Biomedical subjects

Avi Karni

Publications and source records attributed to Avi Karni.

11 recordsLinked to original sources

PubMed2007

The acquisition and implementation of the smoothness maximization motion strategy is dependent on spatial accuracy demands.

We recently showed that extensive training on a sequence of planar hand trajectories passing through several targets resulted in the co-articulation of movement components and in the formation of new movement elements (primitives) (Sosnik et al. in Exp Brain Res 156(4):422-438, 2004). Reduction in movement duration was accompanied by the gradual replacing of a piecewise combination of rectilinear trajectories with a single, longer curved one, the latter affording the maximization of movement smoothness ("global motion planning"). The results from transfer experiments, conducted by the end of the last training session, have suggested that the participants have acquired movement elements whose attributes were solely dictated by the figural (i.e., geometrical) form of the path, rather than by both path geometry and its time derivatives. Here we show that the acquired movement generation strategy ("global motion planning") was not specific to the trained configuration or total movement duration. Performance gain (i.e., movement smoothness, defined by the fit of the data to the behavior, predicted by the "global planning" model) transferred to non-trained configurations in which the targets were spatially co-aligned or when participants were instructed to perform the task in a definite amount of time. Surprisingly, stringent accuracy demands, in transfer conditions, resulted not only in an increased movement duration but also in reverting to the straight trajectories (loss of co-articulation), implying that the performance gain was dependent on accuracy constraints. Only 28.5% of the participants (two out of seven) who were trained in the absence of visual feedback from the hand (dark condition) co-articulated by the end of the last training session compared to 75% (six out of eight) who were trained in the light, and none of them has acquired a geometrical motion primitive. Furthermore, six naive participants who trained in dark condition on large size targets have all co-articulated by the end of the last training session, still, none of them has acquired a geometrical motion primitive. Taken together, our results indicate that the acquisition of a geometrical motion primitive is dependent on the existence of visual feedback from the hand and that the implementation of the smoothness-maximization motion strategy is dependent on spatial accuracy demands. These findings imply that the specific features of the training experience (i.e., temporal or spatial task demands) determine the attributes of an acquired motion planning strategy and primitive.

Adolescent↗

PubMed2006

When practice does not make perfect: well-practiced handwriting interferes with the consolidation phase gains in learning a movement sequence.

Practice on a novel sequence of movements can lead to two expressions of procedural memory consolidation: delayed performance gains evolving hours after training, and a decrease in the susceptibility of the training-related gains to interference by subsequent experience. It has been assumed that behavioral interference occurs only if a critical overlap between the representations of the two tasks exists, and that such overlap is more likely when the two tasks are novel, competing for general resources for their execution. We investigated whether the delayed gains in the simple finger-opposition sequence (FOS) learning task are more prone to interference by well practiced than by less practiced complex hand movements. Participants were trained on the FOS task in a baseline (no interference) and an interference training condition. In the Interference condition, after FOS practice, participants wrote Hebrew common words in Hebrew (native script) or a Latin script (Heblatin). Native script writing but not the less practiced Heblatin, interfered with FOS learning, with significantly reduced delayed gains. Our results show that interference can occur even when two tasks share little or no kinematic or dynamic features and indicate that the representation of complex but well-practiced movement sequences may overlap with the representation of simpler ones. This result is in line with the notion that well-practiced complex movement sequences come to be represented as simpler ones in long-term motor memory.

Adult↗

PubMed2006

A link between perceptual learning, adaptation and sleep.

Between-sessions gains in the texture discrimination task have been attributed to memory consolidation. A strong dependence of consolidation on sleep was suggested though not always supported by experimental results. Here we suggest that the interaction between consolidation and sleep depends on the adaptation level obtained during the training session. We find that both discrimination thresholds and learning depend on the number of trials used during training, with more trials producing higher discrimination thresholds due to suppressive processes related to adaptation. In addition, while learning benefits from increasing number of trials, a further increase in number of trials reduces learning. Consolidation may benefit from between-session sleep in the adapted states.

Adaptation, Psychological↗

PubMed2006

Behavioral interference and C/EBPbeta expression in the insular-cortex reveal a prolonged time period for taste memory consolidation.

Memory consolidation is defined as the time window during which the memory trace is susceptible to behavioral, electrical, or pharmacological interventions. Here, we presented rats with two novel tastes at consecutive time intervals. Clear interference was evident when a novel taste formed the second taste input whereby, surprisingly, the time window for interference was found to last more than 10 h. In addition, we detected an increase of C/EBPbeta protein expression in the gustatory cortex 18 h after novel taste learning. This modulation was attenuated by a subsequent novel taste. Our findings reveal temporal constraints and a lingering nature of taste memory consolidation.

Animals↗

PubMed2005

The predictive value of the leveling off of within session performance for procedural memory consolidation.

In addition to performance gains accrued concurrently with a given training experience (within-session gains) robust, delayed (between-session) performance gains may slowly evolve in the absence of any additional practice in a variety of tasks. The latter is regarded as a behavioral manifestation of skill memory consolidation. It is not known, however, how much practice is necessary for the triggering of these consolidation effects. Here, using an enumeration task, we show that the triggering of delayed gains could be robustly predicted from each individual's performance curve. Delayed performance gains evolved consistently only when practice continued to the point at which within-session performance leveled off (saturation). No delayed gains were found when training was stopped before this individually determined point. Our results support the notion that the triggering of consolidation processes depends on the saturation of a distinct, early phase of learning rather than on the absolute number of task repetitions, and suggest the possibility that training and rehabilitation protocols could be optimized on an individual basis.

