6699
Previous studies have shown that estrogen affects whether a hippocampus - mediated place ( allocentric ) or a striatum - mediated response ( egocentric ) memory system is employed by female rats when searching for a food reward in a maze .
 Chemical: estrogen
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: estrogen