Fig. 4: Alpha rhythms associate with modified synaptic inhibition onto L4 pyramids and stellate neurons.

a Example of two electrophysiologically distinct fast-spiking (FS) neurons recorded in V1 L4. FS1 neurons generate stable trains of action potentials on depolarising current injection (0.2 nA) up to 250 Hz (upper panel), producing single or doublet action potentials on most periods of the initial gamma rhythm in the presence of kainate alone (middle panel) and 2–5 spikes per period during the subsequent alpha rhythm (lower panel). FS2 neurons also generated high-frequency trains of action potentials on depolarising current injection but note the additional, slower component of the AHP and a prominent post-spike-train afterhyperpolarisation (upper panel). This subtype of FS neuron generated robust single spikes per period during the kainate alone-induced gamma rhythm (middle panel), but fell silent during the subsequent alpha rhythm (lower panel). Scale bars 40 mV, 200 ms. b Incidence histograms for the IPSP decay times onto the two main principal cell subtypes in L4 V1—stellate neurons and small pyramidal neurons—during the initial kainate alone-induced gamma rhythm and the subsequent LFP alpha rhythm. Note only stellate neurons, during the initial gamma rhythm, demonstrated longer IPSP decay times. c Example IPSP profiles (at −30 mV holding potential) in the two principal neuron types (n = 4 from each) in the two oscillatory conditions. Individual examples are plotted as thin lines, averages as thick lines, aligned to the onset of each sequence of IPSPs. Note the introduction of a mismatch in time spent in receipt of synaptic inhibition for the two neuron types during the alpha rhythm. Scale bars 4 mV, 50 ms.