Fig. 1.

γ-aminobutyric acid (GABA) neurons are efficient at synchronizing neuronal activity in cortical networks. (A) Top, a local field potential (LFP) recorded with an extracellular electrode in the vicinity of the pyramidal neurons reflects the synchronization of pyramidal cell activity. Note the negative (downward) components of the LFP, roughly coincident with the periods of spike synchronization recorded simultaneously, as shown in the traces below. Bottom: superimposed traces of intracellular membrane potential recording, illustrating how the asynchronous firing of pyramidal neurons in response to continuous excitatory drive becomes transiently synchronized by phasic synaptic inhibition. Stimulation of an inhibitory input at the times indicated by the black arrows produces hyperpolarizing inhibitory postsynaptic potentials (IPSPs) that transiently inhibit spike firing and produce nearly synchronous spikes shortly after the IPSPs end. Data in part (A): unpublished results from G. Gonzalez-Burgos. (B) Diagram indicating that the axon of an individual GABA neuron makes multiple synaptic contacts onto multiple postsynaptic pyramidal cells and also onto other GABA neurons. The proportion of postsynaptic target cells (3 pyramidal:1 GABA) reflected in the diagram matches their relative numbers in real circuits. However, certain interneuron subtypes display marked target selectivity. For instance, chandelier neurons make synapses onto pyramidal cells but not onto other GABA neurons. In contrast, calretinin-containing interneurons synapse frequently onto other GABA neurons but rarely onto pyramidal cells (see figures 2,3 and main text).