![]() ![]() ![]() Boggio and colleagues (2009) aimed to investigate the impact of anodal tDCS on recognition memory, working memory, and selective attention in AD. No changes were observed in a visual attention task, suggesting that the effects of tDCS were specific for recognition memory. Anodal tDCS significantly improved recognition memory, whereas cathodal tDCS significantly decreased accuracy in the word recognition task, and sham tDCS did not change it. Ferrucci and colleagues (2008) delivered, in 10 patients with mild AD, anodal tDCS, cathodal tDCS, and sham tDCS over the temporoparietal cortex in three separate sessions (15 min at 1.5 mA, at least 1 week apart). Two crossover studies using tDCS have been performed to enhance recognition memory in patients with AD ( Ferrucci et al., 2008 Boggio et al., 2009). Eugen Trinka, in Handbook of Clinical Neurology, 2013 Transcranial direct current stimulation A randomized, double-blind, crossover, placebo-controlled trial is an example of a desirable study design. Study design is the combination of the awareness level of the tested drug or vaccine, the chosen comparative reference, study subject allocation and follow-up methods, the planned duration of the study, the number of groups and subgroups, and the exams involved – all adjusted to provide an answer to the investigator’s hypothesis. The limitation of crossover studies is the need for a washout period between study phases. They afford comparison between groups in a self-paired manner that is, groups A and B can be compared against themselves at the end of the study, and this allows for greater biological homogeneity. They corroborate the findings of the first phase of the study by reproducing them in the second phase, reinforcing the final conclusion of the study. After regimen swap, group B subjects showed the same symptom decrease first associated with group A subjects, and the latter presented the same symptoms level that group B subjects did in the first phase of the study. For example, a new ergot alkaloid derivative + acetaminophen combination showed a significant decrease in migraine symptoms in group A subjects compared to group B subjects, who took only acetaminophen. In crossover studies, the groups change their respective arms at a specific point during the investigation. ![]() There is also potential for unblinding, when the effects of the active drug are more obvious to the participants than those of placebo, and for carry-over effects between evaluation phases, particularly for drugs with long elimination half-lives. There may be difficulty in incorporating multiple dosage arms and in dealing with drop-outs patients who only complete the first evaluation phase contribute little to the analysis. Cross-over studies are often of longer duration than parallel-group studies. The advantages of the cross-over design are that each subject acts as his or her own control, and that a smaller number of patients are required in comparison to parallel-group studies. There is then a second evaluation period, before the participants are either withdrawn from the study or given the opportunity to enter a long-term extension phase. After a washout period of around 2–4 weeks, they are titrated onto the alternative treatment (active drug or placebo). There then follows an evaluation period (usually 8–12 weeks), after which patients are tapered off their initial treatment. Participants are generally randomized in 1:1 ratio to active drug or placebo, with titration over the subsequent 2–6 weeks. Crossover investors aim to achieve high returns in the short term as opposed to buy and hold investors who are focused more on long-term growth.Cross-over studies ( Figure 1) recruit a cohort of epilepsy patients, who are followed-up for a baseline period of approximately 8 weeks prior to randomization. Crossover investing is different from buy and hold investing, where the investor does not trade during the period from when a security is first bought to when it is finally sold. Asset classes and market sectors with a high proportion of crossover investors suffer if there is a sudden drop in investors' appetite for risk.Ī crossover investor's goal is to realize the highest returns possible by investing in attractive companies at various stages (early, mid, late), for example, Series B and C funding rounds, mezzanine debt, or IPO-of the business life cycle.Crossover investors aim to achieve high returns in the short term.Crossover investors invest in traditional mutual funds, hedge funds, and family businesses among others.A crossover investor is involved in multiple segments of the private investment markets, from pre-IPO to the post-IPO stage. ![]()
0 Comments
Leave a Reply. |