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: The current study aimed to assess the impact of MDMA use on three separate central executive processes ( set shifting , inhibition and memory updating ) and also on " prefrontal " mediated social and emotional judgement processes .
### Output Text:
The current study aimed to assess the impact of <span class="chemical">MDMA</span> use on three separate central executive processes ( set shifting , inhibition and memory updating ) and also on " prefrontal " mediated social and emotional judgement processes . 