James F. Zolman

Homeothermic Development of the Young Chick.

Summary One-to 5-day old chicks were exposed to a 10°C ambient temperature and cloacal temperatures Were recorded every 15 minutes for one hour. Young chicks show a rapid development of thermoregulation the first 5 days after hatching, with significant changes apparent even during the first day and one-half. This rapid homeothermic development is correlated with age and cannot be explained by increases in body weight, food intake, or insulation.

Effects of apomorphine and haloperidol on response suppression learning of young chicks.

In four experiments, the effects of augmenting or blocking dopamine receptor activity on response suppression learning of Colburn X Colburn chicks were determined. In each experiment, 4-day-old chicks were trained to key peck for heat reward and then tested for response suppression learning by using either a response-contingent punishment or an extinction-punishment task. Before response suppression testing, different groups of chicks were injected ip with apomorphine (1.0, 2.0, or 4.0 mg/kg) either alone or after pretreatment with haloperidol (0.5 or 1.0 mg/kg). Regardless of the response suppression task used, chicks injected with apomorphine had difficulty inhibiting their responding; whereas, chicks injected with haloperidol, either alone or before apomorphine treatment, responded on fewer trials than saline-treated chicks. During extinction testing, 4-day-old chicks given only apomorphine showed the typical suppressive effect of punishment on responding rather than the paradoxical punishment-induced increase in responding found in normal 1-day-old chicks. These results indicate that activation of dopamine receptors retards response suppression learning of the 4-day-old chick, but functional changes in central dopaminergic mechanisms are not primarily responsible for the normal age-dependent improvement in response suppression learning of the young chick.

Discrimination Learning in Young Chicks with Heat Reinforcement

Effects of age, rearing condition, and heat reinforcement on a visual discrimination problem were studied in 2 experiments with young chicks. In Experiment 1, 90 Vantress chicks of 3 ages (17-, 47-, and 67-hr.), one-half reared in isolation and the rest in groups of 15, were tested for 20 trials in a 10°C. room with 15 sec. exposure to heat as reinforcement. Ss made significantly more correct choices (red circle SD) as training progressed (p <.001), and Ss reared in isolation made more correct choices than Ss reared communally (p <.001). Age was not significant across all 20 trials, but was significant on the initial block of 5 trials with the 1-day Ss making more correct choices than the older Ss. In Experiment 2, the effects of stimulus exposure (SE) and stimulus-heat (SH) pairing on discrimination performance were compared in 60 dark reared Vantress chicks of 2 ages (14- and 34-hr.). The SH group made more correct choices than the SE group (p <.001), and 14-hr. Ss made more correct choices than 34-hr. Ss (p. <.005). The implications of heat as a reinforcer for the young chick are discussed.

Motor neuronal function in old Aplysia is improved by long-term stimulation of the siphon/gill reflex.

As Aplysia age, motor neuronal (L7) elicited gill-pinnule contractions are significantly decreased, as is transmission at pinnule junctions. To determine whether this reduced function of L7 with increased age could be altered, the siphon/gill reflex, which involves the L7-pinnule pathway, was stimulated regularly in unrestrained old animals. Aplysia, more than 240 days old, were assigned randomly into trained and untrained groups. For more than 3 weeks, a 1-s, 25-g water jet stimulus was administered to the siphon of the trained animals 10 times per day at 20-min intervals. The duration of siphon withdrawal increased significantly during training. In semi-intact preparations, pinnule contractions and junctional transmissions were then measured during 3-s depolarized pulses to L7 (frequency range = 1-44 per 3-s interval). The trained animals had (a) significantly higher pinnule contractions, (b) a significantly greater increase in pinnule contractions elicited by increasing L7 spike rates, (c) significantly higher double-spike facilitation, and (d) significantly higher facilitation per spike across the four spike trains below or at pinnule contraction threshold. Long-term stimulation of the siphon/gill reflex in old Aplysia did not produce the same functional efficiency observed in mature Aplysia; nevertheless, the significant training-induced increases in both pinnule contraction and junction transmission indicate that a considerable level of plasticity still exists in an aging nervous system. Whether this long-term training of Aplysia retards the same processes responsible for the age-related decline in neuromuscular transmission or produces a compensatory change in other neuronal processes is discussed.

Stimulus Preferences and form Discrimination Learning in Young Chicks

Effects of age and stimulus exposure-heat reinforcement on form preferences and form discrimination learning were studied in 2 experiments with young Vantress chicks. In Experiment 1, 48 socially reared Ss of 2 ages (16- and 76-hr) were tested for 3 days on a simultaneous circle-triangle discrimination problem in a 10°C room with 15 sec. exposure to heat as reinforcement. A red circle was the S+ for one-half of the Ss of each age group and for the rest a red triangle was the S+. Ss made significantly more correct responses as testing progressed (p <.001) and the younger Ss had a significant circle preference during testing while the older Ss had no preference (p <.01). In Experiment 2, 48 dark-reared Ss, one-half exposed during the critical period of imprinting to the circle and heat and the rest exposed to the triangle and heat, were then tested for 4 days on the form discrimination problem. Both exposure groups had a significant preference for the circle during discrimination testing (p <.001). It was concluded that approaching some stimulus on the first post-hatch day is necessary for subsequent form preferences to be established.

