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Results showed that deep brain stimulation ( DBS ) by applying high frequency stimulation to the nucleus accumbens ( ventral striatum ) during extinction training , indeed significantly reduced fear during extinction retrieval compared to sham stimulation controls .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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