Haptic communication between humans is tuned by the hard or soft mechanics of interaction.

To move a hard table together, humans may coordinate by following the dominant partner's motion [1-4], but this strategy is unsuitable for a soft mattress where the perceived forces are small. How do partners readily coordinate in such differing interaction dynamics? To address this, we investigated how pairs tracked a target using flexion-extension of their wrists, which were coupled by a hard, medium or soft virtual elastic band. Tracking performance monotonically increased with a stiffer band for the worse partner, who had higher tracking error, at the cost of the skilled partner's muscular effort. This suggests that the worse partner followed the skilled one's lead, but simulations show that the results are better explained by a model where partners share movement goals through the forces, whilst the coupling dynamics determine the capacity of communicable information. This model elucidates the versatile mechanism by which humans can coordinate during both hard and soft physical interactions to ensure maximum performance with minimal effort.

Intensity of acute aerobic exercise but not aerobic fitness impacts on corticospinal excitability.

Aerobic exercise (AE) modulates cortical excitability. It can alter both corticospinal excitability and intra-cortical networks, which has implications for its use as a tool to facilitate processes such as motor learning, where increased levels of excitability are conducive to the induction of neural plasticity. Little is known about how different intensities of AE modulate cortical excitability or how individual-level characteristics impact on it. Therefore, we investigated whether AE intensities, lower than those previously employed, would be effective in increasing cortical excitability. We also examined whether the aerobic fitness of individual participants was related to the magnitude of change in AE-induced cortical excitability. In both experiments we employed transcranial magnetic stimulation to probe corticospinal excitability before and after AE. We show that 20 min of continuous moderate- (40% and 50% of heart rate reserve, HRR), but not low- (30% HRR) intensity AE was effective at increasing corticospinal excitability. We also found that while we observed increased corticospinal excitability following 20 min of continuous moderate-intensity (50% HRR) AE, aerobic fitness was not related to the magnitude of change. Our results suggest that there is a lower bound intensity of AE that is effective at driving changes in cortical excitability, and that while individual-level characteristics are important predictors of response to AE, aerobic fitness is not. Overall these findings have implication for the way that AE is used to facilitate processes such as motor learning, where increased levels of cortical excitability and plasticity are favourable.

Early changes in hepatitis C viral quasispecies during interferon therapy predict the therapeutic outcome.

Despite recent treatment advances, the majority of patients with chronic hepatitis C fail to respond to antiviral therapy. Although the genetic basis for this resistance is unknown, accumulated evidence suggests that changes in the heterogeneous viral population (quasispecies) may be an important determinant of viral persistence and response to therapy. Sequences within hepatitis C virus (HCV) envelope 1 and envelope 2 genes, inclusive of the hypervariable region 1, were analyzed in parallel with the level of viral replication in serial serum samples obtained from 23 patients who exhibited different patterns of response to therapy and from untreated controls. Our study provides evidence that although the viral diversity before treatment does not predict the response to treatment, the early emergence and dominance of a single viral variant distinguishes patients who will have a sustained therapeutic response from those who subsequently will experience a breakthrough or relapse. A dramatic reduction in genetic diversity leading to an increasingly homogeneous viral population was a consistent feature associated with viral clearance in sustained responders and was independent of HCV genotype. The persistence of variants present before treatment in patients who fail to respond or who experience a breakthrough during therapy strongly suggests the preexistence of viral strains with inherent resistance to IFN. Thus, the study of the evolution of the HCV quasispecies provides prognostic information as early as the first 2 weeks after starting therapy and opens perspectives for elucidating the mechanisms of treatment failure in chronic hepatitis C.