Figure 6.

Responses of PER neurons to optical stimulation in vitro and in vivo. a, In vitro responses were recorded from 29 cells. Expressing cells generated large amplitude depolarizations with short latencies; one-third of such cells, including this one, reliably generated action potentials. Light stimuli (8 ms pulses) are indicated by tick marks. b, Example of synaptic responses to 10 Hz optical stimulation from a cell that did not express ChR2. c, ChR2-expressing and non-ChR2-expressing neurons were identifiable by the latency of light-evoked changes in membrane potential or current. (d), When steady depolarizing current was used to activate low-frequency spiking in a non-ChR2-expressing neuron, trains of light pulses triggered mixed effects, including stimulus-entrained spikes (at 10 Hz), net inhibition of baseline spiking (at 30 Hz), and poststimulus hyperpolarization and spike suppression. e, After termination of trains of light stimuli (10–40 Hz) the membrane of most neurons hyperpolarized for durations of 0.5–10 s (depending on train length and frequency). f–h, In vivo activity during optical stimulation in PER. MUA 500 ms before and 500 ms during 11 Hz (f) and 30 Hz (g) stimulation in a virally transduced animal. h, Spiking activity during stimulation trials (20 trials per condition per rat) shows a frequency-dependent increase in activity during optogenetic stimulation in the transduced group (virus, n = 3), but not in the no virus group (n = 3). ***p < 0.001. Data are means + SEM.