Showing papers on "Receptive field published in 2003"
TL;DR: Although inhibition is typically as strong as excitation, it is not necessary to establish tuning, even in the receptive field surround, and Balanced inhibition might serve to increase the temporal precision and thereby reduce the randomness of cortical operation, rather than to increase noise as has been proposed previously.
Abstract: Neurons in the primary auditory cortex are tuned to the intensity and specific frequencies of sounds, but the synaptic mechanisms underlying this tuning remain uncertain. Inhibition seems to have a functional role in the formation of cortical receptive fields, because stimuli often suppress similar or neighbouring responses, and pharmacological blockade of inhibition broadens tuning curves. Here we use whole-cell recordings in vivo to disentangle the roles of excitatory and inhibitory activity in the tone-evoked responses of single neurons in the auditory cortex. The excitatory and inhibitory receptive fields cover almost exactly the same areas, in contrast to the predictions of classical lateral inhibition models. Thus, although inhibition is typically as strong as excitation, it is not necessary to establish tuning, even in the receptive field surround. However, inhibition and excitation occurred in a precise and stereotyped temporal sequence: an initial barrage of excitatory input was rapidly quenched by inhibition, truncating the spiking response within a few (1-4) milliseconds. Balanced inhibition might thus serve to increase the temporal precision and thereby reduce the randomness of cortical operation, rather than to increase noise as has been proposed previously.
1,341 citations
TL;DR: This work shows that visual responses in area V4 could be enhanced after brief stimulation of retinotopically corresponding sites within the FEF using currents below that needed to evoke saccades, and suggests that the gain of visual signals is modified according to the strength of spatially corresponding eye movement commands.
Abstract: Several decades of psychophysical and neurophysiological studies have established that visual signals are enhanced at the locus of attention1,2,3,4,5. What remains a mystery is the mechanism that initiates biases in the strength of visual representations6. Recent evidence argues that, during spatial attention, these biases reflect nascent saccadic eye movement commands7,8. We examined the functional interaction of saccade preparation and visual coding by electrically stimulating sites within the frontal eye fields (FEF) and measuring its effect on the activity of neurons in extrastriate visual cortex. Here we show that visual responses in area V4 could be enhanced after brief stimulation of retinotopically corresponding sites within the FEF using currents below that needed to evoke saccades. The magnitude of the enhancement depended on the effectiveness of receptive field stimuli as well as on the presence of competing stimuli outside the receptive field. Stimulation of non-corresponding FEF representations could suppress V4 responses. The results suggest that the gain of visual signals is modified according to the strength of spatially corresponding eye movement commands.
1,071 citations
TL;DR: It is reported that neurons in cat primary auditory cortex (A1) responded more strongly to a rarely presented sound than to the same sound when it was common, indicating that A1 neurons, in addition to processing the acoustic features of sounds, may also be involved in sensory memory and novelty detection.
Abstract: The ability to detect rare auditory events can be critical for survival. We report here that neurons in cat primary auditory cortex (A1) responded more strongly to a rarely presented sound than to the same sound when it was common. For the rare stimuli, we used both frequency and amplitude deviants. Moreover, some A1 neurons showed hyperacuity for frequency deviants--a frequency resolution one order of magnitude better than receptive field widths in A1. In contrast, auditory thalamic neurons were insensitive to the probability of frequency deviants. These phenomena resulted from stimulus-specific adaptation in A1, which may be a single-neuron correlate of an extensively studied cortical potential--mismatch negativity--that is evoked by rare sounds. Our results thus indicate that A1 neurons, in addition to processing the acoustic features of sounds, may also be involved in sensory memory and novelty detection.
961 citations
TL;DR: Investigation of the hypothesis that task performance can rapidly and adaptively reshape cortical receptive field properties in accord with specific task demands and salient sensory cues found that attending to a specific target frequency during the detection task consistently induced localized facilitative changes in STRF shape.
