A psychopharmacological exploration of memory for emotional material
It is often assumed that emotional events are remembered in great clarity and detail. This thesis begins with a review of the literature on memory enhancement by emotional material. This enhancement may involve mechanisms that are psychologically and neurobiologically distinct from the mechanisms usually employed in memory for neutral material, such as modulation of consolidation by emotional arousal via noradrenaline action in the amygdala. Theoretically, pharmacological manipulation of noradrenaline by methylphenidate and benzodiazepines should affect the function of specialised 'emotional memory' mechanisms, altering the balance of emotional and neutral material remembered. A set of four double blind, placebo controlled experiments were designed to investigate this theory. Each was carried out with three groups of 16 healthy human volunteers. Experiment 1 produced some evidence that both 1.5mg lorazepam and 40mg methylphenidate reduced the mnemonic advantage of emotional sections of a story. Experiment 2 compared diazepam (15mg) with placebo and propranolol (80mg) (a ?-blocker which has been reported to impair emotional memory) on two new tasks. Diazepam left implicit memory intact, but impaired explicit memory, particularly for emotional material. In Experiment 3 both diazepam (15mg) and methylphenidate (40mg) altered relative levels of recall for emotional and neutral pictures. In Experiment 4 diazepam (10mg) clearly impaired fear conditioning. However there was no evidence that diazepam (10mg) or methylphenidate (40mg) affected emotional memory during consolidation. Taken together these studies provide evidence for a pharmacological dissociation of fear conditioning and perceptual priming. There was some evidence that benzodiazepines disproportionately impaired explicit emotional memory. However these effects were subtle. Methylphenidate increased the relative amount of emotional material retained on some measures, and decreased or left it unchanged in others. This may be due to differing levels of arousal. A central issue throughout the thesis was the difficulty of separating the 'emotional memory' mechanism from other co-occurring mnemonic properties of emotional stimuli. These may mask effects of the pharmacological manipulations that would be informative to any theory of 'emotional memory'.