CiteULike: brembs's visual

Honeybee memory: navigation by associative grouping and recall of visual stimuli

SW Zhang — 2008-07-30T12:58:27-00:00

Neurobiol Learn Mem, Vol. 72, No. 3. (1999), 180-201.

Studies of navigation in bees and ants are beginning to reveal that foraging insects traveling repeatedly to a food source navigate by using a series of visual images of the environment acquired en route (Collett, 1996; Collett et al., 1993; Judd & Collett, 1998; Wehner et al., 1990, 1996). By comparing the currently viewed scene with the appropriate stored image, the insect is able to ascertain whether or not it is on the correct path and make any necessary corrections. If a bee happens to forage at more than one site, then she needs not only to memorize a separate set of images for each route that she has learned but also to retrieve the set of images that is appropriate to each route. Here we examine the bee's capacity to learn and later retrieve from memory two different sets of visual stimuli. Bees were trained to fly through a compound Y-maze where they were presented alternately with two different sequences of visual stimuli on their route to a food reward. We find that bees can indeed store two different sequences of images simultaneously. Furthermore, the trained bees are able to classify the memorized images into two groups, one pertaining to each three-stimulus set. Exposure to any of the images pertaining to one set triggers recall of all of the other images associated with that set. Associative grouping and recall of visual stimuli, demonstrated here for the first time in honeybees, provide an effective means of retrieving the appropriate navigational information from memory.

Receptor noise as a determinant of colour thresholds

M Vorobyev — 2008-07-30T12:58:02-00:00

Proc Biol Sci, Vol. 265, No. 1394. (1998), 351-8.

Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded. Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.

Salience modulates 20-30 Hz brain activity in Drosophila

B van Swinderen — 2008-07-30T12:57:58-00:00

Nature Neuroscience, Vol. 6, No. 6. (2003), 579-86.

Fruit flies selectively orient toward the visual stimuli that are most salient in their environment. We recorded local field potentials (LFPs) from the brains of Drosophila melanogaster as they responded to the presentation of visual stimuli. Coupling of salience effects (odor, heat or novelty) to these stimuli modulated LFPs in the 20-30 Hz range by evoking a transient, selective increase. We demonstrated the association of these responses with behavioral tracking and initiated a genetic approach to investigating neural correlates of perception.

Spatial organization of visuomotor reflexes in Drosophila

LF Tammero — 2008-07-30T12:57:47-00:00

J Exp Biol, Vol. 207, No. Pt 1. (2004), 113-22.

In most animals, the visual system plays a central role in locomotor guidance. Here, we examined the functional organization of visuomotor reflexes in the fruit fly, Drosophila, using an electronic flight simulator. Flies exhibit powerful avoidance responses to visual expansion centered laterally. The amplitude of these expansion responses is three times larger than those generated by image rotation. Avoidance of a laterally positioned focus of expansion emerges from an inversion of the optomotor response when motion is restricted to the rear visual hemisphere. Furthermore, motion restricted to rear quarter-fields elicits turning responses that are independent of the direction of image motion about the animal's yaw axis. The spatial heterogeneity of visuomotor responses explains a seemingly peculiar behavior in which flies robustly fixate the contracting pole of a translating flow field.

Blocking between occasion setters and contextual stimuli

D Swartzentruber — 2008-07-30T12:57:46-00:00

J Exp Psychol Anim Behav Process, Vol. 17, No. 2. (1991), 163-73.

Two appetitive conditioning experiments with rats used a blocking procedure to compare the mechanisms through which contexts and positive occasion setters control responding to conditioned stimuli (CSs) in discrimination learning. In Experiment 1, a light (L) initially set the occasion for food reinforcement of a tone CS (T). Then a compound of L and a novel context signaled reinforcement of T. Previous learning about L blocked contextual control of responding to T. Blocking was not due to simple excitation conditioned to L during discrimination training; comparable excitation to L in a control group did not result in blocking. Conversely, in Experiment 2, initial learning about the context blocked the acquisition of occasion setting to L. Excitation conditioned to the context could not account for the blocking. In general, the results suggest that contexts and occasion setters may control responding to CSs through similar mechanisms.

Processing of artificial visual feedback in the walking fruit fly Drosophila melanogaster

R Strauss — 2008-07-30T12:57:43-00:00

J Exp Biol, Vol. 200, No. Pt 9. (1997), 1281-96.