Abstract: We investigated the hypothesis that task performance can rapidly and adaptively reshape cortical receptive field properties in accord with specific task demands and salient sensory cues. We recorded neuronal responses in the primary auditory cortex of behaving ferrets that were trained to detect a target tone of any frequency. Cortical plasticity was quantified by measuring focal changes in each cell's spectrotemporal response field (STRF) in a series of passive and active behavioral conditions. STRF measurements were made simultaneously with task performance, providing multiple snapshots of the dynamic STRF during ongoing behavior. Attending to a specific target frequency during the detection task consistently induced localized facilitative changes in STRF shape, which were swift in onset. Such modulatory changes may enhance overall cortical responsiveness to the target tone and increase the likelihood of 'capturing' the attended target during the detection task. Some receptive field changes persisted for hours after the task was over and hence may contribute to long-term sensory memory.
787 citations
TL;DR: It is shown how a population of ganglion cells selective for differential motion can rapidly flag moving objects, and even segregate multiple moving objects.
Abstract: An important task in vision is to detect objects moving within a stationary scene. During normal viewing this is complicated by the presence of eye movements that continually scan the image across the retina, even during fixation. To detect moving objects, the brain must distinguish local motion within the scene from the global retinal image drift due to fixational eye movements. We have found that this process begins in the retina: a subset of retinal ganglion cells responds to motion in the receptive field centre, but only if the wider surround moves with a different trajectory. This selectivity for differential motion is independent of direction, and can be explained by a model of retinal circuitry that invokes pooling over nonlinear interneurons. The suppression by global image motion is probably mediated by polyaxonal, wide-field amacrine cells with transient responses. We show how a population of ganglion cells selective for differential motion can rapidly flag moving objects, and even segregate multiple moving objects.
418 citations
TL;DR: This research suggests that cortical cells may be "hard wired" to respond preferentially to the highest-contrast stimulus in their RF, and neural systems for attention capitalize on this mechanism by dynamically increasing the effective contrast of the stimulus that is task relevant.
409 citations
TL;DR: In the rat A1, direction selectivity is topographically ordered in parallel with characteristic frequency (CF): low CF neurons preferred upward sweeps, whereas highCF neurons preferred downward sweeps, and thus suggested a synaptic mechanism for the shaping of FM directionSelectivity and its topographic ordering.
Abstract: The direction of frequency-modulated (FM) sweeps is an important temporal cue in animal and human communication. FM direction-selective neurons are found in the primary auditory cortex (A1), but their topography and the mechanisms underlying their selectivity remain largely unknown. Here we report that in the rat A1, direction selectivity is topographically ordered in parallel with characteristic frequency (CF): low CF neurons preferred upward sweeps, whereas high CF neurons preferred downward sweeps. The asymmetry of 'inhibitory sidebands', suppressive regions flanking the tonal receptive field (TRF) of the spike response, also co-varied with CF. In vivo whole-cell recordings showed that the direction selectivity already present in the synaptic inputs was enhanced by cortical synaptic inhibition, which suppressed the synaptic excitation of the non-preferred direction more than that of the preferred. The excitatory and inhibitory synaptic TRFs had identical spectral tuning, but with inhibition delayed relative to excitation. The spectral asymmetry of the synaptic TRFs co-varied with CF, as had direction selectivity and sideband asymmetry, and thus suggested a synaptic mechanism for the shaping of FM direction selectivity and its topographic ordering.
386 citations
TL;DR: Competitive interactions between barrel and septal circuits in the establishment of precise intracortical circuits are revealed.
369 citations
TL;DR: This fast, synchronous, highly sensitive and broadly tuned feed-forward inhibitory network is well suited to suppress spike generation in spiny neurons following all but the most optimal feedforward excitatory inputs.
Abstract: ‘Fast-spike’ interneurons of layer 4 mediate thalamocortical feedforward inhibition and can, with some confidence, be identified using extracellular methods. In somatosensory barrel cortex of awake rabbits, these ‘suspected inhibitory interneurons’ (SINs) have distinct receptive field properties: they respond to vibrissa displacement with very high sensitivity and temporal fidelity. However, they lack the directional specificity that is clearly seen in most of their ventrobasal thalamocortical afferents. Several lines of evidence show that layer-4 SINs receive a potent and highly convergent and divergent functional input from topographically aligned thalamocortical neurons. Whereas the unselective pooling of convergent thalamocortical inputs onto SINs generates sensitive and broadly tuned inhibitory receptive fields, the potent divergence of single thalamocortical neurons onto many SINs generates sharply synchronous (±1 ms) activity (because of coincident EPSPs). Synchronous discharge of these interneurons following thalamocortical impulses will generate a synchronous feedforward release of GABA within the barrel. Thalamocortical impulses will, therefore, generate only a brief ‘window of excitability’ during which spikes can occur in the post-synaptic targets of fast-spike interneurons. This fast, synchronous, highly sensitive and broadly tuned feedforward inhibitory network is well suited to suppress spike generation in spiny neurons following all but the most optimal feedforward excitatory inputs.
