Enhancing cognitive control with transcranial magnetic stimulation in subject-specific frontoparietal networks.

BACKGROUND: Cognitive control processes, including those involving frontoparietal networks, are highly variable between individuals, posing challenges to basic and clinical sciences. While distinct frontoparietal networks have been associated with specific cognitive control functions such as switching, inhibition, and working memory updating functions, there have been few basic tests of the role of these networks at the individual level. METHODS: To examine the role of cognitive control at the individual level, we conducted a within-subject excitatory transcranial magnetic stimulation (TMS) study in 19 healthy individuals that targeted intrinsic ("resting") frontoparietal networks. Person-specific intrinsic networks were identified with resting state functional magnetic resonance imaging scans to determine TMS targets. The participants performed three cognitive control tasks: an adapted Navon figure-ground task (requiring set switching), n-back (working memory), and Stroop color-word (inhibition). OBJECTIVE: Hypothesis: We predicted that stimulating a network associated with externally oriented control [the "FPCN-B" (fronto-parietal control network)] would improve performance on the set switching and working memory task relative to a network associated with attention (the Dorsal Attention Network, DAN) and cranial vertex in a full within-subjects crossover design. RESULTS: We found that set switching performance was enhanced by FPCN-B stimulation along with some evidence of enhancement in the higher-demand n-back conditions. CONCLUSION: Higher task demands or proactive control might be a distinguishing role of the FPCN-B, and personalized intrinsic network targeting is feasible in TMS designs.

The mechanical axes of the wrist are oriented obliquely to the anatomical axes.

BACKGROUND: the complex motions of the wrist are described in terms of four anatomical directions that are accomplished through the multiple articulations of the carpus. With minimal tendinous insertions, the carpus is primarily a passive structure. This emphasizes the importance of its mechanical properties, which few studies have examined to date. The purpose of the present study was to determine the mechanical properties of the wrist in twenty-four different directions of wrist motion. METHODS: the moment-rotation mechanical behavior of six fresh-frozen cadaver wrists was determined in four directions: flexion, extension, ulnar deviation, and radial deviation. Twenty other directions that were a combination of these anatomical directions were also studied. A custom-designed jig was interfaced with a standard materials testing system to apply unconstrained moments. Moments of ± 2 Nm were applied, and the moment-rotation data were recorded and analyzed to determine the neutral zone, range of motion, and stiffness values as well as the orientation of the envelope of these values. RESULTS: the envelope of wrist range-of-motion values was ellipsoidal in shape and was oriented obliquely (p < 0.001) to the direction of pure flexion-extension by a mean (and standard deviation) of 26.6° ± 4.4°. The largest wrist range of motion was a mean of 111.5° ± 10.2°, in the direction of ulnar flexion, 30° from pure flexion. The largest stiffness (mean, 0.4 Nm/deg) was in the direction of radial flexion, while the smallest stiffness (mean, 0.15 Nm/deg) was in the direction of ulnar flexion. CONCLUSIONS: the mechanical axes of the wrist are oriented obliquely to the anatomical axes. The primary mechanical direction is one of radial extension and ulnar flexion, a direction along a path of the dart thrower's wrist motion. CLINICAL RELEVANCE: understanding the mechanical function of the wrist can aid clinical treatment decisions, arthroplasty, and implant designs. The findings of this study provide new evidence that the mechanical axes of the wrist are not collinear with the anatomical axes.