Relative Timing Of Activity Research Articles

Theta-phase locking of single neurons during human spatial memory.

The precise timing of single-neuron activity in relation to local field potentials may support various cognitive functions. Extensive research in rodents, along with some evidence in humans, suggests that single-neuron activity at specific phases of theta oscillations plays a crucial role in memory processes. Our fundamental understanding of such theta-phase locking in humans and its dependency on basic electrophysiological properties of the local field potential is still limited, however. Here, using single-neuron recordings in epilepsy patients performing a spatial memory task, we thus aimed at improving our understanding of factors modulating theta-phase locking in the human brain. Combining a generalized-phase approach for frequency-adaptive theta-phase estimation with time-resolved spectral parameterization, our results show that theta-phase locking is a strong and prevalent phenomenon across human medial temporal lobe regions, both during spatial memory encoding and retrieval. Neuronal theta-phase locking increased during periods of elevated theta power, when clear theta oscillations were present, and when aperiodic activity exhibited steeper slopes. Theta-phase locking was similarly strong during successful and unsuccessful memory, and most neurons activated at similar theta phases between encoding and retrieval. Some neurons changed their preferred theta phases between encoding and retrieval, in line with the idea that different memory processes are separated within the theta cycle. Together, these results help disentangle how different properties of local field potentials and memory states influence theta-phase locking of human single neurons. This contributes to a better understanding of how interactions between single neurons and local field potentials may support human spatial memory.

Old basalts, young soils ‐ Age constraints for the Golan Heights plateau volcanic soils

AbstractThe Golan Heights plateau in northern Israel is underlaid by volcanic rocks ranging in age from ~5.5 to 0.1 Ma. Throughout the Golan Heights, these rocks are covered by shallow soils that rarely exceed 0.5 m in depth. The soils are generally assumed to form a chronosequence, in which their ages correspond to those of the basalts they cover. Such age correspondence would imply that the soils have been slowly accumulating over hundreds of thousands to a few million years, suggesting a generally stable system. The ages of these soils and their temporal correlation to the basalts, however, have never been determined or tested.Here, we present age constraints for the soils of the Golan Heights. Soils were surveyed and sampled with their corresponding basalt bedrock. Mass balance calculations based on conservative immobile elements, coupled with 36Cl‐based basalt denudation rates, suggest that the soil ages are decoupled from the ages of the underlying basalts, and represent up to a few thousand years of soil production, at most. This time frame is orders of magnitude shorter than the basalt age, challenging the prevalent assumption that the soils form a chronosequence.Our findings strongly suggest that erosion is a significant factor controlling soil formation and accumulation on the plateau, despite the generally flat morphology of the Golan Heights. The erosion is associated with tectonic activity along the Dead Sea transform, with the development of the Kinarot and Hula valleys, and with the consequential development of drainage systems of various sizes on the plateau. Throughout the Golan Heights, the timing of volcanic activity in relation to the development of the valleys and drainage systems also appears to strongly affect soil development and accumulation.

Sincronización entre la videodeglución y la electromiografía de superficie en pacientes con afectación neurológica y síntomas de disfagia

Introducción. La disfagia se define como la dificultad para movilizar la comida desde la boca hasta el estómago. La prueba diagnóstica para esta condición es la videofluoroscopia, la cual no es totalmente inocua pues utiliza radiación ionizante. La electromiografía de superficie registra la actividad eléctrica de los músculos de manera no invasiva, por lo que puede considerarse como una alternativa para evaluar la deglución y estudiar la disfagia. Objetivo. Evaluar la relación entre los tiempos relativos de activación de los músculos implicados en la fase oral y faríngea de la deglución, con los movimientos registrados durante la videofluoroscopia. Materiales y métodos. Se analizaron las señales de la electromiografía de superficie de 10 pacientes neurológicos con síntomas de disfagia, captadas en forma simultánea con la videofluoroscopia. Se suministraron 5 ml de yogur y 10 ml de agua, y 3 g de galleta. Se estudiaron bilateralmente los grupos musculares maseteros, suprahioideos e infrahioideos. Se analizó el paso del bolo por la línea mandibular, las valleculas y el músculo cricofaríngeo, correlacionándolo con el tiempo inicial y el final de la activación de cada uno de los grupos musculares. Resultados. El tiempo promedio de la fase faríngea fue de 0,89 ± 0,12 s. En la mayoría de los casos, hubo activación muscular antes del paso por la línea mandibular y las valleculas. La terminación de la actividad muscular parece corresponder al momento en que se completa el paso del bolo alimenticio por el músculo cricofaríngeo. Conclusión. Se determinaron los tiempos de actividad muscular, la duración de la fase faríngea y la secuencia de la activación de los grupos musculares involucrados en la deglución, mediante electromiografía de superficie, validada con la videofluoroscopia.

