Fig. 1

Intracollicular optogenetic stimulation associated with electrophysiological recordings of IC and MLR neurons activity. (A) Experiment timeline and experimental protocol summary. (B) Left—Illustrative representation of the IC and MLR neuronal activity recordings with 4 electrodes associated with IC optogenetic stimulation via a single optical fiber in the middle of the electrode array. Center—IC transfected neurons expressing the fluorescent marker after ChR2 AAVs injection. Right—Example of electrodes and optical fiber bilateral placements on IC. (C) Left—Example of two extracellular signals recorded simultaneously from two electrodes, Middle—averaged spike shapes detected from the adjacent raw signals. Right—Raster plots of spike activity during 15 repetitions of 2 s with 30 Hz light stimulation (2 ms pulses). Red and blue lines represent the stimulation onset and offset, respectively. (D) Total number of recorded neurons. From 209 cells recorded while the optical fiber was positioned in the IC, 45 were localized in the IC and 43 were from MLR. (E) Electrophysiological response of IC and MLR neurons during IC optogenetic stimulation. A total of 40 IC cells responded with a significantly increased spike rate during light application, whereas diminished activity was observed in 5 IC cells. In one IC cell, this inhibition reached significance (p < 0.05; T-test). In MLR, IC stimulation-induced inhibition was significant in 9 cells, and below significance in further 5 cells. A significant increase of spike rate during the 30 Hz stimulation was observed in 19 cells, and below significance in further 10 cells; (F) Top—Example for a neuron’s pulse response relative to pulse onset (at t = 0). This example shows an IC-recorded neuron with a peak onset latency of 3.23 ms. Bottom—Response latency for IC and MLR neurons. The IC neuron responded with a significantly shorter latency (2.32 ms) than MLR cells (4.74 ms, P < 0.005, T-test). Box plots indicate the median and quartiles. Individual subjects’ data are represented by circles. *P < 0.005 after IC and MLR comparison.