Long-distance amplitude correlations in the high γ band reveal segregation and integration within the reading network.

Reading sentences involves a distributed network of brain regions acting in concert surrounding the left sylvian fissure. The mechanisms of neural communication underlying the extraction and integration of verbal information across subcomponents of this reading network are still largely unknown. We recorded intracranial EEG activity in 12 epileptic human patients performing natural sentence reading and analyzed long-range corticocortical interactions between local neural activations. During a simple task contrasting semantic, phonological, and purely visual processes, we found process-specific neural activity elicited at the single-trial level, characterized by energy increases in a broad gamma band (40-150 Hz). Correlation analysis between task-induced gamma-band activations revealed a selective fragmentation of the network into specialized subnetworks supporting sentence-level semantic analysis and phonological processing. We extend the implications of our results beyond reading, to propose that gamma-band amplitude correlations might constitute a fundamental mechanism for large-scale neural integration during high-level cognition.

Watching brain TV and playing brain ball exploring novel BCI strategies using real-time analysis of human intracranial data.

A large body of evidence from animal studies indicates that motor intention can be decoded via multiple single-unit recordings or from local field potentials (LFPs) recorded not only in primary motor cortex, but also in premotor or parietal areas. In humans, reports of invasive data acquisition for the purpose of BCI developments are less numerous and signal selection for optimal control still remains poorly investigated. Here we report on our recent implementation of a real-time analysis platform for the investigation of ongoing oscillations in human intracerebral recordings and review various results illustrating its utility for the development of novel brain-computer and brain-robot interfaces. Our findings show that the insight gained both from off-line experiments and from online functional exploration can be used to guide future selection of the sites and frequency bands to be used in a translation algorithm such as the one needed for a BCI-driven cursor control. Overall, the findings reported with our online spectral analysis platforms (Brain TV and Brain Ball) indicate the feasibility of online functional exploration via intracranial recordings in humans and outline the direct benefits of this approach for the improvement of invasive BCI strategies in humans. In particular, our findings suggest that current BCI performance may be improved by using signals recorded from various systems previously unexplored in the context of BCI research such as the oscillatory activity recorded in the oculomotor networks as well as higher cognitive processes including working memory, attention, and mental calculation networks. Finally, we discuss current limitations of the methodology and outline future paths for innovative BCI research.

Saccade related gamma-band activity in intracerebral EEG: dissociating neural from ocular muscle activity.

Recent evidence suggests that transient increases in scalp electroencephalography (EEG) gamma band power (above 30 Hz) can be due to miniature eye movements. Although, these findings do not raise doubts about the widely established role of gamma range neural synchrony, it does call for caution when it comes to interpreting high frequency scalp EEG data. By contrast, gamma-band activity detected with intracerebral EEG (iEEG) is assumed to be immune to such miniature saccade artefacts. Here, we show for the first time, that while this is indeed largely the case, intracerebral recordings in the temporal pole of implanted patients can be contaminated by saccadic eye muscle artefacts resulting in typical high gamma-band power increases. By analyzing data from multiple depth electrodes, we show that this artefact is confined to the pole of the temporal lobe because of its immediate vicinity to extraocular muscles (rectus lateralis). For other brain structures, our analysis shows that the use of stereotactic EEG with a bipolar montage provides a robust and convenient tool to explore the functional role of gamma synchronization in humans with high anatomical accuracy during a wide range of cognitive processes, including oculomotor behaviour.