Useful Papers - Your Friend, The Hemodynamic Response Function
Summary: In order to evaluate how much variability exists in the shape of HRFs collected from different sessions, days, and subjects, Aguirre et. al tested various sets of 40 subjects tested on various days and in various sessions. They found a good deal of variance accounted for by differences in subjects, and significant differences for many subjects between different scanning days. Within the same day and subject, thought, the HRF seemed relatively stable.
Summary: A long paper describing a number of different studies/analyses looking at linearity of the HRF (as stimulus presentation rate and sampling procedure varies) and the variance between regions, subjects, and different aspects of the HRF (amplitude, time-to-onset, etc.).
Summary: Another find-the-best-analysis-parameters study, this time using Monte Carlo simulations on simulated data to study power and false-positive rate as various SPM parameters changed. Of particular interest here is the contrast between using the canonical HRF alone vs. the HRF with temporal derivative. The HRF with temporal derivative is found to significantly reduce power in many circumstances.
Summary: Neumann et. al investigate how variable the HRF is within a subject, over several scanning sessions spanning days or weeks. They look at stability of a number of parameters - time to onset, time to peak, time to baseline, etc. and use a couple different methods to extract HRFs. Time-to-peak is the most stable parameter they found, and voxels activated in all sessions had much lower variability than those only activated in some.
Summary: Participants learned an object map by touch and then imagined discs flying from object to object during ERP and FMRI acquisition. ERP amplitude parametrically varied with disc-flying distance, as did BOLD in left parietal cortex; source modeling suggested the ERP originated from that left parietal source.
Summary: Comprehensive and excellent review of the complete chain of events in the head leading to the BOLD signal, including a bit of physics and a lot of neurophysiology. Several studies containing both cellular and BOLD recordings are reviewed, as are studies of neural vasculature and other regional differences influencing the HRF, and some suggestions are made for interpreting the BOLD signal.
Summary:LFP and multi-unit activity were extracted simultaneously from speed- and direction-sensitive areas of MT to try and get a handle on the spatial sensitivity of the LFP signal; presumably if its spatial resolution is very low, it wouldn't exhibit the same kind of direction- or speed-sensitivity found at the single- or multi-unit level. LFP activity did exhibit both speed and direction tuning, but only at higher frequencies (gamma band), suggesting that spatially localized information is mostly carried in the upper bands. Speed tuning was present only at higher frequencies than direction tuning, perhaps reflecting the finer-grained spatial organization of speed-tuned neurons.
Summary:Pretty mathematical paper using current models of the BOLD-neuronal firing relationship and parameters derived from ERP literature to derive the theoretical BOLD response for various shapes of neuronal responses (damped sinusoids, like ERPs). Also derives optimal block-stimulation frequencies.