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Showing papers on "Receptive field published in 1993"


Journal ArticleDOI
TL;DR: Neural correlates of focal attentive processes can be observed in visual cortical processing in areas V1 and V2 as well as area V4 under conditions that require stimulus feature analysis and selective spatial processing within a field of competing stimuli.
Abstract: 1. The activity of single neurons was recorded in Macaca mulatta monkeys while they performed tasks requiring them to select a cued stimulus from an array of three to eight stimuli and report the orientation of that stimulus. Stimuli were presented in a circular array centered on the fixation target and scaled to place a single stimulus element within the receptive field of the neuron under study. The timing of the cuing event permitted the directing of visual attention to the spatial location of the correct stimulus before its presentation. 2. The effects of focal attention were examined in cortical visual areas V1, V2, and V4, where a total of 672 neurons were isolated with complete studies obtained for 94 V1, 74 V2, and 74 V4 neurons with receptive-field center eccentricities in the range 1.8-8 degrees. Under certain conditions, directed focal attention results in changes in the response of V1, V2, and V4 neurons to otherwise identical stimuli at spatially specific locations. 3. More than one-third of the neurons in each area displayed differential sensitivity when attention was directed toward versus away from the spatial location of the receptive field just before and during stimulus presentation. Both relative increases and decreases in neural activity were observed in association with attention directed at receptive-field stimuli. 4. The presence of multiple competing stimuli in the visual field was a major factor determining the presence or absence of differential sensitivity. About two-thirds of the neurons that were differentially sensitive to the attending condition in the presence of competing stimuli were not differentially sensitive when single stimuli were presented in control studies. For V1 and V2 neurons the presence of only a few (3-4) competing stimuli was sufficient for a majority of the neurons studied; a majority of the V4 neurons required six to eight stimuli in the array before significant differences between attending conditions occurred. 5. For V1 and V2 neurons the neuronal sensitivity differences between attending conditions were observed primarily at or near the peak of the orientation tuning sensitivity for each neuron; the differences were evident over a broader range of orientations in V4 neurons. 6. In conclusion, neural correlates of focal attentive processes can be observed in visual cortical processing in areas V1 and V2 as well as area V4 under conditions that require stimulus feature analysis and selective spatial processing within a field of competing stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

998 citations


Journal ArticleDOI
TL;DR: There is a potential mechanism for the plasticity of representational maps that is demonstrable in somatic sensory, motor, auditory, and visual cortex as well as in primate neocortex.
Abstract: GABA neurons and GABA receptors are conspicuous elements of cerebral cortical organization. They serve to shape the stimulus-response properties of neurons in the sensory areas and undoubtedly play a comparable role in the nonsensory areas as well. Although non-GABAergic local circuit neurons exist in the cerebral cortex, the variety of forms adopted by the GABAergic neurons and their important functional role have served to focus attention on the latter in investigations of local cortical circuitry. In primate neocortex, GABAergic neurons constitute approximately 25-30% of the neuronal population. In addition to their known or postulated functions in shaping neuronal receptive fields and response profiles, some of which are still controversial (Sillito, 1984; Ferster, 1986), their transmitter, GABA, and the major class of receptor upon which it acts are regulated in an activity-dependent manner even in the adult (Jones, 1990). In this, there is a potential mechanism for the plasticity of representational maps that is demonstrable in somatic sensory, motor, auditory, and visual cortex (Merzenich et al., 1983; Sanes et al., 1988; Robertson and Irvine, 1989; Kaas et al., 1990).

