Abstract
Neurons in the visual system display varying degrees of selectivity for stimulus features such as orientation and direction. Such feature selectivity is generated and processed by intricate circuit and synaptic mechanisms. A key factor in this process is the input-output transformation from membrane potential (Vm) to spikes in individual neurons. Here, we use in vivo whole-cell recording to study Vm-to-spike transformation of visual feature selectivity in the superficial neurons of the mouse superior colliculus (SC). As expected from the spike threshold effect, direction and orientation selectivity increase from Vm to spike responses. The degree of this increase is highly variable, and interestingly, it is correlated with the receptive field size of the recorded neurons. We find that the relationships between Vm and spike rate and between Vm dynamics and spike initiation are also correlated with receptive field size, which likely contribute to the observed input-output transformation of feature selectivity. Together, our findings provide useful information for understanding information processing and visual transformation in the mouse SC.
Highlights
Each neuron functions as an information processing unit that transforms synaptic input to spiking output
With in vivo whole-cell recording, we show that the transformation of direction and orientation selectivity from Vm to spikes is highly variable in the mouse stratum griseum superficiale (SGS)
Using the normalized vector sum as an index, which we refer to as global direction selectivity index (gDSI) and global orientation selectivity index (gOSI), we quantified the degree of direction selectivity (DS) and orientation selectivity (OS) of spiking and Vm responses, respectively, of the recorded SGS neurons
Summary
Each neuron functions as an information processing unit that transforms synaptic input to spiking output. In the mouse SC, we recently revealed that the direction selectivity (DS) in the SC originates from the direction selective ganglion cells in the retina (Shi et al, 2017) Another prominent characteristic of the SC is that it contains a much higher proportion of inhibitory neurons than in cortex (Mize, 1988, 1992; Endo et al, 2003; Inayat et al, 2015). Several biophysical factors, including Vm-to-spike-rate relationship and the Vmrising slope for spike initiation, but not dendritic processing, are correlated with RF size and likely contribute to the observed input-output transformation of feature selectivity. Together, these findings provide useful information for understanding information processing and visual transformation in the SC
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