It depends which part of entorhinal cortex you want to target (and the age of the mouse), but for adults I'd say starting with 3.2-4 mm lateral from the midline and ~200 µm anterior to the transverse sinus would be a good start. Then adjust the distance from the sinus, the depth, and the angle to reach the specific area you're interested in.

Hi Chen Xx

You can check the following protocols.

1. https://www.nature.com/articles/s41467-021-20936-8

2. Article Medial and Lateral Entorhinal Cortex Differentially Excite D...

Thanks

Samir