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Implicit Learning and Stress Hormones

Implizites Lernen und Stresshormone

  • There is a lot of evidence for the impact of acute glucocorticoid treatment on hippocampus-dependent explicit learning and memory (memory for facts and events). But there have been few studies, investigating the effect of glucocorticoids on implicit learning and memory. We conducted three studies with different methodology to investigate the effect of glucocorticoids on different forms of implicit learning. In Study 1, we investigated the effect of cortisol depletion on short-term habituation in 49 healthy subjects. 25 participants received oral metyrapone (1500 mg) to suppress endogenous cortisol production, while 24 controls received oral placebo. Eye blink electromyogram (EMG) responses to 105 dB acoustic startle stimuli were assessed. Effective endogenous cortisol suppression had no effect on short-term habituation of the startle reflex, but startle eye blink responses were significantly increased in the metyrapone group. The latter findings are in line with previous human studies, which have shown that excess cortisol, sufficient to fully occupy central nervous system (CNS) corticosteroid receptors, may reduce startle eye blink. This effect may be mediated by CNS mechanisms controlling cortisol feedback. In Study 2, we investigated delay or trace eyeblink conditioning in a patient group with a relative hypocortisolism (30 patients with fibromyaligia syndrome/FMS) compared to 20 healthy control subjects. Conditioned eyeblink response probability was assessed by EMG. Morning cortisol levels, ratings of depression, anxiety and psychosomatic complaints as well as general symptomatology and psychological distress were assessed. As compared to healthy controls FMS patients showed lower morning cortisol levels, and trace eyeblink conditioning was facilitated whereas delay eyeblink conditioning was reduced. Cortisol measures correlate significantly only with trace eyeblink conditioning. Our results are in line with studies of pharmacologically induced hyper- and hypocortisolism, which affected trace eyeblink conditioning. We suggest that endocrine mechanisms affecting hippocampus-mediated forms of associative learning may play a role in the generation of symptoms in these patients.rnIn Study 3, we investigated the effect of excess cortisol on implicit sequence learning in healthy subjects. Oral cortisol (30 mg) was given to 29 participants, whereas 31 control subjects received placebo. All volunteers performed a 5-choice serial reaction time task (SRTT). The reaction speed of every button-press was determined and difference-scores were calculated as a proof of learning. Compared to the control group, we found a delayed learning in the cortisol group at the very beginning of the task. This study is the first human investigation, indicating impaired implicit memory function after exogenous administration of the stress hormone cortisol. Our findings support a previous neuroimaging study, which suggested that the medial temporal lobe (including the hippocampus) is also active in implicit sequence learning, but our results may also depend on the engagement of other brain structures.
  • Implizites Lernen findet weitgehend unbewusst und ohne Absicht statt und größtenteils auch ohne explizites Wissen über das Gelernte. Lange Zeit wurde angenommen, dass solche impliziten Lernprozesse kaum durch Stress beeinflusst werden. Im Rahmen von 3 Studien wurde die Wirkung des "Stresshormons" Cortisol auf verschiedene Formen impliziten Lernens untersucht. Es zeigte sich, dass Cortisol einen Einfluss auf "komplexere" Formen impliziten Lernens hat, bei denen der Hippocampus möglicherweise eine Rolle spielt. Im Fall des impliziten Sequenzlernens, bei dem das Gelernte bis zuletzt nicht bewusst erkannt wird, könnte dies außerdem bedeuten, dass eine Beteiligung des Hippocampus nicht zwangsläufig mit explizitem Wissen über das Gelernte verbunden ist.

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Author:Sonja Römer
Advisor:Sonja Römer
Document Type:Doctoral Thesis
Date of completion:2012/01/25
Publishing institution:Universität Trier
Granting institution:Universität Trier, Fachbereich 1
Date of final exam:2011/12/19
Release Date:2012/01/25
Tag:Habituation; Implizites Sequenzlernen; Schreckreflex
cortisol; glucocorticoids; implicit learning; neuroendocrine system; stress
GND Keyword:Glucocorticosteroide; Hydrocortison; Implizites Lernen; Klassische Konditionierung; Neuroendokrines System; Stress
Source:Hormones and Behavior , Psychosomatic Medicine , Psychopharmacology
Institutes:Fachbereich 1 / Psychologie
Dewey Decimal Classification:1 Philosophie und Psychologie / 15 Psychologie / 150 Psychologie

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