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: Cerebellar sensory processing alterations impact motor cortical plasticity in Parkinson ' s disease : clues from dyskinetic patients .
### Output Text:
Cerebellar sensory processing alterations impact motor cortical plasticity in Parkinson ' s disease : clues from dyskinetic patients . 