Bursting Neurons in the Hippocampal Formation Encode Features of LFP Rhythms

Abstract

Burst spike patterns are common in regions of the hippocampal formation such as the subiculum and medial entorhinal cortex (MEC). Neurons in these areas are immersed in extracellular electrical potential fluctuations often recorded as the local field potential (LFP). LFP rhythms within different frequency bands are linked to different behavioral states. For example, delta rhythms are often associated with slow-wave sleep, inactivity and anesthesia; whereas theta rhythms are prominent during awake exploratory behavior and REM sleep. Recent evidence suggests that bursting neurons in the hippocampal formation can encode LFP features. We explored this hypothesis using a two-compartment model of a bursting pyramidal neuron driven by time-varying input signals containing spectral peaks at either delta or theta rhythms. The model predicted a neural code in which bursts represented the instantaneous value, phase, slope and amplitude of the driving signal both in their timing and size (spike number). To verify whether this code is employed in vivo, we examined electrophysiological recordings from the subiculum of anesthetized rats and the MEC of a behaving rat containing prevalent delta or theta rhythms, respectively. In both areas, we found bursting cells that encoded information about the instantaneous voltage, phase, slope and/or amplitude of the dominant LFP rhythm with essentially the same neural code as the simulated neurons. A fraction of the cells encoded part of the information in burst size, in agreement with model predictions. These results provide in-vivo evidence that the output of bursting neurons in the mammalian brain is tuned to features of the LFP.

Topography in the Bursting Dynamics of Entorhinal Neurons

“…The bursting score was computed as the number of burst spikes (spikes that preceded or followed another spike within 10 ms) divided by the number of total spikes. This threshold is consistent with previous studies characterizing bursts in the hippocampus (Harris et al, 2000;Hussaini et al, 2011;Mizuseki et al, 2009), MEC (Constantinou et al, 2016;Mizuseki et al, 2009), septum (Ranck, 1973), Bursting score versus firing rate curves were generated by first computing the average firing and bursting score in 500 ms time bins, and then computing the average bursting score per 3-Hz wide firing rate bins. For further analysis, only curves with more than 5 bins were considered.…”

Optogenetic “low‐theta” pacing of the septohippocampal circuit is sufficient for spatial goal finding and is influenced by behavioral state and cognitive demand

“…This was particularly evident during the hidden goal condition. The increased amplitude of both the 6 Hz ATS signal in the LFP at all speeds, and the dominance of 6 Hz cellular burst‐timing in the hidden goal task, provide further evidence that cell rhythmicity represents the temporal features of the predominant frequency band in extracellular oscillations (Constantinou et al, 2016; Takahashi & Magee, 2009; Zutshi et al, 2018). Although it is unlikely that LFPs and burst‐timing rhythmicity are dissociable phenomena, at least with regard to the baseline integration of dendrite to soma input and output processes (Vaidya & Johnston, 2013), future work will need to study the mechanistic relationship between these timing levels during ATS.…”

Neural Coding With Bursts—Current State and Future Perspectives

“…Bursts are also highly relevant in predictive coding (Mumford, 1992 ; Rao and Ballard, 1999 ). Here, Constantinou et al ( 2016 ) demonstrate that hippocampal bursts encode current and future characteristics (instantaneous value, phase, slope and amplitude) of the local field potential (LFP). Future LFP values can be represented because of temporal correlations in the LFP signal.…”