Limitations of temporal resolution in functional MRI.
In fMRI, images can be collected in a very short time; therefore, high temporal resolution is possible in principle. However, the temporal resolution is limited by a blurred intrinsic hemodynamic response and a finite signal-to-noise ratio. To determine the upper limit of temporal resolution in a single area during repeated tasks, motor cortex activity was investigated during visually instructed finger movements. Without averaging, a sequence of four single-finger movements with an execution time of approximately 2 s can be resolved when the delay time between consecutive sequences is at least 3 s. The hemodynamic response time is constant for each subject, but not among different subjects. The temporal resolution can be better when the signal from spatially distinct regions is examined. For a series of experiments involving a visually instructed delayed cued finger movement task with a well-defined, independently determined, variable delay time, time courses in the motor area are distinct from each other in two experiments if the difference in delay time is as little as 2 s. The activation in the visual area due to the presentation of the task serves here as an internal time reference. By comparing a set of fMRI time courses in multiple distinct areas, serial neural processing may be investigated.
Kim
S G
SG
Department of Radiology, University of Minnesota Medical School, Minneapolis 55455, USA.
Richter
W
W
Uğurbil
K
K
D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology; D002560:Cerebrovascular Circulation; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000592:standards; D009044:Motor Cortex / Q000502:physiology; D011597:Psychomotor Performance; D014793:Visual Cortex / Q000502:physiology