Figure 16.

Alerting signals can massively modulate learning. Neuromodulators such as serotonin, acetylcholine, and dopamine, whose signals are broadcast to much of the cortex, tell us when to pay attention and seem to force the brain to learn. In the experiment shown at the bottom, rats listened to a nine-kilohertz sound which was associated with an electrical stimulation of the basal nucleus of Meynert, thus triggering the release of acetylcholine in the cortex. After a few days of exposure, the entire auditory cortex was invaded by this sound frequency and its neighbors (regions in blue).