Conflicting processes in the extinction of conditioned taste aversion: behavioral and molecular aspects of latency,apparent stagnation,and spontaneous recovery

The study of experimental extinction and of the spontaneous recovery of the extinguished memory could cast light on neurobiological mechanisms by which internal representations compete to control behavior. In this work, we use a combination of behavioral and molecular methods to dissect subprocesses of experimental extinction of conditioned taste aversion (CTA). Extinction of CTA becomes apparent only 90 min after the extinction trial. This latency is insensitive to muscarinic and β-adrenergic modulation and to protein synthesis inhibition in the insular cortex (IC). Immediately afterwards, however, the extinguishing trace becomes sensitive to β-adrenergic blockade and protein synthesis inhibition. The subsequent kinetics and magnitude of extinction depend on whether a spaced or massed extinction protocol is used. A massed protocol is highly effective in the short run, but results in apparent stagnation of extinction in the long-run, which conceals fast spontaneous recovery of the preextinguished trace. This recovery can be truncated by a β-adrenergic agonist or a cAMP analog in the insular cortex, suggesting that spontaneous overtaking of the behavioral control by the original association is regulated at least in part by β-adrenergic input, probably operating via the cAMP cascade, long after the offset of the conditioned stimulus. Hence, the performance of the subject in experimental extinction is the sum total of multiple, sometimes conflicting, time-dependent processes.     

Effective learning and retention of braille letter tactile discrimination skills in children with developmental dyslexia

Children with developmental dyslexia (DD) may differ from typical readers in aspects other than reading. The notion of a general deficit in the ability to acquire and retain procedural (‘how to’) knowledge as long‐term procedural memory has been proposed. Here, we compared the ability of elementary school children, with and without reading difficulties (DD, typical readers), to improve their tactile discrimination with practice and tested the children's ability to retain the gains. Forty 10–11‐year‐olds practiced the tactile discrimination of four braille letters, presented as pairs, while blindfolded. In a trial, participants were asked to report whether the target stimuli were identical or different from each other. The structured training session consisted of six blocks of 16 trials each. Performance was re‐tested at 24 hours and two weeks post‐training. Both groups improved in speed and in accuracy. In session 1, children with DD started as significantly less accurate and were slower than the typical readers but showed rapid learning and successfully closed the gap. Only two children with DD failed to benefit from training and were not included in subsequent data analyses. At 24 hours post‐training both groups showed effective retention of the gains in speed and accuracy. Importantly, children with DD were able to retain the gains in speed and accuracy, over a two‐week interval as effectively as typical readers. Thus, children with DD were as effective in the acquisition and retention of tactile discrimination of braille letters as typical readers of the same age. The results do not support the notion of a general procedural learning disability in DD.