Experimental Brain Research

Levy-Tzedek, S.; Krebs, Hermano; Song, D.; Hogan, N.; Poizner, H.

doi: 10.1007/s00221-010-2176-8pmid: 20169338

We tested 23 healthy participants who performed rhythmic horizontal movements of the elbow. The required amplitude and frequency ranges of the movements were specified to the participants using a closed shape on a phase-plane display, showing angular velocity versus angular position, such that participants had to continuously control both the speed and the displacement of their forearm. We found that the combined accuracy in velocity and position throughout the movement was not a monotonic function of movement speed. Our findings suggest that specific combinations of required movement frequency and amplitude give rise to two distinct types of movements: one of a more rhythmic nature, and the other of a more discrete nature.

Kim, Jung-Kyong; Zatorre, Robert

doi: 10.1007/s00221-010-2178-6pmid: 20165840

Shape is an inherent property of objects existing in both vision and touch but not audition. Can shape then be represented by sound artificially? It has previously been shown that sound can convey visual information by means of image-to-sound coding, but whether sound can code tactile information is not clear. Blindfolded sighted individuals were trained to recognize tactile spatial information using sounds mapped from abstract shapes. After training, subjects were able to match auditory input to tactually discerned shapes and showed generalization to novel auditory–tactile pairings. Furthermore, they showed complete transfer to novel visual shapes, despite the fact that training did not involve any visual exposure. In addition, we found enhanced tactile acuity specific to the training stimuli. The present study demonstrates that as long as tactile space is coded in a systematic way, shape can be conveyed via a medium that is not spatial, suggesting a metamodal representation.

Ranganathan, Rajiv; Newell, Karl

doi: 10.1007/s00221-010-2177-7pmid: 20151301

We examined the effect of exploring redundant solutions during practice in enhancing the ability to flexibly use them to achieve a task goal. Three groups used different degrees of path redundancy to perform a virtual interception task in which they attempted to hit a stationary target by moving around a stationary obstacle. The low-variability group always practiced with the same position of the obstacle on all trials. The medium-variability and high-variability groups practiced with the obstacle in different positions within a range of 1 and 2 cm respectively. After eight blocks of practice, all participants were transferred to two tests: (a) a fixed obstacle test where the condition was the same as that practiced by the low-variability group, and (b) a variable obstacle test where the condition was the same as that practiced by the high-variability group. Results showed that the low-variability group had the most accurate performance both in the fixed obstacle and the variable obstacle test. The low-variability group showed the least path variability during the fixed obstacle test but was also able to adapt to the different positions of the obstacle during the variable obstacle test. It appears that flexibility in interceptive tasks is emergent from learning a particular task-relevant parameter related to the target location.

Putrino, David; Mastaglia, Frank; Ghosh, Soumya

doi: 10.1007/s00221-010-2180-zpmid: 20165839

To study the interlimb coordination of reaching and postural movements, chronically implanted microelectrodes were used to record single unit activity from the primary motor cortex (MI) of cats during performance of a trained reaching task. Recordings were made from both cerebral hemispheres to record neurons that modulated their activity during reaching (reach-related neurons) and supportive (posture-related neurons) movements of either forelimb. Evidence of temporal associations in the activities of simultaneously recorded reach- and posture-related neurons was evaluated using shuffle-corrected cross correlograms. The spike activity of approximately 34% of reach-related neurons was temporally correlated with the spike activity of simultaneously recorded posture-related neurons in the opposite motor cortex. Significant associations in the spike activity of neurons recorded from homotopic representational areas of the motor cortex in opposite hemispheres have not previously been reported. These interactions may have an important role in the coordination of opposite forelimbs during reaching movements and postural actions.

Vanneste, Sven; Plazier, Mark; Ost, Jan; Loo, Elsa; Heyning, Paul; Ridder, Dirk

doi: 10.1007/s00221-010-2183-9pmid: 20186404

Tinnitus is considered as an auditory phantom percept. Preliminary evidence indicates that transcranial direct current stimulation (tDCS) of the temporo-parietal area might reduce tinnitus. tDCS studies of the prefrontal cortex have been successful in reducing depression, impulsiveness and pain. Recently, it was shown that the prefrontal cortex is important for the integration of sensory and emotional aspects of tinnitus. As such, frontal tDCS might suppress tinnitus as well. In an open label study, a total of 478 tinnitus patients received bilateral tDCS on dorsolateral prefrontal cortex (448 patients anode right, cathode left and 30 anode left, cathode right) for 20 min. Treatment effects were assessed with visual analogue scale for tinnitus intensity and distress. No tinnitus-suppressing effect was found for tDCS with left anode and right cathode. Analyses show that tDCS with right anode and left cathode modulates tinnitus perception in 29.9% of the tinnitus patients. For these responders a significant reduction was found for both tinnitus-related distress and tinnitus intensity. In addition, the amount of suppression for tinnitus-related distress is moderated by an interaction between tinnitus type and tinnitus laterality. This was, however, not the case for tinnitus intensity. Our study supports the involvement of the prefrontal cortex in the pathophysiology of tinnitus.

