Formalin-induced pain prolongs sub- to supra-second time estimation in rats

Area of Science:

• Neuroscience
• Behavioral Science
• Chronobiology

Background:

• Pain perception significantly influences temporal estimation, a complex interplay of psychological and physiological factors.
• The precise time intervals most susceptible to pain's influence on time perception remain incompletely understood.

Purpose of the Study:

• To investigate the impact of acute inflammatory pain on time perception in rats across sub- to supra-second (0.6-2.4s) and supra-second (2-8s) temporal ranges.
• To determine if pain affects subjective duration and temporal sensitivity within these specific timeframes.

Main Methods:

• Rats were subjected to plantar formalin injection to induce acute inflammatory pain.
• A temporal bisection task was employed to assess time perception over five consecutive days: baseline, immediately post-injection, and three days thereafter.
• Key metrics analyzed included the point of subjective equality (PSE) for subjective duration and the Weber fraction for temporal sensitivity.

Main Results:

• Immediately following formalin injection, the sub- to supra-second range (0.6-2.4s) showed a significantly lower PSE in the formalin group, indicating a prolonged subjective duration compared to the saline group (p=0.049).
• A trend of lengthened time perception was observed in the 0.6-2.4s range on post-injection days 2 and 3.
• No significant effects of formalin-induced pain on PSE or Weber fraction were found in the supra-second range (2-8s).

Conclusions:

• Pain exerts a more pronounced effect on temporal perception within the sub- to supra-second range.
• This heightened influence of pain on time perception is attenuated as the estimated duration increases, even in rodent models.