IntroductionSeveral authors have reported the effects of lysergic acid diethylamide (LSD) on evoked potentials in primary sensory path-$ ways. The areas studied were retina,2 lateral geniculate body,8 and visual,9,14,18 auditory,14,18 and somatic cortex.14 There is incomplete agreement on the effects of LSD on visual and auditory cortex. Purpura14 found facilitation of visual cortical potentials with small doses, whereas Evarts8 found no significant effect with very large doses. Rovetta 18 used LSD topically and intravenously in small doses and reported an absence of effect onboth visual and auditory potentials. Large doses of the drug have been used infrequently.Numerous authors have described the effects of LSD on the electrocorticogram of several species of animals.* There is a great variation in the dose reported to produce a significant change in frequency and amplitude, as well as disagreement regarding the character of the changes.The current study was designed to investigate the effects of LSD on cortical visual, auditory, and somatic evoked potentials and also to correlate these observations with the electrocorticogram by recording simultane¬ ously with a cathode-ray oscilloscope (CRO) and an ink-writing oscillograph. Finally, an attempt was made to determine the minimal change in evoked potentials indica¬ tive of a drug effect.
MethodsA total of 89 cats were used in this study. Sensory evoked potentials were studied in 39 cats which received LSD one or more times. The data from 27 were analyzed in detail and appear in the text.Twenty animals were anesthetized with ether, then paralyzed with succinylcholine after the sur¬ gical procedures (Anectinized animals). Skin edges and pressure points were infiltrated with 0.5% procaine hydrochloride. Electrical recording was begun no less than two hours following cessa¬ tion of ether anesthesia. The initial paralyzing dose of succinylcholine chloride was 20 mg., fol¬ lowed by 20-mg. supplements as required to pre¬ vent spontaneous movement. The animals were ventilated with a Marshall respirator.Seven cats were anesthetized with pentobarbital sodium, 30 mg/kg., injected íntraperitoneally, and additional intravenous injections were given as required to produce moderately deep anesthesia. Most of the animals were artificially ventilated to obviate any possibility of hypoxia.Visual stimulation was produced by a small sealed bulb which delivered a narrow beam of light for 10 msec, to the eye contralateral to the record¬ ing electrode. Clicks from a loud-speaker mounted near the animal's head were used for auditory stimulation. Tactile stimulation was produced by a Goodman Industries "vibrator," mounted over a pad of the contralateral forefoot. All three sources of stimulation were operated by Tektromx pulse generators and wave-form generators with variable delays. In most experiments the three stimuli were delivered simultaneously at 2.5 second intervals.A bank of 10 electrodes was used for recording from the cortex. The electrodes were springmounted, cylindrical, ...
