Cerebral Activation During Initial Motor Learning Forecasts Subsequent Sleep-Facilitated Memory Consolidation in Older Adults.

Older adults exhibit deficits in motor memory consolidation; however, little is known about the cerebral correlates of this impairment. We thus employed fMRI to investigate the neural substrates underlying motor sequence memory consolidation, and the modulatory influence of post-learning sleep, in healthy older adults. Participants were trained on a motor sequence and retested following an 8-h interval including wake or diurnal sleep as well as a 22-h interval including a night of sleep. Results demonstrated that a post-learning nap improved offline consolidation across same- and next-day retests. This enhanced consolidation was reflected by increased activity in the putamen and the medial temporal lobe, including the hippocampus, regions that have previously been implicated in sleep-dependent neural plasticity in young adults. Moreover, for the first time in older adults, the neural substrates subserving initial motor learning, including the putamen, cerebellum, and parietal cortex, were shown to forecast subsequent consolidation depending on whether a post-learning nap was afforded. Specifically, sufficient activation in a motor-related network appears to be necessary to trigger sleep-facilitated consolidation in older adults. Our findings not only demonstrate that post-learning sleep can enhance motor memory consolidation in older adults, but also provide the system-level neural correlates of this beneficial effect.

Anthropomorphic or non-anthropomorphic? Effects of biological sex in observation of actions in a digital human model and a gantry robot model.

Robots are ever more relevant for everyday life, such as healthcare or rehabilitation, as well as for modern industrial environment. One important issue in this context is the way we perceive robots and their actions. From our previous study, evidence exists that sex can affect the way people perceive certain robot's actions. In our fMRI study, we analyzed brain activations of female and male participants, while they observed anthropomorphic and robotic movements performed by a human or a robot model. While lying in the scanner, participants rated the perceived level of anthropomorphic and robotic likeness of movements in the two models. The observation of the human model and the anthropomorphic movements similarly activated the biological motion coding areas in posterior temporal and parietal areas. The observation of the robot model activated predominantly areas of the ventral stream, whereas the observation of robotic movements activated predominantly the primary and higher order motor areas. To note, this later activation originated mainly from female participants, whereas male participants activated, in both robot model and robotic movements contrasts, areas in the posterior parietal cortex. Accordingly, the general contrast of sex suggests that men tend to use the ventro-dorsal stream most plausibly to rely on available previous knowledge to analyze the movements, whereas female participants use the dorso-dorsal and the ventral streams to analyze online the differences between the movement types and between the different models. The study is a first step toward the understanding of sex differences in the processing of anthropomorphic and robotic movements.

Motor sequence learning in patients with ideomotor apraxia: Effects of long-term training.

Recent studies show that limb apraxia is a quite frequent, yet often underdiagnosed, higher motor impairment following stroke. Because it adversely affects every-day life and personal independence, successful rehabilitation of apraxia is essential for personal well-being. Nevertheless, evidence of long-term efficacy of training schemes and generalization to untrained actions is still scarce. One possible reason for the tendency of this neurological disorder to persist may be a deficit in planning, conceptualisation and storage of complex motor acts. This pilot study aims at investigating explicit motor learning in apractic stroke patients. In particular, we addressed the ability of apractic patients to learn and to retain new explicit sequential finger movements across 10 training sessions over a 3-week interval. Nine stroke patients with ideomotor apraxia in its chronic stage participated in a multi-session training regimen and were included in data analyses. Patients performed an explicit finger sequence learning task (MSLT - motor sequence learning task), which is a well-established paradigm to investigate motor learning and memory processes. Patients improved task performance in terms of speed and accuracy across sessions. Specifically, they showed a noticeable reduction in the mean time needed to perform a correct sequence and the number of erroneous sequences. We found also a trend for improved performance at the Goldenberg apraxia test protocol: "imitation of meaningless hand and finger gestures" relative to when assessed before the MSLT training. Patients with ideomotor apraxia demonstrated the ability to acquire and maintain a novel sequence of movements; and, this training was associated with hints towards improvement of apraxia symptoms.

