FDTest: Fluctuation-dissipation theorem as a test for memory effects in brain dynamics.

FDTest detects stronger local memory effects in individualized whole-brain models during wakefulness than during deep sleep, using generalized fluctuation–dissipation theorem violations.

• Why it matters: The brain’s ability to balance local and distributed processing depends on whether future activity reflects past network feedback, but local memory signatures are hard to measure directly.
• What they did: The authors introduce FDTest, which quantifies generalized FDT violations to assess local memory in multidimensional systems, first in whole-brain models fit to human neuroimaging data and then in individualized wakefulness and deep-sleep models.
• The result: Memory effects are consistently stronger in wakefulness, linking the measured memory structure to underlying connectivity and supporting FDTest as a dynamical marker of brain state.

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