Effects of chronic marijuana use on circadian rhythms, sleep, and cognitive performance

Marijuana use has been linked to various circadian related activities like sleep and cognitive performance (Bolla et al., 2002; 2008; Budney et al., 2002; Cohen-Zion et al., 2010; Iverson et al., 2005; Meier et al., 2012; NIDA, 2012; Pope & Yugulen-Todd, 1996; WHO, 2013). Animal literature suggests a connection between marijuana use and altered circadian rhythms; however, the effect has not yet been studied in humans (Acuna-Goycolea et al., 2010; Sanford et al., 2008). The present study seeks to examine the effect of chronic marijuana use on circadian function in humans and extend the knowledge surrounding marijuana’s effect on neurocognition and sleep quality. Participants consisted of chronic marijuana users and age-matched non-drug user controls. Participant substance abuse was verified through urine samples obtained at the initial and final visits. Participants wore actigraphs and maintained sleep diaries for 3 weeks and both marijuana users and non-users took the Automated Neuropsychological Assessment Metrics (ANAM) to measure cognitive performance. Data analyses reveal chronic marijuana use may act as a zeitgeber and lead to increased entrainment in human users, however use may also result in slight cognitive impairment and significant sleep disturbance

Comparing the cardiac autonomic activity profile of daytime naps and nighttime sleep.

Heart rate variability (HRV) is a reliable technique to evaluate autonomic activity and shows marked changes across a night of sleep. Previous nighttime sleep findings report changes in HRV during non-rapid eye movement sleep (NREM), which have been associated with cardiovascular health benefits. Daytime sleep, however, has been linked with both positive and negative cardiovascular outcomes. Yet, no studies have directly compared HRV profiles during an ecologically-valid daytime nap in healthy, well-rested adults to that of nighttime sleep. Using a within-subjects design, 32 people took a daytime nap and slept overnight in the lab at least one week apart; both sleep sessions had polysomnography, including electrocardiography (ECG), recorded. We measured inter-beat intervals (RR), total power (TP), low frequency power (LF; .04-.15 Hz), and high frequency power (HF; .15-.40 Hz) components of HRV during NREM and rapid eye movement (REM) sleep. Compared to the nap, we found longer RR intervals and decreased heart rate during the night for both Stage 2 and SWS and increased TP, LF and HF power during nighttime Stage 2 sleep only; however, no differences in the LFHF ratio or normalized HF power were found between the nap and the night. Also, no differences in REM sleep between the nap and night were detected. Similar relationships emerged when comparing the nap to one cycle of nighttime sleep. These findings suggest that longer daytime naps, with both SWS and REM, may provide similar cardiovascular benefits as nocturnal sleep. In light of the on-going debate surrounding the health benefits and/or risks associated with napping, these results suggest that longer daytime naps in young, healthy adults may support cardiac down-regulation similar to nighttime sleep. In addition, napping paradigms may serve as tools to explore sleep-related changes in autonomic activity in both healthy and at-risk populations

The Impact of Off-Label Psychostimulant Use on Sleep Physiology and Sleep-Related Cognitive Function

The off-label use of prescription psychostimulants in healthy individuals is becoming more prevalent, particularly in college populations, prompting the new label “Generation Adderall”. Although these drugs have been shown to improve cognition in children with attention-deficit disorder (ADHD), the efficacy of stimulant medications for cognitive enhancement in healthy adults has not been definitively shown, with some research indicating positive effects on cognition, others indicating negative effects, and still others showing no effects of stimulant interventions. Further, discrepant results have been reported between, but also within cognitive domains, suggesting more research is needed to carefully illuminate and replicate these effects. I propose that one of the primary outcomes of psychostimulants, namely decreased sleep, may play an important, and as of yet, unacknowledged role in the effect of these drugs on cognition. Sleep, a basic biological need, has been shown to be important for cognitive processing, including learning, memory and attention. Remarkably, however, the interaction between stimulants, sleep and cognition in healthy adults has received little scientific attention. Here, I first present experimental evidence from two different within-subjects, crossover, double-blind, placebo-controlled studies where I examine the immediate and long-term impact of psychostimulants on two different cognitive domains; sustained attention, which has previously shown stimulant-related performance enhancement, and emotional memory, which has reliably been shown to benefit from sleep. Next, in light of these two studies’ novel contributions, I review the existing literature on stimulant cognitive enhancement and propose a theoretical model that includes sleep as the missing link in the story of psychostimulant cognitive enhancement

Determining the Effects of Herbivory on Population Variation in an Herbaceous Plant

Plants subjected to herbivory tend to suffer from reductions in fitness. In addition, herbivory may delay reproduction, which in turn may negatively affect certain life history traits. Deer are overabundant and dramatically affect herbaceous plants through herbivory, possibly leading to selection for tolerance. The environment and length of the growing season can also affect tolerance to herbivory. This research investigated potential evolutionary responses to variation in herbivory. Specifically, it used the model organism American Bellflower [C. americanum] to investigate whether plants have evolved to tolerate deer herbivory and if tolerance varies among populations. Using this plant species, delays in reproduction associated with herbivory among populations were compared to determine if this could result in observed life history schedules. To provide insight into the selection pressure by deer on C. americanum, this project determined if deer preference depends on population or plant size. There is phenological variation among these populations, therefore we experimentally evaluated whether this difference in phenology contribute to response to herbivory by using three clipping treatments 1) plants clipped at the same calendar date, 2) plants clipped at a similar phenological stage, and 3) controls (unclipped). Additional plants open to natural deer herbivory were also observed and the fitness components of these plants were compared to those plants kept from natural herbivory. Population variation in tolerance to herbivory was determined by measuring vegetative growth and reproductive fitness components. This research project took place in Michigan and Georgia to allow the role of growing season on tolerance to deer herbivory to be evaluated. Knowledge of the association between deer herbivory and C. americanum performance and reproductive phenology will directly inform understanding of evolutionary responses to herbivory. The research will determine if tolerance to herbivory and delays in reproductive phenology following herbivory vary among populations and if this difference depends on environment

The Impact of Off-Label Psychostimulant Use on Sleep Physiology and Sleep-Related Cognitive Function

The off-label use of prescription psychostimulants in healthy individuals is becoming more prevalent, particularly in college populations, prompting the new label “Generation Adderall”. Although these drugs have been shown to improve cognition in children with attention-deficit disorder (ADHD), the efficacy of stimulant medications for cognitive enhancement in healthy adults has not been definitively shown, with some research indicating positive effects on cognition, others indicating negative effects, and still others showing no effects of stimulant interventions. Further, discrepant results have been reported between, but also within cognitive domains, suggesting more research is needed to carefully illuminate and replicate these effects. I propose that one of the primary outcomes of psychostimulants, namely decreased sleep, may play an important, and as of yet, unacknowledged role in the effect of these drugs on cognition. Sleep, a basic biological need, has been shown to be important for cognitive processing, including learning, memory and attention. Remarkably, however, the interaction between stimulants, sleep and cognition in healthy adults has received little scientific attention. Here, I first present experimental evidence from two different within-subjects, crossover, double-blind, placebo-controlled studies where I examine the immediate and long-term impact of psychostimulants on two different cognitive domains; sustained attention, which has previously shown stimulant-related performance enhancement, and emotional memory, which has reliably been shown to benefit from sleep. Next, in light of these two studies’ novel contributions, I review the existing literature on stimulant cognitive enhancement and propose a theoretical model that includes sleep as the missing link in the story of psychostimulant cognitive enhancement

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Belgium Herbarium image of Meise Botanic Garden