Objectives HIV-associated neurocognitive disorders are highly prevalent, and physical activity (PA) is a modifiable behaviour that may affect neurocognitive function. Our objective was to determine the association between PA and neurocognitive function and the effect of HIV on this association. Methods PA was assessed in the Multicenter AIDS Cohort Study with the International Physical Activity Questionnaire. A neuropsychological test battery assessed global impairment and domain-specific impairment (executive function, speed of processing, working memory, learning, memory, and motor function) every 2 years. Semiannually, the Symbol Digit Modalities Test and Trail Making Test Parts A and B were performed. Adjusted logistic regression models were used to assess the PA–neurocognitive function association. Using longitudinal data, we also assessed the PA category–decline of neurocognitive function association with multivariate simple regression. Results Of 601 men, 44% were HIV-infected. Low, moderate, and high PA was reported in 27%, 25%, and 48% of the HIV-infected men vs. 19%, 32% and 49% of the HIV-uninfected men, respectively. High PA was associated with lower odds of impairment of learning, memory, and motor function [odds ratio (OR) ranging from 0.52 to 0.57; P < 0.05 for all]. The high PA–global impairment association OR was 0.63 [95% confidence interval (CI) 0.39, 1.02]. Among HIV-infected men only, across multiple domains, the high PA–impairment association was even more pronounced (OR from 0.27 to 0.49). Baseline high/moderate PA was not associated with decline of any domain score over time. HIV infection was marginally associated with a higher speed of decline in motor function. Conclusions A protective effect of high PA on impairment in neurocognitive domains was observed cross-sectionally. Longitudinal PA measurements are needed to elucidate the PA–neurocognitive function relationship over time.

The two-photon transition c ð3686Þ ! J=c is studied in a sample of 1:06 Â 10 8 c ð3686Þ decays collected by the BESIII detector. The branching fraction is measured to be ð3:1 AE 0:6ðstatÞ þ0:8 À1:0 ðsystÞÞ Â 10 À4 using J=c ! e þ e À and J=c ! þ À decays, and its upper limit is estimated to be 4:5 Â 10 À4 at the 90% confidence level. This work represents the first measurement of a two-photon transition among charmonium states. The orientation of the c ð3686Þ decay plane and the J=c polarization in this decay are also studied. In addition, the product branching fractions of sequential E1 transitions c ð3686Þ ! cJ and cJ ! J=c ðJ ¼ 0; 1; 2Þ are reported. DOI: 10.1103/PhysRevLett.109.172002 PACS numbers: 14.40.Pq, 13.20.Gd The XYZ [1] particles, which do not fit potential model expectations in QCD theory, have been a key challenge to the QCD description of charmoniumlike states [2]. To fully understand those states, it is necessary to consider the coupling of a charmonium state to a D " D meson pair. These coupled-channel effects, which also play an important role in the charmonium transitions of low-lying states [i.e., from c ð3686Þ to J=c ], are especially relevant for the radiative transition processes [3]. In the well-known electric dipole transitions, the strength of coupled-channel effects will likely be hard to establish, since the accompanying relativistic corrections may be more important [4]. However, the two-photon transition c ð3686Þ ! J=c is more sensitive to the coupled-channel effect and thus provides a unique opportunity to investigate these issues [5].Two-photon spectroscopy has been a very powerful tool for the study of the excitation spectra of a variety of PRL 109, 172002 (2012) P H Y S I C A L R E V I E W L E T T E R S week ending 26 OCTOBER 2012172002-2 systems with a wide range of sizes, such as molecules, atomic hydrogen, and positronium [6]. Studying the analogous process in quarkonium states is a natural extension of this work, in order to gain insight into nonperturbative QCD phenomena. But, so far, two-photon transitions in quarkonia have eluded experimental observation [7][8][9]. For example, in a study of c ð3686Þ ! cJ ðJ ¼ 0; 1; 2Þ reported by the CLEO Collaboration [9], the upper limit for Bðc ð3686Þ ! J=c Þ was estimated to be 1 Â 10 À3 . This Letter presents the first evidence for the two-photon transition c ð3686Þ ! J=c , as well as studies of the orientation of the c ð3686Þ decay plane and the J=c polarization in the decay. The branching fractions of double E1 transitions c ð3686Þ ! ðJ=c Þ cJ through cJ intermediate states are also reported. The upgraded BEPCII [12] at Beijing is a two-ring electron-positron collider. The BESIII detector [10] is an approximately cylindrically symmetric detector which covers 93% of the solid angle around the collision point. In the order of increasing distance from the interaction point, the subdetectors include a 43-layer main wire drift chamber (MDC), a time-of-flight system with two layers in the barrel region and one layer for each end c...