487 citations


Journal ArticleDOI
TL;DR: This study has studied the spatiotemporal receptive-field structure of 233 simple cells recorded from the striate cortex of adult cats and kittens at 4 and 8 wk postnatal and examined the postnatal development of spatial and temporal selectivity in the frequency domain.
Abstract: 1. Most studies of cortical neurons have focused on the spatial structure of receptive fields. For a more complete functional description of these neurons, it is necessary to consider receptive-field structure in the joint domain of space and time. We have studied the spatiotemporal receptive-field structure of 233 simple cells recorded from the striate cortex of adult cats and kittens at 4 and 8 wk postnatal. The dual goal of this study is to provide a detailed quantitative description of spatiotemporal receptive-field structure and to compare the developmental time courses of spatial and temporal response properties. 2. Spatiotemporal receptive-field profiles have been measured with the use of a reverse correlation method, in which we compute the cross-correlation between a neuron's response and a random sequence of small, briefly presented bright and dark stimuli. The receptive-field profiles of some simple cells are space-time separable, meaning that spatial and temporal response characteristics can be dissociated. Other cells have receptive-field profiles that are space-time inseparable. In these cases, a particular spatial location cannot be designated, unambiguously, as belonging to either an on or off subregion. However, separate on and off subregions may be clearly distinguished in the joint space-time domain. These subregions are generally tilted along an oblique axis. 3. Our observations show that spatial and temporal aspects of receptive-field structure mature with clearly different time courses. By 4 wk postnatal, the spatial symmetry and periodicity of simple-cell receptive fields have reached maturity. The spatial extent (or size) of these receptive fields is adult-like by 8 wk postnatal. In contrast, the response latency and time duration of spatiotemporal receptive fields do not mature until well beyond 8 wk postnatal. 4. By applying Fourier analysis to spatiotemporal receptive-field profiles, we have examined the postnatal development of spatial and temporal selectivity in the frequency domain. By 8 wk postnatal, spatial frequency tuning has clearly reached maturity. On the contrary, temporal frequency selectivity remains markedly immature at 8 wk. We have also examined the joint distribution of optimal spatial and temporal frequencies. From 4 wk postnatal until 8 wk postnatal, the range of optimal spatial frequencies increases substantially, whereas the range of optimal temporal frequencies remains largely unchanged. From 8 wk postnatal until adulthood, there is a large increase in optimal temporal frequencies for cells tuned to low spatial frequencies. For cells tuned to high spatial frequencies, the distribution of optimal temporal frequencies does not change much beyond 8 wk postnatal.(ABSTRACT TRUNCATED AT 400 WORDS)

447 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that simple cells in the cat's visual cortex perform a linear spatio-temporal filtering of the visual image, using the Fourier transform to determine the preferred direction of motion of a visual stimulus.
Abstract: 1. We have tested the hypothesis that simple cells in the cat's visual cortex perform a linear spatiotemporal filtering of the visual image. To conduct this study we note that a visual neuron behaves linearly if the responses to small, brief flashes of light are mathematically related, via the Fourier transform, to the responses elicited by sinusoidal grating stimuli. 2. We have evaluated the linearity of temporal and spatial summation for 118 simple cells recorded from the striate cortex (area 17) of adult cats and kittens at ages 4 and 8 wk postnatal. These neurons represent a subset of the population of cells for which we have described the postnatal development of spatiotemporal receptive-field structure in the preceding paper. Spatiotemporal receptive-field profiles are constructed, with the use of a reverse correlation technique, from the responses to random sequences of small bar stimuli that are brighter or darker than the background. Fourier analysis of spatiotemporal receptive-field profiles yields linear predictions of the cells' spatial and temporal frequency tuning. These predicted responses are compared with spatial and temporal frequency tuning curves measured by the use of drifting, sinusoidal-luminance grating stimuli. 3. For most simple cells, there is good agreement between spatial and temporal frequency tuning curves predicted from the receptive-field profile and those measured by the use of sinusoidal gratings. These results suggest that both spatial and temporal summation within simple cells are approximately linear. There is a tendency for predicted tuning curves to be slightly broader than measured tuning curves, a finding that is consistent with the effects of a threshold nonlinearity at the output of these neurons. In some cases, however, predicted tuning curves deviate from measured responses only at low spatial and temporal frequencies. This cannot be explained by a simple threshold nonlinearity. 4. If linearity is assumed, it should be possible to predict the direction selectivity of simple cells from the structure of their spatiotemporal receptive-field profiles. For virtually all cells, linear predictions correctly determine the preferred direction of motion of a visual stimulus. However, the strength of the directional bias is typically underestimated by a factor of about two on the basis of linear predictions. Consideration of the expansive exponential nonlinearity revealed in the contrast-response function permits a reconciliation of the discrepancy between measured and predicted direction selectivity indexes. 5. Overall, these findings show that spatiotemporal receptive-field profiles obtained with the use of reverse correlation may be used to predict a variety of response properties for simple cells.(ABSTRACT TRUNCATED AT 400 WORDS)

443 citations


Journal ArticleDOI
02 Dec 1993-Nature
TL;DR: This work investigated target selection in rhesus monkeys performing a visual search task by recording neurons in the frontal eye field, an area known to be responsible for generating purposive eye movements, and found that the initial visual responses to search stimulus arrays were the same whether the target or a distraction was in the response field.
Abstract: CONSPICUOUS visual features commonly attract gaze1,2, but how the brain selects targets for eye movements is not known. We investigated target selection in rhesus monkeys performing a visual search task3 by recording neurons in the frontal eye field, an area known to be responsible for generating purposive eye movements4,5. Neurons with combined visual- and eye movement-related activity were analysed. We found that the initial visual responses to search stimulus arrays were the same whether the target or a distractor was in the response field. We also found that the neural activity evolved to specify target location before the execution of eye movements, ultimately peaking when the target was in the response field and being suppressed when the target was beside but not distant from the response field. These results demonstrate a possible mechanism by which a desired target is fixated and inappropriate eye movements are prevented.

