The high temporal resolution of scalp EEG allows observation of dynamic neural processes, but activity in deep subcortical structures is difficult to detect. Furthermore, source localization is essentially an ill-posed problem, with skull and cerebral spinal fluid (CSF) impedance resulting in poor spatial resolution. On the other hand, BOLD fMRI can localize both superficial and deep sources of activity with mm-scale resolution, but its temporal resolution is limited due to the slow nature of the BOLD response and the low sampling rate required for acquisition of whole-brain fMRI data.
