Joseph D. Allen

Functional dissociation of the prefrontal cortex and the hippocampus in timing behavior

Using the peak procedure, rats with aspiration lesions to the medial prefrontal cortex (PFC) or the hippocampus were tested for the acquisition of timing behavior and temporal memory. After surgery, rats were 1st trained to discriminate a 40-s interval and then tested for temporal memory with gap trials. Results indicated that lesions to the medial PFC disrupted the acquisition of timing behavior. Medial PFC animals needed significantly more trials to reach criterion, and their temporal discrimination function was less uniform and steep, indicating a general deficit in timing ability. In hippocampal rats, the ability to estimate the duration of the discriminative stimulus was unaffected by the lesion. It was concluded that the hippocampus is not necessary for the acquisition of timing behavior in this task. Gap trials failed to produce a deficit in the memory for temporal events for either lesion. Thus, it was further concluded that neither the medial PFC nor the hippocampus is necessary for the memory of temporal events.

Topographic differences in CNV amplitude reflect different preparatory processes.

Topographic differences in Contingent Negative Variation (CNV) were recorded while people were preparing for cognitive versus motor tasks in an S1-S2 paradigm. CNV had a frontal distribution when people prepared to encode words into long-term memory, whereas CNV was more centrally distributed when the tasks were predominantly motoric. These topographic differences appeared to be related to the type of task rather than the amount of information extracted from the S2, because a direct manipulation of the level of S2 processing had little effect on CNV amplitude. The topographic differences in CNV suggest that preparation for motor activity is a different psychological process from preparation for stimulus processing and that these two processes are subserved by different neural structures. This experiment also demonstrated that a recognition memory paradigm can be useful in the investigation of the psychological correlates of CNV.

Effect of lesions in the amygdala on behavioral contrast

Abstract Amygdalectomy in rats prevented the occurrence of behavioral contrast. After the animals were trained to lever press on a multiple schedule where responses were reinforced on the average of once per min in two alternating components, one component of the multiple schedule was switched to extinction while reinforcement in the other component remained unaltered. Response rates during the unaltered component increased significantly over pre-change rates in that component (i.e., behavioral contrast) for the controls, but remained substantially unchanged for animals with amygdala lesions. Response rates were clearly differentiated in the reinforced and nonreinforced components for both groups, signifying that discrimination between the two reinforcement contingencies was not impaired in the amygdala group. The lack of contrast in the latter group was attributed to a reduction in extinction-induced emotionality resulting from the lesion.

Effects of selective dopamine D1- and D2-agonists and antagonists on timing performance in rats

Dopamine (DA) D1- and D2-agonists and antagonists were administered at fixed doses to assess putative dopaminergic involvement in timing behavior in rats performing under a peak-interval schedule. Significant shifts in response distributions to the left (consistent with the overestimation of the passage of time) were observed after treatment with the D1- and D2-agonists SKF 38393 and quinpirole, respectively. Both DA antagonists, eticlopride (D2) and SCH 23390 (D1), shifted the response distributions to the right (consistent with the underestimation of the passage of time), but neither drug produced statistically significant shifts. Based on percent shift in peak time from predrug baseline values, no significant differences were detected between agents as a function of their reported affinities for the D1- or D2-receptors. Results indicate the need for a systematic evaluation of each drug at various doses and a more detailed examination of the use of temporal schedules in predicting the efficacy of psychotherapeutic agents.

Performance correlates of social behavior and organization: Social rank and omission of reinforcement in rhesus monkeys (M. mulatta)

The performance of 22 adult male rhesus monkeys on a Fixed Interval 1-min reinforcement schedule was examined under conditions where the reinforcement probabilities were either 1.00 or .80. The results were then related to the social rank of animals at the time that they were taken from their social groups. Both high and low ranked animals reached criterion performance in the same number of trials. In general, high ranking animals responded at lower rates than low ranking animals when the reinforcement probability was 1.00. When the reinforcement probability was shifted to .80, all animals showed an increase in responding after nonreinforced intervals as compared with responses after reinforced intervals. The higher ranked animals tended to have a higher ratio of nonreinforced to reinforced responses than lower ranked animals.