419 citations


Journal ArticleDOI
TL;DR: It is suggested that the bimodal cells in area 6, 7b, VIP, and the putamen form part of an interconnected system that represents extrapersonal space in a somatotopic fashion.
Abstract: The macaque putamen contains neurons that respond to somatosensory stimuli such as light touch, joint movement, or deep muscle pressure. Their receptive fields are arranged to form a map of the body. In the face and arm region of this somatotopic map we found neurons that responded to visual stimuli. Some neurons were bimodal, responding to both visual and somatosensory stimuli, while others were purely visual, or purely somatosensory. The bimodal neurons usually responded to light cutaneous stimulation, rather than to joint movement or deep muscle pressure. They responded to visual stimuli near their tactile receptive field and were not selective for the shape or the color of the stimuli. For cells with tactile receptive fields on the face, the visual receptive field subtended a solid angle extending from the tactile receptive field to about 10 cm. For cells with tactile receptive fields on the arm, the visual receptive field often extended further from the animal. These bimodal properties provide a map of the visual space that immediately surrounds the monkey. The map is organized somatotopically, that is, by body part, rather than retinotopical ly as in most visual areas. It could function to guide movements in the animal's immediate vicinity. Cortical areas 6, 7b, and VIP contain bimodal cells with very similar properties to those in the putamen. We suggest that the bimodal cells in area 6, 7b, VIP, and the putamen form part of an interconnected system that represents extrapersonal space in a somatotopic fashion.

357 citations


Journal ArticleDOI
TL;DR: Findings indicate that a brief change in the pattern of sensory activity can alter the configuration of cortical RFs, even in adult animals.
Abstract: This study tested the hypothesis that the receptive fields (RFs) of neurons in the adult sensory cortex are shaped by the recent history of sensory experience. Sensory experience was altered by a brief period of "whisker pairing": whiskers D2 and either D1 or D3 were left intact, while all other whiskers on the right side of the face were trimmed close to the fur. The animals were anesthetized 64-66 h later and the responses of single neurons in contralateral cortical barrel D2 to stimulation of whisker D2 (the center RF) and the four neighboring whiskers (D1, D3, C2, and E2; the excitatory surround RF) were measured. Data from 79 cells in four rats with whiskers paired were compared to data from 52 cells in four rats with untrimmed whiskers (control cases). During the period of whisker pairing, the RFs of cells in barrel D2 changed in three ways: (i) the response to the center RF, whisker D2, increased by 39%, (ii) the response to the paired surround RF whisker increased by 85-100%, and (iii) the response to all clipped (unpaired) surround RF whiskers decreased by 9-42%. In the control condition, the response of barrel D2 cells to the two neighboring whiskers, D1 and D3, was equal. After whisker pairing, the response to the paired neighbor of D2 was more than twice as large as the response to the cut neighbor of D2. These findings indicate that a brief change in the pattern of sensory activity can alter the configuration of cortical RFs, even in adult animals.

308 citations


Journal ArticleDOI
TL;DR: While it is likely that these three distinct multisensory neural circuits have different functional roles, their constituent neurons appear to integrate their various sensory inputs in much the same way.
Abstract: 1. Physiological methods were used to examine the pattern of inputs from different sensory cortices onto individual superior colliculus neurons. 2. Visual, auditory, and somatosensory influences fr...

279 citations


Journal ArticleDOI
TL;DR: The existence in the monkey parietal cortex of cells (called “real-position” cells) whose receptive field does not systematically move with gaze is reported, which directly encode visual space in craniotopic instead of retinotopic coordinates.
Abstract: The receptive fields of visual neurons are known to be retinotopically arranged, and in awake animals they "move" with gaze, maintaining the same retinotopic location regardless of eye position. Here, we report the existence in the monkey parietal cortex of cells (called "real-position" cells) whose receptive field does not systematically move with gaze. These cells respond to the visual stimulation of the same spatial location regardless of eye position and therefore directly encode visual space in craniotopic instead of retinotopic coordinates.

