Novel Method And Its Applications For Analyzing The Phase-locking Relationship Between Ronal Spike Firings And Field Potentials

The phase-locking relationship between the firings of neuronal action potentials (i.e., spikes) and the oscillations of local field potentials (LFP) reflects the information of neuron participates in the brain nerve activity, which may contain neural coding information of brain. To reveal the phase-locking relationship, the bin statistics method (Bin method) has been widely used since last decades. However, this method can only decide whether the phase-locking relationship exists or not instead of estimating the effect of the phase-locking quantitatively. Besides, Bin method also has other shortages. First, Bin method requires short LFP segments for analysis. Thus original long LFP signal has to be fragmented artificially before analysis. Such signal fragment may cause important information lost which only exists in long LFP. Second, Bin method has very low computational efficiency. It has to compute multiple times if the LFP segment for analysis contained more than one rhythm. Last, the size of the phase bin will also affect the final result, since the Bin method needs to count the spike numbers in each phase bin.In order to make up for the traditional Bin method’s shortages, a new method called the spike-triggered average method (STA method) was proposed for estimating the phase-locking neuron. In this method, the percentage ratio of the power of STA wave to the power of original LFP was utilized as a new quantitative index to estimate the strength of phase-locking. Applying the STA method to the experimental data obtained from anaesthetic rat hippocampal CA1region, it could be seen that the value of the index changes with the strength of phase-locking monotonically. Besides, the application of STA method to the simulating data indicated that the index has an effective critical value for phase-locking positive judgment, and the greater the index, the stronger the phase-locking relationship.When the phase-locking neurons were defined, the average phases between phase-locking neuron spikes and LFP could also be calculated from the STA waves. This paper took advantage of a16-chanel microelectrode to record LFP in different layers (including stratum radiatum, stratum pyramidale and stratum oriens layers) of hippocampal CA1region. Then, the STA method was applied to analyze the average phases between spikes and θ rhythm and y rhythm in those three layers. It could be seen that the average phases between spikes and different rhythms in different layers were different.Comparing to the Bin method, the STA method was more computational efficiency for calculating the average phases. It obtained the average phases between spikes and any rhythm only by filtering once, while Bin method needed to count phases between every spike and a particular rhythm respectively and then computed an average phase by circular statistics respectively if it analyzed more than one rhythm.In conclusion, this paper proposed a new method—the STA method—to quantitatively analyze the phase-locking relationship between the firings of neuronal spikes and LFP. The STA method provides a quantitative index to decide the phase-locking strength, but also avoid adverse effects in Bin method by repeated prior filtering and artificially limiting LFP frequency in Bin method. Consequently, STA method is of great significance to investigate the mechanisms underlying neuronal coding in brain.