Statistical hypothesis testing - Wikipedia
What Is a Scientific Hypothesis? | Definition of Hypothesis
Background: Negative feedback regulation of the hypothalamic-pituitary-adrenal axis occurs through a dual-receptor system of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Their affinity for cortisol and their distribution in the brain differ. Studies using an MR antagonist have demonstrated that MR is active throughout the circadian rhythm. Because major depression is accompanied by increased glucocorticoid secretion and insensitivity to glucocorticoid feedback, and because glucocorticoids are capable of down-regulating MR and GR, we expected that major depression would be accompanied by decreased MR activity. Methods: To test this hypothesis, we administered spironolactone, an MR antagonist, to individuals with major depression and matched control subjects and assessed levels of corticotropin and cortisol secretion in response to this acute challenge. Studies were conducted in the morning, the time of peak activation of the hypothalamic-pituitary-adrenal axis. All patients were currently depressed and free of all medications. All controls were free of all psychiatric diagnoses and of all medications. Results: Spironolactone treatment resulted in a significant increase in cortisol secretion levels in both groups. Depressed patients demonstrated higher cortisol secretion levels than control subjects. In addition, depressed patients demonstrated a different pattern of increase in cortisol secretion levels after spironolactone administration. Furthermore, a significant effect of spironolactone treatment on corticotropin secretion levels can be observed in depressed patients, whereas controls show no such effect. Conclusions: Despite high baseline cortisol levels, patients with major depression show high functional activity of the MR system. Paired with the body of evidence regarding decreased sensitivity to GR agonists, these data suggest an imbalance in the MR/GR ratio. The balance of MR and GR is known to affect brain serotonin systems and may play an etiologic role in serotonin receptor changes observed in patients with major depression.
Appendix - Anatomy Pictures and Information
A major problem with the Critical Period Hypothesis is that there appears to be no universally accepted definition of a critical period within linguistics. Bialystok (1997) bases her discussion of the critical/sensitive period (which she takes to be synonymous1) on a specific technical definition used in ethology, which includes 14 essential structural characteristics that describe such a period (Bornstein 1989). She argues that one of these characteristics is especially problematic – the system: “structure or function altered in the sensitive period” (Bornstein 1989:184). In other words, she argues that there is no period where a structure in the brain is modified in a way that makes subsequent language learning harder or impossible. Bialystok does, however, agree that there is an optimal period for language learning – something that can be characterised by the statement “On average, children are more successful than adults when faced with the task of learning a second language” (Bialystok 1997:117). Despite the controversy around other issues, this fact is uncontested and has been verified by numerous studies.