Biomedical subjects

Johan Lauwereyns

Publications and source records attributed to Johan Lauwereyns.

8 recordsLinked to original sources

PubMed2006

A reaction-time paradigm to measure reward-oriented bias in rats.

The authors devised a nose-poke task with asymmetric position-reward mapping to distinguish between effects of bias and sensitivity in reaction times of rats. In all trials, the rats had to poke their noses into the hole to the left or to the right of center, corresponding to the side at which 4 lights were illuminated, while ignoring distracters on the other side. Reaction times were faster for large-reward trials than for small-reward trials. In large-reward trials, there was no influence of the number of distracters, whereas in small-reward trials, distracters produced an increase in reaction time. Analysis of reaction-time distributions according to a linear model of decision making suggests that most of the systematic variability was due to a reward-oriented bias.

Animals↗

PubMed2005

Voluntary control of unavoidable action.

Goal-oriented behavior is usually portrayed to be directly related to incentive values. Underlying mechanisms are thought to include reward-oriented response bias and perceptual sensitivity. A recent electrophysiological study by Minamimoto et al. challenges this view, and reports neural activity in the thalamus that appears to counteract response bias. This type of activity might be crucial for our ability to engage voluntarily in actions that give little or no immediate return, but are necessary in the pursuit of long-term goals.

Conditioning, Operant↗

PubMed2005

Crosstalk between on-line and off-line processing of visual features.

Three dual-task experiments were conducted to investigate the relation between immediate, "on-line" judgments about visual features and delayed, "off-line" judgments. One hypothesis ("selective interference") predicted that dual-task performance would be challenged specifically within a visual dimension, as both tasks compete for the same resources. Another hypothesis ("cost of switching") made the opposite prediction. In Experiment 1, participants performed either color or shape discriminations in the on-line and off-line visual tasks, with systematic variation of feature similarity between the on-line and off-line features. In Experiment 2, participants performed either color or shape discriminations in the off-line task and color discriminations in the on-line task, with no overlap between the on-line and off-line features. In Experiment 3, participants performed color discriminations in both the on-line and off-line tasks, with partially overlapping stimulus sets. Altogether, the data from the three experiments provided evidence in favor of the hypothesis of cost of switching. Stimulus-stimulus compatibility effects between features in the off-line task and those in the on-line task further underscored the perceptual nature of the crosstalk.

Discrimination, Psychological↗

PubMed2003

Neural correlates of rewarded and unrewarded eye movements in the primate caudate nucleus.

The prospect of immediate reward elicits goal-oriented behavior. However, animals often have to perform actions that do not immediately lead to reward in the pursuit of a long-term goal. Here we identify neural activity in monkey caudate nucleus that specifically correlates with rewarded and unrewarded eye movements. The monkey performed a visually guided saccade task in which only one position was associated with positive reinforcement. To advance in the experimental session, however, the monkey had no choice but to complete a saccade to an unrewarded position as well as to a rewarded position. Some caudate saccadic neurons showed enhanced activity around the time of the saccade in rewarded trials (rewarded-saccade neurons). Another subset of neurons discharged selectively around the execution of the saccade in unrewarded trials (unrewarded-saccade neurons). In both rewarded and unrewarded trials, stronger activity of these neurons was associated with reduced saccade latency. These results suggest that both rewarded and unrewarded saccades are facilitated by caudate saccadic activity. The neuronal activity of unrewarded-saccade neurons might reflect the required execution of unrewarded eye movements on the way to future reward.

Action Potentials↗

PubMed2003

Effects of motivational conflicts on visually elicited saccades in monkeys.

