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In this episode, I dive into the neurobiology of testing fatigue and why it is much more than just a simple lack of energy. We explore how high-demand cognitive tasks lead to a measurable buildup of glutamate in the prefrontal cortex, essentially creating metabolic debris that forces the brain into a self-preservation mode. I discuss the specific hierarchy of cognitive decline, noting why executive functioning and fluid reasoning are the first to fail while crystallized intelligence often remains deceptive and intact. To help you maintain the validity of your data during long assessment days, I share three concrete strategies: implementing a heavy-to-light task rotation, scheduling mandatory 90 minute movement resets, and utilizing proactive glycemic management through low-glycemic snacks.

Main Topics

01:34: The neurobiology of cognitive fatigue and the role of the anterior cingulate cortex in cost-benefit analysis.
02:30: How intensive cognitive work leads to an accumulation of glutamate in the lateral prefrontal cortex.
03:45: Applying cognitive load theory and the “overflowing glass” metaphor to the six-hour assessment session.
04:54: Why executive functioning and fluid reasoning fail first while vocabulary and general knowledge remain resistant to fatigue.
06:15: The diagnostic trap of crystallized intelligence and how an articulate patient can mask underlying cognitive exhaustion.
07:45: Strategy 1—Heavy-to-light rotation and the importance of front-loading high-effort tasks.
09:10: Strategy 2—The 90-minute pivot and movement reset to clear adenosine and reset performance cycles.
10:15: Strategy 3—Glycemic management and using small, low-glycemic snacks to prevent the afternoon “food coma.”

Cool Things Mentioned

The Testing Psychologist mastermind groups and business consulting
Reverb: the premier AI-powered report-writing platform for testing psychologists

Featured Resources

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About Dr. Jeremy Sharp

I’m a licensed psychologist and Clinical Director at the Colorado Center for Assessment & Counseling, a private practice that I founded in 2009 and have grown to over 20 clinicians. I earned my undergraduate degree in Experimental Psychology from the University of South Carolina before getting my Master’s and PhD in Counseling Psychology from Colorado State University. These days, I specialize in psychological and neuropsychological evaluation with kids and adolescents.

As the host of the Testing Psychologist Podcast, I provide private practice consulting for psychologists and other mental health professionals who want to start or grow psychological testing services in their practices. I live in Fort Collins, Colorado with my wife (also a therapist) and two young kids.

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553. The Science of Testing Fatigue