353 citations
TL;DR: The effect of prolonged stimulation on neuronal responsivity in the macaque's area MT, a cortical area whose importance to visual motion perception is well established, was studied.
350 citations
TL;DR: It is found that orientation-tuned suppression could effectively propagate across 6 - 8 mm of cortex at ∼1 m/sec, considerably faster than expected for horizontal cortical connections previously implicated in surround suppression.
Abstract: Iso-orientation surround suppression is a powerful form of visual contextual modulation in which a stimulus of the preferred orientation of a neuron placed outside the classical receptive field (CRF) of the neuron suppresses the response to stimuli within the CRF. This suppression is most often attributed to orientation-tuned signals that propagate laterally across the cortex, activating local inhibition. By studying the temporal properties of surround suppression, we have uncovered characteristics that challenge standard notions of surround suppression. We found that the latency of suppression depended on its strength. Across cells, strong suppression arrived on average 30 msec earlier than weak suppression, and suppression sometimes arrived faster than the excitatory CRF response. We compared the relative latency of CRF response onset and offset with the relative latency of suppression onset and offset. Response onset was delayed relative to response offset in the CRF but not in the surround. This is not the expected result if neurons targeted by suppression are like those that generate it. We examined the time course of suppression as a function of distance of the surround stimulus from the CRF and found that suppression was predominantly sustained for nearby stimuli and predominantly transient for distant stimuli. By comparing the latency of suppression for nearby and distant stimuli, we found that orientation-tuned suppression could effectively propagate across 6 - 8 mm of cortex at ∼1 m/sec. This is considerably faster than expected for horizontal cortical connections previously implicated in surround suppression. We offer refinements to circuits for surround suppression that account for these results and describe how feedback from cells with large CRFs can account for the rapid propagation of suppression within V1.
TL;DR: It is proposed that this is a perceptual correlate of centre–surround antagonism, possibly within a population of neurons in the middle temporal visual area, and the spatial antagonism of motion signals observed at high contrast gives way to spatial summation as contrast decreases.
Abstract: Centre–surround receptive field organization is a ubiquitous property in mammalian visual systems, presumably tailored for extracting image features that are differentially distributed over space1. In visual motion, this is evident as antagonistic interactions between centre and surround regions of the receptive fields of many direction-selective neurons in visual cortex2,3,4,5,6. In a series of psychophysical experiments we make the counterintuitive observation that increasing the size of a high-contrast moving pattern renders its direction of motion more difficult to perceive and reduces its effectiveness as an adaptation stimulus. We propose that this is a perceptual correlate of centre–surround antagonism, possibly within a population of neurons in the middle temporal visual area. The spatial antagonism of motion signals observed at high contrast gives way to spatial summation as contrast decreases. Evidently, integration of motion signals over space depends crucially on the visibility of those signals, thereby allowing the visual system to register motion information efficiently and adaptively.
TL;DR: It is concluded that the lemniscal (barrel‐ related) and paralemniscal (septum‐related) afferent inputs remain anatomically and functionally segregated in L2/3 and their broad subthreshold RF suggests that L2 /3 cells integrate PSPs from several barrel columns.
Abstract: A major aim of sensory physiology is to identify those synaptic connections in cortical representational areas (functional maps) by which sensory stimuli are transformed into a specific pattern of sub- (PSPs) and suprathreshold (APs) electrical activity. In the neocortex such maps consist of functional units, referred to as columns (Mountcastle, 1957; Hubel & Wiesel, 1962). These comprise the cells in different cortical layers that respond to a particular sensory stimulus. To understand sensory maps mechanistically and at a subcellular resolution, firstly the synaptic connections between cells that constitute a column and also those between different columns have to be identified in a layer-specific manner. Secondly the spatial and temporal transformations of PSP and AP patterns along sensory pathways and in the different cortical layers have to be understood.
