Hormetic and Non-Hormetic Dose-Response Functions in Stress Effects on Memory and Synaptic Plasticity: Issues and Mechanisms

Abstract

Over a century of behavioral research has shown that stress can exert both positive and negative effects on memory. We have explored the idea that the complex effects of stress on learning and memory can be characterized by hormetic-and non-hormetic dose-response functions, in which stress may either stimulate or impair brain memory mechanisms, depending, in part, on the timing and duration of the stress experience. Extensive work has shown that acute stress or corticosteroid administration has a biphasic effect specifically on hippocampus-dependent learning, memory and synaptic plasticity. We suggest that brief stress exerts a rapid enhancement of memory-related functions of the hippocampus, produced by the amygdala-induced activation of hippocampal synaptic plasticity in conjunction with excitatory effects of neuromodulators, including glucocorticoids, norepinephrine, corticotropin-releasing hormone, acetylcholine and dopamine. We propose that the rapid stress-induced activation of the amygdala-hippocampus brain memory system results in a linear (non-hormetic) dose-response relation between emotional strength and memory formation. In response to more prolonged stress, a delayed inhibition of hippocampal function develops, which can be attributed to compensatory cellular responses which protect hippocampal neurons from excitotoxicity. The inhibition of hippocampal functioning in response to prolonged stress is potentially relevant to the well-described curvilinear (hormetic) dose-response relationship between arousal and memory. In summary, our emphasis on the temporal features of stress-brain interactions addresses how stress can activate, as well as impair, hippocampal functioning to produce differently shaped (nonhormetic/hormetic) stress-memory dose response functions.

Screening Neuropharmacological Activities of <i>Kaempferia parviflora</i> (Krachai Dam) in Healthy Adult Male Rats

“…It was found that serotonin contributed a crucial role on both acquisition and consolidation processes (Kumar et al, 2007). However, numerous neurotransmitters had been proposed to contribute the important role on learning and memory including acetylcholine (Zoladz and Diamond, 2008;Bustamam et al, 2008). Our findings clearly demonstrated that the alcoholic extract of K. parviflora rhizome enhanced swimming time while decreased immobility time in forced swimming test in the same manner as Fluoxetine, a Serotonin Reuptake Inhibitor (SSRI) (Mohajeri et al, 2007).…”

Responding to Campus Shootings: Two Studies Exploring the Effects of Sex and Placement Strategy on Knowledge Acquisition and Organizational Reputation

“…Because past research has suggested that emotional arousal augments or impairs learning, it may be the case that printed information concerning a crisis of this magnitude is alarming enough; presenting graphic and vivid images of the threatening and uncertain crisis, without complementing them with "cool" media accounts of the events, may lead to an excessive level of arousal that inhibits learning. This would be consistent with the curvilinear relationship between arousal and learning posited by numerous authors (see Zoladz & Diamond, 2008).…”

“…Furthermore, there is evidence that people are inclined to remember general (or "gist") information after a moderately arousing event but will lose details when pushed to extreme levels of emotional arousal (Zoladz & Diamond, 2008). Because emotional arousal may augment or impair learning depending on the circumstances, past research has not clearly indicated how much people will learn from coverage of a crisis, especially if they are directly affected.…”

Learning From the Media in the Aftermath of a Crisis: Findings from the Minneapolis Bridge Collapse

“…It's believed that the hormones released in response to stressful events act to better preserve the gist of experiences (McGaugh, 1992), whereas a number of mechanisms, such as restricted attentional focus at the time of events, serve to impair memory for details when events are highly arousing (Safer, Christianson, Autry, & Österlund, 1998). Because emotional arousal both preserves and impairs learning depending on the degree of arousal, nature of the material tested, and temporal relationships between the aroused state and learning (Zoladz & Diamond, 2008), it's unclear how much people will learn when exposed to educational information embedded in disaster coverage.…”