McGaughy J, Sarter M.
Behavioral vigilance in rats: task validation and effects of age, amphetamine, and benzodiazepine receptor ligands. Psychopharmacology (Berl). 1995;117 (3) :340-57.
AbstractAn operant task for the measurement of sustained attention or vigilance in rats was characterized. The task requires the animals to respond to the presentation of visual signals (presented for 25, 50, or 500 ms) by operating one lever ("hits") and to the absence of a signal by operating the opposite lever ("correct rejection"). Incorrect responses ("misses" and "false alarms", respectively) were not rewarded. Performance in this task is a function of signal length, i.e., the shorter the signals the higher the number of misses. An increase in "background noise" by flashing the chamber houselight (at 0.5 Hz) impaired the animals' ability to discriminate between signal and non-signal events. Also flashing the houselight augmented the vigilance decrement observed for shortest signals. An increase in the event-rate also resulted in a vigilance decrement. Finally, the inability of the animals to time signals was examined by testing the effects of an increase in event asynchrony. In a second experiment, the performance of differently aged rats (6- and 20 month-old male BNNia/F344 rats) was studied. Compared to young animals, 20-month-old rats showed a decrease in their ability to discriminate between shortest signals (25 ms) and non-signal events but did not differ in their ability to correctly reject non-signal trials. Administration of the benzodiazepine receptor (BZR) agonist chlordiazepoxide (CDP; 3, 5, 8 mg/kg) resulted in an impairment of the animals' ability to discriminate between signal and non-signal events and, similar to the effects of age, this effect was exclusively due to an increase in the number of misses. CDP generally produced potent effects while affecting the aged animals to a greater degree. BZR-ligands with weak or "selective" inverse agonist properties (ZK 93426; beta-CCtB) did not affect vigilance performance. The BZR partial inverse agonist RU 33965 (0.1, 0.5 mg/kg) dose-dependently impaired vigilance performance. The administration of amphetamine (0.4, 0.8 mg/kg) also impaired performance, but these impairments were possibly based on effects unrelated to attentional mechanisms. The finding that performance in this task revealed the interactions between the effects of age and BZR agonists on attentional abilities further supports the validity of measures of performance generated by this task.
McGaughy J, Sarter M.
Effects of chlordiazepoxide and scopolamine, but not aging, on the detection and identification of conditional visual stimuli. J Gerontol A Biol Sci Med Sci. 1995;50 (2) :B90-6.
AbstractOur previous studies revealed impairments in the ability of aged rats to detect brief, rarely and unpredictably occurring stimuli. The failure of these impairments to interact with the effects of benzodiazepine receptor (BZR) ligands was attributed to low demands on stimulus-related information processing. Thus, in the present experiment, rats of different ages were trained to detect visual stimuli that were flashing at 20 Hz, or were constantly illuminated, for 8, 3, or 5 sec. Additionally, selection of the correct lever to report detection required the processing of propositional rules (e.g., flashing-go left; constant-go right), i.e., the identification of the stimulus. All measures of performance varied with stimulus duration. Subsedative doses of the BZR agonist chlordiazepoxide (CDP; 3.13, 4.69 mg/kg), similar to the effects of the muscarinic antagonist scopolamine (.025, 0.1 mg/kg), impaired response accuracy, increased the number of errors of omission and decreased response latencies. Animals aged 28 months omitted more trials following the administration of CDP than 12-month-old rats. Age did not produce main effects and did not interact with the effects of the drugs on response accuracy. It is speculated that, as stimuli had to be presented for relatively long periods of time (to maintain above chance-level discrimination performance), demands on detection remained too low to replicate previously documented effects of age. The demonstration of interactions between the effects of age and of BZR-ligands appears to depend on combined demands for stimulus detection and identification.