Mirams, Laura; Poliakoff, Ellen; Brown, Richard; Lloyd, Donna

doi: 10.1007/s00221-010-2185-7pmid: 20186403

Research suggests that attention has a significant effect on somatic perception in both healthy people and those who suffer from somatic disturbance. The current study investigates the effects of attending to the body on somatic awareness and a particular type of somatic disturbance: erroneous reports of touch sensation, as measured by the Somatic Signal Detection Task (SSDT). During the SSDT, participants are required to detect near-threshold tactile stimulation at their fingertip. Previous research has found that healthy participants erroneously report touch sensations in the absence of a stimulus on this task and that such false alarms are increased when a simultaneous light flash is presented next to their fingertip. Thirty-seven participants completed the SSDT under two conditions: non-informative vision of the hand and no vision of the hand. False alarms were significantly higher in light trials in the non-informative vision condition compared to light trials in the no-vision condition. However, hit rates, sensitivity ( d ′) and response criterion ( c ) were not affected by non-informative vision of the hand. Using the SSDT, we found that viewing the body increased somatic interference, possibly due to raised awareness of internal bodily sensations. This work provides evidence that viewing the body can have a detrimental effect on simple detection of near-threshold tactile stimulation.

Gheysen, Freja; Opstal, Filip; Roggeman, Chantal; Waelvelde, Hilde; Fias, Wim

doi: 10.1007/s00221-010-2186-6pmid: 20195849

Implicit motor sequence learning refers to an important human ability to acquire new motor skills through the repeated performance of a motor sequence. This learning process is characterized by slow, incremental gains of motor performance. The present fMRI study was developed to better delineate the areas supporting these temporal dynamics of learning. By using the serial color matching paradigm, our study focused on the motor level of sequence learning and tracked the time course of learning-related neural changes. Imaging results showed a significant contribution of the left anterior hippocampus in an early sequence acquisition stage (first scanning session) as well as during a later stage with stabilized learning effects (second scanning session). Hippocampal activation significantly correlated with the behavioral learning process and was affected by a change of the motor sequence. These results suggest a strong involvement of the hippocampus in implicit motor sequence learning. On the other hand, a very extensive and bilateral neural network of parietal, temporal and frontal cortical areas (including SMA, pre-SMA) together with parts of the cerebellum and striatum were found to play a role during random visuo-motor task performance.

Kim, Seok; Banala, Sai; Brackbill, Elizabeth; Agrawal, Sunil; Krishnamoorthy, Vijaya; Scholz, John

doi: 10.1007/s00221-010-2187-5pmid: 20186402

This study investigated whether short-term modifications of gait could be induced in healthy adults and whether a combination of kinetic (a compliant force resisting deviation of the foot from the prescribed footpath) and visual guidance was superior to either kinetic guidance or visual guidance alone in producing this modification. Thirty-nine healthy adults, 20–33 years old, were randomly assigned to the three groups receiving six 10-min blocks of treadmill training requiring them to modify their footpath to match a scaled-down path. Changes of the footpath, specific joint events and joint moments were analyzed. Persons receiving combined kinetic and visual guidance showed larger modifications of their gait patterns that were maintained longer, persisting up to 2 h after intervening over-ground activities, than did persons receiving training with primarily kinetic guidance or with visual guidance alone. The results emphasize the short-term plasticity of locomotor circuits and provide a possible basis for persons learning to achieve more functional gait patterns following a stroke or other neurological disorders.

Priot, Anne-Emmanuelle; Laboissière, Rafael; Sillan, Olivier; Roumes, Corinne; Prablanc, Claude

doi: 10.1007/s00221-010-2188-4pmid: 20198365

Telestereoscopic viewing provides a method to distort egocentric distance perception by artificially increasing the interpupillary distance. Adaptation to such a visual rearrangement is little understood. Two experiments were performed in order to dissociate the effects of a sustained increased vergence demand, from those of an active calibration of the vergence/distance mapping. Egocentric distances were assessed within reaching space through open-loop pointing to small targets in the dark. During the exposure condition of the first experiment, subjects were instructed to point to the targets without feedback, whereas in the second experiment, hand visual feedback was available, resulting in a modified relationship between vergence-specified distance and reach distance. The visual component of adaptation in the second experiment was assessed on the unexposed hand. In the post-tests of both experiments, subjects exhibited a constant distance overestimation across all targets, with a more than twice larger aftereffect in the second one. These findings suggest two different processes: (1) an alteration in the vergence effort following sustained increased vergence; (2) a calibration of the vergence/distance mapping uncovering the visual component of adaptation.

Hesse, Constanze; Nakagawa, Tristan; Deubel, Heiner

doi: 10.1007/s00221-010-2189-3pmid: 20217402

Our study examined the effects of performing a pointing movement with the left hand on the kinematics of a simultaneous grasping movement executed with the right hand. We were especially interested in the question of whether both movements can be controlled independently or whether interference effects occur. Since previous studies suggested that eye movements may play a crucial role in bimanual movement control, the effects of different fixation strategies were also studied. Human participants were either free to move their eyes (Experiment 1) or they had to fixate (Experiment 2) while doing the task. The results show that bimanual movement control differed fundamentally depending on the fixation condition: if free viewing was allowed, participants tended to perform the task sequentially, as reflected in grasping kinematics by a delayed grip opening and a poor adaptation of the grip to the object properties for the duration of the pointing movement. This behavior was accompanied by a serial fixation of the targets for the pointing and grasping movements. In contrast, when central fixation was required, both movements were performed fast and with no obvious interference effects. The results support the notion that bimanual movement control is moderated by fixation strategies. By default, participants seem to prefer a sequential behavior in which the eyes monitor what the hands are doing. However, when forced to fixate, they do surprisingly well in performing both movements in parallel.