Layer V pyramidal cells action potentials are coherent with and phase-locked to LFPs.

<p>(A) membrane potential (Vm) recording (without DC current injection), with spontaneous action potentials (spikes), together with concurrent (unfiltered) records of LFPs. (B), left panels: Power spectral densities in LFPs are significant (99% above red lines) in beta range, but for Vm are close to spontaneous spike firing rate. Right panels: coherence between Vm and layers V and II LFP is seen in beta range, and harmonics thereof (same recordings as A). (C), upper panel: spike-triggered averages of LFPs from layer V (red) and II (blue), time-locked to each of 84 spikes occurring over a 10 s period (at t = 0 on x-axis). Spikes precede by 2–3 ms the trough, and peak, of the layer V and II oscillations respectively, both of which display a period of around 40 ms. Taken from same cell as in A and B. Lower panel: pooled, normalised, layer V LFP spike-triggered average data (mean ± SEM) from all the 10 recordings that showed significant coherence in the 15–40 Hz range between layer V LFP and Vm (during spontaneous firing). The layer V LFP peak follows the spike by approximately 20 ms. (D), upper panels: Records of (Vm) recorded at rest, during spontaneous spike firing, and of layer V and II LFPs, in absence (left) and presence (right) of bicuculline (10 µM). While spikes persist in bicuculline, LFP oscillations are abolished. Lower panels: significant beta range coherence between Vm and both layer V and II LFP (left) is abolished in bicuculline (right). Different preparation from panels A–C. (E), data pooled from all recordings showing the distribution of frequencies at which significant coherence between LFPs in layer II and layer V, and spikes, was detected, grouped into 3 frequency bands (mean ± SEM in red, n in parentheses).</p

Basic intracellular properties of recorded cells used in this study.

<p>¹ 4 cells were quiescent; ² at ½ maximal amplitude; ³ in range −55 to −75 mV.</p

Properties of a layer V pyramidal cell, demonstrated with sharp microelectrode intracellular recording.

<p>(A), recording of resting membrane potential, showing spontaneous action potential firing at 18.1 Hz. Right panel: a single action potential on an expanded time scale, with dashed cursor lines indicating method of measuring amplitude (between top and bottom horizontal cursors: 65.3 mV) and duration at ½ maximal amplitude (between vertical cursors: 1.10 ms). (B), superimposed records of membrane potential showing response to successive 200 ms hyperpolarizing pulses of current (not shown) injected in multiples of 0.2 nA from baseline of zero (ie. resting potential). (C), voltage-current plot derived from a series of current pulses injected in multiples of 0.1 nA into the same cell [including those in (B)] in which steady-state voltage attained near end of current pulse [dashed vertical line in (B)] is plotted. Slope of line (best fit in range −55 to −75 mV) yields input resistance value of 45 MΩ. All records from the same cell.</p

Characteristics of beta activity in local field potentials (LFPs).

<p>Layer II and V LFPs show significant power in the beta frequency range, which is both correlated and significantly coherent between layers II and V. (A), sample of filtered recording showing LFPs acquired concurrently in layer II (upper record) and layer V (lower record). (B), power spectra derived from these LFPs, plotted on log scales as power spectral densities (PSD), showing peaks in beta (20–30 Hz) range. (C) and (D), power spectra of same LFPs from layer II and layer V respectively, on linear scales, showing 99% significance levels above red lines. Significant peaks are present at 25.7 Hz (layer II), and at both 26.6 and 51.9 Hz (layer V), with no single clear peak shown in range 40–100 Hz in layer II, although significant power is evident. (E), strong cross-correlation of LFPs from layers II and V, with period of around 34 ms. (F), coherence between LFPs in layer V and layer II (in same recordings as (A) is significant at 99% confidence level (above red line) at 10.3 and 50.3 Hz, but most markedly at 27.6 Hz.</p

IPSPs in layer V cells are strongly coherent with LFPs in the beta range.

<p>(A) Concurrent LFPs from layers V and II, and intracellularly recorded membrane potential (Vm) from a cell in layer V. Oscillations and IPSPs (at −80 mV, optimised for IPSPs) are blocked following application of GABA_A receptor antagonist bicuculline (right panel). (B) Power spectral densities (PSD) of LFPs from layers V and II, and of Vm (with IPSPs), showing 99% significance levels (above red lines) at beta frequencies, and harmonics thereof, which (right panels) are blocked by bicuculline. Vertical dashed lines indicate 27 Hz for reference. Same recordings as (A). (C), upper panel: cross-correlograms of LFPs from layers II (blue) and V (red) with Vm from same recordings as in (A) and (B). Lower panel: normalised, cross-correlated data (means+SEM) between Vm (displaying IPSPs) and LFPs in layer V (red) and layer II (blue) pooled from all 20 recordings showing significant IPSP-LFP coherence in 15–40 Hz range. The IPSP leads layer V peak (red dashed line) by 7.2 ms and layer II peak (blue dashed line) by 20.5 ms. (D) Left column: coherence between each of layer II and layer V LFP (top row), layer II LFP and IPSPs (middle row), and layer V LFP and IPSPs (bottom row) in each case demonstrates single significant (>99%) peaks at beta frequencies, and harmonics thereof, which is abolished by bicuculline (right panels). Same recordings as A, B and C. (E) and (F), data pooled from all recordings within 3 frequency ranges (demarked by vertical dashed lines, with mean ± SEM in red, n in parentheses) showing (E) the distribution of the single largest significant (>99%) power spectrum peaks for Vm (optimised for IPSPs), and (F) peak frequencies of coherence between LII, LV, and Vm (IPSPs).</p