A computerized 360 degrees panorama allowed us to suppress most of the locomotion-induced visual feedback of a freely walking fly without neutralizing its mechanosensory system ('virtual open-loop' conditions). This novel paradigm achieves control over the fly's visual input by continuously evaluating its actual position and orientation. In experiments with natural visual feedback (closed-loop conditions), the optomotor turning induced by horizontal pattern motion in freely walking Drosophila melanogaster increased with the contrast and brightness of the stimulus. Conspicuously striped patterns were followed with variable speed but often without significant overall slippage. Using standard open-loop conditions in stationary walking flies and virtual open-loop or closed-loop conditions in freely walking flies, we compared horizontal turning induced by either horizontal or vertical motion of appropriately oriented rhombic figures. We found (i) that horizontal displacements and the horizontal-motion illusion induced by vertical displacements of the oblique edges of the rhombic figures elicited equivalent open-loop turning responses; (ii) that locomotion-induced visual feedback from the vertical edges of the rhombic figures in a stationary horizontal position diminished the closed-loop turning elicited by vertical displacements to only one-fifth of the response to horizontal displacements; and (iii) that virtual open-loop responses of mobile flies and open-loop responses of immobilized flies were equivalent in spite of delays of up to 0.1 s in the generation of the virtual stimulus. Horizontal compensatory turning upon vertical displacements of oblique edges is quantitatively consistent with the direction-selective summation of signals from an array of elementary motion detectors for the horizontal stimulus components within their narrow receptive fields. A compensation of the aperture-induced ambiguity can be excluded under these conditions. However, locomotion-induced visual feedback greatly diminished the horizontal-motion illusion in a freely walking fly. The illusion was used to assay the quality of open-loop simulation in the new paradigm.

[Physiology of higher nervous activity: developmental perspective]

EN Sokolov — 2008-07-30T12:57:40-00:00

Zh Vyssh Nerv Deiat Im I P Pavlova, Vol. 36, No. 2. (1986), 252-64.

Neural correlates of decision processes: neural and mental chronometry

JD Schall — 2008-07-30T12:57:31-00:00

Curr Opin Neurobiol, Vol. 13, No. 2. (2003), 182-6.

Recent studies aim to explain the duration and variability of behavioral reaction time in terms of neural processes. The time taken to make choices is occupied by at least two processes. Neurons in sensorimotor structures accumulate evidence that leads to alternative categorizations, while other neurons within these structures prepare and initiate overt responses. These distinct stages of stimulus encoding and response preparation support variable but flexible behavior.

Symmetry is in the eye of the beeholder: innate preference for bilateral symmetry in flower-naive bumblebees

I Rodriguez — 2008-07-30T12:57:22-00:00

Naturwissenschaften, Vol. 91, No. 8. (2004), 374-7.

Bilateral symmetry has been considered as an indicator of phenotypic and genotypic quality supporting innate preferences for highly symmetric partners. Insect pollinators preferentially visit flowers of a particular symmetry type, thus leading to the suggestion that they have innate preferences for symmetrical flowers or flower models. Here we show that flower-naive bumblebees (Bombus terrestris), with no experience of symmetric or asymmetric patterns and whose visual experience was accurately controlled, have innate preferences for bilateral symmetry. The presence of color cues did not influence the bees' original preference. Our results thus show that bilateral symmetry is innately preferred in the context of food search, a fact that supports the selection of symmetry in flower displays. Furthermore, such innate preferences indicate that the nervous system of naive animals may be primed to respond to relevant sensory cues in the environment.

Analysis of the unique cue in configural discriminations

RA Rescorla — 2008-07-30T12:57:11-00:00

J Exp Psychol Anim Behav Process, Vol. 11, No. 3. (1985), 356-66.

Four experiments used an autoshaping procedure with pigeons to investigate the basis of configural discriminations. The elements of both a negative patterning (A+, B+, AB-) and a conditional discrimination (AC+, BD+, AD-, BC-) were paired, in a second-order procedure with two new key lights, X and Y. Responding was then tested to X and Y presented in compound with each other and with A and B. The pattern of responding to compounds containing X and Y was like the pattern of responding to compounds containing their associates, A and B. This suggests that A and B can be replaced by their associates without disrupting responding to their compounds. Because X and Y are physically different from A and B, this in turn suggests that any unique cue controlling responding to their compounds does not depend on the physical presence of the component stimuli. Instead the unique stimulus appears to arise from the joint activation of memory representations.

An analysis of the facilitative effect of similarity on second-order conditioning

RA Rescorla — 2008-07-30T12:57:11-00:00

J Exp Psychol Anim Behav Process, Vol. 6, No. 4. (1980), 339-51.

Five experiments used autoshaping in pigeons to investigate the effect of stimulus similarity on second-order conditioning of one stimulus (S2) when it signals another, previously conditioned stimulus (S1). Experiment 1 found that the artificial induction of similarity between S2 and S1, by the addition of experimentally separable common elements, improved performance during second-order conditioning of S2. An analysis of these results is given in terms of stimulus similarity encouraging the selection of particular components of S1 for association with S2. That selection is described as a natural consequence of the temporal relations among components of S2 and S1 which their similarity ensures. The analysis is used to generate circumstances under which the normal facilitative effect of similarity could be reversed once observed (Experiment 2A and 2B) or prevented from developing initially (Experiments 3 and 4). These experiments support a particular account of how a qualitative relation can affect the course of conditioning. However, that account requires the introduction of no special principles of conditioning unique to the case of similarity.

