Task-Dependent Changes in Cross-Level Coupling between Single Neurons and Oscillatory Activity in Multiscale Networks
Figure 11
Neuro-computational consequences of amplitude- and phase-to-rate mappings.
For a given neuron, the amplitude- and phase-to-rate mappings are produced by the combined synaptic input to that cell. But since information about the population rhythm is broadly accessible, neurons may use this information to dynamically organize relative activity within a functional ensemble. This activity includes winner-take-all interactions arising from recurrent local connectivity and relative spike timing among ordered sets of cells. A) Two excitatory cells (E1 and E2, red) that connect to a common inhibitory cell (I, blue) – and which in turn provides inhibitory synaptic connections to E1 and E2 to form re-entrant or recurrent excitatory-inhibitory loops – can act as a simple winner-take-all (WTA) module. That is, given different levels of input to E1 and E2, then either E1 or E2 (but not both) will produce tonic spike output. B–C) If two cells with different amplitude-to-rate mappings provide input to such a WTA module, then the WTA module will provide different output at low and high beta amplitudes. For example, given the purple (sig045a) and gold (sig062a) amplitude to rate mappings shown in Figure S10, then WTA cell E1 generates spike output only at low amplitudes while E2 spikes at high amplitudes; E1 and E2 switch roles at the beta amplitude where the amplitude-to-rate sigmoids intersect. Critically, task-dependent remapping implies that this intersection point can shift to different values for each pair of input neurons. D) One second example trace of filtered LFP activity during BC showing beta amplitude (black) and phase (grey) variation over time. E) Amplitude-to-rate mappings for seven example neurons: sig015a (blue), sig029a (green), sig029b (red), sig031a (cyan), sig045a (purple), sig062a (gold), and sig081b (black). Baseline rate has been removed to emphasize rate changes associated with amplitude variation. F) Changes in spike rates (relative to baseline) over one second induced by the amplitude-to-rate mappings (color as in E). Colors are as in Figure 4A. Note the two alternating periods of rank-ordered regimes. G) Close up of 180 ms of beta activity, showing amplitude (grey) and phase (black) variation. H) Rate changes induced by the amplitude-weighted phase-to-rate mapping for sig081a (black) and sig062a (gold). I) Periods of high beta amplitude are associated with a bias towards a relative spike timing order, while periods of low beta amplitude are not. Task-dependent remapping of preferred phases can switch this order. Task-dependent changes in the relative spike timing order of an ensemble – via the independent phase-to-rate remapping of each cell – provides a potential mechanism linking the global or top-down input changes associated with task switching to local features such as cell assembly activation or synfire chain propagation (thus influencing local cortical computation) as well as spike-timing dependent plasticity (thus influencing learning).