In 2012, Albert Lee’s lab at Janelia published a paper describing a remarkable finding. During whole-cell recordings from CA1 pyramidal neurons in freely moving rats, silent cells (i.e., those not firing in the environment) could be induced to fire in a location-specific manner if the neuron was continuously depolarized (Lee et al., 2012). On the surface, this may seem unremarkable, if all that were happening is that spatially modulated, but subthreshold synaptic input was brought above threshold by the continuous depolarization. However, what actually happened is that the depolarization revealed previously occult, spatially modulated synaptic input. In other words, prior to depolarization, there was no evidence of spatially modulated synaptic input, but after depolarization there was.
Using somatic and dendritic recordings from CA1 pyramidal neurons in slices, Ching-Lung Hsu has begun to explore the cellular mechanisms that could be responsible for this effect. We have successfully reproduced the steep voltage dependence of synaptic responses in slices and are now investigating the types of ion channels responsible.