Fig. 6: Downward neuroplasticity within the larger and complementary perspective of an entangled brain.

The main goal of this review is to work on the idea of how neuroplasticity, in all its complexity, should be conceptually understood as a balance between what we have called here as “upward and downward neuroplasticity”. Developing brains, and partially also the adult ones, are flexible, moldable, and as it is, any capability for decreasing the density levels or structural complexity of spines and/or dendrites should be considered part of the neuroplasticity program, rather than being a deficiency of it. Thus, comparable to how puzzles fit together, upward and downward neuroplasticity work to complement each other so that the brain would eventually be able to reshape its connections by neuronal tuning to optimize network’s efficiency under certain demands. Within a broader landscape as seen with assembled puzzles, although neuroplasticity happens at first glance from the microscale changes of spines and dendrites according to a neuronal perspective, its consequences expand toward a macroscale outlook where individual orchestrated changes integrate into the account of different neuronal populations and neurocircuits. So, any cause or consequence neuroplastic change from an entangled brain, whether up or down, may be directly or indirectly connected to at least some other part of the brain that could still show a completely opposite direction of neuroplasticity. The orange, red and gray puzzles represent different populations of neurons that in the sum of the events globally present upward plasticity, while the green, yellow and purple puzzles represent different populations of neurons that in the sum of the events present global downward plasticity. Meanwhile, the blue and white puzzles represent neurons with a balanced number of events that represent both upward and downward neuroplasticity. Their connections should maintain the brain largescale of neuroplasticity at zero sum when considering downward and upward neuroplasticity within the topography of neuronal matter.