274 citations


Journal ArticleDOI
TL;DR: There was a group of neurons in the nerve-injured rats that had low thresholds, failed to encode stimulus intensity, and did not have a C-fiber input; however, there was also a group that showed abnormal characteristics; these included responses to very gentle mechanical stimulation of the nerves and to manipulations that resulted in movement of this site.
Abstract: 1. Extracellular single-unit recordings have been made from 295 dorsal horn neurons in the lumbar enlargement of rat spinal cord; 191 neurons in 20 rats with an experimental peripheral neuropathy, and 104 in 10 sham-operated rats. Recordings were made 9-11 days after inducing the neuropathy by tying four loose ligatures around the sciatic nerve in the nerve-injured rats or performing a sham procedure in the sham-operated rats. 2. A survey of the general properties of all neurons encountered was made in the 10 sham-operated rats (104 neurons) and compared with those seen in 17 of the nerve-injured animals (180 neurons). The vast majority (87%; 156/180) of neurons recorded in the nerve-injured animals showed abnormal characteristics; these included responses to very gentle mechanical stimulation of the nerve-injury site and to manipulations that resulted in movement of this site such as extension of the leg and probing of the skin and muscle of the thigh (53%), absence of detectable peripheral receptive fields (RFs; 56%), and very high spontaneous activity (7%). In the sham-operated rats none of the neurons recorded could be activated by gentle mechanical stimulation of the sciatic nerve, and only 6% had no detectable peripheral RF. 3. In the nerve-injured animals, 31% (55/180) of cells had both a peripheral RF, and a response to gentle mechanical stimulation of the nerve-injury site. All cells of this type tested (n = 5) showed very prolonged responses (up to 10 min long) to 15 s pinch stimuli applied to the RF and to 15 s gentle tapping of the injury site. The majority of cells in this group were excited by noxious stimuli (71%; 39/55) and had C-fiber inputs (60%; 33/55). 4. The mean threshold temperatures for evoking responses to heat stimuli in cells tested in nerve-injured rats and in sham-operated animals were not different. However, there was a group of neurons in the nerve-injured rats that had low thresholds, failed to encode stimulus intensity, and did not have a C-fiber input. 5. There were significantly fewer neurons excited by low-intensity stimulation of the skin in the nerve-injured (24%; 43/180) than in the sham-operated rats (71%; 74/104). Measurements of mechanical threshold with von Frey hairs showed that, although the mean threshold did not change, none of the cells tested in the nerve-injured animals had thresholds < 12 mN, whereas the lowest threshold recorded in the sham-operated animals was 0.2 mN.(ABSTRACT TRUNCATED AT 400 WORDS)

264 citations


Journal ArticleDOI
TL;DR: To test the hypothesis that painful stimuli to skeletal muscle lead to a widespread unmasking of synaptic connections in dorsal horn neurons, intramuscular injections of bradykinin were made outside the receptive fields (RFs) of these cells in the rat.

Journal ArticleDOI
11 Feb 1993-Nature
TL;DR: Thalamic reorganization demonstrates that peripheral sensory deprivation may induce immediate plastic changes at multiple levels of the somatosensory system, and suggests a disruption of the normal dynamic equilibrium between multiple ascending and descending influences on the VPM.
Abstract: PERIPHERAL sensory deprivation induces reorganization within the somatosensory cortex of adult animals1-6. Although most studies have focused on the somatosensory cortex1–6, changes at subcortical levels (for example the thalamus) could also play a fundamental role in sensory plasticity7–11. To investigate this, we made chronic simultaneous recordings of large numbers of single neurons across the ventral posterior medial thalamus (VPM) in adult rats. This allowed a continuous and quantitative evaluation of the receptive fields of the same sample of single VPM neurons per animal, before and after sensory deprivation. Local anaesthesia in the face induced an immediate and reversible reorganization of a large portion of the VPM map. This differentially affected the short latency (4–6 ms) responses (SLRs) and long latency (15–25 ms) responses (LLRs) of single VPM neurons. The SLRs and LLRs normally define spatiotemporally complex receptive fields in the VPM12. Here we report that 73% of single neurons whose original receptive fields included the anaesthetized zone showed immediate unmasking of SLRs in response to stimulation of adjacent cutaneous regions, and/or loss of SLRs with preservation or enhancement of LLRs in response to stimulation of regions just surrounding the anaesthetized zone. This thalamic reorganization demonstrates that peripheral sensory deprivation may induce immediate plastic changes at multiple levels of the somatosensory system. Further, its spatiotemporally complex character suggests a disruption of the normal dynamic equilibrium between multiple ascending and descending influences on the VPM.

Journal ArticleDOI
TL;DR: Most neurons in inferior temporal cortex of the awake macaque were weaker to pairs of stimuli than to the best single stimulus of that pair presented alone, which suggests competitive interactions between IT neurons that may be involved in visual attention or learning or both.

Journal ArticleDOI
TL;DR: The rapid development of RF plasticity satisfies a criterion for its involvement in the neural bases of a specific associative memory.
Abstract: Classical conditioning induces frequency-specific receptive field (RF) plasticity in the auditory cortex after relatively brief training (30 trials), characterized by increased response to the frequency of the conditioned stimulus (CS) and decreased responses to other frequencies, including the pretraining best frequency (BF). This experiment determined the development of this CS-specific RF plasticity. Guinea pigs underwent classical conditioning to a tonal frequency, and receptive fields of neurons in the auditory cortex were determined before and after 5, 15, and 30 CS-US (unconditioned stimulus) pairings, as well as 1 hr posttraining. Highly selective RF changes were observed as early as the first 5 training trials. They culminated after 15 trials, then stabilized after 30 trials and 1 hr posttraining. The rapid development of RF plasticity satisfies a criterion for its involvement in the neural bases of a specific associative memory.

