Sensitivity of locus ceruleus neurons to reward value for goal-directed actions.
The noradrenergic nucleus locus ceruleus (LC) is associated classically with arousal and attention. Recent data suggest that it might also play a role in motivation. To study how LC neuronal responses are related to motivational intensity, we recorded 121 single neurons from two monkeys while reward size (one, two, or four drops) and the manner of obtaining reward (passive vs active) were both manipulated. The monkeys received reward under three conditions: (1) releasing a bar when a visual target changed color; (2) passively holding a bar; or (3) touching and releasing a bar. In the first two conditions, a visual cue indicated the size of the upcoming reward, and, in the third, the reward was constant through each block of 25 trials. Performance levels and lipping intensity (an appetitive behavior) both showed that the monkeys' motivation in the task was related to the predicted reward size. In conditions 1 and 2, LC neurons were activated phasically in relation to cue onset, and this activation strengthened with increasing expected reward size. In conditions 1 and 3, LC neurons were activated before the bar-release action, and the activation weakened with increasing expected reward size but only in task 1. These effects evolved as monkeys progressed through behavioral sessions, because increasing fatigue and satiety presumably progressively decreased the value of the upcoming reward. These data indicate that LC neurons integrate motivationally relevant information: both external cues and internal drives. The LC might provide the impetus to act when the predicted outcome value is low.
Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, and Motivation, Brain Behavior (MBB) team, Institut du Cerveau et de la Moelle épinière (ICM), Groupe Hospitalier Pitié-Salpêtrière, 75013 Paris, France sebastien.bouret@icm-institute.org.
Sebastien
http://orcid.org/0000-0003-2279-6161
S
Bouret
Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, and.
Barry J
http://orcid.org/0000-0002-8234-1540
BJ
Richmond
D000818:Animals; D003216:Conditioning, Operant / Q000502:physiology; D003463:Cues; D006040:Goals; D008125:Locus Coeruleus / Q000502:physiology*; D008253:Macaca mulatta; D008297:Male; D009042:Motivation / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology; D012201:Reward
decision-making; locus ceruleus; motivation; neuromodulation; noradrenaline; reward