Title: Inputs from single neurons in the visual cortex affect spike-timing of locally connected neurons but do not modulate their firing rate and sensory tuning curves
Authors: *H. TANAKA, Y. ASADA, R. MIZOGUCHI, I. OHZAWA, I. FUJITA, H. TAMURA;
Osaka Univ., Toyonaka, Japan
Abstract: Nearby cells in the sensory cortex are often functionally connected. Although slice studies showed that inputs from a nearby single cell evoke post-synaptic potentials up to 2 mV, it is not clear how such inputs affect spiking activities of post-synaptic neurons and their tuning properties to sensory stimuli. We conducted the present study to address this question. Using juxtacellular recording and current stimulation with single glass electrodes we evoked and recorded spikes from single cells (juxta-cells) in the cat visual cortex (area 17). Simultaneously we recorded activities of neighboring cells (nearby-cells) using silicon multi-site electrodes. Current (0.5~3nA) was repetitively applied (0.5 sec ON and 0.5 sec OFF) while blank screen or sinusoidal gratings of various orientations were presented to the eyes. Cross-correlograms (CCGs) were compiled using spikes from pairs of juxta-cells and nearby-cells during the current stimulation period. Of 287 pairs tested for blank stimuli, 67 pairs (23%) showed delayed peaks in the CCGs, showing that probability of the nearby-cells to produce a spike increased shortly after a spike of the juxta-cells. However, while firing rate of the juxta-cells increased by current application, that of the nearby-cells, including those with delayed peaks in their CCGs, did not change. Similar results were obtained in the presence of sinusoidal grating. These results show that inputs from single cells affect spike timing of post-synaptic cells but cannot change their firing rate and orientation tuning curves. This suggests that information contained in accurate spike timing of cortical neurons can be modulated by inputs from just single pre-synaptic neurons, while that in spike rate may require convergent inputs from multiple pre-synaptic neurons for its modulation.
Disclosures: H. Tanaka, None; Y. Asada, None; R. Mizoguchi, None; I. Ohzawa,
None; I. Fujita, None; H. Tamura, None.