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 addition , working memory processing in ecstasy users has been shown to be associated with neural alterations in hippocampal and / or cortical regions as measured by functional magnetic resonance imaging ( fMRI ) .
### Output Text:
In addition , working memory processing in <span class="chemical">ecstasy</span> users has been shown to be associated with neural alterations in hippocampal and / or cortical regions as measured by functional magnetic resonance imaging ( fMRI ) . 