PROLONGED EFFECTS OF LSD ON EEG RECORDS DURING DISCRIMINATIVE PERFORMANCE IN CAT: EVALUATION BY COMPUTER ANALYSIS,

The effects of LSD were studied in relation to changes induced in computed averages of epochs of EEG records during a discriminative task performance in a series of six cats repeatedly exposed to LSD over a period of many months. Computed averages were prepared from daily training tests of 20 and 40 trials. LSD 75 microgramskg was given in single doses by intraperitoneal injection at intervals of not less than 3 weeks. The findings indicate persistent electrophysiological effects of LSD beyond the period of acute drug action. However, these changes ran a shorter course than the tolerance to LSD exhibited by man and animals. They showed a differential distribution in different brain regions, with maximal changes in the hippocampus, and smaller effects in the entorhinal cortex and the rostral midbrain reticular formation. Evidence is presented of highly focal differences in late responses within the hippocampus. Differential susceptibility of hippocampal tissue is discussed in relation to a similar sensitivity to the acute effects of both LSD and psychotomimetic cyclohexamines, and to the pattern of propagation of hippocampal after-discharges. Author