Timing of physical activity in relation to liver fat content and insulin resistance

Aims/hypothesisWe hypothesised that the insulin-sensitising effect of physical activity depends on the timing of the activity. Here, we examined cross-sectional associations of breaks in sedentary time and timing of physical activity with liver fat content and insulin resistance in a Dutch cohort.MethodsIn 775 participants of the Netherlands Epidemiology of Obesity (NEO) study, we assessed sedentary time, breaks in sedentary time and different intensities of physical activity using activity sensors, and liver fat content by magnetic resonance spectroscopy (n=256). Participants were categorised as being most active in the morning (06:00–12:00 hours), afternoon (12:00–18:00 hours) or evening (18:00–00:00 hours) or as engaging in moderate-to-vigorous-physical activity (MVPA) evenly distributed throughout the day. Most active in a certain time block was defined as spending the majority (%) of total daily MVPA in that block. We examined associations between sedentary time, breaks and timing of MVPA with liver fat content and HOMA-IR using linear regression analyses, adjusted for demographic and lifestyle factors including total body fat. Associations of timing of MVPA were additionally adjusted for total MVPA.ResultsThe participants (42% men) had a mean (SD) age of 56 (4) years and a mean (SD) BMI of 26.2 (4.1) kg/m2. Total sedentary time was not associated with liver fat content or insulin resistance, whereas the amount of breaks in sedentary time was associated with higher liver fat content. Total MVPA (−5%/h [95% CI −10%/h, 0%/h]) and timing of MVPA were associated with reduced insulin resistance but not with liver fat content. Compared with participants who had an even distribution of MVPA throughout the day, insulin resistance was similar (−3% [95% CI −25%, 16%]) in those most active in morning, whereas it was reduced in participants who were most active in the afternoon (−18% [95% CI −33%, −2%]) or evening (−25% [95% CI −49%, −4%]).Conclusions/interpretationThe number of daily breaks in sedentary time was not associated with lower liver fat content or reduced insulin resistance. Moderate-to-vigorous activity in the afternoon or evening was associated with a reduction of up to 25% in insulin resistance. Further studies should assess whether timing of physical activity is also important for the occurrence of type 2 diabetes.Graphical abstract

Timing of objectively-collected physical activity in relation to body weight and metabolic health in sedentary older people: a cross-sectional and prospective analysis.

Little is known about the impact of timing as opposed to frequency and intensity of daily physical activity on metabolic health. Therefore, we assessed the association between accelerometery-based daily timing of physical activity and measures of metabolic health in sedentary older people. Hourly mean physical activity derived from wrist-worn accelerometers over a 6-day period was collected at baseline and after 3 months in sedentary participants from the Active and Healthy Ageing study. A principal component analysis (PCA) was performed to reduce the number of dimensions (e.g. define periods instead of separate hours) of hourly physical activity at baseline and change during follow-up. Cross-sectionally, a multivariable-adjusted linear regression analysis was used to associate the principal components, particularly correlated with increased physical activity in data-driven periods during the day, with body mass index (BMI), fasting glucose and insulin, HbA1c and the homeostatic model assessment for insulin resistance (HOMA-IR). For the longitudinal analyses, we calculated the hourly changes in physical activity and change in metabolic health after follow-up. We included 207 individuals (61.4% male, mean age: 64.8 [SD 2.9], mean BMI: 28.9 [4.7]). Higher physical activity in the early morning was associated with lower fasting glucose (-2.22%, 95% CI: -4.19, -0.40), fasting insulin (-13.54%, 95%CI: -23.49, -4.39), and HOMA-IR (-16.07%, 95%CI: -27.63, -5.65). Higher physical activity in the late afternoon to evening was associated with lower BMI (-2.84%, 95% CI: -4.92, -0.70). Higher physical activity at night was associated with higher BMI (2.86%, 95% CI: 0.90, 4.78), fasting glucose (2.57%, 95% CI: 0.70, 4.30), and HbA1c (2.37%, 95% CI: 1.00, 3.82). Similar results were present in the prospective analysis. Specific physical activity timing patterns were associated with more beneficial metabolic health, suggesting particular time-dependent physical activity interventions might maximise health benefits.

