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: MRI - based maps suggest that chronic methamphetamine abuse causes a selective pattern of cerebral deterioration that contributes to impaired memory performance .
### Output Text:
MRI - based maps suggest that chronic <span class="chemical">methamphetamine</span> abuse causes a selective pattern of cerebral deterioration that contributes to impaired memory performance . 