Effect of dopamine agents on schedule- and deprivation-induced drinking in rats.

The dopamine agonist, apomorphine, or its antagonist, haloperidol, was administered to rats whose drinking was induced by fixed-interval schedules of pellet delivery or by water deprivation. The first study revealed that both drugs produced dose-dependent decreases in bar-pressing and schedule-induced polydipsia (SIP). At higher doses, haloperidol also depressed the rate of pellet delivery. The second study demonstrated that the suppression in SIP obtained in the first study was primarily due to the direct effect of the drugs and not to changes they produced on the underlying food reinforcement schedule. The third study showed that both drugs suppressed water deprivation-induced drinking during a ten-minute session. Apomorphine delayed the onset of drinking, while haloperidol accelerated the cessation of drinking. The results indicated that apomorphine produced motor deficits that interfered with consummatory behavior, and that haloperidol interfered with the sensory feedback necessary to sustain consummatory behavior.

Vasopressin and memory: I. The vasopressin analogue AVP4–9 enhances working memory as well as reference memory in the radial arm maze

The present study examined the effects of vasopressin on memory. Healthy rats were injected with the arginine vasopressin fragment AVP4-9 and the AVP antagonist [beta-mercapto-beta,beta-cyclopentamethylenepropionyl1,O-Et-Pyr 2,Val4,Arg8] and were tested in an eight-arm radial maze for 60 sessions. All injections were given s.c. 30 min prior to testing. AVP4-9 enhanced radial arm maze performance. AVP4-9 treated animals showed enhancement in performance as well as increases in the rate of learning, indicating that they learned the task faster. Furthermore, the overall memory enhancement was due to improved working memory as well as to improved reference memory. These results cannot be explained in terms of changes in locomotor activity because an open field test revealed no differences between groups for both of these compounds. The AVP antagonist did not impair performance in the radial maze. It is concluded that AVP4-9 has a more general effect on memory, one that is not limited to a specific type of memory.

Effects of caudate lesions on signaled and nonsignaled sidman avoidance in the rat

Rats with caudate lesions were clearly deficient on a nonsignaled Sidman avoidance schedule when compared with both normal subjects and subjects with cortical control lesions. Caudate subjects responded at lower rates, avoided a lower percentage of shocks, and failed to develop a temporal discrimination. In contrast with its effects upon normals and controls, the addition of a 5-sec warning cue failed to improve the performance of the caudate subjects.

Discrimination of gamma-hydroxybutyrate and ethanol administered separately and as a mixture in rats.

The physiological effects of gamma-hydroxybutyrate (GHB) are complex and not yet clearly defined. GHB has been labeled as a recreational drug and is reported to be frequently coabused with ethanol (ETH). Other studies have yielded discrepant results as to the interaction between GHB and ETH. Thus, the present study investigated extensively the discriminative stimulus of GHB and ETH and a mixture of the two compounds. Thirty male Long-Evans rats were divided into three groups and trained to discriminate doses of either 300 mg/kg GHB, 1000 mg/kg ETH, or a mixture (MIX: 150 mg/kg GHB+500 mg/kg ETH) from vehicle on a two-lever fixed-ratio (FR) 10 schedule of food reinforcement. Dose-response curves were attained in each group with its respective training drugs. GHB and ETH did not cross-generalize in the ETH- and GHB-trained rats, respectively. However, when the effects of the MIX were tested in the GHB- and ETH-trained rats, a greater than additive response was observed. Testing also revealed that the MIX-trained rats did not perceive a novel stimulus but a near-equal contribution from GHB and ETH. This study provides evidence of a complex relationship between GHB and ETH and opposes previous work reporting cross-generalization between GHB and ETH.

Assessment of adjunctive behaviors in humans using a stringent control procedure

Abstract Nine male and eight female undergraduate students played three consecutive games of backgammon. When visual access to the opponents play was occluded by a curtain during the middle game, eating, drinking, grooming, and restless movement increased over baseline rates prevailing in the first and third games.