Maria Korman

Multiple shifts in the representation of a motor sequence during the acquisition of skilled performance.

When do learning-related changes in performance occur? Here we show that the knowledge of a sequence of movements evolves through several distinctive phases that depend on two critical factors: the amount of practice as well as the passage of time. Our results show the following. (i) Within a given session, large performance gains constituted a signature for motor novelty. Such gains occurred only for newly introduced conditions irrespective of the absolute level of performance. (ii) A single training session resulted in both immediate but also time-dependent, latent learning hours after the termination of practice. Time in sleep determined the time of expression of these delayed gains. Moreover, the delayed gains were sequence-specific, indicating a qualitative change in the representation of the task within 24 h posttraining. (iii) Prolonged training resulted in additional between-session gains that, unlike the effects of a single training session, were confined to the trained hand. Thus, the effects of multisession training were qualitatively different than the immediate and time-dependent effects of a single session. Altogether, our results indicate multiple time-dependent shifts in the representation of motor experience during the acquisition of skilled performance.

Daytime sleep condenses the time course of motor memory consolidation

Two behavioral phenomena characterize human motor memory consolidation: diminishing susceptibility to interference by a subsequent experience and the emergence of delayed, offline gains in performance. A recent model proposes that the sleep-independent reduction in interference is followed by the sleep-dependent expression of offline gains. Here, using the finger-opposition sequence–learning task, we show that an interference experienced at 2 h, but not 8 h, following the initial training prevented the expression of delayed gains at 24 h post-training. However, a 90-min nap, immediately post-training, markedly reduced the susceptibility to interference, with robust delayed gains expressed overnight, despite interference at 2 h post-training. With no interference, a nap resulted in much earlier expression of delayed gains, within 8 h post-training. These results suggest that the evolution of robustness to interference and the evolution of delayed gains can coincide immediately post-training and that both effects reflect sleep-sensitive processes.

Retinotopic Axis Specificity and Selective Clustering of Feedback Projections from V2 to V1 in the Owl Monkey

Cortical maps and feedback connections are ubiquitous features of the visual cerebral cortex. The role of the feedback connections, however, is unclear. This study was aimed at revealing possible organizational relationships between the feedback projections from area V2 and the functional maps of orientation and retinotopy in area V1. Optical imaging of intrinsic signals was combined with cytochrome oxidase histochemistry and connectional anatomy in owl monkeys. Tracer injections were administered at orientation-selective domains in regions of pale and thick cytochrome oxidase stripes adjacent to the border between these stripes. The feedback projections from V2 were found to be more diffuse than the intrinsic horizontal connections within V1, but they nevertheless demonstrated clustering. The clusters of feedback axons projected preferentially to interblob cytochrome oxidase regions. The distribution of preferred orientations of the recipient domains in V1 was broad but appeared biased toward values similar to the preferred orientation of the projecting cells in V2. The global spatial distribution of the feedback projections in V1 was anisotropic. The major axis of anisotropy was systematically parallel to a retinotopic axis in V1 corresponding to the preferred orientation of the cells of origin in V2. We conclude that the feedback connections from V2 to V1 might play a role in enhancing the response in V1 to collinear contour elements.

Cerebral Activity Associated with Transient Sleep-Facilitated Reduction in Motor Memory Vulnerability to Interference.

Motor memory consolidation is characterized, in part, by a sleep-facilitated decrease in susceptibility to subsequent interfering experiences. Surprisingly, the cerebral substrates supporting this phenomenon have never been examined. We used fMRI to investigate the neural correlates of the influence of sleep on interference to motor memory consolidation. Healthy young adults were trained on a sequential motor task, and subsequently practiced a second competing sequence after an interval including diurnal sleep or wakefulness. Participants were then retested on the initial sequence 8 h and 24 h (including nocturnal sleep) after training. Results demonstrated that a post-training nap significantly protected memory against interference at 8 h and modulated the link between cerebral activity and behavior, such that a smaller post-interference decrease in cortico-striatal activity was associated with better performance. Interestingly, the protective effect of a nap was only transitory, as both groups performed similarly at 24 h. Activity in cortico-striatal areas that was disrupted during the day, presumably due to interference and accentuated in the absence of a nap, was restored overnight. Altogether, our findings offer the first evidence that cortico-striatal areas play a critical role in the transient sleep-facilitated reduction in motor memory vulnerability and in the overnight restoration of previously degraded memories.

Kinematic Strategies Underlying Improvement in the Acquisition of a Sequential Finger Task with Self-Generated vs. Cued Repetition Training

Many motor skills, such as typing, consist of articulating simple movements into novel sequences that are executed faster and smoother with practice. Dynamics of re-organization of these movement sequences with multi-session training and its dependence on the amount of self-regulation of pace during training is not yet fully understood. In this study, participants practiced a sequence of key presses. Training sessions consisted of either externally (Cued) or self-initiated (Uncued) training. Long-term improvements in performance speed were mainly due to reducing gaps between finger movements in both groups, but Uncued training induced higher gains. The underlying kinematic strategies producing these changes and the representation of the trained sequence differed significantly across subjects, although net gains in speed were similar. The differences in long-term memory due to the type of training and the variation in strategies between subjects, suggest that the different neural mechanisms may subserve the improvements observed in overall performance.

Offline Optimization of the Relative Timing of Movements in a Sequence Is Blocked by Retroactive Behavioral Interference.

