Amnesic effects of bilateral lesions placed in the hyperstriatum ventrale of the chick after imprinting

Summary The purpose of this study was to investigate whether bilateral lesions to a part of the hyperstriatum ventrale (IMHV) impair retention if they are placed after chicks have been imprinted. Domestic chicks were hatched and reared in darkness and exposed to an imprinting (training) stimulus for 2 h commencing 22 h post hatch. The chicks were then anaesthetised and bilateral lesions placed in IMHV (N = 16) birds, hyperstriatum accessorium (HA; N = 16) or the lateral part of the cerebral hemispheres (LCA; N = 16). Forty-eight sham-operated chicks served as controls. Chicks were returned to the dark incubator, and, 15–20 h after the operation, their approach towards the training stimulus and to a second novel stimulus was measured. The controls and the chicks with lesions in HA and LCA showed a strong preference for the training stimulus and hence a high level of retention. The preferences of these three experimental groups did not differ significantly from one another. The mean preference of chicks with lesions in IMHV was significantly less than that of the sham-operated controls (P<0.01) and of chicks lesioned in HA (P<0.05). Bilateral lesions to IMHV therefore selectively impair retention of a preference acquired through imprinting. This impairment is unlikely to be a non-specific consequence of defective sensory processing or motor performance because the four groups did not differ from each other in (i) the time taken accurately to peck a rocking bead, (ii) the accuracy of pecking millet seeds and (iii) the performance of a simultaneous visual discrimination task involving heat reinforcement.Supported by grants from the Science Research Council, the Leverhulme Trust, the Wellcome Trust and FAPESP (Brazil)     

Learning and retention of a shock avoidance task by rat using deafferented hind limb

Learning and retention of a shock avoidance task were studied in the absence of proprioceptive or other topographic feedback. Rats with a deafferented hind limb were trained using the instrumental shock avoidance and retention paradigm of Horridge. Rats received shock whenever they lowered an electrode attached to a deafferented hind foot into an electrolyte bath; yoked-control rats received the shocks to a deafferented hind food along with the experimental animals. Experimental animals consistently held their feet above the electrolyte (p<0.01). During the early minutes of the second phase (a testing situation, in which the experimental and control animals were both shocked for leg lowering) the experimentals received fewer shocks than the controls (p<0.001); the controls eventually withheld their feet (p<0.001). These results indicate that rats with deafferented hind limbs provide a simple system for the study of learning and retention in the absence of proprioceptive or other topographic feedback.     

On-line compensation for perturbations of a reaching movement is cerebellar dependent: support for the task dependency hypothesis

Although the cerebellum has been shown to be critical for the acquisition and retention of adaptive modifications in certain reflex behaviors, this structures role in the learning of motor skills required to execute complex voluntary goal-directed movements still is unclear. This study explores this issue by analyzing the effects of inactivating the interposed and dentate cerebellar nuclei on the adaptation required to compensate for an external elastic load applied during a reaching movement. We show that cats with these nuclei inactivated can adapt to predictable perturbations of the forelimb during a goal-directed reach by including a compensatory component in the motor plan prior to movement initiation. In contrast, when comparable compensatory modifications must be triggered on-line because the perturbations are applied in randomized trials (i.e., unpredictably), such adaptive responses cannot be executed or reacquired after the interposed and dentate nuclei are inactivated. These findings provide the first demonstration of the condition-dependent nature of the cerebellums contribution to the learning of a specific volitional task.     

Dorsal bundle extinction effect: Motivation or attention?

Male albino Wistar rats were injected bilaterally with 4 micrograms of 6-hydroxydopamine into the dorsal noradrenergic bundle to deplete forebrain noradrenaline to less than 5% of control values. Acquisition learning of a fixed interval schedule or a continuously reinforced schedule was not altered but resistance to extinction was seen after food reinforced training on either schedule but not after water reinforced training. A possible increase in food motivation was tested by the use of preloading with free food prior to a fixed interval session but both control and lesioned rats reacted similarly to this manipulation thus appearing to exclude an increase in food motivation. An attentional explanation is proposed and tested by the demonstration that resistance to extinction does not occur after a partially (variable ratio 4), as opposed to a continuously, reinforced schedule. Further evidence in favour of an attentional mechanism comes from the finding that on both a fixed interval and a continuously reinforced schedule the lesion has to be present during the acquisition phase to result in subsequent resistance to extinction. Intact animals trained on either schedule and subsequently subjected to the lesion failed to show an increased resistance to extinction.     

Selective impairment of paired associate learning after administration of a centrally-acting adrenergic agonist (clonidine)

Eight normal volunteers had IV infusions of 200 g clonidine (a centrally-acting adrenergic agonist which reduces noradrenaline release), and saline in a double-blind cross-over design. Clonidine reduced subjective estimates of arousal but did not affect performance on the Digit Symbol Substitution Test. Clonidine impaired pairedassociate learning, but it did not affect performance on a number of measures of short and long term memory. The findings suggest either 1) that there is a specific (adrenergic) mechanism involved in the acquisition of novel associations, but not in other types of learning, or 2) that paired associate learning is more vulnerable than other learning tasks to disruption of adrenergic transmission.     