Neural correlates of narrative shifts during auditory story comprehension.

The ability to segment continuous linguistic information online into larger, meaningful units is a key element in narrative comprehension. Narrative shifts, i.e. transitions between individual units, are postulated to continuously update the mental situation model. Their cerebral correlates, however, have hardly been investigated. Under highly naturalistic conditions this study seeks to identify the neural correlates of implicit processing of narrative shifts during continuous speech comprehension. 16 male native German speakers listened passively to a German novella for 23 min while BOLD signal was recorded with fMRI. Text comprehension was tested in a short post-scan interview asking for critical episodes of the story. Narrative shifts were defined on the basis of a macropropositional analysis. Compared to listening to text passages of the narrative that neither contained narrative shifts nor structurally similar linguistic control events (i.e., sentence boundaries), narrative shifts evoked increased BOLD signal changes in the right temporal gyrus, precuneus and posterior/middle cingulate cortex bilaterally. When narrative shifts were contrasted with sentence boundaries, activation in the right precuneus and cingulate cortex remained significant. The results strengthen the relevance of medial parietal structures for natural language comprehension. More precisely, the precuneus and posterior cingulate appear to be the neural substrate for updating mental story representations and can be regarded as critical parts of a more complex, distributed neural network underlying story comprehension.

Enhancement of motor consolidation by post-training transcranial direct current stimulation in older people.

Consolidation, by which performance increments after a training intervention are secured and sometimes generated, is reduced in elderly humans. The present study addressed the question whether transcranial direct current stimulation (tDCS) applied after motor training improves consolidation of explicit motor sequence learning in healthy older humans. In the first experiment, anodal or cathodal tDCS to the left primary motor cortex, anodal tDCS to premotor cortex, or sham tDCS was applied immediately after completion of a finger sequence learning task. Performance was retested at 8 and 22 hours after the initial training session. Whereas all groups achieved similar performance at the end of training, off-line improvements differed between groups at later retesting, depending on the type of intervention. Relative to the other 3 interventions, anodal tDCS to primary motor cortex (M1) led to performance improvements already at retesting 8 hours after initial learning and were maintained on the next day. In the second experiment, effects of the timing of post-training anodal tDCS to M1 with respect to the end of training were studied. Participants received anodal tDCS of M1 immediately or 60 or 120 minutes after training and were retested on sequence performance 8 hours post training. Only application of tDCS immediately after the end of training, but not after 1 or 2 hours, enhanced off-line consolidation. These findings suggest that anodal tDCS applied off-line immediately post training to M1 interacts specifically with early processes promoting consolidation of motor sequence learning in healthy older individuals.

A Nap But Not Rest or Activity Consolidates Language Learning.

Recent evidence suggests that a period of sleep after a motor learning task is a relevant factor for memory consolidation. However, it is yet open whether this also holds true for language-related learning. Therefore, the present study compared the short- and long-term effects of a daytime nap, rest, or an activity task after vocabulary learning on learning outcome. Thirty healthy subjects were divided into three treatment groups. Each group received a pseudo-word learning task in which pictures of monsters were associated with unique pseudo-word names. At the end of the learning block a first test was administered. Then, one group went for a 90-min nap, one for a waking rest period, and one for a resting session with interfering activity at the end during which a new set of monster names was to be learned. After this block, all groups performed a first re-test of the names that they initially learned. On the morning of the following day, a second re-test was administered to all groups. The nap group showed significant improvement from test to re-test and a stable performance onto the second re-test. In contrast, the rest and the interference groups showed decline in performance from test to re-test, with persistently low performance at re-test 2. The 3 (GROUP) × 3 (TIME) ANOVA revealed a significant interaction, indicating that the type of activity (nap/rest/interfering action) after initial learning actually had an influence on the memory outcome. These data are discussed with respect to translation to clinical settings with suggestions for improvement of intervention outcome after speech-language therapy if it is followed by a nap rather than interfering activity.