Why do foetal cells migrate in mother’s limbic system? During pregnancy the mother’s brain undergoes both microscopic and macroscopic changes. The foetus, throughout the whole pregnancy, sends its own cells (Pregnancy Associated Progenitor Cells, PAPCs) to colonize many maternal organs, inclu- ding the brain and the limbic system. This phenomenon is known as “micro- chimerism”. The migration of PAPCs has both an evolutionary and affective meaning because the limbic system is the department of the brain dedicated to the regulation of emotions and memory. Here, the PAPCs will differen- tiate into neurons and glial cells, forming new synapses and therefore new connections with and among maternal neurons. This process is accompanied by structural alterations (documented by magnetic resonance imaging and orchestrated by the hormonal changes characteristic of gestation) invol- ving the limbic system and the other brain structures closely connected to it, which are the very same areas colonized by the migration of the foetal cells. Instrumental diagnostics and specific tests showed that greater volumetric losses of grey matter during pregnancy were strongly related to the quality of mother-child attachment and absence of hostility towards the newborn in the postpartum period. Greater brain alterations during gestation were asso- ciated to a higher degree of maternal attachment to her child after birth. For the first time in literature. In this review we have integrated the studies on the migration of PAPCs in the maternal brain with those, very recent, on the morphological and functional alterations that the maternal brain undergoes during pregnancy, indicating a possible synergistic effect of these two com- ponents. Part of the biologic base of the maternal-child attachment takes place during this migration suggesting that the foetus could play a surprising active role in modulating the mother’s ability to love him, right from its life in uterus.

Keywords: limbic system; pregnancy associated progenitor cells (PAPCs); pregnancy; microchimerism; stem-cell migration.