The prospect of reward evoked by external stimuli is a central element of goal-oriented behavior. To elucidate behavioral effects of reward expectation on saccade latency, we employed a visually guided saccade task with asymmetrical reward schedule. The monkey had to make an immediate saccade to a peripheral visual target in every trial, but was rewarded for a correct saccade to only one of four possible target positions. Reward availability was predictable on the basis of the spatial position of the target throughout a daily session. Compared with the condition where all positions were rewarded with a smaller amount, the mean saccade latency in the asymmetrical reward schedule was significantly shorter when the saccade was made toward the position associated with reward than when it was directed to no-reward positions. Furthermore, a divergence-point analysis on cumulative latency distributions showed that the expectation of reward facilitated saccades at all latency ranges. In contrast, the expected lack of reward delayed the initiation of saccades with latencies longer than about 200 ms, irrespective of whether the saccade was made to a position orthogonal or opposite to the reward position. For saccades with latencies of more than approximately 240 ms, an additional delay was observed when the saccade was made to a position opposite, as compared to orthogonal, to the reward position. These results suggest that the facilitation by predictive reward is mediated by a preparatory process that is location-specific, whereas the inhibition by the absence of reward takes about 200 ms after the target onset to become effective and is initially location nonspecific but turns location-specific over time.

Animals↗

PubMed2002

A neural correlate of response bias in monkey caudate nucleus.

Primates are equipped with neural circuits in the prefrontal cortex, the parietal cortex and the basal ganglia that predict the availability of reward during the performance of behavioural tasks. It is not known, however, how reward value is incorporated in the control of action. Here we identify neurons in the monkey caudate nucleus that create a spatially selective response bias depending on the expected gain. In behavioural tasks, the monkey had to make a visually guided eye movement in every trial, but was rewarded for a correct response in only half of the trials. Reward availability was predictable on the basis of the spatial position of the visual target. We found that caudate neurons change their discharge rate systematically, even before the appearance of the visual target, and usually fire more when the contralateral position is associated with reward. Strong anticipatory activity of neurons with a contralateral preference is associated with decreased latency for eye movements in the contralateral direction. We conclude that this neuronal mechanism creates an advance bias that favours a spatial response when it is associated with a high reward value.

Action Potentials↗

PubMed2002

Feature-based anticipation of cues that predict reward in monkey caudate nucleus.

A subset of caudate neurons fires before cues that instruct the monkey what he should do. To test the hypothesis that the anticipatory activity of such neurons depends on the context of stimulus-reward mapping, we examined their activity while the monkeys performed a memory-guided saccade task in which either the position or the color of a cue indicated presence or absence of reward. Some neurons showed anticipatory activity only when a particular position was associated with reward, while others fired selectively for color-reward associations. The functional segregation suggests that caudate neurons participate in feature-based anticipation of visual information that predicts reward. This neuronal code influences the general activity level in response to visual features without improving the quality of visual discrimination.

Animals↗

PubMed2002

Influence of reward expectation on visuospatial processing in macaque lateral prefrontal cortex.

The lateral prefrontal cortex (LPFC) has been implicated in visuospatial processing, especially when it is required to hold spatial information during a delay period. It has also been reported that the LPFC receives information about expected reward outcome. However, the interaction between visuospatial processing and reward processing is still unclear because the two types of processing could not be dissociated in conventional delayed response tasks. To examine this, we used a memory-guided saccade task with an asymmetric reward schedule and recorded 228 LPFC neurons. The position of the target cue indicated the spatial location for the following saccade and the color of the target cue indicated the reward outcome for a correct saccade. Activity of LPFC was classified into three main types: S-type activity carried only spatial signals, R-type activity carried only reward signals, and SR-type activity carried both. Therefore only SR-type cells were potentially involved in both visuospatial processing and reward processing. SR-type activity was enhanced (SR+) or depressed (SR-) by the reward expectation. The spatial discriminability as expressed by the transmitted information was improved by reward expectation in SR+ type. In contrast, when reward information was coded by an increase of activity in the reward-absent condition (SR- type), it did not improve the spatial representation. This activity appeared to be involved in gaze fixation. These results extend previous findings suggesting that the LPFC exerts dual influences based on predicted reward outcome: improvement of memory-guided saccades (when reward is expected) and suppression of inappropriate behavior (when reward is not expected).

Animals↗