Responses of putative medium spiny neurons and fast-spiking interneurons to reward-related sensory signals in Wistar and genetically hypertensive rats.

Medium spiny neurons (MSN) are the primary output neurons of the striatum. Their activity is modulated by exogenous afferents and local circuit inputs, including fast-spiking interneurons (FSI). Altered responses of MSN and FSI may account for altered reward-driven behaviour in hyperactive rat strains, such as the genetically hypertensive (GH) rat. To investigate whether striatal neuron responses differ between GH and Wistar rats, we recorded putative MSNs (pMSN) and FSI (pFSI) from freely moving GH and Wistar rats in a classically conditioned (Pavlovian) cue-reward association paradigm. Here, the same auditory cue signal predicted reward delivery in one block of trials, but was not followed by reward in another. The significance of the cue as a reward predictor was indicated during each block by an environmental context provided by the house light. The results showed that pMSN in GH rats, but not Wistar rats, were more sensitive to the auditory signal in the context indicating no-reward, than in the reward context. Such enhanced sensitivity to cues in a no-reward context may contribute to a specific deficit in instrumental behaviour seen in GH rats, which maintain higher levels of instrumental responding in a context that indicates responding will not be rewarded. In addition, pFSI also responded to auditory signals, but there was no significant effect of reward context. Surprisingly, given their known feed-forward role, pFSI responded at longer latency than pMSN, suggesting that relative timing of activity in the two populations may be task specific.

Novel Insights in the Activation Patterns at the Pulmonary Vein Area.

Extensiveness of conduction delay and block at the pulmonary vein area (PVA) was quantified in a previous study. We hypothesized that the combination of lines of conduction block with multiple concomitantly entering sinus rhythm wavefronts at the PVA may result in increased arrhythmogenicity and susceptibility to atrial fibrillation (AF). Intraoperative high-density epicardial mapping of PVA (N≈450 sites, interelectrode distances: 2 mm) was performed during sinus rhythm in 327 patients (241 male [74%], 67±10 [21-84] years) with and without preoperative AF. For each patient, activation patterns at the PVA were quantified, including the location of entry sites of wavefronts, direction of propagation, and their relative activation times. The association between activation patterns and the presence of AF was examined. Excitation of the PVA occurred via multiple consecutive wavefronts in the vast majority of patient (N=216, 81%). In total, 561 wavefronts were observed, which mostly propagated through the septal or paraseptal regions towards the PVA (N=461, 82%). A substantial dissociation of consecutive wavefronts was observed with Δactivation times of 10.6±8.8 (0-46) ms. No difference was observed in Δactivation times of consecutive wavefronts during sinus rhythm between patients without and with AF. An excitation-based risk factor model, including conduction delay ≥6 mm, conduction block ≥6 mm, and conduction delay and block ≥16 mm, wavefronts via the posteroinferior to posterosuperior regions and multiple opposing wavefronts, demonstrated a 5-fold risk of AF when multiple risk factors were present. In contrast to previous findings, quantification of activation patterns at the PVA on high-resolution scale demonstrated complex patterns with often multiple entry sites and high interindividual variability. Altered patterns of activation, consisting of multiple opposing wavefronts combined with long lines of conduction slowing, were associated with the presence of AF.

Co-imaging extrinsic, intrinsic and effector caspase activity by fluorescence anisotropy microscopy

In order to overcome intercellular variability and thereby effectively assess signal propagation in biological networks it is imperative to simultaneously quantify multiple biological observables in single living cells. While fluorescent biosensors have been the tool of choice to monitor the dynamics of protein interaction and enzymatic activity, co-measuring more than two of them has proven challenging. In this work, we designed three spectrally separated anisotropy-based Förster Resonant Energy Transfer (FRET) biosensors to overcome this difficulty. We demonstrate this principle by monitoring the activation of extrinsic, intrinsic and effector caspases upon apoptotic stimulus. Together with modelling and simulations we show that time of maximum activity for each caspase can be derived from the anisotropy of the corresponding biosensor. Such measurements correlate relative activation times and refine existing models of biological signalling networks, providing valuable insight into signal propagation.

Pelvic floor muscle activity during impact activities in continent and incontinent women: a systematic review.

