Behavioral and pharmacological modification of attentional processes involved in peak-interval timing

Penney, Trevor B. (1993) Behavioral and pharmacological modification of attentional processes involved in peak-interval timing. Masters thesis, Memorial University of Newfoundland.

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Abstract

The involvement of attentional processes in interval timing was investigated, both behaviorally and pharmacologically, in rats trained on 10-sec and 30-sec peak-interval timing procedures. Three behavioral procedures were used: standard peak-interval, prior-entry, and prior-entry reversal. Brain levels of norepinephrine were manipulated using the α₂-agonist clonidine (0.025 mg/kg i.p.) and the α₂-antagonist idazoxan (2 mg/kg i.p.). In the prior-entry procedure a cue of the same modality as the signal to be timed preceded signal presentation, in the prior-entry reversal procedure the cue was of a different modality from the signal to be timed, and in the standard peak-interval procedure a cue was not presented. Relative to the peak-interval procedure the rats showed a horizontal rightward shift in their peak functions for the prior-entry reversal procedure. The α₂-agonist clonidine caused a rightward shift in peak functions for all behavioral procedures. The α₂-antagonist idazoxan also caused an unexpected horizontal rightward shift in peak functions. These horizontal shifts may be interpreted within the framework of an increase (rightward shift) in the latency to start the internal clock that is influenced both by the attentional demands of the task and the effective level of brain norepinephrine. The presentation of a cue directs the rat's attention toward a particular signal modality. If the cue directs attention to a different modality from the subsequently presented timing signal the rat takes longer to notice the signal. The effect of clonidine administration implicates the noradrenergic system in the attentional aspect of interval timing and also provides further support for the role of norepinephrine in general attentional processing.

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