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Locus coeruleus, emotion and motivation| old_uid | 3052 |
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| title | Locus coeruleus, emotion and motivation |
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| start_date | 2007/06/15 |
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| schedule | 14h |
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| online | no |
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| details | Jour inhabituel |
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| summary | The noradrenergic nucleus locus coeruleus (LC) is thought important for processes related to cognitive functions, such as attention, motivation and behavioral flexibility. This study was undertaken to characterize the relationship between LC activity and motivational processes. In a first series of experiment, LC activity was recorded simultaneously with that of medial frontal cortex (mFCx) in rats performing an olfactory Go/NoGo task. The orienting stimulus (light) induced a phasic LC activation, which preceded a sustained inhibition of mFCx neurons related to the engagement in the trial. LC neurons were also activated right before the ‘go’ response to the CS+ odor, while mFCx activity only changed during the 500 ms delay between the behavioral response and the trial outcome (reward delivery). In several sessions, novel odors were introduced and rats had to discover the odor-reward contingency. During these sessions, LC activation before the ‘go’ response appeared before animals exhibited a significant behavioral discrimination and before mFCx response-reward delay activity. Thus, when stimuli induce a behavioral adjustment, a transient LC activation precedes neuronal responses in the mFCx, both within a trial and across trials during learning. In order to further specify the relationship between LC activity and motivational/emotional processes underlying behavioral adaptation, the activity of single LC neurons was monitored in a monkey performing a reward schedule task, in which a series of 1, 2 or 3 operant trials had to be successfully completed to obtain a reward. Each trial began with the appearance of a visual cue signaling how many trials remained to be completed before a reward could be obtained. The level of motivation in each trial was measured by the reaction time and the proportion of correct operant responses. We also monitored an instinctive behavioral response, sucking of the reward spout, observed both after cue onset and during the operant response. The animal used the cues to adjust its motivation; errors were fewest in the rewarded trials. By contrast, sucking was maximal in first trials of the schedules, even though first trials were only rewarded in 1-trial schedules. The activity of 45 LC neurons was examined during this task. Thirty six neurons were activated at the onset of the cue (median latency = 95 ms) and 45 before the operant response (median latency= -155 ms). Twenty six of the 36 neurons responding to cues and 13/45 units activated before the operant response discriminated among the schedule states. Responses to cues were more frequent and more intense in the first trials of a schedule. Responses before the operant response were less discriminative than response to cues, with an equivalent proportion of cells sensitive to first and rewarded trials. Thus, LC neurons are activated around the two critical events in the task that evoke a conditioned instinctive response. The magnitude of their responses varies with motivational and especially instinctive processes. In conclusion, in operant tasks, LC neurons are most strongly activated when strong instinctive responses and high motivational states occur together. The short latency of LC responses means that noradrenaline levels will increase in the numerous target areas at the times where salient, emotionally arousing events occur, possibly enhancing interactions among these structures during complex functions and promoting behavioral adaptation. |
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| oncancel | CPLT |
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| responsibles | Burle |
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