If the interval between CS offset and US onset (trace interval) is prolonged (long-trace conditioning), conditioning is relatively weak in comparison with conditioning using brief (less than 1 min) trace intervals (short-trace conditioning).
While this exceptionally long interval in long-trace conditioning is the most striking feature of CTA, it is also one of the most perplexing in the sense that the maximum effective trace interval appears not only to differ from laboratory to laboratory, for example, 9 hr (Green & Rachlin, 1976), 12 hr (Smith & Roll, 1967), and 24 hr (Etscorn & Stephens, 1973), but also from study to study within laboratories.
An organism's metabolic rate seems to be a determining factor in the effectiveness of any given CS-US trace interval during taste-aversion conditioning.
The hypothesized reduced stress could have slowed their metabolic rate and, thus, extended the effective CS-US trace interval.
2006) that handling may reduce stress and thus slow down metabolic processing, the results of this study may also help explain reported differences in the maximum effective trace interval reported across laboratories where handling and CTA conditioning procedures have not been universally adopted.