Neural substrates of time perception and impulsivity

Abstract

Several studies provide empirical evidence for the association between impulsivity and time perception. However, little is known about the neural substrates underlying this function. This investigation examined the influence of impulsivity on neural activation patterns during the encoding and reproduction of intervals with durations of 3, 9 and 18s using event-related functional magnetic resonance imaging (fMRI). Twenty-seven subjects participated in this study, including 15 high impulsive subjects that were classified based on their self-rating. FMRI activation during the duration reproduction task was correlated with measures of two self-report questionnaires related to the concept of impulsivity (Barratt Impulsiveness Scale, BIS; Zimbardo Time Perspective Inventory, ZTPI). Behaviorally, those individuals who under-reproduced temporal intervals also showed lower scores on the ZTPI future perspective subscale and higher scores on the BIS. FMRI activation revealed an accumulating pattern of neural activity peaking at the end of the 9- and 18-s intervals within right posterior insula. Activations of brain regions during the reproduction phase of the timing task, such as those related to motor execution as well as to the 'core control network' - encompassing the inferior frontal and medial frontal cortices, the anterior insula as well as the inferior parietal cortex - were significantly correlated with reproduced duration, as well as with BIS and ZTPI subscales. In particular, the greater activation in these regions the shorter were the reproduced intervals, the more impulsive was an individual and the less pronounced the future perspective. Activation in the core control network, thus, may form a biological marker for cognitive time management and for impulsiveness.

Figure 1

Significant Pearson correlations between the behavioral measure of duration reproduction (DKM parameter κ) and the scores of the questionnaire subscales ZTPI future perspective and BIS attention/cognition (r = 0.578, p < 0.004). The more subjects under-reproduce the temporal intervals (indicated by a larger κ) the less pronounced is the future time perspective and the more impulsiveness is reported (r = 0.645, p < 0.001).

Figure 2

Significant brain activation for the contrast reproduction phase versus encoding phase (p < 0.01, corrected) on one axial (z = 9) and two sagittal (x = −1, x = 36) planes separately for the three temporal intervals. Stronger activation in the reproduction phase is colored in yellow to red, stronger activation in the encoding phase is coded in blue.

Figure 3

Time activity curves during the encoding phases of the 9-s (right posterior insula, x = 32) and 18-s duration reproduction task (left and right posterior insula, x = −37, x = 34, respectively). The red line represents the end of the stimulus (= interval length plus 6 s delay of the hemodynamic function). On the left side activation plots across all 27 subjects are presented, on the right side time activity curves are plotted separately for the control subjects and the stimulant using individuals (the two subject groups with comparable group size).

Figure 4

Significant Pearson correlations between activation in regions of interest for the reproduction versus encoding contrast for the 9-s duration condition and behavioral variables. Activation in the right cerebellum (x = 12) correlated with DKM parameter κ of duration reproduction (r = 0.632, p < 0.001) and with the ZTPI future perspective score (r = −0.647, p < 0.0001). Activation in the left inferior parietal and post-central cortex (z = 47) correlated with DKM parameter κ (r = 0.551, p < 0.005).

Figure 5

Significant Pearson correlations between activation in regions of interest for the reproduction versus encoding contrast for the 18-s duration condition and behavioral variables. The BIS subscale motor impulsivity correlated with activation in the left and right medial frontal cortex (x = 12) (r = 0.521, p < 0.005) and with activation in the left anterior insula and inferior frontal cortex (x = −35) (r = 0.564, p < 0.002). DKM parameter κ correlated with activation in the left anterior insula and inferior frontal cortex (x = −35) (r = 0.562, p < 0.004). The ZTPI future perspective score correlated with activation in right inferior parietal cortex (z = 41) (r = −0.636, p < 0.0001).

Figure 6

Experimental Design. Trial events in the duration reproduction and the control reaction time task: First, subjects saw for 3 s four numbers on the screen. Then a continuous 1.2 Hz tone was presented for one of three durations (3-, 9-, 18-s). After the tone had stopped subjects had to press a button as fast as possible. In the duration reproduction task, after a short pause a continuous 2 Hz tone was presented that had to be stopped by pressing a button when the subjects thought that it has lasted as long as the first stimulus. After both the duration reproduction and the control task one single number appeared at the end of each trial on the screen and subjects had to decide by pressing one of two buttons whether it was one of the four numbers seen at the beginning of the trial.