Mapping of the Central Sulcus using g.Pangolin Ultra High-Density EEG/EMG/ECG System
Understanding how the brain works is really important. One way to do this is by mapping the brain’s activity with electroencephalography (EEG). It’s easy, cheap, and doesn’t involve surgery. In our latest publication, we wanted to see if we could make brain mapping even better by using a new type of EEG system called g.Pangolin ultra-high-density EEG (uHD EEG). This system has more sensors and therefore a higher resolution than traditional EEG systems, which means we can get more detailed information about the brain.
We employed g.Pangolin 1024-channel EEG system, to conduct central sulcus mapping via median nerve electrical stimulation on five subjects. Subsequently, an algorithm, co-developed with Nuri Firat Ince and Priscella Asman, PhD, was utilized to detect the phase reversal of the evoked potentials for central sulcus identification. Following this procedure, our five participants underwent MR scanning to validate the central sulcus location. The precise correspondence observed between the MRI and EEG data in pinpointing the central sulcus was remarkable. The following image is illustrating the spatial resolution achievable with g.Pangolin.
In neurology, the central sulcus is typically discerned by placing ECoG grids directly onto the brain, followed by electrical stimulation of the median nerve at the wrist. This elicits EPs in both the sensory and motor cortices. Phase reversal occurs, manifesting as an early positive wave over the motor cortex and an early negative wave over the sensory cortex. The central sulcus lies between the ECoG electrode locations exhibiting negative and positive responses. Although this technique is clinically efficient, requiring only a few minutes to precisely identify this neurosurgical landmark, it is invasive.
We’ve created visual representations of brain activity using SSEP classification. In the first row (a), we show the actual distribution of channels on the head model, with red indicating channels in front of the central sulcus and blue behind it. Grey spheres represent channels with poor signal quality. The second row (b) displays results from peak detection, with colors indicating the intensity of brain activity. The central sulcus is highlighted similarly to the ground truth. In the third row (c), results from spectral clustering show a clear distinction between sensory (blue) and motor (red) areas, with bad channels shown in grey.
With the g.Pangolin Ultra High-Density system, participants are prepared by shaving to facilitate the placement of the 1024 EEG channels on the scalp. Adhesive washers are utilized to secure the electrode grids to the skin, filled with special electrode paste to ensure optimal contact and reduce impedance. A pre-amplifier is then connected to the electrode grid to facilitate the recording of high-quality EEG data. Following electrical stimulation, EPs are registered, and an automatic detection algorithm identifies the positive and negative waves, thereby pinpointing the phase reversal and locating the central sulcus.
The g.Pangolin electrodes interface with g.HIamp, a 256-channel biosignal amplifier boasting 24-bit resolution. Equipped with four processors, this amplifier features ultra-steep anti-aliasing filtering and high oversampling, yielding impressive signal-to-noise ratios. The data stream is then transmitted to g.HIsys Professional software for real-time processing, a component of the g.tec Suite 2020 software environment, facilitating the execution of such experiments.
Our results showed that we could accurately identify the central sulcus using uHD EEG, with a success rate similar to more invasive methods. This means we can understand how different parts of the brain work together without needing surgery. This new approach could be useful for many things, like brain research, surgery planning, monitoring patients in hospitals, detecting consciousness, controlling computers with the mind, helping people recover from injuries, and improving mental health treatments.