Context: Learning and cognition
A team of researchers studying how animals learn from rewards trained them on a simple task. On each trial a light came on, the animal pressed a lever, and a drop of juice followed. Early in training, recordings from dopamine-producing neurons showed a burst of activity each time the juice arrived. As training went on and the animals learned that the light predicted the juice, the burst moved earlier: it now occurred when the light came on, and the juice itself produced little extra activity. On the occasional trial when the expected juice did not arrive, activity in these neurons dipped below its normal level at the moment the juice was due.
With reference to this study, the role of one neurotransmitter in learning.