Question: where is serotonin released from in the brain
[{'answer': 'neurons of the raphe nuclei', 'provenance': [{'wikipedia_id': '28764', 'title': 'Serotonin', 'start_paragraph_id': 21, 'start_character': 4, 'end_paragraph_id': 21, 'end_character': 31, 'bleu_score': 1.0, 'section': 'Section::::Perception of resource availability.:Nervous system.\n'}]}]