Effects of Cocaine on Simple Reaction Times and Sensory Thresholds in Baboons

Abstract

The effects of chronic, daily administration of cocaine on auditory and visual reaction times and thresholds were studied in baboons. Single intramuscular injections of cocaine hydrochloride (0.1 to 5.6 mg/kg) were given once daily for periods of 10 to 25 days, and were followed immediately by psychophysical tests designed to assess cocaine's effects on simple reaction times as well as on auditory and visual threshold functions. Consistent reductions in reaction times were frequently observed over the cocaine dose range of 0.32 to 1.0 mg/kg; at higher doses, either decreases or increases in reaction times were observed, depending upon the animal. Lowered reaction times generally occurred immediately following the 1st day's cocaine injection, and continued through all subsequent days during the dose administration period, suggesting little development of tolerance or sensitivity to these reactiontime effects. Reaction-time decreases showed a U-shaped dose-effect function. The greatest decreases in reaction times occurred from 0.32 to 1.0 mg/kg, and produced an average reaction-time decrease of 10 to 12%. Concurrently measured auditory and visual thresholds showed no systematic changes as a function of cocaine dose. Pausing was observed during performance of the psychophysical tasks, with the length of total session pause times being directly related to cocaine dose.

Effects of cocaine and quinpirole on perceptual and motor functions in baboons

“…Figure 2 (bottom) shows the "peak" effect of each drug in either shortening reaction times for cocaine, or lengthening reaction times for quinpirole. As in previous studies (Hienz et al 1993(Hienz et al , 1994, cocaine lowered reaction times, an effect that occurred for two of three baboons in the mean data (upper graphs), and for all three baboons in the peak-effect data (lower graphs). For baboon BE, reaction times returned to baseline levels at higher doses.…”

Cocaine's effects on speech sound identification and reaction times in baboons

“…In the present study, cocaine did not produce the consistent decreases in reaction times reported previously (Hienz et al 1993(Hienz et al , 1994(Hienz et al , 1995. In a tone-threshold procedure, for example, acute administration of cocaine decreased reaction times by about 10-30 ms, when compared to the immediately preceding saline days (Hienz et al 1993).…”

“…Because cocaine does not affect behavioral thresholds for the detection of pure tones (Hienz et al 1993(Hienz et al , 1994), cocaine's effects on hearing may be focused moreso upon mechanisms involved in the processing of complex acoustic cues (i.e., "pitch location"), as opposed to auditory intensity cues (i.e., "loudness"). This suggestion is supported by the fact that the reductions in human event-related potentials following cocaine found by Herning et al (1985) and Robledo et al (1993) were observed in an "oddball" task in which humans were detecting infrequently-presented tones of differing frequencies.…”

“…In these studies the discriminability of speech sounds was measured by requiring subjects to release a lever when a different speech sound occurred within a series of pulses of a standard speech sound (Hienz et al 1995). Cocaine was found to decrease reaction times to the speech sounds, an effect demonstrated previously for the detection of simple tones (Hienz et al 1993(Hienz et al , 1994. Cocaine also reduced speech sound discriminability, however, an effect not seen with the detection of simple tones.…”

“…In the present study baboons were trained to release a lever only when certain vowel sounds occurred (i.e., to identify particular vowel sounds), as opposed to simply releasing a lever when a change occurred from one vowel sound to another (i.e., to discriminate a change in vowel sounds). Additionally, reaction times to the vowel stimuli were mea-121 sured to assess whether cocaine had similar effects to those previously reported (Hienz et al 1993(Hienz et al , 1994.…”