Adult↗

PubMed2005

Effects of alphabeticality, practice and type of instruction on reading an artificial script: an fMRI study.

In neuroimaging studies of word reading in natural scripts, the effect of alphabeticality is often confounded with the effect of practice. We used an artificial script to separately manipulate the effects of practice and alphabeticality following training with and without explicit letter instructions. Participants received multi-session training in reading nonsense words, written in an artificial script, wherein each phoneme was represented by 2 discrete symbols . Three training conditions were compared: alphabetical whole words with letter decoding instruction (explicit); alphabetical whole-words (implicit) and non-alphabetical whole-words (arbitrary). Each participant was trained on the arbitrary condition and on one of the alphabetical conditions (explicit or implicit). fMRI scans were acquired after training during reading of trained words and relatively novel words in the alphabetical and arbitrary conditions. Our results showed greater activation in the explicit compared to the arbitrary conditions, but only for relatively-novel words, in the left posterior inferior frontal gyrus (IFG). In the implicit condition, the left posterior IFG was active in both trained and relatively novel words. These results indicate the involvement of the left posterior IFG in letter decoding, and suggest that reading of explicitly well-trained words did not rely on letter decoding, while in implicitly trained words letter decoding persisted into later stages. The superior parietal lobules showed reduced activation for items that received more practice, across all training conditions. Altogether, our results suggest that the alphabeticality of the word, the amount of practice and type of instructions have independent and interacting effects on brain activation during reading.

Adult↗

PubMed2004

When practice leads to co-articulation: the evolution of geometrically defined movement primitives.

The skilled generation of motor sequences involves the appropriate choice, ordering and timing of a sequence of simple, stereotyped movement elements. Nevertheless, a given movement element within a well-rehearsed sequence can be modified through interaction with its neighboring elements (co-articulation). We show that extensive training on a sequence of planar hand trajectories passing through several targets resulted in the co-articulation of movement components, and in the formation of new movement elements (primitives). Reduction in movement duration was accompanied by the gradual replacement of straight trajectories by longer curved ones, the latter affording the maximization of movement smoothness. Surprisingly, the curved trajectories were generated even when new target configurations were introduced, i.e., when target distances were scaled, movement direction reversed or when different start and end positions were used, indicating the acquisition of geometrically defined movement elements. However, the new trajectories were not shared by the untrained hand. Altogether, our results suggest that novel movement elements can be acquired through extensive training in adults.

Adolescent↗

PubMed2003

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.

Adolescent↗

PubMed2002

Experience-dependent changes in cerebellar contributions to motor sequence learning.

Studies in experimental animals and humans have stressed the role of the cerebellum in motor skill learning. Yet, the relative importance of the cerebellar cortex and deep nuclei, as well as the nature of the dynamic functional changes occurring between these and other motor-related structures during learning, remains in dispute. Using functional magnetic resonance imaging and a motor sequence learning paradigm in humans, we found evidence of an experience-dependent shift of activation from the cerebellar cortex to the dentate nucleus during early learning, and from a cerebellar-cortical to a striatal-cortical network with extended practice. The results indicate that intrinsic modulation within the cerebellum, in concert with activation of motor-related cortical regions, serves to set up a procedurally acquired sequence of movements that is then maintained elsewhere in the brain.

Adult↗

PubMed2002

Imaging brain plasticity during motor skill learning.

The search for the neural substrates mediating the incremental acquisition of skilled motor behaviors has been the focus of a large body of animal and human studies in the past decade. Much less is known, however, with regard to the dynamic neural changes that occur in the motor system during the different phases of learning. In this paper, we review recent findings, mainly from our own work using fMRI, which suggest that: (i) the learning of sequential finger movements produces a slowly evolving reorganization within primary motor cortex (M1) over the course of weeks and (ii) this change in M1 follows more dynamic, rapid changes in the cerebellum, striatum, and other motor-related cortical areas over the course of days. We also briefly review neurophysiological and psychophysical evidence for the consolidation of motor skills, and we propose a working hypothesis of its underlying neural substrate in motor sequence learning.

Brain↗

PubMedDate not supplied

A latent consolidation phase in auditory identification learning: time in the awake state is sufficient.

Large gains in performance, evolving hours after practice has terminated, were reported in a number of visual and some motor learning tasks, as well as recently in an auditory nonverbal discrimination task. It was proposed that these gains reflect a latent phase of experience-triggered memory consolidation in human skill learning. It is not clear, however, whether and when delayed gains in performance evolve following training in an auditory verbal identification task. Here we show that normal-hearing young adults trained to identify consonant-vowel stimuli in increasing levels of background noise showed significant, robust, delayed gains in performance that became effective not earlier than 4 h post-training, with most participants improving at more than 6 h post-training. These gains were retained for over 6 mo. Moreover, although it has been recently argued that time including sleep, rather than time per se, is necessary for the evolution of delayed gains in human perceptual learning, our results show that 12 h post-training in the waking state were as effective as 12 h, including no less than 6 h night's sleep. Altogether, the results indicate, for the first time, the existence of a latent, hours-long, consolidation phase in a human auditory verbal learning task, which occurs even during the awake state.

Adult↗