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Publications (4)16.18 Total impact

  • Marc Deffains, Eric Legallet, Paul Apicella
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    ABSTRACT: The capacity to acquire motor skills through repeated practice of a sequence of movements underlies many everyday activities. Extensive research in humans has dealt with the importance of spatial and temporal factors on motor sequence learning, standing in contrast to the few studies available in animals, particularly in nonhuman primates. In the present experiments, we studied the effect of the serial order of stimuli and associated movements in macaque monkeys overtrained to make arm-reaching movements in response to spatially distinct visual targets. Under different conditions, the temporal structure of the motor sequence was varied by changing the duration of the interval between successive target stimuli or by adding a cue that reliably signaled the onset time of the forthcoming target stimulus. In each condition, the extent to which the monkeys are sensitive to the spatial regularities was assessed by comparing performance when stimulus locations follow a repeating sequence, as opposed to a random sequence. We observed no improvement in task performance on repeated sequence blocks, compared to random sequence blocks, when target stimuli are relatively distant from each other in time. On the other hand, the shortening of the time interval between successive target stimuli or, more efficiently, the addition of a temporal cue before the target stimulus yielded a performance advantage under repeated sequence, reflected in a decrease in the latency of arm and saccadic eye movements accompanied by an increased tendency for eye movements to occur in an anticipatory manner. Contrary to the effects on movement initiation, the serial order of stimuli and movements did not markedly affect the execution of movement. Moreover, the location of a given target in the random sequence influenced task performance based on the location of the preceding target, monkeys being faster in responding as a result of familiarity caused by extensive practice with some target transitions also used in the repeated sequence. This performance advantage was most prominently detectable when temporal prediction of forthcoming target stimuli was optimized. Taken together, the present findings demonstrate that the monkey's capacity to make use of serial order information to speed task performance was dependent on the temporal structure of the motor sequence.
    Experimental Brain Research 08/2011; 214(3):415-25. · 2.22 Impact Factor
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    ABSTRACT: The detection of differences between predictions and actual outcomes is important for associative learning and for selecting actions according to their potential future reward. There are reports that tonically active neurons (TANs) in the primate striatum may carry information about errors in the prediction of rewards. However, this property seems to be expressed in classical conditioning tasks but not during performance of an instrumental task. To address this issue, we recorded the activity of TANs in the putamen of two monkeys performing an instrumental task in which probabilistic rewarding outcomes were contingent on an action in block-design experiments. Behavioral evidence suggests that animals adjusted their performance according to the level of probability for reward on each trial block. We found that the TAN response to reward was stronger as the reward probability decreased; this effect was especially prominent on the late component of the pause-rebound pattern of typical response seen in these neurons. The responsiveness to reward omission was also increased with increasing reward probability, whereas there were no detectable effects on responses to the stimulus that triggered the movement. Overall, the modulation of TAN responses by reward probability appeared relatively weak compared with that observed previously in a probabilistic classical conditioning task using the same block design. These data indicate that instrumental conditioning was less effective at demonstrating prediction error signaling in TANs. We conclude that the sensitivity of the TAN system to reward probability depends on the specific learning situation in which animals experienced the stimulus-reward associations.
    Journal of Neuroscience 01/2011; 31(4):1507-15. · 6.91 Impact Factor
  • Marc Deffains, Eric Legallet, Paul Apicella
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    ABSTRACT: The striatum, especially its dorsolateral part, plays a major role in motor skill learning and habit formation, but it is still unclear how this contribution might be mediated at the neuronal level. We recorded single neurons in the posterior putamen of two monkeys performing an overlearned sequence of arm reaching movements to examine whether task-related activities are sensitive to manipulations of the serial order of stimulus-target locations. The monkeys' capacity to learn sequential regularities was assessed by comparing arm movement latencies and saccadic ocular reactions when a fixed repeating sequence was replaced with a random sequence. We examined neurons classified as phasically active projection neurons (PANs) and tonically active presumed cholinergic interneurons (TANs). About one-third of the PANs (35/106, 33%) activated during specific parts of a trial displayed modulations of their level of activation when the sequential structure was changed. This differential activity consisted of either decreases or increases in activity without altering the time period during which task-related activations occurred. In addition, half of the TANs (41/80, 51%) changed their responses to task stimuli with the sequence switch, indicating that the response selectivity of TANs reflects the detection of the context that requires adaptation to changes in the serial order of stimulus presentations. Our findings suggest that task-related changes in activity of projection neurons may be an important factor contributing to the production and adjustment of sequential behavior executed in an automatic fashion, whereas putative interneurons may provide a signal for performance monitoring in specific contexts.
    Journal of Neurophysiology 09/2010; 104(3):1355-69. · 3.30 Impact Factor
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    ABSTRACT: Tonically active neurons (TANs) in the primate striatum are responsive to rewarding stimuli and they are thought to be involved in the storage of stimulus-reward associations or habits. However, it is unclear whether these neurons may signal the difference between the prediction of reward and its actual outcome as a possible neuronal correlate of reward prediction errors at the striatal level. To address this question, we studied the activity of TANs from three monkeys trained in a classical conditioning task in which a liquid reward was preceded by a visual stimulus and reward probability was systematically varied between blocks of trials. The monkeys' ability to discriminate the conditions according to probability was assessed by monitoring their mouth movements during the stimulus-reward interval. We found that the typical TAN pause responses to the delivery of reward were markedly enhanced as the probability of reward decreased, whereas responses to the predictive stimulus were somewhat stronger for high reward probability. In addition, TAN responses to the omission of reward consisted of either decreases or increases in activity that became stronger with increasing reward probability. It therefore appears that one group of neurons differentially responded to reward delivery and reward omission with changes in activity into opposite directions, while another group responded in the same direction. These data indicate that only a subset of TANs could detect the extent to which reward occurs differently than predicted, thus contributing to the encoding of positive and negative reward prediction errors that is relevant to reinforcement learning.
    European Journal of Neuroscience 08/2009; 30(3):515-26. · 3.75 Impact Factor