Biomedical subjects

Juan D Delius

Publications and source records attributed to Juan D Delius.

8 recordsLinked to original sources

PubMed2005

Learning processes in matching and oddity: the oddity preference effect and sample reinforcement.

Eight pigeons learned either matching (to sample) or oddity (from sample) with or without reward for sample responding. The training stimuli were coarse-white, fine-black, or smooth-mauve gravels in pots with buried grain as the reinforcer. Oddity without sample reward was learned most rapidly, followed by matching with sample reward, oddity with sample reward, and matching without sample reward. Transfer was related to acquisition rate: The oddity group without sample reward showed full (equal to baseline) color and texture transfer; the matching group with sample reward showed partial texture transfer; other groups showed no transfer. Sample reward was shown to determine rate of acquisition of matching and oddity and the oddity preference effect. The results are discussed in terms of item-specific associations operating early in learning prior to any relational learning between sample and comparison stimuli.

Analysis of Variance↗

PubMed2004

Repeated apomorphine administration alters dopamine D1 and D2 receptor densities in pigeon basal telencephalon.

When pigeons are repeatedly administered a dose of apomorphine they show an increasing behavioral response, much as rodents do. In birds this expresses itself in an augmented pecking response. This sensitization is assumed to be largely due to a conditioning process. Here we present evidence that sensitization is accompanied by an alteration of the D(1) to D(2) dopamine receptor densities. An experimental group of pigeons was repeatedly injected with apomorphine, and a control group with saline. The basal forebrain tissue, known to be rich in dopamine receptors, was subjected to binding assays using tritiated specific D(1) and D(2) dopamine receptor antagonists. There was a trend towards an increase in D(1) and a significant decrease in D(2) receptor densities in apomorphine-treated birds compared to the saline-treated controls. We conclude that extended apomorphine treatment modifies the D(1) dopamine receptor density in the opposite manner to the D(2) dopamine receptor density.

Animals↗

PubMed2004

Sensitization to apomorphine, effects of dizocilpine NMDA receptor blockades.

The dopamine agonist apomorphine (apo) elicits bouts of stereotyped pecking in pigeons, a response which increases with successive apo injections. This sensitization is strongly context-specific and has been suggested to arise through a Pavlovian conditioning to both external and internal cues. We hypothetized that this learning involves dopamino-glutamatergic interactions and investigated the issue by inducing NMDA glutamate receptor blockades with the antagonist dizocilpine (diz). A first experiment examined the effects that four different doses (ranging between 0.05 and 0.12 mg/kg) of diz co-administered with a standard dose of 0.5 mg/kg of apo had on the development of the incremented response and on the later expression of the conditioned pecking response. Both responses were impaired by doses of around 0.10 mg/kg diz. A second experiment assessed whether either a diz treatment or a diz plus apo co-treatment affected the development of a subsequent sensitization to apo. The first treatment had no effect on the latter sensitization. A part sensitization that arose with the second treatment did not transfer to the final sensitization. The last experiment examined whether the administration of diz had an immediate effect on the incremented responding to apo and on the conditioned response shown by already sensitized pigeons. No effect was apparent with the first treatment, but there was a marked response inhibition with the second treatment. It is concluded that NMDA glutamate receptors play an important role in apo-induced sensitization in pigeons which is compatible with the Pavlovian conditioning account of sensitization.

Animals↗

PubMed2004

Behavioral sensitization to apomorphine in pigeons (Columba livia): blockade by the D1 dopamine antagonist SCH-23390.

Repeated administration of apomorphine leads to a context-dependent pecking response sensitization. Previously sensitized pigeons (Columba livia) challenged with saline in the same context show a conditioned response (CR). The authors studied the effects of intrastriatal injections of the dopamine (D(1)) antagonist SCH-23390 on both the sensitized response and the CR. When coadministered with apomorphine, SCH-23390 inhibited the initial response to apomorphine, prevented the development of sensitization, and impaired the maintenance of an already developed sensitization. However, SCH-23390 had no effect on the retrieval of a previously established CR. It is concluded that the activation of D(1) receptors in the caudal avian striatum is necessary for the acquisition and maintenance of the sensitization, but not for the expression, of the CR.

Animals↗

PubMed2003

Right or wrong, familiar or novel in pictorial list discrimination learning.

