Brain information processing complexity is conventionally recognized as derived from neuronal activity, with neurons and their dynamic signalling responsible for the transfer and processing of information . However, the brain also contains other non-neuronal cells, glial cells, which exceed the number of neurons and have been largely ignored, in the past, as being involved in the processes related with information coding by neural networks and underlying brain functions. Nonetheless, decisive advances in the characterization of the molecular and physiological properties of glial cells shed light on their active roles in neurotransmission and neuronal physio-pathology. Thus, in order to understand the brain functions we need to consider the complexity of the relationship between neurons and glial cells. This expanded relationship between neurons and glia is challenging traditional neurobiology, representing a typical ‘chicken and egg ‘problem. A philosophical tool, the ‘Theory of Complexity’ of Edgard Morin can help to better explain and study the complexity of neuronal- glia interactions. Morin’s proposal on complexity is useful to transform brain knowledge, in order to review the brain molecular functions in anti-reductionist pattern. In this manuscript, we will discuss how to use the ‘retroactive loop’ principle from the Morin’s ‘Theory of Complexity’ at the brain molecular level, proposing a new philosophical-experimental grid that can help neuroscientists for a better understanding of the glia-neurons interactions in the brain.