Another possible reason why brainstorming feels good:

...unpredictable rewards were more pleasurable than predictable ones...this must be occurring at a subconscious level.

Gregory S. Berns, Samuel M. McClure, Giuseppe Pagnoni, and P. Read Montague. 2001. Predictability Modulates Human Brain Response to Reward. The Journal of Neuroscience, April 15, 2001, 21(8):2793–2798

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