Beneath every thought, every emotion, and every decision lies a primitive engine that neuroscience has ignored for 60 years. Donald Pfaff makes the case that generalized arousal is the essential foundation of all brain function, from fear to physics exams.

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Pfaff argues that arousal has been wrongly dismissed as non-specific background noise. He reframes it as the necessary precondition for all motivated behavior: alertness to sensory stimuli, motor activity, and emotional reactivity. The hyperthyroid individual who responds to every stimulus, cannot stand still, and weeps or laughs readily exemplifies high arousal; the hypothyroid couch potato who is sluggish, unreactive, and emotionally flat exemplifies the opposite. His high-throughput behavioral assay measures m ...