No abstract

The roles that psychostimulant sensitization and tolerance play in temporal perception in the secondsto-minutes range were assessed in rats. Cocaine (20 mg/kg/day) was administered for 2 weeks either intermittently via daily injections (induces sensitization) or continuously via an osmotic minipump (induces tolerance). Interval timing was evaluated throughout administration and withdrawal. Injections of cocaine caused immediate, proportional, leftward shifts in peak times, indicating an increase in the speed of an internal clock. These shifts grew progressively larger with repeated administration, indicating that stimulant-induced increases in clock speed can be sensitized. Continuous cocaine administration produced no reliable effects. These results suggest that the mechanisms of sensitization may play a considerable role in drug-induced alterations of the perception of time.

No abstract

Cannabis is the most abused illegal substance in the United States. Alterations in brain function and motor behavior have been reported in chronic cannabis users, but the results have been variable. The current study aimed to determine whether chronic active cannabis use in humans may alter psychomotor function, brain activation, and hypothalamic-pituitary-axis (HPA) function in men and women. 30 cannabis users (16 men and 14 women, 18 to 45 years old) and 30 non-drug user controls (16 men and 14 women, 19 to 44 years old) were evaluated with neuropsychological tests designed to assess motor behavior and functional MRI (fMRI), using a 3 Tesla scanner, during a visually paced finger-sequencing task, cued by a flashing checkerboard (at 2 or 4 Hz). Salivary cortisol was measured to assess HPA function. Male, but not female, cannabis users had significantly slower performance on psychomotor speed tests. As a group, cannabis users had greater activation in BA 6 than controls, while controls had greater activation in the visual area BA 17 than cannabis users. Cannabis users also had higher salivary cortisol levels than controls (p = 0.002). Chronic active cannabis use is associated with slower and less efficient psychomotor function, especially in the male users, as indicated by a shift from regions involved with automated visually guided responses to more executive or attentional control areas. These brain activities may be attenuated by the higher cortisol levels in the cannabis users which in turn may lead to less efficient visual-motor function.