Book ChapterDOI
01 Jan 1993
TL;DR: There is a long history for dividing the pain system into two theoretical components: one involved in localization and sensory discrimination and the other involved in affective responses to noxious stimuli.
Abstract: The processing of sensory afferents in the cerebral cortex involves divergent processing of components of each sensory space. In the visual system, for example, there are separate and sequential, corticocortical projections for the analysis of form, color, movement, and depth (DeYoe and Van Essen, 1988; Livingstone and Hubel, 1988; Zeki and Shipp, 1988). A divergence of functional processing of different features of noci-ceptor-evoked activity may also occur in the cerebral cortex. Thus, there is a long history for dividing the pain system into two theoretical components: one involved in localization and sensory discrimination and the other involved in affective responses to noxious stimuli (e.g., Melzack and Casey, 1968; Melzack, 1975; Kenshalo and Willis, 1991).

Journal ArticleDOI
TL;DR: Conditioned-stimulus-specific RF plasticity was expressed under both types of anesthesia and included shifts of the pretraining best frequency toward or even to the frequency of the conditioned stimulus, which satisfies a criterion for the long-term storage of information in the auditory cortex.
Abstract: Brief learning experience (classical conditioning) induces frequency-specific receptive-field (RF) plasticity in the auditory cortex, characterized as increased response to the frequency of the conditioned stimulus and decreased responses to most other frequencies, including the pretraining best frequency. This experiment asked (i) whether learning-induced RF plasticity, established in the waking state, can be expressed under general anesthesia and if so (ii) whether it exhibits long-term retention. Pure-tone-frequency RFs were obtained from adult guinea pigs under general anesthesia (sodium pentobarbital or ketamine) before and repeatedly after (1 hr-8 weeks) a 20- to 30-trial session of pairing a non-best-frequency tone with mild footshock. Conditioned-stimulus-specific RF plasticity was expressed under both types of anesthesia and included shifts of the pretraining best frequency toward or even to the frequency of the conditioned stimulus. Moreover, this RF plasticity exhibits long-term retention, being evident 1-8 weeks after training. This satisfies a criterion for the long-term storage of information in the auditory cortex.

Journal ArticleDOI
TL;DR: Along the rostrocaudal axis of the postcentral gyrus, there is a gradual and continuous increase in the number of neurons with converging receptive fields and those in which receptive field positions or submodalities were not determined.
Abstract: In the primate postcentral gyrus, the cytoarchitectonic characteristics gradually shift from those of koniocortex to more homotypical parakoniocortex along its rostrocaudal axis. To find the physiological correlates of these changes we examined a large body of data accumulated during a series of our experiments with alert monkeys. Along the rostrocaudal axis of the postcentral gyrus, we found a gradual and continuous increase in the number of neurons with converging receptive fields and those in which receptive field positions or submodalities were not determined. Deep or skin submodality neurons were dominant in area 3a or 3b respectively. The proportion of skin submodality neurons decreased gradually from area 3b to the more caudal part of the gyrus. The proportion of deep submodality neurons was almost constant from area 3b to area 2 inclusive; they were not the majority in area 2. The data are consistent with the hierarchical scheme, i.e., within the postcentral gyrus sensory information is processed from the primary sensory receiving stage to the more associative, integrative stages.

Journal ArticleDOI
TL;DR: Using very simple single-cell models, quantitative agreement is obtained with Moran and Desimone's (1985) experiments on the implementation of selective visual attention based on the temporal structure of neuronal activity.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated whether this shift in the auditory map is intrinsic to the optic tectum or whether it reflects plasticity at an earlier stage of the auditory pathway.
Abstract: The optic tectum (homolog of the superior colliculus) contains mutually aligned neural maps of auditory and visual space. During development, the organization of the auditory map is guided by spatial information provided by vision: barn owls raised wearing prismatic spectacles, which optically shift the visual field and the visual map in the optic tectum, develop an auditory map that is shifted by an approximately equivalent amount, such that alignment between the two maps is preserved (Knudsen and Brainard, 1991). In this study we investigated whether this shift in the auditory map is intrinsic to the optic tectum or whether it reflects plasticity at an earlier stage in the auditory pathway. Owls were raised wearing prismatic spectacles that displaced the visual field by 23 degrees to the left or right. This manipulation alters the normal correspondence between locations in the visual field and interaural time difference (ITD), the primary cue for the azimuth of a sound source. In normal owls and in owls with at least 150 d of prism experience, extracellular unit recordings were used to assess the representations of ITD at anatomically and physiologically defined sites in the optic tectum and in the two prior stages of the auditory pathway, the external and central nuclei of the inferior colliculus (ICx and ICc). In the optic tectum of normal owls, the values of ITD to which units responded most strongly (best ITDs) varied systematically with the azimuths of unit visual receptive fields (VRFs). In the prism-reared owls, best ITDs were shifted from normal toward the values of ITD produced by sounds at the locations of the units' optically displaced VRFs. In the ICx of prism-reared owls, the representation of ITD also was shifted from normal, by an amount and in a direction that could completely account for the shift in ITD measured in the optic tectum. At some sites in the ICx, the shift in ITD tuning was apparent within the first 7-8 msec of the response; shifted tuning at such short latencies argues that the altered representation of ITD in the ICx reflects plasticity in the ascending auditory pathway, and is not the result of descending activity from higher auditory centers. In the ICc, which immediately precedes the ICx in the ascending pathway, the representation of ITD was normal. The results indicate that the visual instruction of auditory spatial tuning of neurons in the optic tectum reflects plasticity at the level of the ICx, the site where the auditory map of space is first synthesized.

