The research results presented in this paper explore the temporal changes in central regions of the prefrontal cortex (PFC) during design brainstorming. Design mobilizes a range of cognitive processes such as problem analysis and framing, concept generation, decision-making, visual reasoning and creative problem solving. Concept generation is supported by an iteration of divergent and convergent thinking. The process of brainstorming focuses primarily on divergent thinking. Measurement techniques from neuroscience were used to quantify neurocognitive activation during concept generation using brainstorming during a design task. Correlations in brain activation were used with graph theory to describe brain network connectivity and present the temporal evolution of network centrality in the PFC during brainstorming. The results reveal shifts of network centrality between the right, medial, and left PFC, suggesting possible shifts in the dominant cognitive functions between divergent and convergent thinking during design brainstorming. The alternations of centrality and connectivity between hemispheres provides a consistent mapping with the theory of dual reasoning process in prior design cognition studies. This empirical study with ten graduate engineering students offers initial results to further explore connections between brain network connectivity and cognitive processes when brainstorming during a design task. It provides new evidence to examine existing theories of design.