One thing that might be interesting is something our subjective sense of time (I've had that on the brain since I recently wrote on Augustine on the subject, and have been wondering what the current research suggests on the specifics of how our sense of time works).Like reasoning, there is a whole hell of a lot of research on time perception, and I've tossed around several ideas about how to approach the topic in a blog post. There are so many issues, and almost all of them are very interesting, that I am still not exactly sure what I want to do. More than likely, it's going to take a series of posts, but I've got to start somewhere, so I'll start with the neuroscience. In a subsequent post, I'll talk about different factors that affect the cognitive perception of time. God only knows what comes after that.
The neuroscience of time perception has recently become a hot area of study. So far, several brain regions have been found to be involved in different aspects of time perception. The most widely studied are the cerebellum and the basal ganglia, but other non-cortical regions, such as the inferior parietal lobes, and cortical regions such as the inferior prefontal cortex, dorsolateral prefrontal cortex, anterior cingulate gyrus, and the supplementary motor area also play roles. I'll take each of these regions in order, and in no particular order.
The cerebellum is best known for its role in movement, but since movements often involve intricate timing, within very short intervals, it's not surprising that the cerebellum also plays a role in time perception. We know this because lesions to parts of the cerebellum can wreak havoc with patients' ability to perform motor tasks that require short-interval timing1, as well as with their ability to estimate very short time intervals2 as well as slightly longer intervals (in seconds)3. Imaging studies have also shown cerebellum activity during tasks that require the perception of intervals that are less than 1 second4. It's likely that the cerebellum is divided into areas that control movement, and areas that are specifically for temporal processing, and imaging research has suggested that medial regions of the cerebellum control movement, while lateral regions and the cerebellar vermis process temporal information5.
Like the cerebellum, the basal ganglia is an important part of the brain's motor system. Also like the cerebellum, it has been shown to be closely involved in time perception. Different areas of the basal ganglia, including the supralenticular white matter, right and left putamen, globus palidum, and caudate nucleus have been shown to be active during temporal tasks including sensorimotor synchronization tasks, time discrimination tasks, and rhythm discrimination tasks of different time scales (ranging from milliseconds to seconds)6.
Supplementary Motor Area
Another motor area associated with temporal processing is the Supplementory Motor Area, or SMA. Lesion and imaging studies have shown this region to be important for motor timing at short and long intervals, as well as non-motor temporal perception with longer (seconds, minutes) intervals7.
Anterior Cingulate Gyrus
Neuroscientific research has consistently shown activation in the anterior cinculate gyrus (ACG) during motor tasks (mostly tasks with intervals on the order of seconds) that involve some sort of temporal processing, including most of those during which the basal ganglia and SMA are active as well. However, the consensus seems to be that instead of being involved in temporal processing directly, the ACG is instead involved in "motor attention functions," where it controls the allocation of attention during motor tasks, as well as the switching of attention8.
The regions (cerebellum, basal ganglia, SMA, and ACG) discussed so far hav traditionally been associated with movement, but have more recently been shown to be involved in temporal processing, especially in motor tasks. Each of these regions has also been shown to be involved in non-motor, cognitive tasks that involve temporal perception. This has led some to believe that the motor system is integral for what is sometimes called "automatic timing" (see here).What is interesting about all of this is that there seems to be a close association between movement and event timing. This implies that embodiment is important for time perception, and may mean that different body plans/sizes yield differences in the processing of temporal information. For instance, one psychologist (sorry, no paper available) has argued that the dynamics of an organism's gait may influence its perception of duration, and in particular its perception of a single moment. This would have interesting implications for James' concept of the specious present.
Click for larger view. From Rubia & Smith (2004), p. 331.
