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At least 541 records · Page 30Linked to original sources
PubMed2002

Developmental sensitivity of associative learning to cholesterol synthesis inhibitors.

Patients with Smith-Lemli-Opitz syndrome, a genetic disorder associated with severe mental retardation, are unable to convert 7-dehydrocholesterol to cholesterol. Treatment of rats with agents that block cholesterol synthesis produces a sterol profile reminiscent of Smith-Lemli-Opitz patients i.e., low levels of cholesterol accompanied by the appearance of its immediate precursor 7-dehydrocholesterol. In previous work, chronic inhibition of cholesterol synthesis in just-weaned rats impaired acquisition of the classically conditioned eyeblink response. The present study had two primary goals--(1) to determine whether the learning impairment depended on the age in which treatment was initiated; and (2) to determine whether the deficit was associative or due to performance factors. Consistent with earlier work, acquisition of the eyeblink conditioned response was impaired when the 30-day treatment was initiated on postnatal day (PND) 21. Reactivity to acoustic stimuli and to eyelid stimulation were normal, suggesting that the learning impairment was associative in nature. The learning impairment was transitory; acquisition was normal when evaluated 30 days after the cessation of treatment. When treatment was initiated 30 days after weaning (PND 51), acquisition of the eyeblink response was normal. However, brain sterols of young adult rats were less affected than those of just-weaned rats. Thus, there is a developmental sensitivity to cholesterol synthesis blocking agents both in terms of their effects on brain sterols and new motor learning.

Aging↗
PubMed1983

Forebrain monoamines and associative learning: II. Superconditioning/unblocking.

The roles of norepinephrine (NE) and serotonin (5-HT) were assessed by comparing the effect of their depletion on the associability of stimuli. NE and 5-HT depleted rats and vehicle controls were assigned to two training conditions and to a control condition. In each of the training conditions rats were pre-exposed to a single stimulus prior to conditioning to a compound stimulus formed from the pre-exposed cue and a new stimulus. The training conditions differed only in the order of testing of each of the stimuli following training. Rats assigned to the control condition received only compound conditioning before the associability of each cue was assessed. The findings show that: (a) vehicle rats in the training tasks evidence superconditioning: the associative strength of the new element exceeds that of the pre-exposed cue; (b) equivalent associative strength was found with either cue regardless of their testing order for NE depleted rats; and (c) 5-HT depleted rats did not show superconditioning: the pre-exposed cue competes with the new cue for available associative strength.

Animals↗
PubMed2006

Task-induced deactivations during successful paired associates learning: an effect of age but not Alzheimer's disease.

Task-induced fMRI deactivations during successful encoding and retrieval of visuospatial paired associates were examined at different levels of task difficulty in younger and older adults (Experiment 1), and older adults with and without mild probable Alzheimer's disease (AD) (Experiment 2). Irrespective of the level of task difficulty, common deactivations (determined through the use of conjunction analyses) were observed in the lateral and medial prefrontal, anterior and posterior cingulate, and temporal brain regions and in the claustrum during both encoding and retrieval in younger and older adults (Experiment 1). In AD patients and healthy older adults, common deactivations were found in posterior cingulate, temporal, and lateral parietal regions and in the insula and claustrum during encoding and retrieval of paired associates (Experiment 2). As task difficulty increased, irrespective of the type of task, the magnitude of task-induced deactivations increased in the medial prefrontal/superior frontal gyrus and middle/posterior cingulate cortex in younger and older adults (Experiment 1), and in the middle cingulate cortex in older adults with and without AD (Experiment 2). In Experiment 1, greater deactivation was observed in the anterior cingulate gyrus in older compared to younger adults during retrieval of paired associates which was attributed to greater suppression of task-unrelated thoughts in the older group. No significant differences in task-induced deactivation, or in the type of relationship exhibited between deactivation and task difficulty, were observed between older adults with and without AD (Experiment 2). It was suggested that this was related to the matching of successful task performance and task difficulty across patient and control groups. Following previous proposals, task-induced deactivations were suggested to underlie a shifting of attentional focus from monitoring of the self and the environment (through attenuation of these activities) to external, goal-directed behaviour.

Adult↗
PubMedDate not supplied

Molecular mechanisms of associative learning in mammal and mollusc.

Recent work in this laboratory has begun to cast light on the biochemical mechanisms by which a cell stores associatively acquired information. This appears to occur principally via two general pathways. The first seems to be a long-term activation of protein kinase C (resulting in long-term alterations in protein phosphorylation) while the second involves changes in RNA synthesis. One striking aspect of these mechanisms in that they seem to be conserved across the species we have studied (rabbit and Hermissenda). In the present paper we review some of the studies that support the role of protein kinase C activation and RNA synthesis in memory formation.

Animals↗