Falls are a leading cause of serious injury and restricted participation among persons with stroke (PwS). Reactive balance control is essential for fall prevention, however, only a few studies have explored the effects of lesion characteristics (location and extent) on balance control in PwS. We aimed to assess the impact of lesion characteristics on reactive and anticipatory balance capacity, gait, and hemiparetic lower limb function, in PwS. Forty-six subacute PwS were exposed to forward, backward, right and left unannounced horizontal surface (...) translations in 6 increasing intensities, while standing. Fall threshold (i.e., perturbation intensity that results in a fall into the harness system) was measured. In addition, the Berg Balance Scale (BBS), 6 Minute Walk Test (6MWT) and Lower Extremity Fugl-Meyer (LEFM) were measured. Lesion effects were analyzed separately for left- and right-hemisphere damaged (LHD, RHD) patients, using voxel-based lesion-symptom mapping (VLSM). Our results show that voxel clusters where damage exerted a significant impact on balance, gait and lower-limb function were found in the corticospinal tract, in its passage in the corona radiata and in the posterior limb of the internal capsule. Additional significant impact was found to lesions affecting the putamen and the external capsule. Balance, gait, and hemiparetic lower limb function showed much overlap of the corresponding ‘significant’ voxel clusters. Test scores of RHD and LHD patients were affected largely by damage to homologous regions, with the LHD group showing a wider distribution of ‘significant’ voxels. The study corroborates and extends previous findings by demonstrating that balance control, gait, and lower limb function are all affected mainly by damage to essentially the same brain structures, namely - the corticospinal tract and adjacent structures in the capsular-putaminal region. (shrink)

The existence of shoulder abduction (SA) and finger extension (FE) movement capacity shortly after stroke onset is an important prognostic factor, indicating favorable functional outcome for the hemiparetic upper limb. Here we asked whether variation in lesion topography affects these two movements in a similar or a distinct way, and whether lesion impact is similar or distinct for left and right hemisphere damage. SA and FE movements were examined in 77 chronic post-stroke patients using relevant items of the Fugl-Meyer test. (...) Lesion effects were analyzed separately for left and right hemispheric damage (LHD, RHD) patient groups using voxel-based lesion-symptom mapping. In the LHD group, SA and FE were affected only by damage to the cortico-spinal tract in its passage through the corona radiata. In contrast, following RHD, these two movements were affected not only by cortico-spinal tract damage but also by damage to white matter association tracts, the putamen and the insular cortex. In both groups, voxel clusters have been found where damage affected SA and also FE, along with voxels where damage affected only one of the two movements. The capacity to execute SA and FE movements following stroke is affected significantly by damage to shared and distinct voxels in the cortico-spinal tract in LHD patients and by damage to shared and distinct voxels in a larger array of cortical and subcortical regions in RHD patients. (shrink)

The impact of stroke on motor functioning is analyzed at different levels. ‘Impairment’ denotes the loss of basic characteristics of voluntary movement. ‘Activity limitation’ denotes the loss of normal capacity for independent execution of daily activities. Recovery from impairment is accomplished by ‘restitution’ and recovery from activity limitation is accomplished by the combined effect of ‘restitution’ and ‘compensation.’ We aimed to unravel the long-term effects of variation in lesion topography on motor impairment of the hemiparetic lower limb (HLL), and gait (...) capacity as a measure of related activity limitation. Gait was assessed by the 3 m walk test (3MWT) in 67 first-event chronic stroke patients, at their homes. Enduring impairment of the HLL was assessed by the Fugl–Meyer Lower Extremity (FMA-LE) test. The impact of variation in lesion topography on HLL impairment and on walking was analyzed separately for left and right hemispheric damage (LHD, RHD) by voxel-based lesion-symptom mapping (VLSM). In the LHD group, HLL impairment tended to be affected by damage to the posterior limb of the internal capsule (PLIC). Walking capacity tended to be affected by a larger array of structures: PLIC and corona radiata, external capsule and caudate nucleus. In the RHD group, both HLL impairment and walking capacity were sensitive to damage in a much larger number of brain voxels. HLL impairment was affected by damage to the corona radiata, superior longitudinal fasciculus and insula. Walking was affected by damage to the same areas, plus the internal and external capsules, putamen, thalamus and parts of the perisylvian cortex. In both groups, voxel clusters have been found where damage affected FMA-LE and also 3MWT, along with voxels where damage affected only one of the measures (mainly 3MWT). In stroke, enduring ‘activity limitation’ is affected by damage to a much larger array of brain structures and voxels within specific structures, compared to enduring ‘impairment.’ Differences between the effects of left and right hemisphere damage are likely to reflect variation in motor-network organization and post-stroke re-organization related to hemispheric dominance. Further studies with larger sample size are required for the validation of these results. (shrink)

