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: Under anesthesia , the superior temporal gyrus of adult macaque monkeys was exposed , and the tonotopic organization of A1 was mapped using conventional microelectrode recording techniques .
### Output Text:
Under anesthesia , the superior temporal gyrus of adult macaque monkeys was exposed , and the tonotopic organization of A1 was mapped using conventional microelectrode recording techniques . 