Unequal associative changes when excitors and neutral stimuli are conditioned in compound

RA Rescorla — 2008-07-30T12:57:11-00:00

Q J Exp Psychol B, Vol. 54, No. 1. (2001), 53-68.

In four experiments a compound of a previously conditioned excitor and a neutral stimulus was either reinforced with food or nonreinforced. Two experiments used a magazine approach procedure in rats, and two used an autoshaping procedure in pigeons. All experiments employed a novel compound test procedure, which permitted evaluation of the size of the associative change that took place for the excitatory and neutral stimuli. Reinforcement of the compound resulted in greater increments in the associative strength of the neutral stimulus than of the excitor. Nonreinforcement of the compound resulted in greater decrements in the associative strength of the excitor than of the neutral stimulus. These results agree with earlier experiments with compounds of excitors and inhibitors and provide an additional challenge to contemporary error-correction models of conditioning.

Evidence for an association between the discriminative stimulus and the response-outcome association in instrumental learning

RA Rescorla — 2008-07-30T12:57:09-00:00

J Exp Psychol Anim Behav Process, Vol. 16, No. 4. (1990), 326-34.

In 4 experiments, rats received 1 of several outcomes for engaging in various instrumental responses in the presence of discriminative stimuli. Discriminative stimuli shared some response-outcome relations but not others. When a response was subsequently extinguished in the presence of 1 discriminative stimulus, that produced relatively more decrement in responding in other stimuli that shared the same response-outcome relation. Other discriminative stimuli, in the presence of which that response had been reinforced by other outcomes and in which the original outcome had reinforced another response, were less affected. Moreover, postextinction devaluation of that outcome suggested that the particular response-outcome relation extinguished had undergone decrement. These results suggest that discriminative stimuli have relatively specific associations with the response-outcome relations that obtain in their presence.

The effect of signaled reinforcement on rats' fixed-interval responding

P Reed — 2008-07-30T12:57:05-00:00

J Exp Anal Behav, Vol. 79, No. 3. (2003), 367-82.

Four experiments examined the effect on rats' response rate of presenting a brief (500 ms) stimulus simultaneously with the delivery of food on fixed-interval (FI) schedules. In Experiment 1, reinforcement signals that were spatially diffuse (both tones and lights) elevated rates of responding, but responding was attenuated by localized visual stimuli. The remaining experiments examined the signal-induced potentiation of responding. In Experiment 2, a tone reinforcement signal potentiated response rates on an FI schedule, but attenuated response rates on a variable-interval (VI) schedule. This difference was obtained even though the overall rate of responding was equated on the two schedules before the introduction of the signal. Signal-induced potentiation of responding occurred over a range of FI values employed in Experiment 3. In Experiment 4, presenting a reinforcement signal when high local rates of response had occurred immediately before reinforcement resulted in potentiated rates of responding on an FI schedule. The opposite effect on response rate occurred when the reinforcement signal followed only low local rates of response. These results indicate that a variety of factors influence the effects of a reinforcement signal. They imply, however, that the local rate of response at the time of reinforcement is a key factor in establishing the nature of the signaling effect.

Visual control of orientation behaviour in the fly. Part II. Towards the underlying neural interactions

T Poggio — 2008-07-30T12:57:00-00:00

Q Rev Biophys, Vol. 9, No. 3. (1976), 377-438.

Nonlinear interactions underlying visual orientation behavior of the fly

T Poggio — 2008-07-30T12:57:00-00:00

Cold Spring Harb Symp Quant Biol, Vol. 40 (1976), 635-45.

A theory of the pattern induced flight orientation of the fly Musca domestica

T Poggio — 2008-07-30T12:57:00-00:00

Kybernetik, Vol. 12, No. 4. (1973), 185-203.

A numerical analysis of the geniculocortical input to striate cortex in the monkey

A Peters — 2008-07-30T12:56:57-00:00

Cereb Cortex, Vol. 4, No. 3. (1994), 215-29.

