In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In both ecstasy and cannabis groups brain activation was decreased in the right medial frontal gyrus , left parahippocampal gyrus , left dorsal cingulate gyrus , and left caudate .
### Output Text:
In both <span class="chemical">ecstasy</span> and <span class="chemical">cannabis</span> groups brain activation was decreased in the right medial frontal gyrus , left parahippocampal gyrus , left dorsal cingulate gyrus , and left caudate . 