Glucocorticoid effects on object recognition memory require training-associated emotional arousal

Abstract

Considerable evidence implicates glucocorticoid hormones in the regulation of memory consolidation and memory retrieval. The present experiments investigated whether the influence of these hormones on memory depends on the level of emotional arousal induced by the training experience. We investigated this issue in male Sprague-Dawley rats by examining the effects of immediate posttraining systemic injections of the glucocorticoid corticosterone on object recognition memory under two conditions that differed in their training-associated emotional arousal. In rats that were not previously habituated to the experimental context, corticosterone (0.3, 1.0, or 3.0 mg͞kg, s.c.) administered immediately after a 3-min training trial enhanced 24-hr retention performance in an inverted-U shaped dose-response relationship. In contrast, corticosterone did not affect 24-hr retention of rats that received extensive prior habituation to the experimental context and, thus, had decreased novelty-induced emotional arousal during training. Additionally, immediate posttraining administration of corticosterone to nonhabituated rats, in doses that enhanced 24-hr retention, impaired object recognition performance at a 1-hr retention interval whereas corticosterone administered after training to well-habituated rats did not impair 1-hr retention. Thus, the present findings suggest that training-induced emotional arousal may be essential for glucocorticoid effects on object recognition memory.corticosterone ͉ stress hormones ͉ memory consolidation ͉ memory retrieval

Memory enhancement by a semantically unrelated emotional arousal source induced after learning

“…Our findings are consistent with this proposition, as were a number of other studies using an arousing treatment after learning of non-emotive stimuli (Colrain et al, 1992;Manning et al, 1992;Nielson & Jensen, 1994;Nielson et al, 1996). However, the present findings contrast with a recent few recent studies that suggest that post-learning arousal may only be effective to modulate inherently arousing stimuli (Cahill, Gorski, & Le, 2003) or that some amount of arousal or novelty at encoding is necessary for post-learning arousal treatments to modulate memory Okuda, Roozendaal, & McGaugh, 2004). The present study cannot directly address these issues because arousal was not measured during encoding.…”

Glucocorticoids act on glutamatergic pathways to affect memory processes

“…A key question to ask is whether these differential effects are due to a putative 'vulnerability' of these different cognitive processes [in either a positive (consolidation) or a negative (retrieval) manner] to stress or elevated glucocorticoids, or whether they are the consequence of serendipitous application of experimental designs in the respective studies with glucocorticoid timing and dosage (see above) being instead the key factors underlying the reported effects. The evidence supports the former possibility because the same glucocorticoid treatment can simultaneously inhibit the immediate recall of information while facilitating consolidation mechanisms involved in long-term memory formation [84,85]. This has been specifically shown for the consolidation of extinction processes related to the information whose recall is inhibited [85][86][87].…”

Emotional memories are not all created equal: Evidence for selective memory enhancement

“…A certain threshold of adrenomedullary activation and associated central arousal may be needed in conjunction with amygdala activation to enhance episodic memory. Consistent with the proposed important role of peripheral and central stress hormone release for arousal memory modulation (Kleinsmith and Kaplan 1963;Cahill et al 1994;Nielson et al 1996;Cahill and McGaugh 1998;LaBar and Phelps 1998;Buchanan and Lovallo 2001;Hamann 2001;Okuda et al 2004), fear faces may induce robust amygdala activation, but a level of systemic arousal insufficient for EEM.…”

“…If amygdala activation is sufficient to alter the course of episodic memory, then activation of the amygdala alone, independently of higher levels of subjective or autonomic indices of arousal, should be sufficient for enhanced memory, predicting EEM for fearful relative to neutral faces. In contrast, arousal may be a critical prerequisite for the amygdala to influence memory Ca-hill et al 2003;McGaugh 2004;Okuda et al 2004), predicting EEM for highly arousing events, but not for fearful faces.…”