Using data that are available in various publications, a quantitative analysis has been made of the geniculocortical input to layer IVC of the macaque striate cortex. The data suggest that only 1.3-1.9% of the excitatory, or asymmetric synapses in layer IVC alpha of striate cortex are provided by the neurons of the magnocellular layers of the LGN. This amounts to only 18-40 of the 1000-2100 asymmetric synapses that the average layer IVC alpha neuron receives. The parvicellular afferents to layer IVC beta, on the other hand, provide 3.7-8.7% of the asymmetric synapses formed by the average layer IVC beta neuron, or 37-191 synapses to each neuron. If it is assumed that the boutons in the geniculocortical axonal plexuses are evenly spread, it can be calculated that the input to an individual layer IVC neuron is provided by some 24 axonal plexuses. This is regardless of whether the neuron lies in layer IVC alpha or in IVC beta. This calculation suggests that a single axonal plexus provides not more than one or two of the excitatory synapses received by an individual layer IVC alpha neuron, and between one and eight excitatory synapses for a layer IVC beta neuron. Consequently, it is unlikely that the response properties of a particular cortical neuron are dominated by its input from a single geniculate neuron. Since the geniculocortical input essentially determines the response properties of neurons in layer IV of macaque striate cortex, it is surprising that this input amounts to such a small number of synapses to an individual neuron, although we obtained a somewhat similar result in our earlier quantitative analysis of the geniculate input to the striate cortex of the cat (Peters and Payne, 1993). But it has to be questioned whether the low values obtained are correct. Interestingly, the geniculocortical input to cortex has been largely neglected in favor of analyses of intracortical circuitry, but in view of the basic importance of this afferent input, it is suggested that more quantitative data about it should be generated, so that a better assessment can be made of its extent.

Optical probing of neuronal circuits with calcium indicators

ZA Peterlin — 2008-07-30T12:56:57-00:00

Proc Natl Acad Sci U S A, Vol. 97, No. 7. (2000), 3619-24.

An experimental difficulty in unraveling circuits in the mammalian nervous system is the identification of postsynaptic targets of a given neuron. Besides ultrastructural reconstructions, simultaneous recordings from pairs of cells in brain slices have been used to identify connected neurons. We describe in this paper a technique using calcium imaging that allows rapid identification of potential postsynaptic targets. This method consists of stimulating one neuron ("trigger") while imaging a population of cells to detect which other neurons ("followers") are activated by the trigger. By using bulk-loading of calcium indicators in slices of mouse visual cortex, we demonstrate that neurons that display somatic calcium transients time-locked to the spikes of a trigger neuron can be monosynaptically connected to it. This technique could be applied to reconstruct and assay circuits in the central nervous system.

Second-order olfactory-mediated fear-potentiated startle

GY Paschall — 2008-07-30T12:56:52-00:00

Learn Mem, Vol. 9, No. 6. (2002), 395-401.

Recently, we reported that discrete (4-sec) olfactory cues paired with footshock serve as effective conditioned stimuli (CSs) for potentiating the acoustic startle response in rats using the fear-potentiated startle paradigm. Because odors are such salient cues for the rat, and because of the robust olfactory conditioning observed previously, the current studies investigated second-order fear conditioning using olfactory and visual cues. In Experiments 1 and 2, we used a small number of first-order and second-order training trials on separate days to investigate second-order fear-potentiated startle. Significant potentiated startle was observed in animals receiving Paired/Paired training in both studies, but surprisingly, control animals in the Unpaired/Paired group (Exp. 1) also showed significant potentiated startle to a light S2 at testing. These findings are addressed in the Discussion. Overall, the results of both experiments suggest that olfactory cues serve as efficient S1 and S2 stimuli in second-order fear-potentiated startle paradigms when only a small number of first and second-order training trials are presented.

A sensory source for motor variation

LC Osborne — 2008-07-30T12:56:49-00:00

Nature, Vol. 437, No. 7057. (2005), 412-6.

Suppose that the variability in our movements is caused not by noise in the motor system itself, nor by fluctuations in our intentions or plans, but rather by errors in our sensory estimates of the external parameters that define the appropriate action. For tasks in which precision is at a premium, performance would be optimal if no noise were added in movement planning and execution: motor output would be as accurate as possible given the quality of sensory inputs. Here we use visually guided smooth-pursuit eye movements in primates as a testing ground for this notion of optimality. In response to repeated presentations of identical target motions, nearly 92% of the variance in eye trajectory can be accounted for as a consequence of errors in sensory estimates of the speed, direction and timing of target motion, plus a small background noise that is observed both during eye movements and during fixations. The magnitudes of the inferred sensory errors agree with the observed thresholds for sensory discrimination by perceptual systems, suggesting that the very different neural processes of perception and action are limited by the same sources of noise.

Insect visual homing strategies in a robot with analog processing

R Moller — 2008-07-30T12:56:29-00:00

Biol Cybern, Vol. 83, No. 3. (2000), 231-43.

The visual homing abilities of insects can be explained by the snapshot hypothesis. It asserts that an animal is guided to a previously visited location by comparing the current view with a snapshot taken at that location. The average landmark vector (ALV) model is a parsimonious navigation model based on the snapshot hypothesis. According to this model, the target location is unambiguously characterized by a signature vector extracted from the snapshot image. This article provides threefold support for the ALV model by synthetic modeling. First, it was shown that a mobile robot using the ALV model returns to the target location with only small position errors. Second, the behavior of the robot resembled the behavior of bees in some experiments. And third, the ALV model was implemented on the robot in analog hardware. This adds validity to the ALV model, since analog electronic circuits share a number of information-processing principles with biological nervous systems; the analog implementation therefore provides suggestions for how visual homing abilities might be implemented in the insect's brain.