Investigating the activity of the pelvic floor muscles (PFMs) in women during impact activities such as jumping, running or coughing may elucidate different aspects of PFM activation and therefore clarify the pathophysiology of stress urinary incontinence (SUI). A systematic review (PROSPERO 2016:CRD42016035624) was conducted to summarize current evidence on PFM activity during impact activities in both continent and incontinent women. PubMed, EMBASE, Cochrane, and SPORTDiscus databases were systematically searched for studies published up to December 2016. The PICO approach (patient, intervention, comparison, outcome) was used to construct the search queries. Original studies were included that investigated PFM activity during impact activities if they included terms related to muscle activity and measurement methods, test positions, activities performed and continence status. Two reviewers screened titles and abstracts independently to ascertain if the included studies fulfilled the inclusion criteria, and extracted data on outcome parameters. The search revealed 28 studies that fulfilled the inclusion criteria, of which 26 were cross-sectional studies. They used different electromyography measurement methods, test activities, test positions, and comparisons with other structures. Ten studies compared continent and incontinent women. The timing of PFM activity in relation to the activity of other trunk muscles seems to be a crucial factor in maintaining continence. Women with SUI have delayed PFM activity. The findings of this systematic review suggest that impact activities causing involuntary and reflex PFM activity should be the subject of further study. This may help guide clinical studies to improve our understanding of how the PFMs react during impact activities and to determine best practices that can be included in rehabilitation programmes.

The role of REM sleep theta activity in emotional memory.

While non-REM (NREM) sleep has been strongly implicated in the reactivation and consolidation of memory traces, the role of rapid-eye movement (REM) sleep remains unclear. A growing body of research on humans and animals provide behavioral evidence for a role of REM sleep in the strengthening and modulation of emotional memories. Theta activity—which describes low frequency oscillations in the local field potential within the hippocampus, amygdala and neocortex—is a prominent feature of both wake and REM sleep in humans and rodents. Theta coherence between the hippocampus and amygdala drives large-scale pontine-geniculo-occipital (PGO) waves, the density of which predicts increases in plasticity-related gene expression. This could potentially facilitate the processing of emotional memory traces within the hippocampus during REM sleep. Further, the timing of hippocampal activity in relation to theta phase is vital in determining subsequent potentiation of neuronal activity. This could allow the emotionally modulated strengthening of novel and gradual weakening of consolidated hippocampal memory traces during REM sleep. Hippocampal theta activity is also correlated with REM sleep levels of achetylcholine - which is thought to reduce hippocampal inputs in the neocortex. The additional low levels of noradrenaline during REM sleep, which facilitate feedback within the neocortex, could allow the integration of novel memory traces previously consolidated during NREM sleep. We therefore propose that REM sleep mediates the prioritized processing of emotional memories within the hippocampus, the integration of previously consolidated memory traces within the neocortex, as well as the disengagement of consolidated neocortical memory traces from the hippocampus.

Editorial: Homeostatic and retrograde signaling mechanisms modulating presynaptic function and plasticity.

Editorial: Homeostatic and retrograde signaling mechanisms modulating presynaptic function and plasticity.

Pre-lexical phonological processing in reading Chinese characters: An ERP study

Abstract Sinograms (i.e., Chinese characters) are usually composed of radicals which do not correspond to phonemes; instead, some radicals can occur as freestanding sinograms and have their own pronunciations. Previous research has demonstrated that the pronunciations of both radicals and sinograms are activated in reading low-frequency sinograms. However, the relative timing of activation between sinogram pronunciation and radical pronunciation has not been addressed. We examine this issue by comparing the interference effects exerted by two types of primes on the targets in an event-related potential (ERP) experiment: RADICAL-RELATED primes, which are homophonic with a radical embedded in the targets; and SINOGRAM-RELATED primes, which are homophonic with the targets. A radical interference effect is found for N170, P200 and N400 responses, whereas a sinogram interference effect is found only for N400. Our findings demonstrate that the pronunciations of radicals are activated pre-lexically, i.e., prior to those of their host sinograms. The role of this early sub-lexical phonology is discussed within an interactive activation framework, wherein two types of pronunciations—(1) the radical pronunciations and (2) the set of pronunciations associated with the sinogram’s orthographical neighbors—are both present and operate interactively.

Delayed onset of vastii muscle activity in response to rapid postural perturbations following eccentric exercise: a mechanism that underpins knee pain after eccentric exercise?

BackgroundAppropriate timing of activity of the vastus medialis obliqus (VMO) and vastus lateralis (VL) muscles is a key factor for proper tracking of the patella in the trochlear groove during...

