(
a) Scatter plot obtained from for all MLI recordings showing the cross-correlation between MLI activity and either eyelid position or velocity at three different interstimulus intervals (ISIs). Very few MLIs correlated more highly with velocity than position. All correlations above the dotted horizontal line (correlation of 0.43) were classified as putative eyelid PC-MLIs. (
b–d) Eyelid movements and the activity of a PC and a putative PC-MLI simultaneously measured at different ISIs. Left – Eyelid movement during a conditioning session. Blue area indicates the duration of the tone stimulus (conditioned stimulus) and upward deflection is the conditioned response of the eyelid. Center – Peri-stimulus time histograms and raster plots of eyelid PC activity measured during the session shown at left. Right – Peri-stimulus time histograms and raster plots of putative eyelid PC-MLI activity measured during the same session. These are the same data shown in
Figure 9a and b and are shown here to illustrate how trial-to-trial variability in conditioned response timing can obscure the appearance of the tight relationship between eyelid MLIs and PCs; this relationship becomes clear once the data are sorted by time of onset of the conditioned response, as in
Figure 9a and b.