Hello Wonderlander,
I'm not really sure whether I understand your question correctly. Are you looking to do research in Neuroscience to improve your chances of getting into a German neurosurgery residency ?
As you may know, in Germany and in continental Europe in general, there is no such a thing as college, so you enter medical school directly after graduating from "Gymnasium" (our "advanced" version of high school), i.e. receiving the "Abitur" diploma. It is therefore totally uncommon for German med students to enroll in another program prior to med school to do research. However, most students commit some time to research parallel to the regular curriculum for their MD thesis. This would be an opportunity to get some research experience.
There are a few universities which offer more structured PhD research opportunities for med students, but research usually takes place after having completed med school. Furthermore, this usually takes around 3 additional years.
Since neurosurgery is not that competitive in Germany, you should be fine with a little MD thesis coupled with "ok" grades.
Hope this helps.
BTW, the grass is not always greener on the other side...there is a good reason why a lot of German MD's leave the country every year ! I'm also currently exploring my options for going abroad, and I'm a German med student in Germany 😱