Journal ArticleDOI
TL;DR: Results indicate that a major portion of Ig is a somatic processing area exclusively, with units that have large and often bilateral receptive fields, consistent with the view that this area serves as a higher-order, modality-specific link in the somatosensory-limbic pathway.

Book ChapterDOI
TL;DR: Although the spatial, temporal, and multiplicative characteristics of multisensory integration were most closely examined in cat cortex, all of the observations in monkey were consistent with those described in cat.
Abstract: Publisher Summary The cat superior colliculus neuron is a major site for the convergence and integration of multisensory information. It is only one of many central nervous system sites in many species where information from several modalities converges. Single cells in cat LS (lateral suprasylvian) and AES (anterior ectosylvian sulcus) and in monkey IPS (intraparietal sulcus) and STS (superior temporal sulcus) were examined. Although the spatial, temporal, and multiplicative characteristics of multisensory integration were most closely examined in cat cortex, all of the observations in monkey were consistent with those described in cat. The multisensory receptive fields of a single neuron overlapped one another in space, such that sensory stimuli that were in close spatial register fell within their excitatory receptive fields and enhanced the neuron's activity; spatially disparate stimuli produced either no interaction or depressed responses. The rules of multisensory integration evident at the level of the single neuron are also consistent with studies of intact behaving animals. The attentive and orientation responses cats make to visual and auditory stimuli were predictable based on the reactions of superior colliculus neurons to these stimuli. The data indicate that the visual responses of many neurons, whether in the superior colliculus or cortex, represent only one facet of their sensory coding capabilities.

Journal ArticleDOI
TL;DR: In the auditory cortex, classical conditioning specifically modifies receptive fields in primary and secondary auditory cortical areas to favor the frequency of a tone signal over other frequencies, including tuning shifts toward, or to, this frequency.

Journal ArticleDOI
24 Dec 1993-Science
TL;DR: In cat dorsal column nuclei (DCN), the injection of local anesthetic into the receptive fields of DCN neurons resulted in the emergence of a new receptive field in all 13 neurons studied, indicating mechanisms underlying somatotopic reorganization exist at the earliest stages of somatosensory processing.
Abstract: Altered sensory input can result in the reorganization of somatosensory maps in the cerebral cortex and thalamus, but the extent to which reorganization occurs at lower levels of the somatosensory system is unknown. In cat dorsal column nuclei (DCN), the injection of local anesthetic into the receptive fields of DCN neurons resulted in the emergence of a new receptive field in all 13 neurons studied. New receptive fields emerged rapidly (within minutes), sometimes accompanied by changes in adaptation rates and stimulus selectivity, suggesting that the new fields arose from the unmasking of previously ineffective inputs. Receptive field reorganization was not imposed by descending cortical inputs to the DCN, because comparable results were obtained in 10 additional cells when the somatosensory and motor cortex were removed before recording. These results suggest that mechanisms underlying somatotopic reorganization exist at the earliest stages of somatosensory processing. Such mechanisms may participate in adaptive responses of the nervous system to injury or continuously changing sensory stimulation.