The coarse layout of sensory information flow within a column is comparable across different sensory cortices. Afferent signals arrive in cortical layer 4 (L4) from thalamic nuclei. They are relayed from L4 to supragranular layers 3 (L3) and 2 (L2) as well as to infragranular layers (L5 and L6). Extracellular unit recording and anatomical work have compiled a detailed picture of the columnar cytoarchitecture and AP activity in columns of some sensory cortices. The detailed anatomy and synaptic mechanisms of the connections that generate specific patterns of PSPs and APs are, however, largely unclear. Few studies have determined both the soma location and the dendritic and axonal morphology of cortical cells as well as their sub- and suprathreshold RFs (e.g. Ito, 1992; Brecht & Sakmann, 2002a,b). Such measurements are, however, a prerequisite if one wants to infer how PSPs or APs represent a sensory stimulus in the different layers of the cortex.
L4 of the rodent somatosensory cortex contains aggregates of neuronal somata referred to as barrels, which are innervated in a strict topographical order by inputs representing individual facial whiskers (Woolsey & Van der Loos, 1970). Anatomical studies have demonstrated that barrel cells are targeted by thalamic inputs from the ventral posterior medial nucleus (VPM), which are part of the lemniscal pathway (Diamond, 1995), while the septa between barrels are innervated by thalamic afferents projecting from the posterior medial nucleus (POM), which belong to the paralemniscal pathway (Koralek et al. 1988; Lu & Lin, 1993). While most lemniscal afferents innervate the barrels, some VPM inputs also target the L5B/L6 border and paralemniscal POM afferents densely innervate L5A (Koralek et al. 1988; Lu & Lin, 1993). Barrel borders and the morphology of a cortical cell can be visualised simultaneously (Ito, 1992), such that the laminar position of a cell and its position relative to barrel column borders as well as its detailed dendritic and axonal morphology can be measured. Such techniques provided physiological evidence that lemniscal (the VPM/barrel projection) and paralemniscal (the POM/septum projection) pathways are largely segregated in L4 (Brecht & Sakmann, 2002a). Furthermore the RFs of barrel and septum cells are dynamic but are narrow and restricted to a PW and at most the first order SuWs.
The homogeneous appearance of L3 and L2 in the horizontal plane may indicate merging of the whisker-specific anatomical pathways, whose strict separation in L4 gives rise to the discontinuous appearance of barrels (Woolsey & Van der Loos, 1970). The projection pattern of L4 spiny neuron axons suggests, however, that selectively connected barrel columns also exist (Petersen & Sakmann, 2000; Petersen et al. 2003; Lubke et al. 2003). The convergence of whisker-evoked responses between columns is also suggested by unit recordings from unidentified cells (Simons, 1978, 1995; Armstrong-James & Fox, 1987; Armstrong-James et al. 1992; Armstrong-James, 1995). They show that suprathreshold RFs in L3 and L2 cells are larger in size than those of L4 cells. The work of Ahissar and colleagues on the representation of temporal frequencies in L2/3 cell spike trains suggests a merging of barrel and septum inputs in supragranular layers (Ahissar et al. 2001). Anatomical data, however, suggest that barrel and septal pathways also remain separate in L3 and L2 (Kim & Ebner, 1999).
We report here in vivo whole-cell voltage recordings of whisker-evoked PSPs and APs from cells in L2/3, combined with reconstruction of their dendritic and axonal arbors. We determined the horizontal and vertical position of these cells with reference to the barrel map to establish relationships between individual cell classes in L3 and L2 located above barrel and septa, and their sub- and suprathreshold RFs. The aim is to construct relationships between anatomical cell classes and their functional properties. Comparison with similar data from L4 cells (Brecht & Sakmann, 2002b) and incorporation of in vitro data (Feldmeyer et al. 2002; Lubke et al. 2003) on connectivity should allow a quantitative description of the flow of excitation through and between cortical barrel columns.
TL;DR: Convergence of bottom-up and top-down processing streams in area V4 results in an adaptive, dynamic map of salience that guides oculomotor planning during natural vision.
TL;DR: Evidence is presented that inactivation of higher order areas leads to a major decrease in the strength of the suppressive surround of neurons in lower order areas, supporting the hypothesis that feedback connections play a major role in center-surround interactions.
