This work used a low-cost wireless electroencephalography (EEG) headset to quantify the human response to different cognitive stress states on a single-trial basis. We used a Stroop-type color⁻word ...interference test to elicit mild stress responses in 18 subjects while recording scalp EEG. Signals recorded from thirteen scalp locations were analyzed using an algorithm that computes the root mean square voltages in the theta (4⁻8 Hz), alpha (8⁻13 Hz), and beta (13⁻30 Hz) bands immediately following the initiation of Stroop stimuli; the mean of the Teager energy in each of these three bands; and the wideband EEG signal line-length and number of peaks. These computational features were extracted from the EEG signals on thirteen electrodes during each stimulus presentation and used as inputs to logistic regression, quadratic discriminant analysis, and k-nearest neighbor classifiers. Two complementary analysis methodologies indicated classification accuracies over subjects of around 80% on a balanced dataset for the logistic regression classifier when information from all electrodes was taken into account simultaneously. Additionally, we found evidence that stress responses were preferentially time-locked to stimulus presentation, and that certain electrode⁻feature combinations worked broadly well across subjects to distinguish stress states.
Arrays of electrodes for recording and stimulating the brain are used throughout clinical medicine and basic neuroscience research, yet are unable to sample large areas of the brain while maintaining ...high spatial resolution because of the need to individually wire each passive sensor at the electrode-tissue interface. To overcome this constraint, we developed new devices that integrate ultrathin and flexible silicon nanomembrane transistors into the electrode array, enabling new dense arrays of thousands of amplified and multiplexed sensors that are connected using fewer wires. We used this system to record spatial properties of cat brain activity in vivo, including sleep spindles, single-trial visual evoked responses and electrographic seizures. We found that seizures may manifest as recurrent spiral waves that propagate in the neocortex. The developments reported here herald a new generation of diagnostic and therapeutic brain-machine interface devices.
Current mapping of epileptic networks in patients prior to epilepsy surgery utilizes electrode arrays with sparse spatial sampling (∼1.0 cm inter-electrode spacing). Recent research demonstrates that ...sub-millimeter, cortical-column-scale domains have a role in seizure generation that may be clinically significant. We use high-resolution, active, flexible surface electrode arrays with 500 μm inter-electrode spacing to explore epileptiform local field potential (LFP) spike propagation patterns in two dimensions recorded from subdural micro-electrocorticographic signals in vivo in cat. In this study, we aimed to develop methods to quantitatively characterize the spatiotemporal dynamics of epileptiform activity at high-resolution.
We topically administered a GABA-antagonist, picrotoxin, to induce acute neocortical epileptiform activity leading up to discrete electrographic seizures. We extracted features from LFP spikes to characterize spatiotemporal patterns in these events. We then tested the hypothesis that two-dimensional spike patterns during seizures were different from those between seizures.
We showed that spatially correlated events can be used to distinguish ictal versus interictal spikes.
We conclude that sub-millimeter-scale spatiotemporal spike patterns reveal network dynamics that are invisible to standard clinical recordings and contain information related to seizure-state.
Currently, clinical electrode arrays with a sparse spatial density (1 cm) are used to map the seizure onset zone (SOZ) and epileptic network in patients prior to epilepsy surgery. However, recent ...research demonstrates that submillimeter, cortical-column-scale domains have a role in seizure generation that may be clinically significant. We used novel high-resolution (500 m), active, flexible, 1-cm2, surface, electrode grid-arrays to explore the behavior of these domains. We employed this new technology to analyze the two-dimensional (2-D), wave-propagation patterns of epileptiform local field potential spikes (LFP spikes). Subdural micro-electrocorticographic ( ECoG) signals were recorded in vivo from anesthetized cats. A GABA antagonist, picrotoxin, was applied to induce acute neocortical epileptiform activity leading up to discrete seizures. Nine hours of data yielding 26,331 LFP spikes was analyzed. Features characteristic of spatio-temporal (ST) patterns were extracted from these events and k-medians clustering was employed to separate the data into 10 distinct classes. We tested the hypothesis that 2-D spike patterns during seizures (ictal spikes) are different from those between seizures (interictal spikes). A permutation test (n=1,000,000) confirmed this hypothesis. A frequent episode discovery algorithm (Temporal Data Mining) was then applied to investigate the relationship of sequences of these patterns to seizure generation, progression and termination. We found that sub-millimeter-scale ST spike wave-propagation patterns reveal network dynamics that may elucidate mechanisms underlying local circuit activity generating seizures. We conclude that sequences of patterns of similar type are less likely to precede seizure generation than sequences of patterns of differing types. Temporal analysis of these patterns also suggests that seizures in this model are not initiated by a single 2-D pathway, but rather by a number of different ST-initiating events. While these findings may be model-specific, reflecting diffusion of picrotoxin across the feline neocortex, the tools we have developed to interpret these events are directly portable to the human condition. We are confident that recording LFP spike ST wave-propagation patterns at high resolution provides a fruitful direction for continued analysis of epileptiform network dynamics and we propose that further study may provide a novel opportunity for therapeutic intervention at the micro-scale to treat epilepsy.
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