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: Whereas cells in a wider area of the GPi may be implicated in parkinsonism , the ventral GPi seems to be crucial for the manifestation of LID .
### Output Text:
Whereas cells in a wider area of the GPi may be implicated in parkinsonism , the ventral GPi seems to be crucial for the manifestation of LID . 