A, Raw traces of three electrode recordings on a tetrode (the fourth
electrode here acts as amplifier reference), of neurons in the cortex of an
awake headfixed mouse (non ChR2-expressing) during 50 Hz LED operation (each
pulse was for 10ms at 500mA, indicated by blue bars). B, Average,
across trials and electrodes, of 33 traces obtained in each of the saline
(left) and in vivo (middle) conditions,
displayed as mean (solid lines) ± standard deviation between electrodes
(shaded area). Right, average of the 33 traces obtained in
vivo, after each trace was preprocessed by subtracting off the
saline-characterized artifact recorded on the same electrode (and averaged
across all trials for that electrode, e.g. 11 trials). C, Schematic
of the “spatially averaged” multichannel coaxial cable utilized to
deliver power to LEDs while minimizing capacitive and inductive coupling to
recording electrodes.