Abstract
Event-related fMRI have been widely used in locating brain regions which respond to specific tasks. However, activities of brain regions which modulate or indirectly participate in the response to a specific task are not event-related. Event-related fMRI can't locate these regulatory regions, detrimental to the integrity of the result that event-related fMRI revealed. Direct-current EEG shifts (DC shifts) have been found linked to the inner brain activity, a fusion DC shifts-fMRI method may have the ability to reveal a more complete response of the brain. In this study, we used DC shifts-fMRI to verify that even when responding to a very simple task, (1) The response of the brain is more complicated than event-related fMRI generally revealed and (2) DC shifts-fMRI have the ability of revealing brain regions whose responses are not in event-related way. We used a classical and simple paradigm which is often used in auditory cortex tonotopic mapping. Data were recorded from 50 subjects (25 male, 25 female) who were presented with randomly presented pure tone sequences with six different frequencies (200, 400, 800, 1,600, 3,200, 6,400 Hz). Our traditional fMRI results are consistent with previous findings that the activations are concentrated on the auditory cortex. Our DC shifts-fMRI results showed that the cingulate-caudate-thalamus network which underpins sustained attention is positively activated while the dorsal attention network and the right middle frontal gyrus which underpin attention orientation are negatively activated. The regional-specific correlations between DC shifts and brain networks indicate the complexity of the response of the brain even to a simple task and that the DC shifts can effectively reflect these non-event-related inner brain activities.
Highlights
The entire response of the brain to a specific task is hard to study due to the complexity of the brain’s response
Plenty of functional magnetic resonance imaging (fMRI) studies have showed that the response of the brain to this paradigm is concentrated on auditory cortex while our DC shifts-fMRI results revealed that there are other activations that can’t be neglected
Heschl’s gyrus (HG) mainly responded to the 200 Hz, while another area responding to 200 Hz was at the lateral posterior superior temporal gyrus (STG)
Summary
The entire response of the brain to a specific task is hard to study due to the complexity of the brain’s response. Besides the event-related response in the core responding areas, there always be some brain regions whose ongoing activities modulate the response of the core areas (Vuilleumier et al, 2005; Crottaz-Herbette and Menon, 2006; David et al, 2017; O’Craven et al, 2018). Ongoing activities of these regulatory areas do not fluctuate in the event-related way (Sadaghiani et al, 2009; Walz et al, 2014). DC shifts are often treated as noise in EEG studies (Palva and Palva, 2012) and the connections between DC shifts and neural activities are often neglected (Northoff, 2017)
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