How Can Laminar Microelectrodes Contribute to Human Neurophysiology?

Abstract

Human laminar microelectrodes (linear arrays implanted acutely or semi-chronically in surgical patients) present an exciting new frontier of intracranial electrophysiology. Though most iEEG is limited to imaging networks, laminars can resolve the cortical microcircuits underlying cognition. Normally implanted in animal models, laminar probes can record the current-source-density, which reflects transmembrane currents, as well as single and multi-unit activity (MUA) throughout the cortical depth. These measures of neural activity allow the mapping of laminar physiology underlying diverse neural phenomena in humans. For instance, several studies have shown laminar activity sensitive to language and perception. They've also discovered motifs of different rhythms during sleep (slow waves, spindles) and wakefulness (delta/theta, alpha). Intriguingly, these studies suggest an outsize role for superficial layers in cortical oscillations which may be human specific. Human laminar recordings have also shed light on cortical physiology in general, such as the spatiotemporal dissociation of high-gamma-power (HGP) and MUA. In disease, laminars have elucidated the structure of epileptiform discharges. However, key conceptual and methodological issues like proper referencing, clinical constraints and comparisons with animal models remain. These difficulties notwithstanding, new innovations in recording density, simultaneous surface-laminar recordings and extracranial source-inference will enable laminars to answer fundamental questions in human neurophysiology.