Abstract
Executive function is thought to originates from the dynamics of frontal cortical networks. We examined the dynamic properties of the blood oxygen level dependent time-series measured with functional MRI (fMRI) within the prefrontal cortex (PFC) to test the hypothesis that temporally persistent neural activity underlies performance in three tasks of executive function. A numerical estimate of signal persistence, the Hurst exponent, postulated to represent the coherent firing of cortical networks, was determined and correlated with task performance. Increasing persistence in the lateral PFC was shown to correlate with improved performance during an n-back task. Conversely, we observed a correlation between persistence and increasing commission error – indicating a failure to inhibit a prepotent response – during a Go/No-Go task. We propose that persistence within the PFC reflects dynamic network formation and these findings underline the importance of frequency analysis of fMRI time-series in the study of executive functions.
Highlights
High-level cognitive functions have traditionally been localized to the anterior frontal association cortex, commonly referred to as the prefrontal cortex (PFC)
Numerous studies have expanded upon this static view of executive localization, identifying functional networks activated by complex executive processes and served by extensive reciprocal connections between the PFC, posterior parietal cortex and various cortical and limbic regions (Selemon and Goldman-Rakic, 1988; Ongur and Price, 2000; Halgren et al, 2002; Honey et al, 2002; Schall et al, 2003; Perianez et al, 2004; Owen et al, 2005; Simmonds et al, 2008)
Gamma frequencies are not measurable with functional MRI, it has been demonstrated that blood oxygen level dependent (BOLD) activation is tightly correlated to the power of local-field potential oscillations in the gamma range in the cat visual cortex (Niessing et al, 2005)
Summary
High-level cognitive functions have traditionally been localized to the anterior frontal association cortex, commonly referred to as the prefrontal cortex (PFC). Gamma frequencies are not measurable with functional MRI (fMRI), it has been demonstrated that blood oxygen level dependent (BOLD) activation is tightly correlated to the power of local-field potential oscillations in the gamma range in the cat visual cortex (Niessing et al, 2005) In humans, this relationship may be more complex (Winterer et al, 2007), but Lachaux et al (2007) has shown experimentally that modulation of the gamma bandwidth of EEG recordings maps to BOLD signal measured with fMRI, demonstrating that the time-envelope of these signals, convoluted with the hemodynamic response, translates into slower dynamics to which the fMRI is sensitive. A recent, simultaneous EEG–fMRI study revealed specific, load-dependent correlations between gamma band signals and BOLD activity in the dorsolateral PFC during a working memory task (Michels et al, 2010)
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