  Long-range temporal coherence (LRTC) is quite common to dynamic systems and
is fundamental to the system function. LRTC in the brain has been shown to be
important to cognition. Assessing LRTC may provide critical information for
understanding the potential underpinnings of brain organization, function, and
cognition. To facilitate this overarching goal, we provide a method, which is
named temporal coherence mapping (TCM), to explicitly quantify LRTC using
resting state fMRI. TCM is based on correlation analysis of the transit states
of the phase space reconstructed by temporal embedding. A few TCM properties
were collected to measure LRTC, including the averaged correlation,
anti-correlation, the ratio of correlation and anticorrelation, the mean
coherent and incoherent duration, and the ratio between the coherent and
incoherent time. TCM was first evaluated with simulations and then with the
large Human Connectome Project data. Evaluation results showed that TCM metrics
can successfully differentiate signals with different temporal coherence
regardless of the parameters used to reconstruct the phase space. In human
brain, TCM metrics except the ratio of the coherent/incoherent time showed high
test-retest reproducibility; TCM metrics are related to age, sex, and total
cognitive scores. In summary, TCM provides a first-of-its-kind tool to assess
LRTC and the imbalance between coherence and incoherence; TCM properties are
physiologically and cognitively meaningful.