Cognition by a mini brain

R Menzel — 2008-07-30T12:56:25-00:00

Nature, Vol. 400, No. 6746. (1999), 718-9.

Segregation of form, color, movement, and depth: anatomy, physiology, and perception

M Livingstone — 2008-07-30T12:56:10-00:00

Science, Vol. 240, No. 4853. (1988), 740-9.

Anatomical and physiological observations in monkeys indicate that the primate visual system consists of several separate and independent subdivisions that analyze different aspects of the same retinal image: cells in cortical visual areas 1 and 2 and higher visual areas are segregated into three interdigitating subdivisions that differ in their selectivity for color, stereopsis, movement, and orientation. The pathways selective for form and color seem to be derived mainly from the parvocellular geniculate subdivisions, the depth- and movement-selective components from the magnocellular. At lower levels, in the retina and in the geniculate, cells in these two subdivisions differ in their color selectivity, contrast sensitivity, temporal properties, and spatial resolution. These major differences in the properties of cells at lower levels in each of the subdivisions led to the prediction that different visual functions, such as color, depth, movement, and form perception, should exhibit corresponding differences. Human perceptual experiments are remarkably consistent with these predictions. Moreover, perceptual experiments can be designed to ask which subdivisions of the system are responsible for particular visual abilities, such as figure/ground discrimination or perception of depth from perspective or relative movement--functions that might be difficult to deduce from single-cell response properties.

The impact of reinforcement density on response differentiation in configural discrimination problems

H Lachnit — 2008-07-30T12:56:04-00:00

Psychophysiology, Vol. 39, No. 5. (2002), 650-6.

Two human Pavlovian conditioning experiments investigated the impact of reinforcement density (the number of reinforced trials divided by the total number of trials) on discrimination learning. Experiment 1 used a negative patterning problem (A+, B+, AB-) and Experiment 2 used a positive patterning problem (A-, B-, AB+). In both experiments, reinforcement density varied across four levels. Response differentiation between reinforced and non-reinforced stimuli was linearly related to the decrease in reinforcement density. Responses to nonreinforced stimuli did not differ between the four groups in either experiment. In contrast to this, responses to reinforced stimuli were considerably more pronounced in conditions with lower reinforcement density. For negative patterning, this replicates and extends similar observations from other species. For positive patterning, this is a finding that has not yet been reported in other experiments. The results are in agreement with the comparator hypothesis (Miller & Matzel, 1988) and with Wagner's (1981) "standard operating procedures" (SOP) model.

Identification of neuronal pathways mediating phototactic modulation of head-waving in Aplysia californica

FM Kuenzi — 2008-07-30T12:55:51-00:00

Behav Neural Biol, Vol. 55, No. 3. (1991), 338-55.

The marine mollusc Aplysia californica exhibits a complex, rhythmic motor response, head-waving, in a variety of naturally occurring behavioral contexts. A cellular analysis of this behavior would be greatly facilitated by achieving stimulus control over the response. We have found that such stimulus control can be readily achieved by exposing a head-waving animal to a directional light source, which rapidly elicits a positive phototactic response: the animal either swings its head to face the light or biases its head waving toward the light source. Moreover, we have found that the neural pathways from the principal photoreceptive organs of Aplysia, the eyes and rhinophores, must be intact for the normal execution of this phototactic response: animals with chronic transection of the optic and rhinophore nerves show no phototactic behavior, whereas sham-operated animals continue to exhibit normal phototaxis.

Stereotyped position of local synaptic targets in neocortex

J Kozloski — 2008-07-30T12:55:46-00:00

Science, Vol. 293, No. 5531. (2001), 868-72.

The microcircuitry of the mammalian neocortex remains largely unknown. Although the neocortex could be composed of scores of precise circuits, an alternative possibility is that local connectivity is probabilistic or even random. To examine the precision and degree of determinism in the neocortical microcircuitry, we used optical probing to reconstruct microcircuits in layer 5 from mouse primary visual cortex. We stimulated "trigger" cells, isolated from a homogenous population of corticotectal pyramidal neurons, while optically detecting "follower" neurons directly driven by the triggers. Followers belonged to a few selective anatomical classes with stereotyped physiological and synaptic responses. Moreover, even the position of the followers appeared determined across animals. Our data reveal precisely organized cortical microcircuits.

Spontaneously emerging cortical representations of visual attributes

T Kenet — 2008-07-30T12:55:40-00:00

Nature, Vol. 425, No. 6961. (2003), 954-6.