Abstract: It is commonly assumed that the orientation-selective surround field of neurons in primary visual cortex (V1) is due to interactions provided solely by intrinsic long-range horizontal connections. We review evidence for and against this proposition and conclude that horizontal connections are too slow and cover too little visual field to subserve all the functions of suppressive surrounds of V1 neurons in the macaque monkey. We show that the extent of visual space covered by horizontal connections corresponds to the region of low contrast summation of the receptive field center mechanism. This region encompasses the classically defined receptive field center and the proximal surround. Beyond this region, feedback connections are the most likely substrate for surround suppression. We present evidence that inactivation of higher order areas leads to a major decrease in the strength of the suppressive surround of neurons in lower order areas, supporting the hypothesis that feedback connections play a major role in center–surround interactions. � 2003 Elsevier Ltd. All rights reserved.
TL;DR: This review suggests that columns relating to different response properties are mapped in cortex at different spatial scales, and suggests that these properties first emerge in mid-layer 4C through a combination of thalamic afferent inputs and local intracortical circuitry.
Abstract: In this review we re-examine the concept of a cortical column in macaque primary visual cortex, and consider to what extent a functionally defined column reflects any sort of anatomical entity that subdivides cortical territory. Functional studies have shown that columns relating to different response properties are mapped in cortex at different spatial scales. We suggest that these properties first emerge in mid-layer 4C through a combination of thalamic afferent inputs and local intracortical circuitry, and are then transferred to other layers in a columnar fashion, via interlaminar relays, where additional processing occurs. However, several properties are not strictly columnar since they do not appear in all cortical layers. In contrast to the functional column, an anatomically based cortical column is defined most clearly in terms of the reciprocal connections it makes, both via intra-areal lateral connections and inter-areal feedback/feedforward pathways. The column boundaries are reinforced by interplay between lateral inhibition spreading beyond the column boundary and disinhibition within the column. The anatomical column acts as a functionally tuned unit and point of information collation from laterally offset regions and feedback pathways. Thalamic inputs provide the highcontrast receptive field sizes of the column’s neurons, intra-areal lateral connections provide their low contrast summation field sizes, and feedback pathways provide surround modulation of receptive fields responses.
TL;DR: In this paper, the authors characterized receptive-field structure in primary auditory cortex (AI) and anterior auditory field (AAF) of anesthetized mice using spectrally complex and temporally dynamic stimuli as well as simple tonal stimuli.
Abstract: The mouse is a promising model system for auditory cortex research because of the powerful genetic tools available for manipulating its neural circuitry. Previous studies have identified two tonotopic auditory areas in the mouse-primary auditory cortex (AI) and anterior auditory field (AAF)-but auditory receptive fields in these areas have not yet been described. To establish a foundation for investigating auditory cortical circuitry and plasticity in the mouse, we characterized receptive-field structure in AI and AAF of anesthetized mice using spectrally complex and temporally dynamic stimuli as well as simple tonal stimuli. Spectrotemporal receptive fields (STRFs) were derived from extracellularly recorded responses to complex stimuli, and frequency-intensity tuning curves were constructed from responses to simple tonal stimuli. Both analyses revealed temporal differences between AI and AAF responses: peak latencies and receptive-field durations for STRFs and first-spike latencies for responses to tone bursts were significantly longer in AI than in AAF. Spectral properties of AI and AAF receptive fields were more similar, although STRF bandwidths were slightly broader in AI than in AAF. Finally, in both AI and AAF, a substantial minority of STRFs were spectrotemporally inseparable. The spectrotemporal interaction typically appeared in the form of clearly disjoint excitatory and inhibitory subfields or an obvious spectrotemporal slant in the STRF. These data provide the first detailed description of auditory receptive fields in the mouse and suggest that although neurons in areas AI and AAF share many response characteristics, area AAF may be specialized for faster temporal processing.
TL;DR: The detailed comparison of electrophysiological and psychophysical data reveals strong correlations between the integrative behavior of V1 cells and some aspects of "low- level" and "mid-level" conscious perception, suggesting that as early as the V1 stage, the visual system is able to make use of contextual cues to recover local visual scene properties or correct their interpretation.