The interaction between nonassociative learning (presentation frequencies) and associative learning (reinforcement rates) in stimulus discrimination performance was investigated. Subjects were taught to discriminate lists of visual pattern pairs. When they chose the stimulus designated as right they were symbolically rewarded and when they chose the stimulus designated as wrong they were symbolically penalised. Subjects first learned one list and then another list. For a "right" group the pairs of the second list consisted of right stimuli from the first list and of novel wrong stimuli. For a "wrong" group it was the other way round. The right group transferred some discriminatory performance from the first to the second list while the control and wrong groups initially only performed near chance with the second list. When the first list involved wrong stimuli presented twice as frequently as right stimuli, the wrong group exhibited a better transfer than the right group. In a final experiment subjects learned lists which consisted of frequent right stimuli paired with scarce wrong stimuli and frequent wrong stimuli paired with scarce right stimuli. In later test trials these stimuli were shown in new combinations and additionally combined with novel stimuli. Subjects preferred to choose the most rewarded stimuli and to avoid the most penalised stimuli when the test pairs included at least one frequent stimulus. With scarce/scarce or scarce/novel stimulus combinations they performed less well or even chose randomly. A simple mathematical model that ascribes stimulus choices to a Cartesian combination of stimulus frequency and stimulus value succeeds in matching all these results with satisfactory precision.

Adolescent↗

PubMed2002

Behavioural consequences of nucleus accumbens dopaminergic stimulation and glutamatergic blocking in pigeons.

Upon systemic administration of apomorphine, a potent dopamine agonist, pigeons show a bout of pecking behaviour. When the drug is repeatedly administered a sensitization takes place that is associated with pronounced discrimination learning. Here we show that intra-cerebral injections of apomorphine in the periphery of the nucleus accumbens of pigeons also elicit pecking. We additionally show that injections of 5-amino-phosphonohepatnoic acid, a NMDA-glutamate receptor blocker, into the Acc impairs the performance of a learned visual discrimination incorporating pecking as a choice response. We conclude that, as it is the case in mammals, the control mechanisms of learned sensory-motor behaviour in birds involves dopaminergic and glutamatergic synaptic transmission within the nucleus accumbens area.

Animals↗

PubMed2002

A new approach to the formation of equivalence classes in pigeons.

Four pigeons were given simultaneous discrimination training with visual patterns arbitrarily divided into two sets, with the stimuli in one set designated A1, B1, C1, and D1 and those in the other set designated A2, B2, C2, and D2. In sequentially introduced training phases, the pigeons were exposed to a series of reversals to establish AB and then CD equivalences. In subsequent testing sessions, a subset of stimuli from one set served as positive stimuli and those from the other set as negative stimuli on training trials, and transfer of the reinforced relation to other members of the sets was tested with nonreinforced probe trials. The pigeons were trained further on AC and BD equivalences and then were tested for the emergence of untrained AD and BC equivalences. Two of the 4 pigeons exhibited the emergence of one of these untrained equivalences, evidence for the emergence of transitive relations. This finding suggests that the pigeons established three-member functional equivalence classes by incorporating separately trained multiple equivalence relations. Repeated reversal training and probe testing enabled us to explore the formation and expansion of functional equivalence classes in pigeons.

Animals↗

PubMed1988

Discrimination of shape reflections and shape orientations by Columba livia.

By using a free-operant instrumental discrimination procedure, it was demonstrated that pigeons find two-dimensional mirror-image visual forms more difficult to distinguish than otherwise similar forms. Variations in orientation of the discriminanda exacerbated the relative confusability of mirror images. No significant difference was found in the pigeons' performance whether the birds were discriminating vertically or horizontally reflected mirror-image pairs. Mirror images of shapes were also shown to be less discriminable than upside-down versions of shapes. The similarity of mirror-image patterns is discussed in relation to the generalized recognition of bilaterally symmetrical forms by pigeons. Pigeons found an orientation discrimination task involving a 45 degree tilt comparatively hard. A second experiment with a discrete-trial conditional paradigm confirmed that discriminations of shape orientations can be difficult for these birds. The addition of shape cues improved the performance on the orientation discrimination task, more so when arbitrary shapes were employed than when mirror images were used, which indicates again that the latter were more difficult to discriminate than the former. The relative insensitivity to shape orientations is ascribed to normal ecological demands on pigeons.

Animals↗