5447
The aim of this review is to expose and discuss findings from positron emission tomography ( PET ) or single - photon - emission computed tomography ( SPECT ) studies investigating DA function in the striatum of medicated , drug - naive or drug - free patients with schizophrenia and in individuals at risk compared with healthy volunteers .
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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:
 None