Prehension and perception of size in left visual neglect

Right hemisphere damaged patients with and without left visual neglect, and age-matched controls had objects of various sizes presented within left or right body hemispace. Subjects were asked to estimate the objects’ sizes or to reach out and grasp them, in order to assess visual size processing in perceptual-experiential and action-based contexts respectively. No impairments of size processing were detected in the prehension performance of the neglect patients but a generalised slowing of movement was observed, associated with an extended deceleration phase. Additionally both patient groups reached maximum grip aperture relatively later in the movement than did controls. For the estimation task it was predicted that the left visual neglect group would systematically underestimate the sizes of objects presented within left hemispace but no such abnormalities were observed. Possible reasons for this unexpected null finding are discussed

Mental practice with motor imagery in stroke recovery: Randomized controlled trial of efficacy

This randomized controlled trial evaluated the therapeutic benefit of mental practice with motor imagery in stroke patients with persistent upper limb motor weakness. There is evidence to suggest that mental rehearsal of movement can produce effects normally attributed to practising the actual movements. Imagining hand movements could stimulate restitution and redistribution of brain activity, which accompanies recovery of hand function, thus resulting in a reduced motor deficit. Current efficacy evidence for mental practice with motor imagery in stroke is insufficient due to methodological limitations. This randomized controlled sequential cohort study included 121 stroke patients with a residual upper limb weakness within 6 months following stroke (on average <3 months post-stroke). Randomization was performed using an automated statistical minimizing procedure. The primary outcome measure was a blinded rating on the Action Research Arm test. The study analysed the outcome of 39 patients involved in 4 weeks of mental rehearsal of upper limb movements during 45-min supervised sessions three times a week and structured independent sessions twice a week, compared to 31 patients who performed equally intensive non-motor mental rehearsal, and 32 patients receiving normal care without additional training. No differences between the treatment groups were found at baseline or outcome on the Action Research Arm Test (ANCOVA statistical P = 0.77, and effect size partial η2 = 0.005) or any of the secondary outcome measures. Results suggest that mental practice with motor imagery does not enhance motor recovery in patients early post-stroke. In light of the evidence, it remains to be seen whether mental practice with motor imagery is a valid rehabilitation technique in its own right

Changes in perceived peripersonal space following the rubber hand illusion

Peripersonal space (PPS), the region immediately surrounding the body is essential for bodily protection and goal directed action. Previous studies have suggested that the PPS is anchored to one’s own body and in the current study we investigated whether the PPS could be modulated by changes in perceived body ownership. While theoretically important, this anchoring can also have implications for patients with altered body perception. The rubber hand illusion (RHI) is a way to manipulate body ownership. We hypothesized that after induction of a left hand RHI, the perceived space around the body shifts to the right. Sixty-five participants performed a landmark task before and after a left hand RHI. In the landmark task, participants had to determine whether a vertical landmark line was left or right from the center of a horizontal screen. One group of the participants was exposed to synchronous stroking, the other group experienced asynchronous stroking. Results showed a shift in space to the right (e.g. away from the own arm), but only for the ‘synchronous stroking’ group. These results suggest that the relevant action space becomes linked to the fake hand. Critically, subjective ownership experience did not correlate with this shift, but proprioceptive drift did. This suggests that multisensory integration of bodily information drives this shift in space around the body and not feelings of ownership

Relative finger position influences whether you can localize tactile stimuli

To investigate whether the relative positions of the fingers influence tactile localization, participants were asked to localize tactile stimuli applied to their fingertips. We measured the location and rate of errors for three finger configurations: fingers stretched out and together so that they are touching each other, fingers stretched out and spread apart maximally and fingers stretched out with the two hands on top of each other so that the fingers are interwoven. When the fingers contact each other, it is likely that the error rate to the adjacent fingers will be higher than when the fingers are spread apart. In particular, we reasoned that localization would probably improve when the fingers are spread. We aimed at assessing whether such adjacency was measured in external coordinates (taking proprioception into account) or on the body (in skin coordinates). The results confirmed that the error rate was lower when the fingers were spread. However, there was no decrease in error rate to neighbouring fingertips in the fingers spread condition in comparison with the fingers together condition. In an additional experiment, we showed that the lower error rate when the fingers were spread was not related to the continuous tactile input from the neighbouring fingers when the fingers were together. The current results suggest that information from proprioception is taken into account in perceiving the location of a stimulus on one of the fingertips

Observing human interaction with physical devices

Previous study has shown that if we observe another person operating a tool or physical device, then the action rule of the observed action is automatically activated and can subsequently facilitate own actions. In this study, the mechanisms responsible for this automatic priming of actions are investigated. In two experiments, the question is raised whether priming arises from the observation of the physical device and its movements, or whether it is modulated by aspects of the person’s behaviour. Whereas experiment 1 shows that priming effects are not influenced by the effector used by the observed person, experiment 2 demonstrates that they are modulated by the handle (and associated action rule) that is used to operate the device. These results suggest that motor resonance mechanisms are sensitive to the specific interaction between movements of an actor and associated movements of a physical device