Physiological and behavioral effects of early embryonic exposure to ethanol and cocaine in the young chick

The physiological and behavioral effects of embryonic exposure to ethanol and cocaine, given during active neurogenesis (embryonic days E3 and E4), were studied in 1- and 2-day-old chicks. Broiler chicks (n = 131) from five embryonic treatment conditions were tested: incubative controls (n = 28), vehicle (saline plus 50 micrograms/ml bacitracin; n = 27), 10 mg ethanol (n = 20), 150 micrograms cocaine (n = 25), or co-drug (10 mg ethanol and 150 micrograms cocaine; n = 31). Compared with controls, embryo mortality for the cocaine alone embryos was significantly increased. No significant embryonic treatment effects among chicks were found for hatching times, body weights at hatch and testing, and temperature regulation when cold stressed. Behaviorally, chicks were first trained to key-peck for heat/light reward (autoshaping). Chicks in all groups increased responding from autoshape session 1 to session 2 (24 trials/session). In an acquisition-extinction session (12 trials/phase), chicks in all groups except those in the co-drug group decreased responding from acquisition to extinction. In a second acquisition-extinction session following a drug challenge of 0.5 mg/kg apomorphine, chicks in all embryonic treatment groups showed enhanced responding. Hence, in those chicks that survived, the selected doses of ethanol and cocaine produced minimal physiological and behavioral effects individually, but when given together did produce a significant deficit in extinction responding.

Separate and combined effects of dopamine D1 and D2 receptor agonists on key pecking in the developing chick

The separate and combined effects of dopamine D1 and D2 agonists on key-peck responding of young chicks for heat reinforcement were determined. In the first experiment, 1- and 4-day-old chicks (n = 96) were injected SC with either distilled water or 5 mg/kg reserpine 18 h before testing. Twenty minutes before a 24-trial autoshaping session, chicks were injected IP with either distilled water or 10 mg/kg SKF 38393 and 2 mg/kg quinpirole. Chicks receiving both dopamine agonists had enhanced key-peck responding in both pretreatment conditions. In Experiment 2, 1- and 4-day-old chicks (n = 192) of two strains received 5 mg/kg reserpine SC 18 h before testing. Twenty minutes before their autoshaping session these chicks were injected IP with either distilled water, 10 mg/kg SKF 38393, 2 mg/kg quinpirole, or 10 mg/kg SKF 38393 and 2 mg/kg quinpirole. After reserpine pretreatment, chicks of both strains responded on more trials when given both dopamine agonists compared with controls given either distilled water or single agonist treatment. No age or strain differences in key pecking were produced by the combined administration of these dopamine agonists. Therefore, functional coupling of the dopamine D1 and D2 receptors is found within 1 day after hatching in the domestic chick.

Ontogenetic changes in [3H]-spiroperidol binding sites in posthatch chick brain

The ontogenetic development of [3H]-spiroperidol binding sites was measured in the optic tectum, cerebellum, forebrain base, and forebrain roof of 1-, 4-, and 16-day-old chicks. In the chick optic tectum and cerebellum both the density and the total number of [3H]-spiroperidol binding sites increased from 4- to 16-days-posthatch, but no significant differences were found in either brain area across the initial four posthatch days. In the forebrain base, [3H]-spiroperidol receptor density and total binding increased significantly between 1- and 4-days-posthatch, but at 16-days-posthatch there was a slight decrease in receptor density. Binding sites in the forebrain roof were minimal at all ages. As expected, saturation experiments yielded curvilinear plots indicating the presence of high- and low-affinity binding sites. The high-affinity sites probably reflect dopamine D-2 receptors; whereas, the low-affinity sites may reflect other receptor types, possibly serotonin S-2. These results suggest that large doses of haloperidol, which are normally used in chick behavioral research, may produce behavioral effects by antagonizing multiple receptors.

The ontogeny of the feature-positive effect in young chicks

The wide generality of the feature-positive effect (FPE) has caused speculation that the FPE may represent innate biases in the stimulus control of discriminative responding. There is little experimental evidence to date ragarding this possibility. In the present study, 1- or 4-day-old chicks were trained on a feature-positive (FP) or feature-negative (FN) discrimination with heat reinforcement. After the acquisition phase, these subjects received extinction training followed by a reacquisition phase. The FP performance was superior to the FN performance in both age groups. Extinction resulted in improved discrimination performance in both the FP and FN conditions. Unmasking of FN learning by the extinction treatment suggests that the FPE represents a deficit in performance, rather than an inability to learn the FN task. These data demonstrate that adult-like performance on feature discriminations is evident as early as the first day post-hatch.

Ontogeny of Learning

In this chapter I begin with a brief review of the major premises of the psychological and ethological approaches to the comparative analysis of learning, and consider a few of the reasons for the current paradigm crisis in the experimental analysis of learning. I then review the correspondence among comparative and ontogenetic research strategies in the psychological analysis of learning, and recent conceptual changes in traditional two-factor learning theory. Within the last decade, the reflexive mechanical view of Pavlovian conditioning has been replaced by a flexible, cognitive view which emphasizes the ability of the animal to both detect causal relations among events in the real world and to use a range of information about those events to make relevant inferences. Furthermore, recent autoshaping evidence indicates that learned responses cannot be fully described by either an independent stimulus-reinforcer (Pavlovian) contingency or a response-reinforcer (instrumental) contingency. Therefore, rather than using Pavlovian and instrumental contingencies merely to classify conditioned responses, they are now used, along with biological and situational events, to analyze conditioned behavior. I consider how these new conceptions are important for an analysis of associative learning influences on developing behavior, and also how nonassociative processes affect the learning of the young animal. In a few illustrative cases, I indicate how a merger of the concepts and techniques of psychology with those of ethology might permit a study of both the associative and nonassociative processes involved in the young animal’s adjustments to its environment.