Toluene and temporal discrimination in rats: effects on accuracy, discriminability, and time estimation

Thirty-five rats acquired a temporal discrimination of seven signal durations in an operant chamber with two levers. If a 2-s or an 8-s tone signal was presented, rats were required to press one lever ("short" response) or the other lever ("long" response) to be reinforced, respectively. Neither response was reinforced when five intermediate signals were presented. Percentages of a long response in each of the seven signals were calculated and the psychophysical function between signal durations and long response percentages was obtained. Intraperitoneal injections of 50 mg/kg and 100 mg/kg toluene steepened a gradient of the psychophysical function and elevated correct responses in 2-s and 8-s signals. The function showed lower difference limen and Weber fraction. Accuracy and discriminability of temporal discrimination were enhanced. However, 400 mg/kg and 600 mg/kg toluene resulted in a shallower gradient and reduced correct responses. Higher difference limen and Weber fraction were also obtained. Accuracy and discriminability deteriorated and, in particular, behavioral depression was observed for 600 mg/kg toluene. The point of indifference was changed and dose-related overestimation or underestimation of time were suggested to occur. Blood toluene levels were reported to be 11-18 microg/ml for 50-100 mg/kg toluene and 47-73 microg/ml for 400-600 mg/kg toluene. It is speculated that temporal discrimination was sharpened by 10-20 microg/ml toluene in blood and disrupted by 50-70 microg/ml toluene in blood.