Separating event-related BOLD components within trials: the partial-trial design revisited

Area of Science:

• Neuroimaging
• Cognitive Neuroscience
• Functional Magnetic Resonance Imaging (fMRI)

Background:

• Event-related fMRI designs often present multiple successive events within trials, posing challenges for separating distinct neural responses due to the slow Blood-Oxygen-Level-Dependent (BOLD) response.
• Traditional partial-trial designs, omitting the second event (S2) in some trials, offer a partial solution but lack the granularity to fully resolve closely timed neural events.

Purpose of the Study:

• To present a novel extension of the partial-trial fMRI design capable of resolving neural activity from sequentially presented events.
• To introduce a method that differentiates transient S1-evoked activity from delay-dependent activity and identifies 'nogo-type' responses from S2 omission.

Main Methods:

• The proposed method incorporates two distinct delay intervals between the first event (S1) and the second event (S2) or its omission.
• Analysis utilizes three BOLD response regressors: one for S1 onset with short S1-S2 delay, another for S1 onset with long S1-S2 delay, and a third for S2 onset.
• Temporal profiling, analyzing onset latency, peak latency, and area under the curve, is employed to characterize S1-related activation time courses.

Main Results:

• The temporal profiling approach successfully distinguishes transient S1-related activity from sustained, delay-related activity.
• The method enables the identification of specific activation patterns associated with 'nogo-type' activity resulting from S2 omission.
• The enhanced design allows for the identification of ambiguous data patterns and provides a decision scheme to prevent erroneous interpretations.

Conclusions:

• This novel partial-trial fMRI design significantly improves the ability to deconvolve closely spaced neural events compared to previous methods.
• The technique offers enhanced resolution for analyzing complex event-related fMRI paradigms, particularly those involving sequential stimuli or omissions.
• While caution in interpretation is still advised, the method provides a more robust framework for analyzing fMRI data in challenging designs.