For the following sentence, is it correct to say "On the left and right side" or "left and right sides", given that it's about two separate sides? Also, would you say "slices 110 and 100" or leave it as it is, with "slice", as it's about more than one slice? For context, the text is for a figure caption for a neuroscience article.
"On the left and right side, the coronal and sagittal cuts at slice 110 and 100 are plotted, respectively."
For both cases, you should indeed use the plurals.
On the left and right sides, the coronal and sagittal cuts at slices 110 and 100 are plotted, respectively.
As a possible style suggestion, you can simplify this and get rid of the complex "respectively" structure by changing to something like this:
Plotted on the left is the coronal cut at slice 110, and on the right is the saggital cut at slice 100.
For a figure caption, I would even drop the constraint that it be a complete sentence. Also, you don't need to mention they are plotted, since it is the caption right next to the figure. Something like this should suffice:
Left side: coronal cut, slice 110. Right side: saggital cut, slice 100.