Abstract: The spiking response of a primary visual cortical cell to a stimulus placed within its receptive field can be up- and down-regulated by the simultaneous presentation of objects or scenes placed in the “silent” regions which surround the receptive field. We here review recent progresses that have been made both at the experimental and theoretical levels in the description of these so-called “Center/Surround” modulations and in the understanding of their neural basis. Without denying the role of a modulatory feedback from higher cortical areas, recent results support the view that some of these phenomena result from the dynamic interplay between feedforward projections and horizontal intracortical connectivity in V1. Uncovering the functional role of the contextual periphery of cortical receptive fields has become an area of active investigation. The detailed comparison of electrophysiological and psychophysical data reveals strong correlations between the integrative behavior of V1 cells and some aspects of “low-level” and “mid-level” conscious perception. These suggest that as early as the V1 stage, the visual system is able to make use of contextual cues to recover local visual scene properties or correct their interpretation. Promising ideas have emerged on the importance of such a strategy for the coding of visual scenes, and the processing of static and moving objects.
TL;DR: In this study, electrical microstimulation of VIP, but not of surrounding tissue, caused a constellation of movements including eye closure, facial grimacing, head withdrawal, elevation of the shoulder, and movements of the hand to the space beside the head or shoulder.
Abstract: Most neurons in the ventral intraparietal area (VIP) of the macaque brain respond to both visual and tactile stimuli. The tactile receptive field is usually on the face, and the visual receptive field usually corresponds spatially to the tactile receptive field. In this study, electrical microstimulation of VIP, but not of surrounding tissue, caused a constellation of movements including eye closure, facial grimacing, head withdrawal, elevation of the shoulder, and movements of the hand to the space beside the head or shoulder. A similar set of movements was evoked by an air puff to the monkey's cheek. One interpretation is that VIP contributes to defensive movements triggered by stimuli on or near the head.
TL;DR: While the extent of activated retinotopic visual cortex increased with the size of the attended region, the level of neural activity in a given subregion decreased, which is consistent with the physiological predictions of the zoom lens model.
Abstract: Attending a certain region in space enhances activity in visual areas retinotopically mapped to this region; stimuli presented in this region are preferentially processed. The zoom lens model of visual attention proposes that the attended region can be adjusted in size and predicts a tradeoff between its size and processing efficiency because of limited processing capacities. By means of event-related functional magnetic resonance imaging, we analyzed neural activity in multiple visual areas as a function of the size of an attended visual field region, which was defined by a spatial cue stimulus. After cueing, a target object, defined by a specific feature conjunction, had to be identified among objects within the cued region. Neural activity preceding the objects in multiple retinotopic visual areas correlated with the size of the attended region, as did subjects' performance. While the extent of activated retinotopic visual cortex increased with the size of the attended region, the level of neural activity in a given subregion decreased. These findings are consistent with the physiological predictions of the zoom lens model. Size-related modulations of neural activity were pronounced in early visual areas. We relate this finding to the small receptive field of these areas, whereby only neuronal units with receptive fields covering the attended region received a top-down bias. This preactivation of neuronal units may then have gated selective processing of the features of the object that appeared at the attended location, thus enabling feature integration and object identification.
28 Nov 2003
TL;DR: Owls can localize sounds by using either the isomorphic map of auditory space in the midbrain or forebrain neural networks in which space is not mapped.
Abstract: Behavioral, anatomical, and physiological approaches can be integrated in the study of sound localization in barn owls. Space representation in owls provides a useful example for discussion of place and ensemble coding. Selectivity for space is broad and ambiguous in low-order neurons. Parallel pathways for binaural cues and for different frequency bands converge on high-order space-specific neurons, which encode space more precisely. An ensemble of broadly tuned place-coding neurons may converge on a single high-order neuron to create an improved labeled line. Thus, the two coding schemes are not alternate methods. Owls can localize sounds by using either the isomorphic map of auditory space in the midbrain or forebrain neural networks in which space is not mapped.
TL;DR: Stimuli flashed <250 ms before the saccade-evoked responses in both the presaccadic and the postsaccadic receptive fields, resulting in an increase in the effective receptive field size, an effect that is suggested is responsible for perisaccadic perceptual inaccuracies.
Abstract: Neurons in the lateral intraparietal area of the monkey (LIP) have visual receptive fields in retinotopic coordinates when studied in a fixation task. However, in the period immediately surrounding...
TL;DR: It is shown that the cellular basis generating individual sensory response properties is separable in the developing neocortex, and the development and plasticity of ocular dominance was unaffected, and orientation preference failed to mature in these mice.
