Wittmann, M., Simmons, A. N., Aron, J. L., & Paulus, M. P. (2010). Accumulation of neural activity in the posterior insula encodes the passage of time. Neuropsychologia, 48(10), 3110-3120.
- A number of studies have examined the perception of time with durations ranging from milliseconds to a few seconds, however the neural basis of these processes are still poorly understood and the neural substrates underlying the perception of multiple-second intervals are unknown. Here we present evidence of neural systems activity in circumscribed areas of the human brain involved in the encoding of intervals with durations of 9 and 18 s in a temporal reproduction task using event-related functional magnetic resonance imaging (fMRI). During the encoding there was greater activation in more posterior parts of the medial frontal and insular cortex whereas the reproduction phase involved more anterior parts of these brain structures. Intriguingly, activation curves over time show an accumulating pattern of neural activity, which peaks at the end of the interval within bilateral posterior insula and superior temporal cortex when individuals are presented with 9- and 18-s tone intervals. This is consistent with an accumulator-type activity, which encodes duration in the multiple seconds range. Given the close connection between the dorsal posterior insula and ascending internal body signals, we suggest that the accumulation of physiological changes in body states constitutes our experience of time. This is the first time that an accumulation function in the posterior insula is detected that might be correlated with the encoding of time intervals.
- This study examined the neural substrates that underlie the processing of time in the seconds domain. In particular, activation was observed in brain regions related to the encoding and reproduction of time intervals which have been implicated as core neural substrates of time-keeping systems, notably the supplementary motor area, the striatum, cerebellum, the right frontal lobe, the inferior parietal gyrus, the posterior temporal cortex as well as the insula (Lewis & Miall, 2003a, 2003b; Rubia & Smith, 2004; Wiener et al., 2010; Wittmann, 1999).[Click here and here for prior posts related to possible underlying brain locations/structures of "brain clock"]
- It seems as if the more posterior regions of the brain are instrumental in coding the duration of a presented interval and that many distributed (more anterior) regions of the brain are involved in keeping a representation of that interval for further processing (pressing the button at the right moment in time).
- The main finding of this study is that the BOLD fMRI results support an integrator-like neuronal function over time involved in the representation of duration in humans. The pattern of activation for the 3-s interval differed from that observed for the longer intervals. This suggests that the perception of duration for shorter durations(up to 3 s) might rely on different brain areas (recruiting sensorimotor systems of the brain) than the estimation of duration in the multiple-second range (Fraisse, 1984; Morillon et al., 2009; Pöppel, 1997, 2009; Wittmann et al., 2007). The separation of the shorter from the two longer time intervals is also suggested by the high correlation in subjects’ behavioral performance between the 9- and 18-s temporal reproduction intervals and the lack of correlation between the 3 s and the two longer durations.
- The finding that neural activity appears to accumulate in the posterior insula provides key evidence for piecing together a theory in which interoception might function as the prime source for our subjective experience of time. Our findings together with existing studies on the influence of emotions on the experience of time (Droit-Volet & Gil, 2009; Noulhiane, Mella, Samson, Ragot, & Pouthas, 2007; Wittmann, Vollmer, Schweiger, & Hiddemann, 2006) may lead the way for a comprehensive understanding of temporal processing in the brain. Our results concerning climbing neural activity in circumscribed regions of the brain and similar more unspecific findings of climbing activity as found in human EEG with shorter intervals are compatible with the pacemaker-accumulator model of time perception (Pfeuty et al., 2005). In line with this conceptualization is it is conceivable that the number and rate of body signals accumulated in the posterior insula over a given time span creates our sense of duration. Although this conclusion is speculative, we propose that the posterior insula, which processes physiological changes in body states, is strongly involved in our experience of time.