homozygous for a targeted disruption of Adcy1 These results provide the first evidence for involvement of cAMP signalling pathways in pattern formation of the brain

Journal ArticleDOI
TL;DR: A biophysically detailed compartmental model is used to investigate whether nonlinear integration of LGN synaptic inputs within the dendrites of individual pyramidal cells could contribute to complex-cell receptive field structure, and concludes that unoriented LGN inputs to a complex cell could contribute in a significant way to its orientation tuning.
Abstract: Hubel and Wiesel (1962) first distinguished “simple” from “complex” cells in visual cortex and proposed a processing hierarchy in which rows of LGN cells are pooled to drive oriented simple cell subunits, which are pooled in turn to drive complex cells. Although parsimonious and highly influential, the pure hierarchical model has since been challenged by results indicating that many complex cells receive excitatory monosynaptic input from LGN cells or do not depend on simple cell input. Alternative accounts of complex cell orientation tuning remain scant, however, and the function of monosynaptic LGN contacts onto complex cell dendrites remains unknown. We have used a biophysically detailed compartmental model to investigate whether nonlinear integration of LGN synaptic inputs within the dendrites of individual pyramidal cells could contribute to complex-cell receptive field structure. We show that an isolated cortical neuron with “active” dendrites, driven only by excitatory inputs from overlapping ON- and OFF-center LGN subfields, can produce clear phase-invariant orientation tuning—a hallmark response characteristic of a complex cell. The tuning is shown to depend critically both on the spatial arrangement of LGN synaptic contacts across the complex cell dendritic tree, established by a Hebbian developmental principle, and on the physiological efficacy of excitatory voltage-dependent dendritic ion channels. We conclude that unoriented LGN inputs to a complex cell could contribute in a significant way to its orientation tuning, acting in concert with oriented inputs to the same cell provided by simple cells or other complex cells. As such, our model provides a novel, experimentally testable hypothesis regarding the basis of orientation tuning in the complex cell population, and more generally underscores the potential importance of nonlinear intradendritic subunit processing in cortical neurophysiology.

Journal ArticleDOI
TL;DR: PET neuroimaging was used to measure regional brain activity in volunteer human subjects during discriminatory classical conditioning of high (8000 Hz) or low (200 Hz) frequency tones by an aversive 100 dB white noise burst, and conditioning–related, frequency–specific modulation of tonotopic neural responses in the auditory cortex was observed.
Abstract: Experience-dependent plasticity of receptive fields in the auditory cortex has been demonstrated by electrophysiological experiments in animals. In the present study we used PET neuroimaging to measure regional brain activity in volunteer human subjects during discriminatory classical conditioning of high (8000 Hz) or low (200 Hz) frequency tones by an aversive 100 dB white noise burst. Conditioning-related, frequency-specific modulation of tonotopic neural responses in the auditory cortex was observed. The modulated regions of the auditory cortex positively covaried with activity in the amygdala, basal forebrain and orbitofrontal cortex, and showed context-specific functional interactions with the medial geniculate nucleus. These results accord with animal single-unit data and support neurobiological models of auditory conditioning and value-dependent neural selection.