Over the past three decades, functional magnetic resonance imaging (fMRI) has become crucial to study how cognitive processes are implemented in the human brain. However, the question of whether... Show moreOver the past three decades, functional magnetic resonance imaging (fMRI) has become crucial to study how cognitive processes are implemented in the human brain. However, the question of whether participants recruited into fMRI studies differ from participants recruited into other study contexts has received little to no attention. This is particularly pertinent when effects fail to generalize across study contexts: for example, a behavioural effect discovered in a non-imaging context not replicating in a neuroimaging environment. Here, we tested the hypothesis, motivated by preliminary findings (N=272), that fMRI participants differ from behaviour-only participants on one fundamental individual difference variable: trait anxiety. Analysing trait anxiety scores and possible confounding variables from healthy volunteers across multiple institutions (N = 3317), we found robust support for lower trait anxiety in fMRI study participants, consistent with a sampling or self-selection bias. The bias was larger in studies that relied on phone screening (compared with full in-person psychiatric screening), recruited at least partly from convenience samples (compared with community samples), and in pharmacology studies. Our findings highlight the need for surveying trait anxiety at recruitment and for appropriate screening procedures or sampling strategies to mitigate this bias. Show less
Over the past three decades, functional MRI (fMRI) has become key to study how cognitive processes are implemented in the human brain. However, the question of whether participants recruited into... Show moreOver the past three decades, functional MRI (fMRI) has become key to study how cognitive processes are implemented in the human brain. However, the question of whether participants recruited into fMRI studies differ from participants recruited into other study contexts has received little to no attention. This is particularly pertinent when effects fail to generalize across study contexts: for example, a behavioural effect discovered in a non-imaging context not replicating in a neuroimaging environment. Here, we tested the hypothesis, motivated by preliminary findings (n = 272), that fMRI participants differ from behaviour-only participants on one fundamental individual difference variable: trait anxiety. Analysing trait anxiety scores and possible confounding variables from healthy volunteers across multiple institutions (n = 3317), we found robust support for lower trait anxiety in fMRI study participants, consistent with a sampling or self-selection bias. The bias was larger in studies that relied on phone screening (compared to full in-person psychiatric screening), recruited at least partly from convenience samples (compared to community samples), and in pharmacology studies. Our findings highlight the need for surveying trait anxiety at recruitment and for appropriate screening procedures or sampling strategies to mitigate this bias. Show less
Acute stress and elevated glucocorticoid hormone levels are well known to impair the retrieval of hippocampus-dependent 'declarative' memory. Recent findings suggest that stress might also impair... Show moreAcute stress and elevated glucocorticoid hormone levels are well known to impair the retrieval of hippocampus-dependent 'declarative' memory. Recent findings suggest that stress might also impair the retrieval of non-hippocampal memories. In particular, stress shortly before retention testing was shown to impair the retrieval of striatal stimulus-response associations in humans. However, the mechanism underlying this stress-induced retrieval impairment of non-hippocampal stimulus-response memory remains elusive. In the present study, we investigated whether an acute elevation in glucocorticoid levels mediates the impairing effects of stress on retrieval of stimulus-response memory. Male Sprague-Dawley rats were trained on a stimulus-response task in an eight-arm radial maze until they learned to associate a stimulus, i.e., cue, with a food reward in one of the arms. Twenty-four hours after successful acquisition, they received a systemic injection of vehicle, corticosterone (1 mg/kg), the corticosterone-synthesis inhibitor metyrapone (35 mg/kg) or were left untreated I h before retention testing. We found that the corticosterone injection impaired the retrieval of stimulus-response memory. We further found that the systemic injection procedure per se was stressful as the vehicle administration also increased plasma corticosterone levels and impaired the retrieval of stimulus-response memory. However, memory retrieval was not impaired when rats were tested 2 min after the systemic vehicle injection, before any stress-induced elevation in corticosterone levels had occurred. Moreover, metyrapone treatment blocked the effect of injection stress on both plasma corticosterone levels and memory retrieval impairment, indicating that the endogenous corticosterone response mediates the stress-induced memory retrieval impairment. None of the treatments affected rats' locomotor activity or motivation to search for the food reward within the maze. These findings show that stress may affect memory processes beyond the hippocampus and that these stress effects are due to the action of glucocorticoids. (C) 2016 Elsevier Ltd. All rights reserved. Show less
