This study investigates the effects of delay in punishment on addiction-like behavior towards sweet food in rats using a progressive shock strength (PSS) procedure. Delayed shock was less effective as a punisher, with higher breakpoints indicating greater tolerance. However, this effect varied among rats, revealing two groups: those sensitive to immediate and delayed punishment, and those resistant to immediate punishment who showed strong temporal discounting of delayed punishment. Shock-sensitive rats exhibited suppressed responding even in subsequent non-punishment sessions and displayed higher anxiety-like behavior, but not pain sensitivity differences. This suggests that the PSS procedure, with delay manipulation, identifies individuals with double vulnerability to addiction: low aversion sensitivity and excessive negative consequence discounting. Conversely, the shock-sensitive group may model humans vulnerable to opportunity loss due to excessive anxiety.
