The mechanisms underlying synchronization of neuronal activity
Our research has uncovered the importance of GABAergic interneurons for the control of spike timing. By interacting with intrinsic conductances in principal neurons, individual GABAergic interneurons are sufficient to synchronise spike discharge in pairs of pyramidal neurons, and, by inference, all of the principal neurons contacted by that same interneuron.
We discovered that the feedback circuitry of principal neurons and GABAergic interneurons in hippocampal area CA3 is sufficient to maintain a fast network oscillatory state (~40 Hz) under cholinergic activation (Cobb et al, Nature 1995 (>700 citations) & Fisahn et al., Nature 1998 (>400 citations).
The mechanism underlying this cholinergically-induced oscillation involves both excitatory and inhibitory synapses as well as intrinsic conductances in neurons, and the oscillation specifically engages, and depends upon, a subpopulation of perisomatic-targeting interneurons.
These findings have implications for our understanding of how information can be stored in and retrieved from cortical circuits.
Synaptic plasticity during network oscillations
Network oscillations naturally organise spike timing in key elements of the neural circuit and could thus form a basis for spike timing-dependent synaptic plasticity.
Our research has confirmed that activation of presynaptic neurons immediately before single spikes in the postsynaptic neuron is sufficient to induce input-specific synaptic potentiation in hippocampal slices prepared from rodents early in their postnatal development.
In adult animals, however, no such potentiation was seen. Rather, there was a requirement of postsynaptic burst firing for potentiation to occur, due to increasing GABAergic inhibition with developmental maturation. This suggests that different logical rules operate at different stages of development, and that different codes might apply during encoding and retrieval of information.