Temporal Resolution

Because of the nature of both radioisotope decay and the slow time course of the hemodynamic response, the temporal resolution of neuroimaging is inherently limited. The sluggish nature of the hemodynamic response prohibits the detection of numerous events that occur on a millisecond time scale and may be conceptualized as a low-pass filter that prevents detection of higher frequency information. The temporal resolution is particularly poor for PET, which is largely insensitive to transient responses unless they are sustained or of large magnitude. The different temporal limitations of PET and fMRI almost certainly lead to situations in which the results of the two techniques disagree with each other, leading to nontrivial differences in conclusions (Zald, 2003). Similarly, both techniques may fail to converge with data from techniques such as single-cell recordings, event-related potentials, and near infrared optical imaging, which are sensitive to changes at the millisecond level.

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