150 Backbone Spiking Sequence as a Basis for Preplay, Replay, and Default States in Human Cortex

INTRODUCTION: Sequences of spiking activity are a fundamental feature of many neural systems, and recent evidence suggests that they play an important role in information coding in the human brain. A parallel set of studies also asserts that sequential activity may in part derive from a pre-existing network structure. Sequential spiking activity therefore may arise as a natural property of the neurophysiologic properties of the human cortex. METHODS: We measured single unit spiking activity in the human cortex by implanting Utah micro-electrode arrays into participants who performed an episodic memory task while undergoing invasive monitoring for potential resective epilepsy surgery. RESULTS: We confirm the presence of an average backbone spiking sequence identified during pre-task rest that is stable over time and different cognitive states. These resting backbone sequences served as a scaffold for cognitively relevant sequential spiking activity occurring later in the recording session. We further demonstrate that backbone sequences are composed of both rigid and flexible sequence elements, and that flexible elements serve to promote memory specificity when forming and retrieving new memories. CONCLUSIONS: Here we demonstrate that backbone sequences can be measured in the human cortex and that they persist over time and through different cognitive states. Our data show that backbone sequences are composed of both rigid and flexible elements, and flexibility around the backbone allows for the formation of memory specific spiking sequences. Taken together, our results provide the first evidence for backbone spiking sequences in the human cortex, and more generally suggest a cognitive role of predetermined spiking network dynamics in the human brain.