Fos expression in the orbital prefrontal cortex after exposure to the fixed-interval peak procedure

Abstract

Highlights► The effect of timing behaviour on cortical and striatal Fos expression was examined. ► Rats trained on the peak procedure (FIPP) and a control schedule were compared. ► Fos expression in the orbital PFC was enhanced following exposure to the FIPP. ► Fos expression in the striatum did not differ between rats trained on the two tasks. ► The results suggest that the orbital PFC is involved in interval timing behaviour.

Fos expression in the prefrontal cortex and ventral striatum after exposure to a free-operant timing schedule

“…However, in contrast to the findings of Valencia-Torres et al [11] with retrospective timing tasks, a recent experiment by the same authors [15] found enhancement of Fos expression in the OPFC but not in the Acb following exposure to the fixed-interval peak procedure. These authors suggested that the difference between the results of their two studies could have reflected the use of an immediate timing task (the fixed-interval peak procedure) in the latter experiment, as opposed to the retrospective timing tasks used in the earlier one [15]. The present results cast doubt on this explanation because the FOPP, like the fixed-interval peak procedure, is regarded as an immediate timing schedule [1,2].…”

“…This is a potentially relevant difference between the FOPP and the yoked VI schedule used in the present experiment, since switching was not under temporal control in the yoked procedure. However, it seems unlikely that this difference could account for the different patterns of enhanced Fos expression seen with different types of timing task, because there is no obvious role for response suppression in performance on the retrospective timing schedules that were associated with enhanced Fos expression in the Acb [11], whereas there is evidence that learned suppression of responding occurs in the acquisition of accurate timing on the fixed-interval peak procedure [47], which was found not to be associated with enhanced Fos expression in this structure [15].…”

“…In contrast to the ventral striatum, the OPFC's role in interval timing appears not to be restricted to choice-based tasks, as enhanced Fos expression has been found in this area following exposure to the single-operandum fixed-interval peak procedure [15]. In the case of inter-temporal choice, the role of the OPFC is not restricted to delay discounting; lesions of this area may alter inter-temporal choice by reducing the incentive value of food reinforcers as well as by increasing the rate of delay discounting [58].…”

“…It was found that rats trained under these schedules showed enhanced Fos expression in the prefrontal cortex and ventral striatum, compared to rats trained under non-temporal (light-intensity) discriminaton tasks, indicating that these structures were activated during performance on the timing schedules. More recently, however, the same authors [15] found no significant enhancement of Fos expression in the ventral striatum following performance on an immediate timing schedule, the fixed-interval peak procedure [12,16].…”

“…One possibility is that the ventral striatum may play a significant role in temporal discrimination in retrospective timing schedules but have little involvement in temporal differentiation in immediate timing schedules [15]. However, there are a number of other important differences between the fixed-interval peak procedure and the retrospective timing tasks used by Valencia-Torres et al [11] apart their membership of different classes of timing schedule, and it is possible that these differences were more important than class membership in determining the differential involvement of the ventral striatum in different timing tasks.…”