Spontaneous cortical activity--ongoing activity in the absence of intentional sensory input--has been studied extensively, using methods ranging from EEG (electroencephalography), through voltage sensitive dye imaging, down to recordings from single neurons. Ongoing cortical activity has been shown to play a critical role in development, and must also be essential for processing sensory perception, because it modulates stimulus-evoked activity, and is correlated with behaviour. Yet its role in the processing of external information and its relationship to internal representations of sensory attributes remains unknown. Using voltage sensitive dye imaging, we previously established a close link between ongoing activity in the visual cortex of anaesthetized cats and the spontaneous firing of a single neuron. Here we report that such activity encompasses a set of dynamically switching cortical states, many of which correspond closely to orientation maps. When such an orientation state emerged spontaneously, it spanned several hypercolumns and was often followed by a state corresponding to a proximal orientation. We suggest that dynamically switching cortical states could represent the brain's internal context, and therefore reflect or influence memory, perception and behaviour.

Performance monitoring by the anterior cingulate cortex during saccade countermanding

S Ito — 2008-07-30T12:55:27-00:00

Science, Vol. 302, No. 5642. (2003), 120-2.

Consensus is emerging that the medial frontal lobe of the brain is involved in monitoring performance, but precisely what is monitored remains unclear. A saccade-countermanding task affords an experimental dissociation of neural signals of error, reinforcement, and conflict. Single-unit activity was monitored in the anterior cingulate cortex of monkeys performing this task. Neurons that signaled errors were found, half of which responded to the omission of earned reinforcement. A further diversity of neurons signaled earned or unexpected reinforcement. No neurons signaled the form of conflict engendered by interruption of saccade preparation produced in this task. These results are consistent with the hypothesis that the anterior cingulate cortex monitors the consequences of actions.

The effect of cumulative experience on the use of elemental and configural visual discrimination strategies in honeybees

M Giurfa — 2008-07-30T12:54:54-00:00

Behav Brain Res, Vol. 145, No. 1-2. (2003), 161-9.

We addressed the question of whether the amount of individual experience determines the use of elemental or configural visual discrimination strategies in free-flying honeybees Apis mellifera. We trained bees to fly into a Y-maze to collect sucrose solution on a rewarded stimulus presented in one of the arms of the maze. Stimuli were colour disks, violet (V), green (G) or yellow (Y), which were of equal psychophysical salience for honeybees. Training followed an A+, BC+ design, followed by an AC versus BC test. Training consisted of 6 (3 A+ and 3 BC+), 20 (10 A+ and 10 BC+) or 40 (20 A+ and 20 BC+) acquisition trials. Elemental models of compound processing predict a preference for the non-trained stimulus AC while configural models predict a preference for the trained stimulus BC. Our results show that increasing the number of acquisition trials results in a change of the internal representation of stimuli. After six training trials, bees favoured an elemental strategy and preferred AC to BC during the tests. Generally, increasing the number of training trials resulted in an increase of the choice of BC. Thus, short training favoured processing of the compound as the sum of its elements (elemental account) while long training favoured its processing as being different from the sum of its elements (configural account). Additionally, we observed that the change in stimulus processing was also influenced by stimulus similarity. Colour perceptual similarity favoured configural processing with increasing experience.

Insect visual perception: complex abilities of simple nervous systems

M Giurfa — 2008-07-30T12:54:53-00:00

Curr Opin Neurobiol, Vol. 7, No. 4. (1997), 505-13.

Despite their relatively simple nervous systems, insects display a rich behavioural repertoire, in which vision plays a major role. In the past two years, much knowledge has been gained about how insects are capable of a variety of flexible, visually guided tasks that involve a high level of complexity. From long-range navigation to median-range orientation and close-up recognition, insects apply different strategies that complement each other, that are used sequentially during their approach flight towards their goals, and that may replace each other, depending on the salience of, and the attention towards, particular visual cues.

Odor localization requires visual feedback during free flight in Drosophila melanogaster

MA Frye — 2008-07-30T12:54:48-00:00

J Exp Biol, Vol. 206, No. Pt 5. (2003), 843-55.

Adult fruit flies follow attractive odors associated with food and oviposition sites through widely varied visual landscapes. To examine the interaction between olfactory and visual cues during search behavior, we recorded three-dimensional flight trajectories as individuals explored controlled sensory landscapes. When presented with the source of an attractive odor invisibly embedded in the floor of a 1 m arena, flies spend most of their time hovering back and forth over the source when flying within a randomly textured visual background but fail to localize the source when searching within a uniform white surround. To test whether flies are associating unique features of the visual background with the strength of odor cues, we flew them within arenas containing evenly spaced vertical stripes. Flies readily localized the odor when flying within visual landscapes lacking azimuthal landmarks provided that vertical edges were present. Flies failed to localize odor when flying within a background pattern consisting of horizontal stripes. These results suggest that, whereas flies do not require spatially unique visual patterns to localize an odor source, they do require visual feedback generated by vertical edges. Quantitative shifts in several components of flight behavior accompanied successful odor localization. Flies decrease flight altitude, turn more often and approach visually textured walls of the arena near an odor source. A simple model based on the statistics of flight behavior supports the hypothesis that a subtle influence on these behaviors is sufficient to lead a fly to its food.

