Figure 1.
Time line representation of the contingency conditions.
A) During instrumental training (positive contingency), the lever becomes inactive for a variable interval (white rectangle) following each reward delivery. The first lever press after this interval triggers an immediate reward. No reward occurs in the absence of lever press (positive contingency). B) During omission training, rewards are delivered following a 20 s delay without lever press (black rectangle). A lever press during the delay resets the delay. Consecutive rewards are delivered at 20 s intervals in the absence of lever press activity (negative contingency). C) During yoked training, rewards are synchronized to the rewards of another rat trained in omission, regardless of the yoked rat's activity. Rewards may occur at any time with respect to lever presses (null contingency).
Figure 2.
Schematic representation of the extent of medial prefrontal cortex lesions.
a) minimal (black area) and maximal (gray area) mPFC lesions affected both the prelimbic and infralimbic parts of the medial prefrontal cortex. b) Photomicrograph of a typical mPFC lesion, illustrating cell loss (outlined by arrowheads). Cg1: Cingulate Cortex 1; PL: Prelimbic Cortex; IL: Infralimbic cortex.
Figure 3.
Adaptation to contingency changes.
a) Evolution of the rate of lever-pressing during the session of contingency change in blocks of 5 min. (mean + s.e.), according to lesion and condition b) final rate of response at test. Data are expressed as mean rates of responding. c) Evolution of the rate of entries into the empty magazine during the session of contingency change (mean + s.e.). d) Evolution of absolute number of rewards delivered during the session of contingency change in blocks of 5 min., according to lesion. Equal rewards are delivered in both conditions. Negative: negative contingency condition; Null: null contingency condition.
Figure 4.
Adaptation to contiguity changes in sham and mPFC-lesioned rats.
Upper panel: Sham, control rats. Lower panel: PFC: rats with lesions of the medial prefrontal cortex. Data points represent average lever-pressing rate across blocks of fixed delay (mean + s.e.). Delay between lever press and reward was increased by 0.5 s after each block of four rewards. Last data points show the recovery of responding with short delays during test on the next day. Grey area shows range of values observed in group no-delay across the whole session (computed over blocks of four rewards).