An interoceptive perspective of time perception in spinal cord injury

How implicit aspects of time perception can be related to interoception remains still relatively unexplored. Interoceptive states of the body would create our experience of duration. The physiological sense of time would thus be associated with the temporal integration of signals from the interoceptive system. Here, we investigate and relate changes in temporal expectation and interoception in cases of brain-body disconnection. 32 participants with spinal lesions (age range: 19-46 years) in the chronic injury phase were grouped according to level of spinal cord lesion, resulting in two groups: 16 patients with cervical lesion and 16 patients with thoracic lesion. Interoceptive accuracy was measured using a heartbeat tracking task consisting of four trials with varying interval durations of 25, 35, and 45 seconds played in a randomized order. Participants were instructed to internally count the heartbeats they perceived and report the number at the end of each trial. The actual number of heartbeats was measured using electrocardiographic signal. Physiological sense of time was measured using temporal expectation task (TT) and controlled by a color control task (CT). Briefly, a white circle (diameter:12.8degrees of visual angle) was shown on a gray background, with a gray annulus superimposed at an eccentricity of 6.4 - 9.6 degrees of visual angle, acting as an occluding band. In each trial, a purple ball moved from the center of the display toward the periphery in a fixed direction and at a constant speed. In the TT, participants were then asked whether the ball re-emerged earlier or later than expected. In the CT, participants assessed whether the ball reappeared more reddish or bluish than before. The Mann-Whitney U test indicated that the cervical lesion group shows lower interoceptive accuracy than the thoracic lesion group (p < 0.01). Therefore, higher deafferentation in SCI patients can decrease interoceptive accuracy. Interoceptive accuracy was also significantly correlated with the difficulty in temporal (0.69; p<0.002) but no control color task (p<0.17) as discriminated by temporal offsets. Our findings suggest that a reduced interoceptive accuracy play a role in the subjective perception of time in participants with higher SCI lesions. The predictive nature of our temporal task is closely related to the predictive feelings depending on bodily signals. Thus, a lower ability to detect and update the interoceptive inputs seems to reflect a distortion in perceiving pulses emitted by the “pacemaker” of the human internal clock. Alignment of interoceptive and temporal dimensions is consistently with the theoretical framework of the embodied models of timing.