Regulated Cerebral Capacity: Insights into Biophysical and Metabolic Boundaries of Neural Networks-A Narrative Review

Abstract

The human beings have an amazing brain capacity but it is limited at the biological, cellular and network level. Common assertions that people use only a minor part (10%) of their brains are not scientifically proven and ignore the complicated control that governs brain activity. Cerebral capacity is the optimal performance of neural systems under physiological conditions, which does not follow any theoretical activation limit. At cellular level, ion channels and refractory periods limit neuronal excitation, whereas receptor concentrations, plasticity exhaustion, and neurotransmitter cycling all limit synaptic communication. On network level, synchronized coordination is required to process information but it is intrinsically restricted to avoid instability and dysfunction. The functional specialization includes selective recruitment of different brain parts according to task demands rather than maximum usage to meet some hypothetical maximized level. Neuroimaging research tends to misinterpret task specific activations as the only functional regions of brain, whereas background neural activity is omnipresent to ensure homeostasis, preparedness, and metabolic stability. The unused brain myth disregards the evolutionary and energetic needs of preservation of metabolically active and functionally necessary structures. This review combines molecular, cellular, and systems neuroscience to explain how cerebral capacity is naturally controlled. By providing historical, conceptual and mechanistic perspectives, it suggests that neural activity does not work for maximum functionality, instead stability, efficiency and adaptability of the system is ensured through biological regulation. Moreover, it discredits the brain capacity related myths and offers fundamental understanding about constraints of human brain capacity, from neurons to large-scale networks.