Direct and Indirect Timing Functions in Unilateral Hemispheric Lesions

Introduction: The neural substrates of temporal processing are not still fully known. The majority of interval timing studies have dealt with this subject in the context of “Explicit timing” (computing the time intervals explicitly). The hypothesis “Implicit timing” (implicitly using temporal processing to improve function) has also proposed. This lesion study addressed explicit and implicit timing paradigms simultaneously using identical experimental tasks. Methods: In this case-control study, 15 patients with Right Hemisphere Damage (RHD) and 15 patients with Left Hemisphere Damage (LHD) and 15 age-matched normal subjects were included. Participants performed a temporal reproduction task (assessing explicit timing) and a temporal prediction task (assessing implicit timing) in two sub- and supra-second intervals. Results: Our results showed that RHD can lead to significantly lower accuracy in the temporal reproduction task in sub-second (p=0.005) and supra-second (p=0.001) intervals, compared with the normal subjects. Also, LHD led to perturbation in temporal prediction task by an increase in reaction time (lower accuracy) in sub- (p=0.011) and supra-second (p=0.006) time intervals than the normal subjects.  Conclusion: Overall, our findings suggested that there is a right hemispheric bias in the neural substrate of explicit timing, in both sub- and supra-second intervals. Furthermore, for the first time in a lesion study, we showed the evidence of left-hemispheric bias in neural substrates of implicit timing.