Biological Bases of Behavior: Nervous and Endocrine Systems (7A) Practice Test

A behavioral endocrinology study examined how chronic sleep restriction affects stress reactivity. After 7 nights of 4-hour sleep, participants showed higher evening cortisol and greater startle responses to mild shocks than well-rested controls. The authors suggested that persistently elevated cortisol can alter neural excitability in circuits that regulate threat responding. Based on the passage, which statement best explains the role of cortisol in the described scenario?

A neurology clinic evaluated a patient with a pituitary adenoma (a tumor that can alter pituitary hormone output). The patient reported fatigue and low stress tolerance. Lab tests showed abnormally low adrenocorticotropic hormone (ACTH; a pituitary hormone that normally promotes cortisol release from the adrenal cortex) and low cortisol. The clinician noted that reduced cortisol would also weaken negative feedback to the hypothalamus. Based on this scenario, what is the most likely change in hypothalamic signaling that initiates HPA-axis activity?