Fig. 1. Generic brain activation map of 8 right-handed male adults (aged 22 to 40 years; mean age 29 years) while performing a sensorimotor synchronisation task of 5 s, after contrasted with a sensorimotor synchronisation task (finger tapping) of 0.6 s in a block design fMRI study. Subjects were instructed to time their motor response to the regular appearance of the visual stimuli on the computer screen. For good sensorimotor timing subjects had to monitor the time interval elapsed since the presentation of the last visual stimulus. The long event rate condition imposes a higher load on time estimation and motor timing compared to the short event rate condition. Areas shown are brain regions that showed significant greater activation during the synchronisation task of 5 s in contrast to finger tapping, presumably reflecting both time estimation and motor timing (corrected P<0.003).
Prefrontal regions in both hemispheres have been associated with temporal processing of time scales up to minutes9. Two regions of the prefrontal cortex, the dorsolateral and inferior prefrontal cortices, seem to be involved in different types of time-perception tasks. The dorsolateral appears to be active in both motor and non-motor tasks, while the inferior prefrontal cortex is largely associated with non-motor tasks. Rubia and Smith provide one explanation for the role of the prefrontal cortex in temporal estimation and motor timing tasks of longer intervals, writing:
Regions of the prefrontal cortex [may] have the function of a hypothetical accumulator within an internal clock model, which is required only with durations of more than several seconds. Indeed, prefrontal activation in timing tasks of durations of several seconds has often been related to other underlying functions besides pure timing processes, such as sustained attention to the time interval or working memory components. (p.332)This view is confirmed by activity in the dorsolateral prefrontal cortex, an area associated with working memory and attention, during time perception. Other evidence comes from animal studies. Rubia and Smith write:
Single cell recordings in prefrontal cortex in monkeys have been shown to be in line with this hypothesis. In an attempt to disentangle timing and working memory processes in delayed response tasks, Fuster (1973) found that different neurons in the DLPFC of monkeys were cue-coupled, presumably related to the mnemonic content, while others were showing sustained activity, presumably reflecting temporal processes. (p. 333)Thus, it appears that one of the primary roles of the prefrontal cortex in temporal processing is the interaction of working memory, attention, and timing. This close association between these three things will become important, in the next post, when we begin to look at the role of things like attention in the subjective perception of time.So, stay tuned until next time, when I'll get all cognitive on time.
1 Ivry, R.B., Keele, S.W., & Diener, H.C.(1988). Dissociation of the lateral and medial cerebellum in movement timing and movement execution. Experimental Brain Research, 73, 167–180, 1988.
2 Ivry R. B. & Diener H. C .(1991). Impaired velocity perception in patients with lesions of the cerebellum. Journal of Cognitive Neuroscience, 3, 355-366.
3Casini L., Ivry R.(1999). Effects of divided attention on temporal processing in patients with lesions of the cerebellum or frontal lobe. Neuropsychologia, 13, 10-21.
4 Coull, J.T., Frith, C.D., Buchel, C., & Nobre, A.C. (2000). Orienting attention in time: behavioural and neuroanatomical distinction between exogenous and endogenous shifts. Neuropsychologia, 38, 808–819; & Coull, J.T. and Nobre, A.C.(1998). Where and when to pay attention: the neural systems for directing attention to spatial locations and to time intervals as revealed by both PET and fMRI. Journal of Neuroscience, 18, 7426–7435, 1998.
5 Rubia, K. & Smith, A. (2004). The neural correlates of cognitive time management: a review. Acta Neurobiologica, 64, 329-340.
6 Riecker, A., Wildgruber, D., Mathiak, K., Grodd, W., Ackermann, H. (2003). Parametric analysis of rate-dependent hemodynamic response functions of cortical and subcortical brain structures during auditorily cued finger tapping: a fMRI study. Neuroimage, 18, 731-739; Rubia & Smith (2004).
7 Rubia & Smith (2004).
8Rubia, R., Overmeyer, S., Taylor, E., Brammer, M., Williams, S., Simmons, A., Andrew, C., Bullmore, E. (1998). Prefrontal involvement in ‘temporal bridging’ and timing movement. Neuropsychologia, 36, 1283-1293.
9 Casini, L., Ivry, R. (1999). Effects of divided attention on temporal processing in patients with lesions of the cerebellum or frontal lobe. Neuropsychologia, 13, 10-21.