Intrinsic frequency biases and profiles across human cortex

Recent findings in monkeys suggest that intrinsic periodic spiking activity in selective cortical areas occurs at timescales that follow a sensory or lower-order to higher-order processing hierarchy (Murray et al. 2014). It has not yet been fully explored if a similar timescale hierarchy is present in humans. Additionally, these measures in the monkey studies have not addressed findings that rhythmic activity within a brain area can occur at multiple frequencies. Here we investigate in humans if regions may be biased towards particular frequencies of intrinsic activity and if a full cortical mapping still reveals an organization that follows this hierarchy. We examined the spectral power in multiple frequency bands (0.5-150Hz) from task-independent data using magnetoencephalography (MEG). We compared standardized power across bands to find regional frequency biases. Our results demonstrate a mix of lower and higher frequency biases across sensory and higher-order regions. Thus they suggest a more complex cortical organization that does not simply follow this hierarchy. Additionally, some regions do not display a bias for a single band, and a data-driven clustering analysis reveals a regional organization with high standardized power in multiple bands. Specifically, theta and beta are both high in dorsal frontal cortex while delta and gamma are high in ventral frontal cortex and temporal cortex. Occipital and parietal regions are biased more narrowly towards alpha power and ventral temporal lobe displays specific biases towards gamma. Thus intrinsic rhythmic neural activity displays a regional organization but one that is not necessarily hierarchical.

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