тархи - brain толгой - head тархи толгой - collocation. Depending on the context may mean either, brain or head. тархи толгой гашилгах - idiom. Meaning: to think a lot (in order to find our some solution). толгой эргэх - dizzy, feel dizzy Ганц энэ асуудлыг ойлгох гэж би тархи толгойгоо эргэтэл бодов. Literally: In order to understand this one problem, I thought so much about it that my head got dizzy.