Schwabe, L.; Schachinger, H.; Kloet, E.R. de; Oitzl, M.S. 2010
Recent evidence indicates that stress modulates multiple memory systems, favoring caudate nucleus-based stimulus-response learning at the expense of hippocampus-based spatial learning. Whether this... Show moreRecent evidence indicates that stress modulates multiple memory systems, favoring caudate nucleus-based stimulus-response learning at the expense of hippocampus-based spatial learning. Whether this is due to a facilitating effect of stress on stimulus-response learning, an impairing effect on spatial learning, or both, is not known. To answer this question, mice were either subjected to restraint stress, injected with vehicle or corticosterone or left untreated before training in two circular hole board tasks that could discriminate spatial and stimulus-response strategies. Stress, vehicle and corticosterone injection all impaired learning performance in the spatial task. Conversely, performance in the stimulus-response task was not affected by stress or corticosterone injection, although performance was generally lower than in the spatial task. Irrespective of the treatment, mice had to overcome the preference to use their spatial memory system to achieve the stimulus-response task. These findings suggest that (i) the caudate nucleus-based memory system is less stress sensitive than the hippocampus-based system and may thus dominate behavior in situations of stress and (ii) that multiple memory systems may compete for control of behavior even in tasks that can solely be solved by one system. (C) 2010 Elsevier B.V. All rights reserved. Show less
Schwabe, L.; Schachinger, H.; Kloet, E.R. de; Oitzl, M.S. 2010
Stress and corticosteroid hormones are known to affect learning and memory processes. In this study, we examined whether stress and corticosteroids are capable of facilitating the switch between... Show moreStress and corticosteroid hormones are known to affect learning and memory processes. In this study, we examined whether stress and corticosteroids are capable of facilitating the switch between multiple memory systems in mice. For this purpose, we designed a task that allowed measurement of nucleus caudate-based stimulus-response and hippocampus-based spatial learning strategies. Naive mice used spatial strategies to locate an exit hole on a circular hole board at a fixed location flagged by a proximal stimulus. When the mice were either stressed or administered corticosterone before the task, 30-50% of the mice switched to a stimulus-response strategy. This switch between learning strategies was accompanied by a rescue of performance, whereas performance declined in the stressed mice that kept using the spatial strategy. Pretreatment with a mineralocorticoid receptor antagonist prevented the switch toward the stimulus-response strategy but led to deterioration of hippocampus-dependent performance. These findings (i) show that corticosteroids promote the transition from spatial to stimulus-response memory systems, (ii) provide evidence that the mineralocorticoid receptor underlies this corticosteroid-mediated switch, and (iii) suggest that a stress-induced switch from hippocampus-based to nucleus caudate-based memory systems can rescue performance. Show less
Stress shapes memory. Depending on the timing of the stress exposure facilitating and impairing effects of stress are reported on how much is learned and remembered. Beyond such stress-induced... Show moreStress shapes memory. Depending on the timing of the stress exposure facilitating and impairing effects of stress are reported on how much is learned and remembered. Beyond such stress-induced changes in the quantity of memory, recent research suggests that stress also affects the contribution of multiple memory systems to performance. Under stress, rigid 'habit' memory gets favored over more flexible 'cognitive' memory. Thus, stress has an impact on the way we learn and remember, that is the quality of memory. This shift between different behavioral strategies on "environmental demands" may facilitate adaptive responses. Here, we review stress effects on both quantity and quality of memory and address possible implications of these effects for the understanding of stress-related psychiatric disorders. (C) 2009 Elsevier Ltd. All rights reserved. Show less
