Quantifying What Is Efficacious Yet Not Observable: Cognitive Neuroscience's Measurement Problem Has a Solution

Cognitive neuroscience faces a measurement problem: core features of the human mind cannot be directly observed in the brain. For example, intentions are efficacious in behavior generation yet cannot be reduced to the sub-personal quantities of neural activity without losing their purpose-driven, normative character. This instrumental limitation is fundamental yet remains insufficiently recognized. To bring this issue to the forefront and reorient the field toward a solution, this brief commentary argues that theories of the mind-brain relation must meet the "Participation Criterion": they must specify what measurable difference the presence of mental efficacy produces compared to its absence. When the Participation Criterion is accepted alongside the measurement problem, a feasible solution arises: the dynamical relevance of unobservable mental efficacy may manifest indirectly as increased unpredictability of observable brain activity, quantifiable via information-theoretic entropy. The concept of "irruption" is introduced to specifically formalize this efficacy-derived part of unexplained variability, thereby reframing context-dependent "noise" in the brain as a key signature of the intentional mind at work. The theoretical proposal offers new avenues for research in cognitive science and clinical interventions.