MFB is a bundle of wire composed of upward and downward wire masses of different origins and target areas. The different masses of thread pack up into a clear bundle in the mesencephalon. The bundle runs into the diencephalon and makes its way under the thalamus on the outside of the hypothalamus with which it has extensive connections. The bundle extends some distance into the basal forebrain where it splits open. In the course of its course, the MFB has a well-developed exchange of threads with the environment.
MFB contains, among other things, the directed inflow of serotoninergic filaments to the cortex cerebri from nucl. raphe dorsalis, of dopaminergic filaments from area tegmentalis ventralis, of noradrenergic filaments from locus coeruleus and also filaments from various hypothalamic nuclei with target areas in the brainstem and spinal cord, etc.