Acquisition of motor skills often involves the concatenation of single movements into sequences. Along the course of learning, sequential performance becomes progressively faster and smoother, presumably by optimization of both motor planning and motor execution. Following its encoding during training, “how-to” memory undergoes consolidation, reflecting transformations in performance and its neurobiological underpinnings over time. This offline post-training memory process is characterized by two phenomena: reduced sensitivity to interference and the emergence of delayed, typically overnight, gains in performance. Here, using a training protocol that effectively induces motor sequence memory consolidation, we tested temporal and kinematic parameters of performance within (online) and between (offline) sessions, and their sensitivity to retroactive interference. One group learned a given finger-to-thumb opposition sequence (FOS), and showed robust delayed (consolidation) gains in the number of correct sequences performed at 24 h. A second group learned an additional (interference) FOS shortly after the first and did not show delayed gains. Reduction of touch times and inter-movement intervals significantly contributed to the overall offline improvement of performance overnight. However, only the offline inter-movement interval shortening was selectively blocked by the interference experience. Velocity and amplitude, comprising movement time, also significantly changed across the consolidation period but were interference –insensitive. Moreover, they paradoxically canceled out each other. Current results suggest that shifts in the representation of the trained sequence are subserved by multiple processes: from distinct changes in kinematic characteristics of individual finger movements to high-level, temporal reorganization of the movements as a unit. Each of these processes has a distinct time course and a specific susceptibility to retroactive interference. This multiple-component view may bridge the gap in understanding the link between the behavioral changes, which define online and offline learning, and the biological mechanisms that support those changes.

Effects of order and sensory modality in stiffness perception

The stiffness properties of an environment are perceived during active manual manipulation primarily by processing force cues and position-based tactile, kinesthetic, and visual information. Using a two alternative forced choice (2AFC) stiffness discrimination task, we tested how the perceiver integrates stiffness-related information based on sensory feedback from one or two modalities and the origins of within-session shifts in stiffness discrimination ability. Two factors were investigated: practice and the amount of available sensory information. Subjects discriminated between the stiffness of two targets that were presented either haptically or visuohaptically in two subsequent blocks. Our results show that prior experience in a unisensory haptic stiffness discrimination block greatly improved performance when visual feedback was subsequently provided along with haptic feedback. This improvement could not be attributed to effects induced by practice or multisensory stimulus presentation. Our findings suggest that optimization integration theories of multisensory perception need to account for past sensory experience that may affect current perception of the task even within a single session.

Resistance to interference and the emergence of delayed gains in newly acquired procedural memories: Synaptic and system consolidation?

The progressive multistage stabilization of memory (consolidation) relies on post-acquisition neural reorganization. We hypothesize that two processes subserve procedural memory consolidation and are reflected in delayed post-acquisition performance gains: (1) synaptic consolidation, which is classical Hebbian, and (2) in some tasks, concurrently or consequently, “system consolidation,” which might in some skills be sleep-dependent. Behavioral interference may affect either type of consolidation.

The effects of aging on the use of handheld augmented reality in a route planning task

Abstract Technology may offer benefits for the older population in keeping their independence and connection to society. However, adopting new technologies, such as augmented reality (AR) by older adults may be difficult due to decline of cognitive and physical abilities as well as due to hostility and apprehension regarding the use of technology. In the current study, we compared performance of older and younger participants in a route planning task of public transportation, implemented using both a handheld see-through AR interface, and a standard non-AR application on a mobile phone. Faster task completion times but also higher error rates were associated with the use of the AR interface, regardless of the age of the participants. Older adults showed significantly slower performance compared to younger participants while using the AR application, however, error rates were not significantly different. No trial-to-trial learning was observed for the AR interface, indicating that the AR see-through technology is intuitive and easily adopted. Finally, elderly participants reported on average better user experience for the AR interface compared to younger participants, and preferred the AR over the non-AR application. Our findings highlight the potential of AR technology for older adults, as a possible aid tool to manage everyday tasks, such as navigation and planning.

Background matters: Minor vibratory stimulation during motor skill acquisition selectively reduces off-line memory consolidation

&NA; Although a ubiquitous situation, it is not clear how effective is a learning experience when task‐irrelevant, sensory noise occurs in the background. Here, young adults were trained on the finger opposition sequence task, in a well‐established training and testing protocol affording measures for online as well as off‐line learning. During the training session, one group experienced a minor background vibratory stimulation to the trunk by the means of vibrating cushion, while the second group experienced recorded sound vibrations. A control group was trained with no extra sensory stimulation. Sensory stimulation during training had no effect on the online within‐session gains, but dampened the expression of the off‐line, consolidation phase, gains in the two sensory stimulation groups. These results suggest that background sensory stimulation can selectively modify off‐line, procedural memory consolidation processes, despite well‐preserved on‐line learning. Classical studies have shown that neural plasticity in sensory systems is modulated by motor input. The current results extend this notion and suggest that some types of task‐irrelevant sensory stimulation, concurrent with motor training, may constitute a ‘gating’ factor ‐ modulating the triggering of long‐term procedural memory consolidation processes. Thus, vibratory stimulation may be considered as a behavioral counterpart of pharmacological interventions that do not interfere with short term neural plasticity but block long‐term plasticity. HighlightsNeuron‐level processes sub‐serving long‐term motor memory formation are triggered by practice.Whether these processes will proceed to a successful completion is under strict control (gating).Vibratory stimulation during motor sequence training did not affect the acquisition phase gains.Off‐line, consolidation phase, gains were selectively reduced by stimulation during training.A motor training resulting in robust online gains does not necessarily ensure skill consolidation.Extra‐task vibratory stimulation during acquisition phase may modulate long‐term plasticity.Exposure to vibration is a counterpart of pharmacologically induced gating of consolidation.