Stress Impairs Cognitive and Electrophysiological Measures of Hippocampal Function

Throughout this century, studies have shown that the strength of the formation of memories is influenced by emotional state. In one of the earliest investigations of the relationship between arousal and cognition, Yerkes and Dodson (1908) demonstrated that the rate of learning declined with low or high levels of arousal. With an intermediate level of arousal, performance reached its optimal level. In the next decade, Stratton (1919) evaluated the complexity of the arousal-related modulation of memory. He discussed how emotions can produce either hypermnesic (enhancing) or hypomnesic (impairing) effects on learning. Subsequent analyses of the modulation of learning by arousal have extended these early observations to a broad range of species and tasks (Kirschbaum et al., 1996; McGaugh, 1989). In recent years much work has been directed at understanding the neurobiological basis of the modulation of memory by behavioral state. In this chapter, we will present our work on the behavioral and hormonal modulation of the hippocampus, a temporal lobe structure necessary for learning and memory (Zola-Morgan and Squire, 1990). Our studies indicate that psychological stress exerts a transient impairment of hippocampal function, which is revealed both behaviorally as retrograde amnesia and physiologically as a blockade of synaptic plasticity