Fig. 2: The learned dictionaries in IOM and EMU recordings.
The figure illustrates four layers of learned dictionaries (D1–D4) and their respective properties across IOM (a–c) and EMU (d–f). a (IOM) and d (EMU) show a patch of 4 ⨯ 4 examples of learned dictionary atoms for each layer, with color shading indicating the depth of the layers: D1 (orange) represents the shallowest layer, D2 (green) the second layer, D3 (red) the third layer, and D4 (blue) the deepest layer. b (IOM) and e (EMU) present the corresponding time–frequency maps for each learned atom, visualized using the Wigner–Ville distribution, enabling time–frequency analysis of the components. c (IOM) and f (EMU) display the power PSD maps for all selected learned atoms, grouped by their respective layers. The PSD plots are color-coded according to the shading of each layer (orange for D1, green for D2, red for D3, and blue for D4). The x-axis represents the individual dictionary atoms, while the y-axis shows their power spectral densities. The combined plots of all atoms reveal how frequency components vary across layers, forming a comprehensive PSD image. In both recording scenarios (IOM and EMU), the learned atoms in D1 primarily captured low-frequency components, below 80 Hz. As the layers deepen (D2–D4), the PSD peaks shift progressively toward higher frequencies, with D4 capturing the highest frequencies, including fast ripples (FR) around 600 Hz. PSD power spectral density, IOM intraoperative monitoring, EMU epilepsy monitoring unit.