Abstract: How individual receptive field properties are formed in the maturing sensory neocortex remains largely unknown. The shortening of N-methyl-d-aspartate (NMDA) receptor currents by 2A subunit (NR2A) insertion has been proposed to delimit the critical period for experience-dependent refinement of circuits in visual cortex. In mice engineered to maintain prolonged NMDA responses by targeted deletion of NR2A, the sensitivity to monocular deprivation was surprisingly weakened but restricted to the typical critical period and delayed normally by dark rearing from birth. Orientation preference instead failed to mature, occluding further effects of dark rearing. Interestingly, a full ocular dominance plasticity (but not orientation bias) was selectively restored by enhanced inhibition, reflecting an imbalanced excitation in the absence of NR2A. Many of the downstream pathways involved in NMDA signaling are coupled to the receptor through a variety of protein–protein interactions and adaptor molecules. To further investigate a mechanistic dissociation of receptive field properties in the developing visual system, mice carrying a targeted disruption of the NR2A-associated 95-kDa postsynaptic density (PSD95) scaffolding protein were analyzed. Although the development and plasticity of ocular dominance was unaffected, orientation preference again failed to mature in these mice. Taken together, our results demonstrate that the cellular basis generating individual sensory response properties is separable in the developing neocortex.
TL;DR: Recent work on the corticothalamic pathways associated with the visual, auditory, and somatosensory systems demonstrates that sensory responses of thalamic neurons result from dynamic interactions between feedforward and feedback pathways.
TL;DR: The work suggests that different sources of inhibition, either selective for specific features or broadly tuned, interact to provide appropriate representations of elements within the environment.
Abstract: Here we explore inhibitory circuits at the thalamocortical stage of processing in layer 4 of the cat’s visual cortex, focusing on the anatomy and physiology of the interneurons themselves. Our immediate aim was to explore the inhibitory mechanisms that contribute to orientation selectivity, perhaps the most dramatic response property to emerge across the thalamocortical synapse. The broader goal was to understand how inhibitory circuits operate. Using whole-cell recording in cats in vivo, we found that layer 4 contains two populations of inhibitory cells defined by receptive field class—simple and complex. The simple cells were selective for stimulus orientation, whereas the complex cells were not. Our observations help to explain how neurons become sensitive to stimulus orientation and maintain that selectivity as stimulus contrast changes. Overall, the work suggests that different sources of inhibition, either selective for specific features or broadly tuned, interact to provide appropriate representations of elements within the environment.
TL;DR: The results show that the temporal visual cortex provides an unambiguous representation in natural scenes by responding to the object shown at or close to the fixation point.
Abstract: Inferior temporal cortex neurons have generally been found to have large visual receptive fields that typically include the fovea and extend throughout much of the visual field However, a problem of such a large receptive field is that it does not easily support object selection by subsequent processing areas, in that all objects within such a large receptive field might activate inferior temporal cortex cells To clarify this, we recorded from inferior temporal cortex neurons while macaques searched for objects in complex natural scenes or in plain backgrounds, as normally used Inferior temporal cortex neuron receptive fields were much smaller in natural scenes (mean radius, 11°) than in plain backgrounds (39°) With two objects in a scene, one of which was a target for action (a touch), the firing rates were equally high during foveation of the effective stimulus when it was the target and when it was the distractor in both the plain and the complex scenes With a plain background and two objects present, the receptive fields were much larger (24°) for the stimulus when it was the target than when it was the distractor (9°) This effect of object-based attention was much less evident in the complex scene, when the receptive fields were small both when the stimulus was a distractor and when it was a target The results show that the temporal visual cortex provides an unambiguous representation in natural scenes by responding to the object shown at or close to the fixation point
TL;DR: The hypothesis that pH changes in the synaptic clefts, which are intimately related to the membrane voltage of the HCs, mediate the feedback from theHCs to cone photoreceptors is proposed.
