Abstract
Purpose :
The brain combines 2-dimensional images collected by the eyes to form a 3-dimensional representation of its surroundings. This process of stereopsis arises from the binocular integration circuitry in the primary visual cortex (V1) that include neurons tuned to certain disparities between visual stimuli viewed by the two eyes. V1 neurons are also known to be tuned to orientations of visual stimuli. We examined whether these two well-known properties of V1 neurons are related in the mouse, expecting cells tuned to vertical orientations to have the strongest disparity selectivity tuning.
Methods :
Adult C57BL/6 mice were surgically fitted with a headplate and had a craniotomy performed over the binocular zone of V1 to facilitate in vivo electrophysiological recording in awake animals. A combined projector and polarizing alternator system was used to display dichoptic visual stimuli. The stimulus set consisted of drifting gratings, in which each binocular condition consisted of a specific combination of orientation and phase disparity, and the associated controls were two monocular conditions at the same orientations. Binocular and monocular conditions were displayed in a randomly interleaved order. A high density 64-channel silicon probe was inserted to collect extracellular voltage signals, which were later sorted into single unit spikes for further analysis.
Results :
We acquired a total of 338 single units across 15 animals. Of this population, 107 were significantly responsive to our set of drifting gratings (random permutation test p<0.05). For each neuron, we measured its tuning in the joint parameter space of orientation and phase disparity, as well as its orientation tuning for monocular stimulation. The strength of tuning along the phase disparity axis was quantified using a selectivity index (gPDSI), and orientation corresponding to highest gPDSI was determined. The distribution of orientations corresponding to highest gPDSI was not equally spread among the 4 orientation conditions in the stimulus set (χ2(3)=8.238, p=0.041). However, there was also no significant correlation between gPDSI and preferred orientation (R2=0.001, F(107,105)=0.065, p=0.8).
Conclusions :
Binocular disparity selectivity in mouse V1 is not significantly stronger in cells tuned to vertical orientations. Studies utilizing only vertical gratings in their stimulus set may be mis-estimating the prevalence of disparity selective cells in binocular V1.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.