Synergy between EngE, XynA and ManA from Clostridium cellulovorans on corn stalk, grass and pineapple pulp substrates

The synergistic interaction between various hemi/cellulolytic enzymes has become more important in order to achieve effective and optimal degradation of complex lignocellulose substrates for biofuel production. This study investigated the synergistic effect of three enzymes endoglucanase (EngE), mannanase (ManA) and xylanase (XynA) on the degradation of corn stalk, grass, and pineapple fruit pulp and determined the optimal degree of synergy between combinations of these enzymes. It was established that EngE was essential for degradation of all of the substrates, while the hemicellulases were able to contribute in a synergistic fashion to increase the activity on these substrates. Maximum specific activity and degree of synergy on the corn stalk and grass was found with EngE:XynA in a ratio of 75:25%, with a specific activity of 41.1 U/mg protein and a degree of synergy of 6.3 for corn stalk, and 44.1 U/mg protein and 3.4 for grass, respectively. The pineapple fruit pulp was optimally digested using a ManA:EngE combination in a 50:50% ratio; the specific activity and degree of synergy achieved were 52.4 U/mg protein and 2.7, respectively. This study highlights the importance of hemicellulases for the synergistic degradation of complex lignocellulose. The inclusion of a mannanase in an enzyme consortium for biomass degradation should be examined further as this study suggests that it may play an important, although mostly overlooked, role in the synergistic saccharification of lignocellulose

Top-down social modulation of interpersonal observation-execution.

Cyclical upper limb movement can involuntarily deviate from its primary movement axis when the performer concurrently observes incongruent biological motion (i.e. interpersonal observation-execution). The current study examined the social modulation of such involuntary motor interference using a protocol that reflected everyday social interactions encountered in a naturalistic social setting. Eighteen participants executed cyclical horizontal arm movements during the observation of horizontal (congruent) or curvilinear (incongruent) biological motion. Both prior to, and during the interpersonal observation-execution task, participants also received a series of social words designed to prime a pro-social or anti-social attitude. The results showed greater orthogonal movement deviation, and thus interference, for the curvilinear compared to horizontal stimuli. Importantly, and opposite to most of the previous findings from work on automatic imitation and mimicry, there was a greater interference effect for the anti-social compared to pro-social prime condition. These findings demonstrate the importance of interpreting the context of social primes, and strongly support predictions of a comparison between the prime construct and the self-concept/-schema and the top-down response modulation of social incentives

On the relation between action selection and movement control in 5- to 9-month-old infants

Although 5-month-old infants select action modes that are adaptive to the size of the object (i.e., one- or two-handed reaching), it has largely remained unclear whether infants of this age control the ensuing movement to the size of the object (i.e., scaling of the aperture between hands). We examined 5-, 7-, and 9-month-olds’ reaching behaviors to gain more insight into the developmental changes occurring in the visual guidance of action mode selection and movement control, and the relationship between these processes. Infants were presented with a small set of objects (i.e., 2, 3, 7, and 8 cm) and a large set of objects (i.e., 6, 9, 12, and 15 cm). For the first set of objects, it was found that the infants more often performed two-handed reaches for the larger objects based on visual information alone (i.e., before making contact with the object), thus showing adaptive action mode selection relative to object size. Kinematical analyses of the two-handed reaches for the second set of objects revealed that inter-trial variance in aperture between the hands decreased with the approach toward the object, indicating that infants’ reaching is constrained by the object. Subsequent analysis showed that between hand aperture scaled to object size, indicating that visual control of the movement is adjusted to object size in infants as young as 5 months. Individual analyses indicated that the two processes were not dependent and followed distinct developmental trajectories. That is, adaptive selection of an action mode was not a prerequisite for appropriate aperture scaling, and vice versa. These findings are consistent with the idea of two separate and independent visual systems (Milner and Goodale in Neuropsychologia 46:774–785, 2008) during early infancy

Effects of hand orientation on motor imagery - event related potentials suggest kinesthetic motor imagery to solve the hand laterality judgment task

Motor imagery (MI) refers to the process of imagining the execution of a specific motor action without actually producing an overt movement. Two forms of MI have been distinguished: visual MI and kinesthetic MI. To distinguish between these forms of MI we employed an event related potential (ERP) study to measure interference effects induced by hand orientation manipulations in a hand laterality judgement task. We hypothesized that this manipulation should only affect kinesthetic MI but not visual MI. The ERPs elicited by rotated hand stimuli contained the classic rotation related negativity (RRN) with respect to palm view stimuli. We observed that laterally rotated stimuli led to a more marked RRN than medially rotated stimuli. This RRN effect was observed when participants had their hands positioned in either a straight (control) or an inward rotated posture, but not when their hands were positioned in an outward rotated posture. Posture effects on the ERP-RRN have not previously been studied. Apparently, a congruent hand posture (hands positioned in an outward rotated fashion) facilitates the judgement of the otherwise more demanding laterally rotated hand stimuli. These ERP findings support a kinesthetic interpretation of MI involved in solving the hand laterality judgement task. The RRN may be used as a non-invasive marker for kinesthetic MI and seems useful in revealing the covert behavior of MI in e.g. rehabilitation programs