6.3.2 Frontal, prefrontal, DLPFC
Imaging studies also reported changes in blood flow during temporal tasks in various cortical areas. In a PET study Belin et al. (2002) report activity in the right fronto-parietal network and prefrontal cortex during a 300- ms duration discrimination task. However, this study did not include a control task, and thus activation could be related to any form of processing. A second PET study in the visual modality reported activation in a number of cortical areas during a 700- ms duration discrimination task but no significant difference regarding an intensity discrimination task (Maquet et al. 1996). Onoe et al. (2001) showed activation of the dorsolateral prefrontal cortex in a monkey PET study. This study used a visual duration discrimination task in the range of 400 to 1500 ms. They report activation of the dorsolateral prefrontal cortex. Although there was no control task, they did report that bicuculline administration to the dorsolateral prefrontal cortex impaired duration discrimination more so than position discrimination.
Two fMRI studies revealed specific increases in BOLDsignal, and both reported activation of the right parietal and dorsolateral prefrontal cortex (Rao et al. 2001, Nenadic et al. 2003). In both these studies the increases were in comparison to a pitch discrimination task using stimuli in the 1-s range. As mentioned above, both these studies also revealed increased signal attributed to temporal processing in the basal ganglia but not in the cerebellum.
Several other brain regions have been identified as being active during time processing. In particular, the right dorsolateral prefrontal cortex (DLPFC) has been implicated in time discrimination studies (Rao et al., 2001; Macar et al., 2002; Lewis & Miall, 2003), although one lesion study suggests that the DLPFC is only important for longer durations (Mangels et al., 1998).