Unique intrinsic properties of Low Rheobase (LR) cells
LR cells in the RSG have intrinsic properties that differ substantially
from those of neighboring RS cells. Most importantly, and the reason we
have suggested their name, is that they fire in response to very little
current input, i.e. they have a low rheobase. This is dependent on their
large input resistance, which in turn is most likely related to their
small soma size and relatively sparse dendritic tree. LR cells also
demonstrate a late-spiking phenotype in response to near-threshold
current injections (Kurotani et al, 2013). Based on our findings, we
argue that the late-spiking behavior of these neurons is not their most
unique or defining feature. FS cells and many RS cells in the RSG also
show late-spiking behavior in response to near-threshold stimuli (Figure
1). Additionally, the name “late-spiking (LS) neuron” is already most
often attributed to neurogliaform cells, inhibitory interneurons found
in the superficial layers of the neocortex, including layer 1
(Cruikshank et al., 2012). Instead, the intrinsic excitability of LR
neurons, facilitated mostly by their high input resistance and low
rheobase, is their most distinct feature and is critical to their
potential computational functions. In addition, their lack of spike
frequency adaptation suggests an ability to respond to high frequency
inputs far more reliably than RS cells can. This, coupled with their low
rheobase, makes them a rare and unique class of neurons that can respond
to both weak inputs as well as sustained or high frequency inputs,
thereby possessing the ability to transfer the incoming synaptic inputs
to their post-synaptic targets with a high degree of precision. Thus,
the name Low-Rheobase (LR) is indicative of both their unique properties
compared to other cell types in this region as well as the computational
functions that they are likely to perform in this circuit.