Figure 6.

Self-administration affects SD responses but not LD responses. A, The blue line, essentially replicated from Figure 2C, is the population histogram (x-axis, time after delivery in seconds; y-axis, firing rate in spikes per second) for SD neurons in response to taste stimuli. The red line shows the population histogram for the same neurons during self-administration of the same tastes. Self-administration had little impact on activity before taste delivery and all but eliminated the taste responses themselves. The insets show an example of a single SD response to experimenter-administrated (left) and self-administrated (right) sucrose (x-axis, time in seconds; y-axis, firing rate in spikes per second). Time of taste delivery is marked with a vertical line. B, Similar population histograms (blue line, experimenter administration; red line, self-administration) for LD neurons. There was no difference in the taste responses themselves, but a significant anticipatory response preceded self-administration. The insets show representative example responses. See Results for statistical details. C, Population histogram for all LD (green line) and SD (orange line) units in the time period immediately surrounding tone onset before self-administration. x-axis, Time in milliseconds; y-axis, firing rate in spikes per second. SD units show fast, phasic response to tone peaking between 25 and 50 ms. LD units show more gradual, lower-amplitude tone responses.