Tali Bitan

Fast sleep spindles and slow-wave sleep (SWS) have been linked to memory consolidation. However, their associations with learning and longer term retention of different aspects of language remain unclear. We investigated the temporal dynamics of learning and consolidation of vocabulary and grammar, and their links with spindle density and SWS duration. Young adult participants were trained in the evening on an artificial language that used plural inflections with an underlying morpho-phonological regularity that was not taught explicitly. Some of the words were presented frequently and others infrequently. Polysomnographic measures were collected during the first night, and participants were tested on the vocabulary, trained inflections and generalisation to untrained words at four time points across nine days.Accuracy on the vocabulary test improved across the first night following learning, and the change was positively associated with SWS duration. Memory for infrequent words declined towards Day 9, but greater spindle density during the first night was associated with a smaller decline. Mean group accuracy on trained inflections did not change overnight, but individually, the change was negatively correlated with spindle density. Accuracy on generalisation showed no change over time and no correlations with sleep characteristics. Overall, the results demonstrate that vocabulary and grammar learning have different temporal dynamics of consolidation, distinct patterns of association with sleep metrics, and emphasise the potentially protective role of spindles for long-term memory retention.

The present study examined the effect of stimulus variability and practice order on generalization to novel stimuli following a single session of response inhibition training. Ninety-six young adults practiced the Go/No-go task online in three training conditions: (1) constant (N = 32)—inhibition practiced on one stimulus; (2) variable-blocked (N = 32)—inhibition practiced on 6 stimuli, each in a separate block; and (3) variable-random (N = 32)—inhibition practiced on 6 stimuli in random order. Generalization was measured by comparing groups on inhibition of novel stimuli and a trained stimulus immediately and 24 h after training. Consistent with our hypothesis, the variable-random and the variable-blocked groups showed better generalization to the novel items than the constant group, demonstrating the benefit of stimulus variability. The variable-random group also showed better generalization than the variable-blocked group, demonstrating the benefit of presenting stimuli in random order. Participants’ capacity for working memory maintenance was found to modulate the effect of practice order. While the benefit of variability was retained 24 h after training, the effect of order was not. Results also show generalization to (1) different type of stimuli using the same task and (2) the same stimuli on a different response inhibition task (the Stop-Signal Task), however, the effect of variable practice and order were not evident in these cases. The study findings illustrate the advantage of using variable stimuli presented in random order for generalization and suggest that these principles of motor learning can be applied to learning of cognitive skills.

The current study explores the effects of time and sleep on the consolidation of a novel language learning task containing both item-specific knowledge and the extraction of grammatical regularities. We also compare consolidation effects in language and motor sequence learning tasks, to ask whether consolidation mechanisms are domain general. Young adults learned to apply plural inflections to novel words based on morphophonological rules embedded in the input, and learned to type a motor sequence using a keyboard. Participants were randomly assigned into one of two groups, practicing each task during either the morning or evening hours. Both groups were retested 12 and 24 hours post-training. Performance on frequent trained items in the language task stabilized only following sleep, consistent with a hippocampal mechanism for item-specific learning. However, regularity extraction, indicated by generalization to untrained items in the linguistic task, as well as performance on motor sequence learning, improved 24 hours post-training, irrespective of the timing of sleep. This consolidation process is consistent with a frontostriatal skill-learning mechanism, common across the language and motor domains. This conclusion is further reinforced by cross-domain correlations at the individual level between improvement across 24 hours in the motor task and in the low-frequency trained items in the linguistic task, which involve regularity extraction. Taken together, our results at the group and individual levels suggest that some aspects of consolidation are shared across the motor and language domains, and more specifically, between motor sequence learning and grammar learning.

Changes in brain connectivity during language therapy were examined among participants with aphasia (PWA), aiming to shed light on neural reorganization in the language network. Four PWA with anomia following left hemisphere stroke and eight healthy controls (HC) participated in the study. Two fMRI scans were administered to all participants with a 3.5-month interval. The fMRI scans included phonological and semantic tasks, each consisting of linguistic and perceptual matching conditions. Between the two fMRI scans, PWA underwent Phonological Components Analysis treatment. Changes in effective connectivity during the treatment were examined within right hemisphere (RH) architecture. The results illustrate that following the treatment, the averaged connectivity of PWA across all perceptual and linguistic conditions in both tasks increased resemblance to HC, reflecting the normalization of neural processes associated with silent object name retrieval. In contrast, connections that were specifically enhanced by the phonological condition in PWA decreased in their resemblance to HC, reflecting emerging compensatory reorganization in RH connectivity to support phonological processing. These findings suggest that both normalization and compensation play a role in neural language reorganization at the chronic stage, occurring simultaneously in the same brain.