KeyError: 'The identifier "astrocyte_index_post" could not be resolved.'

Hi @amanforthepeople , it’s unfortunately impossible to help you with an overly general question like that (“keep running into some errors”).
The code in the image seems to be from here: comp-glia-book/example_6_COBA_with_astro.py at master · mdepitta/comp-glia-book · GitHub (BTW, there’s a cleaner version of the same code in the Brian documentation: Example: example_6_COBA_with_astro — Brian 2 2.5.1 documentation), but that code should run correctly. The error message complains about a missing definition of astrocyte_index in the synaptic equations, but the above linked code contains that definition in synapses_eqs. So I guess you are running a different version of the code? Please be more specific and/or post some code (preferably as text surrounded by triple backtick quotes – see e.g. Basic writing and formatting syntax - GitHub Docs – and not as an image). Thanks!