Theta Driving Cell And Theta Pulsing Cell In Hippocampal CA1

Hippocampal theta oscillation (4-12Hz) is characteristic oscillation of local field potential (LFP) recorded in hippocampus of rodents during active exploration and REM sleep. Plenty of studies indicated critical roles of hippocampal theta oscillations in information processing of hippocampus during learning and memory. We recorded two types of highly theta-correlated neuron by multichannel extracellular recording in hippocampal CA1of freely moving mice:theta-driving cell and theta pulsing cell. Theta-driving cell fired in high rates (88.05±4.45Hz, n=5) during theta oscillation and were highly correlated with LFP theta rhythm. Different from other theta-correlated neurons, the firing of theta-driving cell has significant Granger causal effect on LFP theta, which is much stronger than that in reverse direction. For other theta-correlated neuron, no significant Granger causality was found in direction from unit to LFP theta. Further analysis indicates that during non-theta period such as slow wave sleep (SWS), the firing of theta-driving cell is still highly correlated with LFP theta component through significant Granger causal influence from unit to LFP theta. Our studies suggest crucial roles of theta-driving cell in theta generation of hippocanpal CA1. It is inferred that theta-driving cell might participated in hippocampal theta formation by generating inhibitory postsynaptic potential on pyramidal soma.Theta pulsing cell is the other type of neuron recorded in hippocampal CA1and never reported before in previous studies. They presented three characteristic firing patterns:firstly, they fire exclusively in theta period and keep silence during non-theta period such as SWS. Secondly, they fire almost one spike during each theta circle, which we called theta-rhythm pulsing pattern: Third, during different behavior states of theta oscillations (AE and REM sleep) their firing pattern correlated with theta rhythm in different ways. In detail, the firing rate of theta pulsing cell is higher than theta rhythm during AE, thus presented phase precession with LFP theta; during REM sleep the firing rate is lower than theta rhythm, thus presented phase recession. The two firing patterns of reversed phase relationship with LFP theta of theta pulsing cell during AE and REM sleep suggest that theta oscillations in different behavior states might play different roles during information processing of hippocampal neural network.