Hormones are a class of chemicals that affect behavior. Unlike neurotransmitters, hormones are not released by the terminal buttons of a neuron; instead, they are secreted by glands in the endocrine system.
Hormones can only influence cells that have receptors for this particular hormone. Such cells are called target cells. When a hormone binds to a receptor, it launches a sequence of changes, some of which are genomic: gene activation or gene suppression. Essentially, this means that hormones do not influence behavior directly. Instead, they change the probability that a certain behavior will occur in response to a certain environmental stimulus.
Cortisol, often referred to as the "stress hormone," plays a crucial role in regulating the body's response to stress through the hypothalamic-pituitary-adrenal (HPA) axis. When an individual encounters a stressful situation, the hypothalamus signals the pituitary gland to release ACTH, which then stimulates the adrenal glands to produce cortisol. This hormone helps mobilize energy by increasing blood sugar levels, suppressing non-essential functions like digestion and immune response, and enhancing cognitive alertness. However, prolonged or excessive cortisol secretion can negatively impact behavior, leading to heightened anxiety, irritability, and difficulty in emotional regulation. Chronic stress and elevated cortisol levels have also been linked to impairments in memory and decision-making, particularly affecting the hippocampus, a brain region critical for learning and memory. Excess cortisol can shrink hippocampal neurons, reducing the brain's ability to form and retrieve memories, leading to forgetfulness and cognitive decline.
Newcomer et al. (1999) aimed to investigate whether high levels of the stress hormone cortisol interfere with verbal declarative memory. Participants, who were employees or students at Washington University Medical Center, were excluded if they were pregnant, had a history of mental illness, head trauma, or corticosteroid treatment. Participants were assigned to one of three conditions: high cortisol (160 mg/day), low cortisol (40 mg/day), or placebo. They listened to and recalled a prose paragraph over four days and were tested before taking cortisol, one day after, four days after, and six days after to check for long-term effects.
Results showed that high cortisol levels significantly impaired memory performance, with participants in the high cortisol group performing the worst on the memory task. This impairment was temporary, as their performance returned to normal after stopping cortisol. There was no significant difference between the low-dose and placebo groups, with performance in these groups improving over time, likely due to practice effects or procedural learning.
Overall, the study demonstrates a clear link between cortisol levels and memory recall, highlighting the impact of stress hormones on cognitive functions. High cortisol levels interfere with the recall of verbal information, while lower doses do not appear to affect memory performance significantly.