Journal ArticleDOI
TL;DR: Data obtained from experiments using a bipartite visual stimulus showed that bringing the stimulus into alignment resulted in a 24.28% increase in the surround antagonism of the centre response, which supports the view that an entire subset of cortical orientation columns generate the feedback influencing any given dLGN cell.
Abstract: In a previous study, we have shown that the corticofugal projection to the dLGN enhances inhibitory mechanisms underlying length tuning. This suggests that the inhibitory influences deriving from the corticofugal feedback should exhibit characteristics that reflect the response properties of orientation-tuned layer VI cells. Here we report data obtained from experiments using a bipartite visual stimulus, with an inner section over the dLGN cell receptive field centre and an outer section extending beyond it. For both X and Y cells there was a modulation of the strength of the surround antagonism of centre responses that was dependent on the orientation alignment of contours in the two components of the stimulus. Layer VI cells showed maximal responses when the two components were aligned to the same orientation; dLGN cells showed a minimal response. Varying the orientation alignment of the inner and outer components of the stimulus in a randomised, interleaved fashion showed that bringing the stimulus into alignment resulted in a 24.28% increase in the surround antagonism of the centre response. Blocking cortical activity showed this effect of alignment to be strongly dependent on corticofugal feedback. This effect of orientation alignment appears to apply for any absolute orientation of the alignment condition and supports the view that an entire subset of cortical orientation columns generate the feedback influencing any given dLGN cell. This mechanism makes dLGN cells sensitive to the orientation domain discontinuities in elongated contours moving across their receptive field.

Journal ArticleDOI
TL;DR: The ventral part of the medial superior temporal area is distinctive from the dorsal part of MST and is mainly involved in the analysis of object movements in external space.
Abstract: 1. The medial superior temporal area (MST) is an extrastriate area of the macaque visual cortex. Cells in MST have large receptive fields and respond to moving stimuli with directional selectivity. We previously suggested that the dorsal part of MST is mainly involved in analysis of field motion caused by movements of the animal itself, because most cells in the dorsal part preferentially responded to movements of a wide textured field rather than to movements of a small stimulus. To determine whether the remaining ventral part of MST differs in function from the dorsal part, we examined properties of cells in the ventral part in comparison with those of cells in the dorsal part, using anesthetized and paralyzed preparation. 2. Most cells in the ventral part preferably responded to movements of a small stimulus rather than to movements of a wide textured field. 3. Although the cells in the ventral part did not respond to movements of a textured field over a large window, many of them began to respond when a small stationary object was introduced in front of the moving field. The direction to which the cells responded in this stimulus configuration was opposite to the direction in which they responded to movements of an object on a stationary background. Activities of these cells thus represented the direction of relative movement of an object on a background, irrespective of whether the image of the object or the background moved on the retina. 4. We conclude that the ventral part of MST is distinctive from the dorsal part of MST and is mainly involved in the analysis of object movements in external space.

Journal ArticleDOI
TL;DR: In this paper, the auditory cortex of Eptesicus bats is characterized by electrical activity recorded from microelectrodes in response to tone bursts, FM sweeps, and combinations of FM sweeps.
Abstract: 1. In Eptesicus the auditory cortex, as defined by electrical activity recorded from microelectrodes in response to tone bursts, FM sweeps, and combinations of FM sweeps, encompasses an average cortical surface area of 5.7 mm2. This area is large with respect to the total cortical surface area and reflects the importance of auditory processing to this species of bat. 2. The predominant pattern of organization in response to tone bursts observed in each cortex is tonotopic, with three discernible divisions revealed by our data. However, although cortical best-frequency (BF) maps from most of the individual bats are similar, no two maps are identical. The largest division contains an average of 84% of the auditory cortical surface area, with BF tonotopically mapped from high to low along the anteroposterior axis and is part of the primary auditory cortex. The medium division encompasses an average of 13% of the auditory cortical surface area, with highly variable BF organization across bats. The third region is the smallest, with an average of only 3% of auditory cortical surface area and is located at the anterolateral edge of the cortex. This region is marked by a reversal of the tonotopic axis and a restriction in the range of BFs as compared with the larger, tonotopically organized division. 3. A population of cortical neurons was found (n = 39) in which each neuron exhibited two BF threshold minima (BF1 and BF2) in response to tone bursts. These neurons thus have multipeaked frequency threshold tuning curves. In Eptesicus the majority of multipeaked frequency-tuned neurons (n = 27) have threshold minima at frequencies that correspond to a harmonic ratio of three-to-one. In contrast, the majority of multipeaked neurons in cats have threshold minima at frequencies in a ratio of three-to-two. A three-to-one harmonic ratio corresponds to the "spectral notches" produced by interference between overlapping echoes from multiple reflective surfaces in complex sonar targets. Behavioral experiments have demonstrated the ability of Eptesicus to use spectral interference notches for perceiving target shape, and this subpopulation of multipeaked frequency-tuned neurons may be involved in coding of spectral notches. 4. The auditory cortex contains delay-tuned neurons that encode target range (n = 99). Most delay-tuned neurons respond poorly to tones or individual FM sweeps and require combinations of FM sweeps. They are combination sensitive and delay tuned.(ABSTRACT TRUNCATED AT 400 WORDS)

Journal ArticleDOI
TL;DR: The correlation method has revealed that neural synchronization is less affected by intensity changes and damage to the hair cells than is neural firing rate and a particular form of second-order analysis, the Spectro Temporal Receptive Field, offers an alternative to first-order cross-correlation when phase-lock is absent.

