The spectral dynamics of visual awareness: An interplay of different frequencies?

The goal of this study was to investigate the neurophysiological correlates of visual awareness, with a specific focus on its event-related spectral perturbation (ERSP) features. To this aim, we tried to disentangle the proper neural correlates of consciousness (NCC) from other prerequisite and post-perceptual processing. To do so, we administered an orientation discrimination task, inducing a response bias through task instructions. EEG results showed that different frequency bands are involved in this kind of task, with different spectral and temporal dynamics. In particular, alpha and beta bands seem to be particularly engaged, especially in the aware-unaware contrast, showing a main power suppression for aware trials and replicating previous literature. Moreover, we demonstrated that the process of visual awareness is orchestrated by a complex interaction of different frequencies (i.e., theta, alpha, beta and gamma) being involved as prerequisites and post-perceptual processes.

Natural oscillation frequencies in the two lateral prefrontal cortices induced by Transcranial Magnetic Stimulation.

Different cortical regions respond with distinct rhythmic patterns of neural oscillations to Transcranial Magnetic Stimulation (TMS). We investigated natural frequencies induced by TMS in left and right homologous dorsolateral prefrontal cortices (DLPFC) and related hemispheric differences. In 12 healthy young adults, single-pulse TMS was delivered in different blocks close to F3 and F4 channels to target left and right DLPFC. An occipital site near PO3 was stimulated as control. TMS-related spectral perturbation analyses were performed on recorded EEG data. A widespread unspecific increase in theta power was observed for all stimulation sites. However, occipital TMS induced greater alpha activity and a 10.58 Hz natural frequency, while TMS over the left and right DLPFC resulted in similar beta band modulations and a natural frequency of 18.77 and 18.5 Hz, respectively. In particular, TMS-related specific increase in beta activity was stronger for the right than the left DLPFC. The right DLPFC is more specifically tuned to its natural beta frequency when it is directly stimulated by TMS than with TMS over the left counterpart (or a posterior region), while the left DLPFC increases its beta activity more similarly irrespective of whether it is directly stimulated or through right homologous stimulation. These results yield important implications for both basic neuroscience research on inter-hemispheric prefrontal interactions and clinical applications.

Cognitive brakes in interference resolution: A mouse-tracking and EEG co-registration study.

Cognitive control is particularly challenged when it is necessary to resolve interference and correct our behavior on-the-fly. To do this, it is necessary to inhibit the ongoing wrong action and reprogram a new motor plan as appropriate for the current task. This ability requires a complex interaction between cognitive and motor control. Here, we aimed at shedding light on this interplay. To do this, we administered a spatial version of the Stroop task comprising blocks with different Proportion Congruency (PC) manipulations (i.e., manipulating the percentage of congruent trials at 25%, 50% or 75%), to elicit different cognitive control demands. Moreover, we used two techniques with high-temporal resolution, as we simultaneously recorded EEG and mouse trajectories, that can be considered the real-time kinematic correlates of the ongoing cognitive processing. Specifically, we analyzed the Event Related Potentials (ERPs) locked to the peak deceleration time, which marks the suppression of ongoing erroneous trajectories, and we estimated their neural sources. We found three PC-dependent ERP components engaging distinct neural regions, which showed a reduction of the Stroop effect for low-PC blocks. By using a novel co-registration of mouse-trajectories and EEG, we suggest that the observed components may reflect different mechanisms engaged by reactive cognitive control to resolve the interference, including the suppression of an ongoing but no longer appropriate response, the selection of the new motor plan and its actual updating.

Brain oscillations in cognitive control: A cross-sectional study with a spatial stroop task.

An important aspect of cognitive control is the ability to overcome interference, by boosting the processing of task-relevant information while suppressing the irrelevant information. This ability is affected by the progressive cognitive decline observed in aging. The aims of this study were to shed light on the neural spectral dynamics involved in interference control and to investigate age-dependent differences in these dynamics. For these reasons two samples of participants of different ages (23 younger and 20 older adults, age range = [18 35] and [66 82], respectively) were recruited and administered a spatial Stroop task while recording electroencephalographic activity. Scalp- and source-based time-frequency analyses revealed a main role of theta and beta frequencies in interference control. Specifically, for the theta band, we found age-dependent differences both for early event-related spectral perturbation (ERSP) Stroop effects at the source level - which involved dorsomedial and dorsolateral prefrontal cortices - and for related brain-behaviour correlations. This ERSP Stroop effect in theta was greatly reduced in magnitude in the older group and, differently from what observed in younger participants, it was not correlated with behavioural performance. These results suggest an age-dependent impairment of the theta-related mechanism signalling the need of cognitive control, in line with existing findings. We also found age-related differences in ERSP and source spectral activity involving beta frequencies. Indeed, younger participants showed a specific ERSP Stroop effect in beta - with the main involvement of left prefrontal cortex - whereas the pattern of older participants was delayed in time and spread bilaterally over the scalp. This study shows clear age-related differences in the neural spectral correlates of cognitive control. These findings open new questions about the causal involvement of specific oscillations in different cognitive processes and may inspire future interventions against age-related cognitive decline.