Why did persons invited to train in cardiopulmonary resuscitation not do so?

All citizens (N = 22066) aged 16 to 65 of a medium-sized Belgiantown were personally invited to CPR training sessions held intheir neighbourhood. 1152 responded by attending a trainingsession. Those who did not so respond were surveyed (randomsample N=600) for reasons of their not coming. The sample fittedwell with census data for gender, age and suburb location butnot for job, because retired persons and women at home wereover represented. 123 persons did not want to answer the questions. 116 personssaid they were already trained in CPR, 276 said they would accepton a future occasion and 82 said they would not. Three personsdid not answer this question. There was no discrimination for job, gender and suburb locationbetween those who did and did not accept a future training opportunity,nor was the existence of a heart patient among relatives. Theolder the person, the less inclined was that person to participatein CPR training (age effect x² = 17.17, d.f. = 9, P<0.05).The 276 who accepted future training, chose their workplace(221) and/or their social meeting place (club etc.) as the placewhere this future training should be held. We suggest that CPR training is well accepted and that the trainingopportunities should be given at places of work and social gatherings.     

Rectal and brain temperatures in ethanol intoxicated mice

The organometal neurotoxin trimethyltin (TMT), induces impaired learning and memory for various tasks. However, administration is also associated with other non-specific behavioral changes which may be responsible for effects on conditioned behaviors. To determine if TMT treatment causes a specific learning impairment, three experiments were done using variations of a delay of reinforcement autoshaping task in which rats learn to associate the presentation and retraction of a lever with the delivery of a food pellet reinforcer. No significant effects of TMT treatment were found with a short (4 s) delay of reinforcement, indicating that rats were motivated and had the sensorimotor capacity for learning. When the delay was increased to 6 s, 3.0 or 6.0 mg TMT/kg produced dose-related reductions in behaviors directed towards the lever. Performance of a group given 7.5 mg TMT/kg, while still impaired relative to controls, appeared to be better than the performance of groups given lower doses. This paradoxical effect was investigated with a latent inhibition paradigm, in which rats were pre-exposed to the Skinner boxes for several sessions without delivery of food reinforcement. Control rats showed retardation of autoshaping when food reinforcement was subsequently introduced. Rats given 7.5 mg TMT/kg exhibited elevated levels of lever responding during pre-exposure and autoshaping sessions. The results indicate that 7.5 mg TMT/kg produces learning impairments which are confounded by hyperreactivity to the environment and an inability to suppress behavior toward irrelevant stimuli. In contrast, low doses of TMT cause learning impairments which are not confounded by hyperreactivity, and may prove to be useful models for studying specific associational dysfunctions.     

Patient involvement in oral hygiene cooperation: a factor analytic study

In a previous study the concept "patient involvement" was found to be strongly predictive of therapy outcome. On the basis of a questionnaire concerning patients' background and motivation, 82 patients were interviewed before treatment. To cover the concept "patient involvement" 16 variables were considered as relevant measures. In a factor analysis four factors accounted for 90% of the common variance. The factors were interpreted in terms of: initial attitudes, attendance, self-confidence and teeth-mindedness.     

Attenuation of ethanol tolerance by a novel stimulus

A Pavlovian conditioning model of tolerance emphasizes that an association between predrug cues and the systemic effects of the drug contributes to tolerance. On the basis of this model, established tolerance should be attenuated by external inhibition, i.e., by presentation of a novel, extraneous stimulus. This prediction was evaluated in the present experiment. Rats that were so tolerant to the hypothermic effect of ethanol that they evidenced no drug-induced decrease in temperature were presented with a bright strobe light following ethanol administration. The light precipitated a large decrease in temperature in these rats. These results provide further evidence that tolerance to the hypothermic effect of ethanol is, in part, mediated by learning.     

Central mediation of the conditioned taste aversion induced in rats by harmaline

The assumption that drugs used as unconditioned stimuli in conditioned taste aversion (CTA) studies act centrally was tested by comparing the effects of systemic and intracerebral injections of harmaline hydrochloride (H) in 340 rats. Intraperitoneal injection of 5–20 mg/kg but not of 2.5 mg/kg H administered 5 min after 15-min saccharin (0.1%) drinking decreased saccharin-water preference in a two-choice retention test, performed 48 h later, from 55% to 20%. Since CTA was not diminished when H (10 mg/kg) was injected into rats anesthetised immediately after saccharin drinking by pentobarbital (40 mg/kg), H (1.7–50 g) was administered intracerebrally to anesthetised rats fixed in the stereotaxic apparatus. Injection of 3–6 g H into the inferior olive elicited CTA comparable to that of systemic injection of 10 mg/kg H. Injections of 6 and 50 g H into cerebellum and bulbar reticular formation elicited weaker CTA while neocortical, hypothalamic and mesencephalic applications were ineffective. CTA could also be elicited when 50 g but not 6 g H was injected into the inferior olive 1 or 2 h after saccharin drinking. This delay-dependent effect and failure of non-contingent H administration to change saccharin preference indicates that the H-induced CTA is not contaminated by a non-specific increase in neophobia. It is concluded that H probably elicits CTA by activation of caudal bulbar structures, including the nucleus of the solitary tract, area postrema and lateral reticular formation.