Olfactory cortical neurons read out a relative time code in the olfactory bulb

Odor stimulation evokes complex spatiotemporal activity in the olfactory bulb, suggesting that the identity of activated neurons as well as the timing of their activity convey information about odors. However, whether and how downstream neurons decipher these temporal patterns remains debated. We addressed this question by measuring the spiking activity of downstream neurons while optogenetically stimulating two foci in the olfactory bulb with varying relative timing in mice. We found that the overall spike rates of piriform cortex neurons were sensitive to the relative timing of activation. Posterior piriform cortex neurons showed higher sensitivity to relative input times than neurons in the anterior piriform cortex. In contrast, olfactory bulb neurons rarely showed such sensitivity. Thus, the brain can transform a relative time code in the periphery into a firing-rate-based representation in central brain areas, providing evidence for the relevance of relative time-based code in the olfactory bulb.

Altered Network Timing in the CA3-CA1 Circuit of Hippocampal Slices from Aged Mice

Network patterns are believed to provide unique temporal contexts for coordinating neuronal activity within and across different regions of the brain. Some of the characteristics of network patterns modeled in vitro are altered in the CA3 or CA1 subregions of hippocampal slices from aged mice. CA3–CA1 network interactions have not been examined previously. We used slices from aged and adult mice to model spontaneous sharp wave ripples and carbachol-induced gamma oscillations, and compared measures of CA3–CA1 network timing between age groups. Coherent sharp wave ripples and gamma oscillations were evident in the CA3–CA1 circuit in both age groups, but the relative timing of activity in CA1 stratum pyramidale was delayed in the aged. In another sample of aged slices, evoked Schaffer collateral responses were attenuated in CA3 (antidromic spike amplitude) and CA1 (orthodromic field EPSP slope). However, the amplitude and timing of spontaneous sharp waves recorded in CA1 stratum radiatum were similar to adults. In both age groups unit activity recorded juxtacellularly from unidentified neurons in CA1 stratum pyramidale and stratum oriens was temporally modulated by CA3 ripples. However, aged neurons exhibited reduced spike probability during the early cycles of the CA3 ripple oscillation. These findings suggest that aging disrupts the coordination of patterned activity in the CA3–CA1 circuit.

Balancing speed and accuracy of polyclonal T cell activation: a role for extracellular feedback

BackgroundExtracellular feedback is an abundant module of intercellular communication networks, yet a detailed understanding of its role is still lacking. Here, we study interactions between polyclonal activated T cells that are mediated by IL-2 extracellular feedback as a model system.ResultsUsing mathematical modeling we show that extracellular feedback can give rise to opposite outcomes: competition or cooperation between interacting T cells, depending on their relative levels of activation. Furthermore, the outcome of the interaction also depends on the relative timing of activation of the cells. A critical time window exists after which a cell that has been more strongly activated nevertheless cannot exclude an inferior competitor.ConclusionsIn a number of experimental studies of polyclonal T-cell systems, outcomes ranging from cooperation to competition as well as time dependent competition were observed. Our model suggests that extracellular feedback can contribute to these observed behaviors as it translates quantitative differences in T cells’ activation strength and in their relative activation time into qualitatively different outcomes. We propose extracellular feedback as a general mechanism that can balance speed and accuracy – choosing the most suitable responders out of a polyclonal population under the clock of an escalating threat.

Cortical activity during speech and non-speech oromotor tasks: A magnetoencephalography (MEG) study

We used whole-head magnetoencephalography to investigate cortical activity during two oromotor activities foundational to speech production. 13 adults performed mouth opening and phoneme (/pa/) production tasks to a visual cue. Jaw movements were tracked with an ultrasound-emitting device. Trials were time-locked to both stimulus onset and peak of jaw displacement. An event-related beamformer source reconstruction algorithm was used to detect areas of cortical activity for each condition. Beamformer output was submitted to iterative K-means clustering analyses. The time course of neural activity at each cluster centroid was computed for each individual and condition. Peaks were identified and latencies submitted for statistical analysis to reveal the relative timing of activity in each brain region. Stimulus locked activations for the mouth open task included a progression from left cuneus to left frontal and then right pre-central gyrus. Phoneme generation revealed the same sequence but with bilateral frontal activation. When time locked to jaw displacement, the mouth open condition showed left frontal followed by right frontal–temporal areas. Phoneme generation showed a complicated sequence of bilateral temporal and frontal areas. This study used three unique approaches (beamforming, clustering and jaw tracking) to demonstrate the temporal progression of neural activations that underlie the motor control of two simple oromotor tasks. These findings have implications for understanding clinical conditions with deficits in articulatory control or motor speech planning.

