The study by Achard and Bullmore investigates the efficiency and cost of human brain functional networks using functional magnetic resonance imaging (fMRI) in a factorial design involving healthy young and old volunteers. The researchers measured functional connectivity between 90 cortical and subcortical regions and constructed undirected graphs to analyze the small-world properties of these networks. They found that brain functional networks exhibit economical small-world properties, characterized by high global and local efficiency for low connection costs. However, these networks show reduced efficiency disproportionately to cost in older individuals, particularly in frontal and temporal cortical and subcortical regions. Additionally, dopamine receptor antagonist treatment impaired global and local efficiency, but this effect was localized and did not interact with age. The findings suggest that brain functional networks support efficient parallel information processing at low cost, and that both normal aging and dopamine transmission blockade impair these networks differently.The study by Achard and Bullmore investigates the efficiency and cost of human brain functional networks using functional magnetic resonance imaging (fMRI) in a factorial design involving healthy young and old volunteers. The researchers measured functional connectivity between 90 cortical and subcortical regions and constructed undirected graphs to analyze the small-world properties of these networks. They found that brain functional networks exhibit economical small-world properties, characterized by high global and local efficiency for low connection costs. However, these networks show reduced efficiency disproportionately to cost in older individuals, particularly in frontal and temporal cortical and subcortical regions. Additionally, dopamine receptor antagonist treatment impaired global and local efficiency, but this effect was localized and did not interact with age. The findings suggest that brain functional networks support efficient parallel information processing at low cost, and that both normal aging and dopamine transmission blockade impair these networks differently.