In our study, 3 different conditions and control tasks of each conditions will be evaluated. Therefore, the duration of the experiment may slightly exceed the time required for a suitable fMRI acquisition. We want to reduce the duration of the experiment by determining the minimum ITI times we can use, which are suitable for measuring the hemodynamic response. In our previous studies, we used ITIs at ranging from 2000-4000-6000 ms, and it is generally recommended in the literature to have a minimum of 2000-5000 ms. However, we also came across some recent event-related fMRI studies using ITI under these times (for example; 600-800-1000 ms or 1500-6000 ms). So I would be very happy if you could help with this.
Many event-related fMRI designs involve multiple successive events occurring within a trial, spaced closely in time (e.g., in cued set-shifting paradigms). Yet, it is notoriously difficult to separate the activation components to these sequentially ordered events, given the long evolution time of the BOLD response. One approach to deal with this problem is to omit the second of two successive events (S1 and S2) in a certain proportion of ‘partial S1-only’ trials. The present article describes a novel method that extends the basic partial-trial design in several ways. As a central new feature it introduces two different delay intervals between S1 onset and S2 presentation, or, in case of S1-only trials, S2 omission. The analysis is based on three BOLD response regressors, one synchronized with S1 onset for short S1–S2 delay trials, another one synchronized with S1 onset for long S1–S2 delay trials, and a third synchronized with S2 onset. The two estimated S1-related activation time courses are then assessed by ‘temporal profiling’ based on the parameterization of onset latencies, peak latencies, and the area under the curves. Based on this information it is possible (1) to distinguish transient activity elicited with S1 onset from delay-related activity and (2) to identify the activation profile associated with possible ‘nogo-type’ activity caused by S2 omission. Despite these two new important possibilities, some caution is still advised when interpreting data from the proposed partial-trial design. Yet, in contrast to previous methods, it is possible to identify ambiguous data patterns and, by following an explicit decision scheme, to avoid erroneous conclusions.
Dear Burcu
It depends what exactly you want to achieve. If you want to observe brain response from two different stimuli you can use this as reference:
Glover, G.H., 1999. Deconvolution of Impulse Response in Event-Related BOLD fMRI1. NeuroImage 9, 416–429. https://doi.org/10.1006/nimg.1998.0419
Glover tested that 9 seconds is enough for auditory cortex (note that it might be different for other areas).
I was able to puch it towards 4.5 seconds and have quite nice responses as well (but it really depends on paradigm). Check this:
Rusiniak, M., Lewandowska, M., Wolak, T., Pluta, A., Milner, R., Ganc, M., Włodarczyk, A., Senderski, A., Śliwa, L., Skarżyński, H., 2013. A modified oddball paradigm for investigation of neural correlates of attention: a simultaneous ERP–fMRI study. Magn Reson Mater Phy 26, 511–526. https://doi.org/10.1007/s10334-013-0374-7
Hi Burcu,
You may find the following article useful in your situation:
Article A comparison of methods for characterizing the event-related...
Best,
Seth
- Badges
- Science topic
- Similar topics
- Psychology