Dennis McFarland

Dorsal hippocampal lesions: Effects of preconditioning CS exposure on flavor aversion

A learned aversion to a walnut solution paired with lithium carbonate was examined in rats with lesions of the dorsal hippocampus. While preconditioning CS exposure retarded conditioning in controls, this same manipulation did not affect suppression to the CS in animals with lesions and, in fact, resulted in greater stimulus control in these subjects. These results support the view that the hippocampus is involved in the modulation of attention.

Marijuana and memory impairment: effect on free recall and recognition memory.

The effect of marijuana on memory was evaluated by presenting two groups of 17 male volunteers with lists of repeated or nonrepeated words following administration of a single marijuana cigarette containing 14 mg delta9-THC. An immediate free recall, final free recall and recognition memory test followed. Results indicated that marijuana significantly decreased immediate and final free recall but only slightly influenced recognition memory. Rate of acquisition on the repeated lists was the same for both groups. Long term retention of encoded information was not influenced by marijuana. The shape of the serial position curves departed slightly from those reported by other investigators in that some effects of the drug on the recency portion of the curve were noted. Both internal and external intrusions were elevated under marijuana.

Lead-Induced Hyperactivity. Chronic Exposure during the Neonatal Period in the Rat

The effects of chronic exposure to low levels of lead via maternal milk during the neonatal period in the rat were evaluated by means of several activity measures, spontaneous alternation in the Y-maze, and weight data. Animals reared at the highest concentrations of lead showed retarded body growth. Lead-treated rats were found to be more active in the Y-maze and in the tilt-box, but not in the running wheel. Lead-treated rats showed lowered spontaneous alternation and increased squealing; results were dependent upon the concentration of lead on which the animals were reared. Activity and alternation data provide suggestive evidence of lead-induced damage of the hippocampus, a structure which undergoes much of its development during the stage in which the lead was administered. Behavioral parallels found between lead poisoning and childhood hyperactivity were discussed with respect to the utility of chronic low level lead administration as an animal model of minimal brain dysfunction hyperactivity.

Effects of Neonatal Lead Exposure on Apomorphine-induced Aggression and Stereotypy in the Rat

Rats were exposed to lead via the maternal milk. At 90 days of age, lead-exposed pairs and control pairs were tested for aggression induced by 5.0 mg/kg apomorphine. The large increase in aggression in response to apomorphine seen in controls was markedly attenuated in lead-treated subjects. In contrast, apomorphine-induced stereotypy was not affected. These results provide a further demonstration of persistent behavioral abnormalities resulting from early exposure to lead at levels which do not affect weight gain or mortality.

Marijuana: effects on storage and retrieval of prose material.

In a two phase design, an attempt was made to differentiate the effect of marijuana on the storage and retrieval of prose material. In the first phase, 40 male subjects were administered a single 500 mg marijuana cigarette containing 2.1% Δ9-TCH or a placebo cigarette. Fifteen minutes after smoking, they listened to and at the same time read a narrative passage of approximately 200 words in length. Subsequently, an immediate free recall test was given in which subjects were required to write down as much of the story as they could remember. The second phase was conducted 24 h later. Marijuana and placebo subjects were randomly subdivided into four groups with half of the subjects participating in the same drug condition as occurred on day one while the others switched drug state. Fifteen minutes after smoking, all subjects recalled the passage pressented on day one and then were given 24 questions concerning facts and events in the story which could be answered in a few words. These questions served as retrieval cues. Following this, a new passage was presented in the same manner as occurred on day one. After an immediate free recall test, another cued recall test was administered.Results indicated that marijuana reduced immediate recall under both cued and uncued conditions in comparison to placebo. No relative cued recall advantage was found in the marijuana groups for the old or new story and marijuana produced only a moderate decrement in recall of the old story on day two. However, marijuana given in the second phase significantly reduced memory for items recalled in the initial phase irrespective of drug or cueing condition in phase one, suggesting that retrieval was also affected. Some decrement in recall of the new story did occur as a function of drug state change in group M-P. This effect was related to the serial position of input items. Serial position did not interact with drug state under any other recall condition.

Marijuana and memory impairment: the effect of retrieval cues on free recall☆

In an attempt to ascertain the effect of retrieval cues on recall deficits which occur following intoxication with marijuana, 40 male volunteers were presented with word lists following the smoking of a single one gram marijuana (0.94% delta 9 -THC) or placebo cigarette and then were required to recall these words immediately after presentation. Recall occurred under a condition in which cues representative of to-be-remembered words were present or in an uncued condition. Results indicated that recall was depressed following marijuana administration under both cued and uncued conditions with cues being only mildly effective in reversing the recall deficit. There was no increase in the number of internal intrusions under marijuana, but the number of external intrusions was significantly elevated under the cued conditions.

Marijuana: dose-response effects on pulse rate, subjective estimates of potency, pleasantness, and recognition memory.

34 experienced marijuana users were divided into four equated groups of eight subjects each based on recognition memory test performance. One week later each group was retested following administration of marijuana containing 0, 5, 10 or 15 mg delta9-tetrahydrocannabinol. A dose-related effect of marijuana on pulse rate and subjective measures of potency and pleasantness occurred. Ratings of potency and changes in pulse rate were highly correlated, but this relationship did not hold within a given dosage group as determined by partial correlations. No effect of marijuana on the distribution of hit and false alarm rates or confidence ratings during the recognition memory test was noted.

Marijuana: Effects on free recall and subjective organization of pictures and words

The free recall of pictures and words was compared following the administration of marijuana or placebo in a multitrial free recall task. Since pictures are thought to be registered in both visual and verbal memory stores with this encoding being mediated by some form of mental imagery, it was predicted that marijuana would produce a greater deficit in word recall in comparison to picture recall because the drug has been reported to facilitate imagery. A trend in the opposite direction followed intoxication; picture recall was inferior to word recall in the later stages of acquisition. Although overall recall was inferior under marijuana, no differences were found between the treatment conditions in subjective organization as determined by a variety of clustering measures. Recall performance following marijuana intoxication was positively related to level of recall performance in the placebo condition.

TRANSFER OF INSTRUCTION IN INTRODUCTORY PSYCHOLOGY

This study examined the extent to which for 2 classes (ns = 72, 68) there would be positive transfer from instruction in introductory psychology to a reading task involving related psychological materials. Positive transfer occurred primarily for students with lower midterm exam scores. Transfer to the reading task was mainly restricted to materials of a non-advanced level of difficulty.