Which neurotransmitter regulates sleep, mood, attention, and learning, and too little of this neurotransmitter can cause depressed mood?

Serotonin and Dopamine

Dopamine is a neurotransmitter which is usually associated with attention and learning, and too of it little can be related to several forms of depression.  

Also, Serotonin plays a part in the development of mood, appetite and is associated with sleep, whereas; too little of serotonin is related to depression.

answer; cultural trait;

sir frederic attributed inaccuracies to schemas. memory reconstruction is one part actual events and one part personal schema, which can result in inaccuracies when memories are reconstructed.