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TL;DR: The results indicate the presence of an extensive system of neurons throughout the caudal spinal cord of the rat, concentrated in separated thoracolumbar and lumbosacral segments, that is concerned with input from the reproductive tract.
Abstract: 1 Previous studies in the rat have shown that the hypogastric nerve conveys input from the cervix and uterus mainly to the T13-L3 segments of the spinal cord, whereas the pelvic nerve conveys input from the cervix and vaginal canal mainly to the L6-S2 segments 2 To study the effects of this input, the dorsal horns of the T13-L1, L6-S2, and L4-L5 segments in 13 decerebrate, T10-spinalized, unanesthetized, and paralyzed adult female rats in estrus were searched for neurons responsive to gentle mechanical stimulation of the cervix The 87 neurons found were then further tested for their responses to gentle mechanical stimulation of the skin and to distension of both uterine horns, distension of the colon, and shearing stimulation of the colon and vaginal canal 3 Neurons responsive to cervix stimulation, primarily by excitation, were readily found in the ventral part of the dorsal horn in T13-L1 and throughout the dorsal horn in L6-S2 Cervix-responsive neurons were less readily found throughout the dorsal horn in L4-L5, where 25% were inhibited by the stimulation All but one neuron had cutaneous receptive fields 4 The 30 cervix-responsive neurons in T13-L1 had large bilateral cutaneous receptive fields covering the perineum and hind-limbs Most (76%) also responded, primarily by excitation, to uterine distension, as well as to colonic stimulation (59%) More than half were activated by both types of stimulation 5 The 33 cervix-responsive neurons in L6-S2 had cutaneous receptive fields in the same regions as those in T13-L1, but generally smaller, particularly for neurons in the dorsal part of the dorsal horn, many of whose receptive fields were confined to the perineum The L6-S2 neurons also exhibited less convergent input from other visceral structures, particularly the uterus Fewer neurons (42%) responded to uterine distension, mostly by being inhibited, whereas about the same proportion (51%) responded with excitation to colonic stimulation Only 24% responded to both uterus and colon 6 All 24 cervix-responsive neurons in medial L4-L5 had small cutaneous receptive fields on the toes, and the neurons received less convergent input from other visceral structures (25% from the uterus, 33% from the colon, 13% from both) 7 These results indicate the presence of an extensive system of neurons throughout the caudal spinal cord of the rat, concentrated in separated thoracolumbar and lumbosacral segments, that is concerned with input from the reproductive tract(ABSTRACT TRUNCATED AT 400 WORDS)

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TL;DR: Evidence is presented that response variability (noise) in primate retinal ganglion cells at photopic light levels is independent of the amplitude of either the stimulus or the response and is therefore additive, independent of receptive field size and retinal eccentricity, and similar for all primate ganglions.
Abstract: The signal encoded by a sensory neuron is usually characterized as the cell's average response to repeated presentations of a stimulus. However, each stimulus presentation elicits a slightly different response. This response variability may obscure the signal represented by neural activity, but it might also be an important aspect of a neuron's message and in some instances may even serve useful function. Here we present evidence that response variability (noise) in primate retinal ganglion cells at photopic light levels is (i) independent of the amplitude of either the stimulus or the response and is therefore additive, (ii) independent of receptive field size and retinal eccentricity, and (iii) similar for all primate ganglion cells. Our results show that the primate retina maintains a uniform noise level across the entire visual field and suggest that the noise originates within the ganglion cells themselves.

Journal ArticleDOI
28 Jan 1993-Nature
TL;DR: It is found that the muscle autonomously defines the synaptic site, whereas the motor neuron directs the development of the muscle's receptive field by stimulating the synthesis and localization of transmitter receptors.
Abstract: IN the Drosophila embryo, motor neurons form stereotyped synapses (neuromuscular junctions) on identified muscles1–3. We have used a mutant (prospero) that removes or delays innervation4,5 to assay the role of the presynaptic motor neuron in the development of the receptive field of the postsynaptic muscle, prospero (pros) is not expressed in the muscles or their precursors. Here we find that the muscle defines the correct synaptic zone in the absence of the motor neuron by restricting putative guidance molecules to this specialized membrane region. Furthermore, the muscle expresses functional transmitter receptors at the correct developmental time without innervation. On the other hand, the muscle does not localize receptors to the synapse without instruction from the motor neuron, nor does a second, much larger, synthesis of receptors occur in muscles deprived of innervation. In muscles receiving delayed innervation, or muscles innervated at aberrant synaptic sites, both receptor clustering and receptor synthesis are delayed or redirected, consistent with the new pattern of innervation. We conclude that the muscle autonomously defines the synaptic site, whereas the motor neuron directs the development of the muscle's receptive field by stimulating the synthesis and localization of transmitter receptors.