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Intraoperative monitoring of leg length and offset using the Intellijoint miniature navigation system. The digitizing probe is used to trace the groove of the disc attached to the femur to establish femoral position and orientation changes

Flash stimulation pads used for surgical intraoperative monitoring. Intraoperative visual evoked potentials (VEPs) results. Contributed by Marco Zeppieri, MD, PhD. Images courtesy of Elisa Ecoretti and Giada Pauletto, MD.

Meta-analysis of intraoperative awareness during BIS monitoring (patients classified at higher risk of awareness)

Monitoring the electrical activity of the brain. (a, top) The traces of wide-band recordings (left) and 30 Hz highpass filtered (right) hippocampal CA1 shown together with their independent components (obtained with independent component analysis). (Bottom) Two-dimensional voltage (LFP) and CSD maps of the three main CA1 independent components from a rat with an electrode array spanning the transverse axis of the hippocampus (seven shanks spaced 300 mm; one shank shown on the left) indicates activation of different projections (CA1pyr pyramidal layer, rad radiatum, lm lacunosum moleculare). (b) Electrocorticography (ECoG) records indicating periods of behavior-relevant slow oscillations (orange) and spindles (gray). (Bottom) Intraoperative ECoG recordings in human patients using new technologies have the ability to detect spiking. Highpass filtered traces from a novel 64-grid electrode containing spiking activity (black traces). Below, sample spike waveforms are shown. (c) Simulation of an individual neuron (layer 5 pyramidal injected with intracellular somatic current by a pipette: intracellular somatic spiking shown in blue is detected in the extracellular space by a proximal electrode (red; part of a silicon depth electrode) as well as by the ECoG strip electrode (simulating the same layout as the one in panel b)). The spike-triggered average ECoG signal from the middle of the ECoG strip is shown (right). (Bottom) The spike triggered average ECoG field for two cell types extending to superficial layers: a layer 23 pyramidal (left) and a layer 5 pyramidal neuron (right). While the amplitude of the spiking ECoG signature is very similar, the spatial extent is markedly different. (d, left) A large-scale, biophysically realistic model of thousands of reconstructed and interconnected neocortical layer 4 (red) and layer 5 (green) pyramidal neurons emulating a patch of deep cortical volume. The population model was used to study the extent to which active membrane conductances impact the extracellular LFP and CSD signals. (Right) Two scenarios were instantiated: passive-only membranes and active ones. The simulated LFPs and CSDs show the result of these simulations (top: passive-only; bottom: active) with the spatiotemporal characteristics of the LFP and CSD being markedly different. (e, left) Hippocampal model of the CA1 region consisting of reconstructed excitatory neurons capturing the various projections during sharp wave ripples accounts for the extracellular signals during such events. (Right) Replay sequences during sharp waves yield consistent LFP patterns in the ripple (150–200 Hz) bandwidth. As observed, simulations point to the spatiotemporal patterned activity that is also observed in the same band in vivo, reflecting the spiking activity of cell assemblies activated during sharp waves. Figure contributions are from (a) Schomburg et al. (2014), (b) Khodagholy et al. (2015), (c) simulations by C.A. Anastassiou and A.S. Shai, (d) Reimann et al. (2013), (e) Taxidis et al. (2015)