It's the holiday season and you've been given a gift in a neatly wrapped box. You pick the box up, shake it, and judge its weight, but you can't figure out what's inside. Your curiosity peaked, you eagerly unwrap the gift. You feel like a kid again.
This sense of anticipation and discovery may make holiday gift exchange fun, but it is also critically important for neurological rehabilitation and recovery. In order for me, cross-eyed since infancy, to develop stereovision or for an individual to regain function after a stroke or other injury, brain circuits have to change. Some synapses, barely effective before the disorder or injury, must become stronger, others weaker, and many of these changes occur in the cerebral cortex. A sense of anticipation and discovery promotes synaptic changes because these feelings are accompanied by excitation of neurons in neuromodulatory areas of the brainstem and basal forebrain. These cells make connections onto cortical neurons where they liberate several different neurotransmitters or neuromodulators including dopamine, noradrenaline, serotonin, and acetylcholine. Release of these chemical messengers triggers and facilitates the synaptic changes among cortical neurons necessary for learning and recovery.