If your intended stay in Norway is less than 90 days, you do not need to apply for a residence permit.
However, depending on your nationality, you might need a visitor's visa to enter Norway. Check if this applies to you and how to proceed on the webpage Want to apply to visit Norway of the Norwegian Directorate of Immigration (UDI). People from EU/EEA do not need a visa.
Please note that an application for a visitor's visa must be supported by a written invitation by your host unit at NIH
Foreign nationals staying in Norway for less than 3 months without formal employment by a Norwegian employer are considered tourists and must have their own travel insurance.
EU/EEA nationals should bring their European Health Insurance Card.
As a rule, anyone who receives salary from a Norwegian institution is taxable on the same basis as Norwegian citizens and must aquire electronic tax deduction. Further information at Norwegian tax office called skatteetaten.