Dynamics of coherent activity between cortical areas defines a two-stage process of top-down attention

Frequency modulation of cortical rhythmicity governs behavioral variability, excitability and synchrony of neurons in the visual cortex

Research in cognitive neuroscience has renewed the idea that brain oscillations are a core organization implicated in fundamental brain functions. Growing evidence reveals that the characteristic features of these oscillations, including power, phase and frequency, are highly non-stationary, fluctuating alongside alternations in sensation, cognition and behavior. However, there is little consensus on the functional implications of the instantaneous frequency variation in cortical excitability and concomitant behavior. Here, we capitalized on intracortical electrophysiology in the macaque monkey's visual area MT performing a visuospatial discrimination task with visual cues. We observed that the instantaneous frequency of the theta-alpha oscillations (4-13 Hz) is modulated among specific neurons whose RFs overlap with the cued stimulus location. Interestingly, we found that such frequency modulation is causally correlated with MT excitability at both scales of individual and ensemble of neurons. Moreover, studying the functional relevance of frequency variations indicated that the average theta-alpha frequencies foreshadow the monkey's reaction time. Our results also revealed that the neural synchronization strength alters with the average frequency shift in theta-alpha oscillations, suggesting frequency modulation is critical for mutually adjusting MTs' rhythms. Overall, our findings propose that theta-alpha frequency variations modulate MT's excitability, regulate mutual neurons' rhythmicity and indicate variability in behavior.

Spectral Distribution Dynamics across Different Attentional Priority States

Anticipatory covert spatial attention improves performance on tests of visual detection and discrimination, and shifts are accompanied by decreases and increases of α band power at electroencephalography (EEG) electrodes corresponding to the attended and unattended location, respectively. Although the increase at the unattended location is often interpreted as an active mechanism (e.g., inhibiting processing at the unattended location), most experiments cannot rule out the alternative possibility that it is a secondary consequence of selection elsewhere. To adjudicate between these accounts, we designed a Posner-style visual cueing task in which male and female human participants made orientation judgments of targets appearing at one of four locations: up, down, right, or left. Critically, trials were blocked such that within a block the locations along one meridian alternated in status between attended and unattended, and targets never appeared at the other two, making them irrelevant. Analyses of the concurrently measured EEG signal were conducted on "traditional" narrowband α (8-14 Hz), as well as on two components resulting from the decomposition of this signal: "periodic" α; and the slope of the aperiodic 1/f-like component. Although data from right-left blocks replicated the familiar pattern of lateralized asymmetry in narrowband α power, with neither α signal could we find evidence for any difference in the time course at unattended versus irrelevant locations, an outcome consistent with the secondary-consequence interpretation of attention-related dynamics in the α band. Additionally, 1/f slope was shallower at attended and unattended locations, relative to irrelevant, suggesting a tonic adjustment of physiological state.SIGNIFICANCE STATEMENT Visual spatial attention, the prioritization of one location in the visual field, is critical for guiding behavior in cluttered environments. Although influential theories posit an important role for α band oscillations in the inhibition of processing at unattended locations, we used a novel procedure to find evidence for an alternative interpretation: selection of one location may simply result in a return to physiological baseline at all others. In addition to determining one way that attention does not work (important for future progress in this field), we also discovered novel evidence for one way that it does work: by modifying the tonic physiological state (indexed by an aperiodic component of the electroencephalography (EEG)] at locations where spatial selection is likely to occur.