Church's Thesis asserts that the only numeric functions that can be calculated by effective means are the recursive ones, which are the same, extensionally, as the Turing-computable numeric functions. The Abstract State Machine Theorem states that every classical algorithm is behaviorally equivalent to an abstract state machine. This theorem presupposes three natural postulates about algorithmic computation. Here, we show that augmenting those postulates with an additional requirement regarding basic operations gives a natural axiomatization of computability and a proof of Church's (...) Thesis, as Gödel and others suggested may be possible. In a similar way, but with a different set of basic operations, one can prove Turing's Thesis, characterizing the effective string functions, and--in particular--the effectively-computable functions on string representations of numbers. (shrink)

In recent years, researchers have tried to unpack the meaning of the term flexibility and test how different constructs of flexibility are associated with various psychopathologies. For example, it is apparent that high levels of flexibility allow individuals to adaptively cope and avoid psychopathology following traumatic events, but the precise nature of this flexibility is ambiguous. In this study we focus on two central constructs: cognitive flexibility – the ability to recognize and implement possible responses to a situation– and regulatory (...) flexibility – the ability to modulate emotional expression and experience across situations. We aim to explore the connection between cognitive and regulatory flexibility and evaluate their relative effect on PTSD symptoms. Trauma-exposed college students were assessed for cognitive and regulatory flexibility and current and lifetime PTSD symptoms. We predicted and found a relatively weak, yet significant, overlap between participants’ cognitive and regulatory flexibility. Importantly, while both cognitive and regulatory flexibility were associated with lifetime PTSD symptoms, only cognitive flexibility was associated with current PTSD symptoms. The findings illuminate the possible value of differentiating between constructs of flexibility in predicting short and long-term effects of traumatic exposure and may pave the ground for developing personalized intervention methods. (shrink)

From its beginnings religious philosophy confronted the challenge to reconcile Divine or natural determinism with man's moral freedom. In ancient Jewish thought, this gave rise to statistical ideas. In some Rabbinic texts, necessity is seen as inhering in collectives rather than in individuals. This is a statistical conception. Some miracles too were understood as highly improbable events, and remarkable phenomena were distinguished from usual ones. Medieval thinkers amplified and developed these ideas. Providential as well as natural determinism were explained as (...) operating in large numbers of individual acts of free will, an idea later taken up by Kant. (shrink)

People usually regard algorithms as more abstract than the programs that implement them. The natural way to formalize this idea is that algorithms are equivalence classes of programs with respect to a suitable equivalence relation. We argue that no such equivalence relation exists.

This festschrift volume is dedicated to Boris (Boaz) Trakhtenbrot on the occasion of his 85th birthday. For over half a century, Trakhtenbrot has been making seminal contributions to virtually all of the central areas of theoretical computer science. He is universally admired as a founding father and long-standing pillar of the discipline of computer science. On Friday, 28 April 2006, the School of Computer Science at Tel Aviv University held a “Computation Day Celebrating Boaz (Boris) Trakhtenbrot's Eighty-Fifth Birthday”. As a (...) follow-up to that event, his students and colleagues were asked to contribute to a volume in his honor and in recognition of his grand contributions to the field. The book opens with two historical overviews and a bibliography. These are followed by 33 thoroughly reviewed technical contributions. The broad range of topics covered include mathematical logic, logics for computer science, mathematics for computer science, automata and formal languages, asynchronous computation, semantics of programming languages, verification, and software engineering. This tapestry of subjects stands as testimony to the vast scope of Trakhtenbrot's achievements and the profound influence he has had on the field. (shrink)

The main powerful method for establishing termination of term rewriting systems was discovered by Nachum Dershowitz through the introduction of certain natural well founded orderings (lexicographic path orderings). This leads to natural decision problems which may be of the highest computational complexity of any decidable problems appearing in a natural established computer science context.