“ Relationships between spike - free local field potentials 1 and spike timing in human temporal cortex

62 Intracortical recordings comprise both fast events, action potentials (APs), and slower 63 events, known as local field potentials (LFPs). While it is believed that LFPs mostly 64 reflect local synaptic activity, it is unclear which of their signal components are most 65 closely related to synaptic potentials, and would therefore be causally related to the 66 occurrence of individual APs. This issue is complicated by the significant contribution 67 from AP waveforms, especially at higher LFP frequencies. In recordings of single-cell 68 activity and LFPs from the human temporal cortex, we computed quantitative, nonlinear, 69 causal dynamic models for the prediction of AP timing from LFPs, at ms resolution, 70 before and after removing AP contributions to the LFP. In many cases the timing of a 71 significant number of single APs could be predicted from spike-free LFPs at different 72 frequencies. Not surprisingly, model performance was superior when spikes were not 73 removed. Cells whose activity was predicted by the spike-free LFPs models generally 74 fell into one of two groups: in the first, neuronal spike activity was associated with 75 specific phases of low LFP frequencies, lower spike activity at high LFP frequencies, and 76 a stronger linear component in the spike-LFP model; in the second group, neuronal spike 77 activity was associated with larger amplitude of high LFP frequencies, less frequent 78 phase-locking, and a stronger nonlinear model component. Spike timing in the first 79 group was better predicted by the sign and level of the LFP preceding the spike, whereas 80 spike timing in the second group was better predicted by LFP power during a certain time 81 window before the spike. 82