Abstract: Feedback from horizontal cells (HCs) to cone photoreceptors plays a key role in the center-surround–receptive field organization of retinal neurons. Recordings from cone photoreceptors in newt retinal slices were obtained by the whole-cell patch-clamp technique, using a superfusate containing a GABA antagonist (100 μM picrotoxin). Surround illumination of the receptive field increased the voltage-dependent calcium current (ICa) in the cones, and shifted the activation voltage of ICa to negative voltages. External alkalinization also increased cone ICa and shifted its activation voltage toward negative voltages. Enrichment of the pH buffering capacity of the extracellular solution increased cone ICa, and blocked any additional increase in cone ICa by surround illumination. Hyperpolarization of the HCs by a glutamate receptor antagonist-augmented cone ICa, whereas depolarization of the HCs by kainate suppressed cone ICa. From these results, we propose the hypothesis that pH changes in the synaptic clefts, which are intimately related to the membrane voltage of the HCs, mediate the feedback from the HCs to cone photoreceptors. The feedback mediated by pH changes in the synaptic cleft may serve as an additional mechanism for the center-surround organization of the receptive field in the outer retina.
TL;DR: Recording from whole-cell patch-clamp recordings from cerebellar stellate and basket cells during natural and electrical activation of cutaneously driven synaptic input confirms previous suggestions that conjunctive PF and CF activation leads to a long-lasting potentiation of PF synaptic input to interneurons.
Abstract: The cutaneous parallel fiber (PF) receptive fields of cerebellar stellate and basket cells in the cerebellar C3 zone in vivo are normally very small but can be dramatically enlarged by climbing fiber (CF)-dependent plasticity. To analyze the effects of this receptive field plasticity, we present for the first time whole-cell patch-clamp recordings from these interneurons during natural and electrical activation of cutaneously driven synaptic input. In "naive" interneurons, peripheral input nearly exclusively activated a few (two to eight) large PF EPSPs from a specific small skin area that overlapped the receptive field of the local CF input. After conjunctive PF and CF stimulation, numerous small and large EPSPs and ramp-like depolarizations could be activated from the entire forelimb skin. These findings therefore confirm previous suggestions that conjunctive PF and CF activation leads to a long-lasting potentiation of PF synaptic input to interneurons. The CF response, which is crucial for the induction of the PF synaptic potentiation, was strong but variable and very different from the conventional EPSPs evoked by PFs.
TL;DR: In dark-reared transgenic mice, visual acuity, receptive field size of visual cortical neurons, critical period for ocular dominance plasticity, and intracortical inhibition were indistinguishable from those observed in light- reared mice, suggesting that BDNF overexpression is sufficient for the development of aspects of visual cortex in the absence of visual experience.
Abstract: Visual deprivation such as dark rearing (DR) prolongs the critical period for ocular dominance plasticity and retards the maturation of γ-aminobutyric acid (GABA)ergic inhibition in visual cortex. The molecular signals that mediate the effects of DR on the development of visual cortex are not well defined. To test the role of brain-derived neurotrophic factor (BDNF), we examined the effects of DR in transgenic mice in which BDNF expression in visual cortex was uncoupled from visual experience and remained elevated during DR. In dark-reared transgenic mice, visual acuity, receptive field size of visual cortical neurons, critical period for ocular dominance plasticity, and intracortical inhibition were indistinguishable from those observed in light-reared mice. Therefore, BDNF overexpression is sufficient for the development of aspects of visual cortex in the absence of visual experience. These results suggest that reduced BDNF expression contributes to retarded maturation of GABAergic inhibition and delayed development of visual cortex during visual deprivation.
TL;DR: It is shown that pyramidal neurons possess a nCRF and that it can modulate the response to CRF stimuli to induce this neurobiological switch in frequency tuning, resulting in the selective and optimal encoding of both stimulus categories.
Abstract: Animals have developed stereotyped communication calls to which specific sensory neurons are well tuned1,2. These communication calls must be discriminated from environmental signals such as those produced by prey. Sensory systems might have evolved neural circuitry to encode both categories. In weakly electric fish, prey and communication signals differ in their spatial extent and frequency content3,4. Here we show that stimuli of different spatial extents mimicking prey and communication signals cause a switch in the frequency tuning and spike-timing precision of electrosensory pyramidal neurons, resulting in the selective and optimal encoding of both stimulus categories. As in other sensory systems5, pyramidal neurons respond only to stimuli located within a restricted region of space known as the classical receptive field (CRF)6. In some systems, stimulation outside the CRF but within a non-classical receptive field (nCRF) can modulate the neural response to CRF stimulation even though nCRF stimulation alone fails to elicit responses7,8. We show that pyramidal neurons possess a nCRF and that it can modulate the response to CRF stimuli to induce this neurobiological switch in frequency tuning.