Perception of sniff phase in mouse olfaction

Olfactory systems encode odours by which neurons respond and by when they respond. In mammals, every sniff evokes a precise, odour-specific sequence of activity across olfactory neurons. Likewise, in a variety of neural systems, ranging from sensory periphery to cognitive centres, neuronal activity is timed relative to sampling behaviour and/or internally generated oscillations. As in these neural systems, relative timing of activity may represent information in the olfactory system. However, there is no evidence that mammalian olfactory systems read such cues. To test whether mice perceive the timing of olfactory activation relative to the sniff cycle ('sniff phase'), we used optogenetics in gene-targeted mice to generate spatially constant, temporally controllable olfactory input. Here we show that mice can behaviourally report the sniff phase of optogenetically driven activation of olfactory sensory neurons. Furthermore, mice can discriminate between light-evoked inputs that are shifted in the sniff cycle by as little as 10 milliseconds, which is similar to the temporal precision of olfactory bulb odour responses. Electrophysiological recordings in the olfactory bulb of awake mice show that individual cells encode the timing of photoactivation in relation to the sniff in both the timing and the amplitude of their responses. Our work provides evidence that the mammalian olfactory system can read temporal patterns, and suggests that timing of activity relative to sampling behaviour is a potent cue that may enable accurate olfactory percepts to form quickly.

The benefits of rapid 3D fMRI

AbstractFunctional magnetic resonance imaging (fMRI) provides the ability to image blood dynamics through the entire brain with a high spatial resolution. However, the temporal resolution is much slower than the underlying neuronal activity one seeks to infer. Recent developments in rapid imaging allow 3D fMRI studies to be performed at a temporal resolution of 100 ms; a 10‐fold increase compared to standard approaches. This increase in temporal resolution offers a number of potential benefits. First, it allows the focus of analysis to be shifted from changes in blood flow taking place 5–8 s after neuronal activity to more transient changes taking place immediately following activation. We argue that studying these changes provides valuable information about the relative timing of activation across different regions of the brain, which is crucial for inferring brain pathways. Second, rapid imaging allows for the efficient modeling of physiological artifacts without problems with aliasing; something that is difficult at standard resolutions. We illustrate how removal of these artifacts provides the increase in signal‐to‐noise ratio required for studying the subtle changes in oxygenation we are interested in. Finally, we show how high temporal resolution data provides the opportunity to focus the analysis on the rate of change in oxygenation rather than the level of oxygenation as is the current practice. The price of performing rapid imaging studies is a decrease in spatial resolution. However, we argue that the resolution is still comparable to the effective resolution used in most fMRI studies. We illustrate our approach using two fMRI data sets. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 14–22, 2010

Intensity and timing of physical activity in relation to postmenopausal breast cancer risk: the prospective NIH-AARP diet and health study.

BackgroundDespite strong evidence of an inverse association of physical activity with postmenopausal breast cancer risk, whether a certain intensity or time of life of physical activity is most effective for lowering breast cancer risk is not known.MethodsIn 118,899 postmenopausal women in the prospective NIH-AARP Diet and Health Study, we examined the relations of light and moderate-to-vigorous intensity physical activity during four periods of life ("historical": ages 15-18, 19-29, 35-39 years; "recent": past 10 years) to postmenopausal breast cancer risk. Physical activity was assessed by self-report at baseline, and 4287 incident breast cancers were identified over 6.6 years of follow-up.ResultsIn age-adjusted and multivariate Cox regression models, >7 hours/week of moderate-to-vigorous activity during the past 10 years was associated with 16% reduced risk of postmenopausal breast cancer (RR:0.84; 95%CI:0.76,0.93) compared with inactivity. The association remained statistically significant after adjustment for BMI (RR:0.87; 95%CI:0.78,0.96). Neither moderate-to-vigorous activity during other periods of life nor light intensity activity during any period of life was related to breast cancer risk, and associations did not vary by tumor characteristics.ConclusionA high level of recent, but not historical, physical activity of moderate-to-vigorous intensity is associated with reduced postmenopausal breast cancer risk. More precise recall of recent physical activity than activity in the distant past is one possible explanation for our findings.