Influence of spiking activity on cortical local field potentials

Abstract

The intra-cortical local field potential (LFP) reflects a variety of electrophysiological processes including synaptic inputs to neurons and their spiking activity. It is still a common assumption that removing high frequencies, often above 300 Hz, is sufficient to exclude spiking activity from LFP activity prior to analysis. Conclusions based on such supposedly spike-free LFPs can result in false interpretations of neurophysiological processes and erroneous correlations between LFPs and behaviour or spiking activity. Such findings might simply arise from spike contamination rather than from genuine changes in synaptic input activity. Although the subject of recent studies, the extent of LFP contamination by spikes is unclear, and the fundamental problem remains. Using spikes recorded in the motor cortex of the awake monkey, we investigated how different factors, including spike amplitude, duration and firing rate, together with the noise statistic, can determine the extent to which spikes contaminate intra-cortical LFPs. We demonstrate that such contamination is realistic for LFPs with a frequency down to ∼10 Hz. For LFP activity below ∼10 Hz, such as movement-related potential, contamination is theoretically possible but unlikely in real situations. Importantly, LFP frequencies up to the (high-) gamma band can remain unaffected. This study shows that spike–LFP crosstalk in intra-cortical recordings should be assessed for each individual dataset to ensure that conclusions based on LFP analysis are valid. To this end, we introduce a method to detect and to visualise spike contamination, and provide a systematic guide to assess spike contamination of intra-cortical LFPs.

The functional profile of the human amygdala in affective processing: Insights from intracranial recordings

“…We, thus, attempt a systematic and exhaustive review of all iEEG studies conducted on the whole human amygdala and discuss amygdala anatomy where appropriate and possible. Fourth, iLFP analyses of the reviewed studies below may incur a degree of contamination due to spiking activity (Waldert, Lemon, & Kraskov, 2013). While this may be particular to the alpha frequency (~10 Hz), it is theoretically possible to observe influences of spiking activity in cortical iLFPs in other ranges such as theta, beta and gamma (Waldert et al, 2013).…”

“…Fourth, iLFP analyses of the reviewed studies below may incur a degree of contamination due to spiking activity (Waldert, Lemon, & Kraskov, 2013). While this may be particular to the alpha frequency (~10 Hz), it is theoretically possible to observe influences of spiking activity in cortical iLFPs in other ranges such as theta, beta and gamma (Waldert et al, 2013). Finally, it is important to note that the recorded potentials of eventrelated potentials (ERPs) depend on the position of the electrode site and its referent electrode (Fabiani, Gratton, & Coles, 2000).…”

HCN channels enhance spike phase coherence and regulate the phase of spikes and LFPs in the theta-frequency range

“…In recent experimental and modeling studies, there has been a lot of debate on the source and spatial extent of LFPs (1-9). However, most of these studies have used neurons with passive dendrites in their models and/or have largely focused on the contribution of spike-generating conductances to LFPs (7,8,10,11). Despite the widely acknowledged regulatory roles of subthreshold-activated ion channels and their somatodendritic gradients in the physiology and pathophysiology of synapses and neurons (12-17), the implications for their existence on LFPs and neuronal spike phase have surprisingly remained unexplored.…”

An implantable microelectrode array for simultaneous L-glutamate and electrophysiological recordings in vivo

“…However, activity in the nervous system includes a complex combination of biochemical and electrical events in space and time [12][13][14] . Local field potential (LFP) integrates predominantly synaptic input signals from a large population of neurons, whereas spikes or action potentials are output signals of a single neuron [15][16][17] . Thus, investigating the extracellular electrophysiological signals corresponding to these activities may enable better understanding of glutamatergic processes 16,18 .…”