A signature of salience in the Drosophila brain

MA Frye — 2008-07-30T12:54:48-00:00

Nat Neurosci, Vol. 6, No. 6. (2003), 544-6.

Lesions of the vertical lobe impair visual discrimination learning by observation in Octopus vulgaris

G Fiorito — 2008-07-30T12:54:42-00:00

Neurosci Lett, Vol. 192, No. 2. (1995), 117-20.

We investigated whether lesions of the vertical lobe of the supraesophageal nervous mass of Octopus vulgaris impair discrimination learning acquired by observation of conspecific behavior. When tested alone, observer octopuses with about 50% of the vertical lobe removed showed a deficit in their learning by observation performance. The level of learning improved 24 h after the observational phase, when observer Octopus vulgaris showed a visual discriminatory performance significantly in agreement with the observed one. Control animals that had no brain tissue removed, did not show any impairment in the discriminative performance they had acquired vicariously. Removal of the vertical lobe of the octopus 'brain' has been reported to induce learning and memory deficits of visual discrimination in direct learning by conditioning experiments. Our findings support the conclusion that the removal of such brain center impairs short-term recall, but does not impair acquisition nor retention of 'observational' long-term memory.

Neural correlates of Pavlovian conditioning in components of the neural network supporting ciliary locomotion in Hermissenda

T Crow — 2008-07-30T12:54:05-00:00

Learn Mem, Vol. 10, No. 3. (2003), 209-16.

Pavlovian conditioning in Hermissenda consists of pairing light, the conditioned stimulus (CS) with activation of statocyst hair cells, the unconditioned stimulus (US). Conditioning produces CS-elicited foot shortening and inhibition of light-elicited locomotion, the two conditioned responses (CRs). Conditioning correlates have been identified in the primary sensory neurons (photoreceptors) of the CS pathway, interneurons that receive monosynaptic input from identified photoreceptors, and putative pedal motor neurons. While cellular mechanisms of acquisition produced by the synaptic interaction between the CS and US pathways are well-documented, little is known about the mechanisms responsible for the generation or expression of the CR. Here we show that in conditioned animals light reduced tonic firing of ciliary activating pedal neurons (VP1) below their pre-CS baseline levels. In contrast, pseudorandom controls expressed a significant increase in CS-elicited tonic firing of VP1 as compared to pre-CS baseline activity. Identified interneurons in the visual pathway that have established polysynaptic connections with VP1 were examined in conditioned animals and pseudorandom controls. Depolarization of identified type Ie interneurons with extrinsic current elicited a significant increase in IPSPs recorded in VP1 pedal neurons of conditioned animals as compared with pseudorandom controls. Conditioning also enhanced intrinsic excitability of type Ie interneurons of conditioned animals as compared to pseudorandom controls. Light evoked a modest increase in IPSP frequency in VP1 of conditioned preparations and a significant decrease in IPSP frequency in VP1 of pseudorandom controls. Our results show that a combination of synaptic facilitation and intrinsic enhanced excitability in identified components of the CS pathway may explain light-elicited inhibition of locomotion in conditioned animals.

Pavlovian conditioning of Hermissenda: current cellular, molecular, and circuit perspectives

T Crow — 2008-07-30T12:54:05-00:00

Learn Mem, Vol. 11, No. 3. (2004), 229-38.

The less-complex central nervous system of many invertebrates make them attractive for not only the molecular analysis of the associative learning and memory, but also in determining how neural circuits are modified by learning to generate changes in behavior. The nudibranch mollusk Hermissenda crassicornis is a preparation that has contributed to an understanding of cellular and molecular mechanisms of Pavlovian conditioning. Identified neurons in the conditioned stimulus (CS) pathway have been studied in detail using biophysical, biochemical, and molecular techniques. These studies have resulted in the identification and characterization of specific membrane conductances contributing to enhanced excitability and synaptic facilitation in the CS pathway of conditioned animals. Second-messenger systems activated by the CS and US have been examined, and proteins that are regulated by one-trial and multi-trial Pavlovian conditioning have been identified in the CS pathway. The recent progress that has been made in the identification of the neural circuitry supporting the unconditioned response (UR) and conditioned response (CR) now provides for the opportunity to understand how Pavlovian conditioning is expressed in behavior.

Context-specificity of target versus feature inhibition in a feature-negative discrimination

ME Bouton — 2008-07-30T12:53:38-00:00

J Exp Psychol Anim Behav Process, Vol. 20, No. 1. (1994), 51-65.

