Figure 7.

Effects of fixed ratio schedules on responses reinforced with food pellets or photo-pulse trains. Fixed-ratio (FR) schedules reinforce lever pressing after a completion of a fixed number of presses counted from the last delivery of reinforcer. (A) Mice were trained to respond for food pellets over 27 sessions. ^*P < 0.005, significantly greater than the session-3 value. During sessions 28–41, pressing was reinforced with VTA photo-pulse trains. ⁺P < 0.05, significantly greater than the session-25 value; ^*1P < 0.005, significantly lower than the session-28 value; ^#P < 0.005, significantly lower than the session-25 value; ^*2P < 0.005, significantly lower than the session-35 value. (B) Mean lever-press latencies (s) as a function of lever-press count in FR schedules and reinforcers. Red arrowheads indicate the latencies to initiate leverpressing for photostimulation. Green and black arrows indicate the latencies to complete FR requirement for pellets and photostimulation, respectively. (C) Lever-press incidents during the first 10 min block during sessions 30–35. Notice that they are plotted on a log² scale (x-axis). Presses shown in blue dots occurring during the train duration (shown in yellow area) were not reinforced. Every lever-press occurring after each pulse train was reinforced for FR1 session, while for FR15 sessions, only the 15th lever-press (indicated by a maroon circle) occurring after each pulse train was reinforced. (D) Mean percent of CR-schedule values. ⁺P < 0.05, significantly greater than reinforcement rate, but not response rate. ^*P < 0.05, significantly different from both reinforcement and response rates.