Four experiments with rats examined the effects of a context switch on inhibition that was acquired during a feature-negative discrimination. A target conditioned stimulus was paired with food when it was presented alone but occurred without food when it was combined with a feature stimulus. A context switch following training did not disrupt inhibition conditioned to the feature. However, responding to the target was more difficult to inhibit when it was tested in a different context. It is suggested that both the target and the feature acquired inhibition and that the target's inhibition was especially sensitive to the context. The feature may inhibit responding to the target (a) by directly suppressing the representation of the food and (b) by activating the target's own inhibitory association with food, which is at least partly context-specific. Implications for theories of inhibition and negative occasion-setting are discussed.

Occasion-setting training renders stimuli more similar: acquired equivalence between the targets of feature-positive discriminations

C Bonardi — 2008-07-30T12:53:37-00:00

Q J Exp Psychol B, Vol. 47, No. 1. (1994), 63-81.

In two experiments rats received training on two concurrent appetitive feature-positive discriminations. A preliminary test in Experiment 1 confirmed previous demonstrations of the transfer of occasion-setting properties--the feature from one of these discriminations was better able to facilitate responding to the occasion-set target CS from the second discrimination than to a control stimulus that had not been the subject of occasion-setting. The source of this transfer was investigated in a second phase of training, and in Experiment 2. In both experiments one of the occasion-set CSs was paired with food, and generalization of appetitive conditioned responding from this stimulus to the second occasion-set CS, and to a control cue, was examined. There was more generalization from the first occasion-set CS to the second CS that had also been occasion-set than to the control cue. This is taken as evidence that occasion-set CSs are rendered more similar as a result of their common training history. The implications of these findings for explaining transfer of occasion setting are discussed.

Visual feature selectivity in frontal eye fields induced by experience in mature macaques

NP Bichot — 2008-07-30T12:53:35-00:00

Nature, Vol. 381, No. 6584. (1996), 697-9.

When examining a complex image, the eye movements of expert observers differ from those of novices; experts have learned to ignore features that are visually salient but are not relevant to the interpretation of the image. We have studied the neural basis of this form of perceptual-motor learning using monkeys that have learned to search for a visual target among distractors. Monkeys trained to search only for, say, a red stimulus among green distractors will ignore green stimuli even if they subsequently appear as targets in a complementary search array, that is, among red distractors. We recorded from neurons in the frontal eye field (FEF), a cortical area that responds to visual stimuli and controls purposive eye movements. Normally, FEF neurons do not exhibit feature selectivity, but their activity evolves to signal the target for an incipient eye movement. In monkeys trained exclusively on targets of one colour, however, FEF neurons show selectivity for stimuli of that colour. Because this selective response occurs so soon after presentation of the stimulus array, and is independent of location within the visual field, we propose that it reflects a form of experience-dependent plasticity that mediates the learning of arbitrary stimulus-response associations.

Dopamine-Mushroom Body Circuit Regulates Saliency-Based Decision-Making in Drosophila

Ke Zhang — 2007-06-29T08:23:23-00:00

Science, Vol. 316, No. 5833. (29 June 2007), pp. 1901-1904.

Drosophila melanogaster can make appropriate choices among alternative flight options on the basis of the relative salience of competing visual cues. We show that this choice behavior consists of early and late phases; the former requires activation of the dopaminergic system and mushroom bodies, whereas the latter is independent of these activities. Immunohistological analysis showed that mushroom bodies are densely innervated by dopaminergic axons. Thus, the circuit from the dopamine system to mushroom bodies is crucial for choice behavior in Drosophila. 10.1126/science.1137357

Context and occasion setting in Drosophila visual learning.

B Brembs — 2006-11-17T14:42:36-00:00

Learn Mem, Vol. 13, No. 5. (t 2006), pp. 618-628.

In a permanently changing environment, it is by no means an easy task to distinguish potentially important events from negligible ones. Yet, to survive, every animal has to continuously face that challenge. How does the brain accomplish this feat? Building on previous work in Drosophila melanogaster visual learning, we have developed an experimental methodology in which combinations of visual stimuli (colors and patterns) can be arranged such that the same stimuli can either be directly predictive, indirectly predictive, or nonpredictive of punishment. Varying this relationship, we found that wild-type flies can establish different memory templates for the same contextual color cues. The colors can either leave no trace in the pattern memory template, leading to context-independent pattern memory (context generalization), or be learned as a higher-order cue indicating the nature of the pattern-heat contingency leading to context-dependent memory (occasion setting) or serve as a conditioned stimulus predicting the punishment directly (simple conditioning). In transgenic flies with compromised mushroom-body function, the sensitivity to these subtle variations is altered. Our methodology constitutes a new concept for designing learning experiments. Our findings suggest that the insect mushroom bodies stabilize visual memories against context changes and are not required for cognition-like higher-order learning.