| Summary: | A large body of evidence indicates that object recognition memory is dependent upon plastic processes in perirhinal cortex. In particular, a decrement in neuronal responses to stimulus repetition is likely to form the core mechanism of the ability to judge the prior occurrence of objects. Local disruption of various neurotransmitter systems by drug infusion or viral transduction of perirhinal cortex produces an impairment in object recognition memory. However, it has yet to be shown that disruption of neuronal response decrements can produce a concurrent impairment in object recognition memory. This is likely to be due, in part, to the difficulty in demonstrating such changes in the acute preparation. The current study reports the development of a new behavioural-neurophysiological task that permits the presentation of multiple visual stimuli, while performing chronic extracellular recordings from, cells held over a period of days to weeks. This task was then used to investigate the effects of drugs on the activity patterns of single neurons, and on population activity (through analysis of the EEG). Of 103 cells recorded from perirhinal and dorsally adjacent cortex, only seven (7 %) exhibited consistent visually-evoked changes in activity. However, 35 (34 %) exhibited activity changes that related to other components of the task. Reasons for these observations are discussed. When administered systemically, scopolamine, MLA, verapamil and lorazepam disrupt object recognition memory in rats performing a test of spontaneous novel object preference. The effects of these drugs on the firing rates of individual neurons, and on the power and frequency of theta oscillations in perirhinal and adjacent c011ex are investigated with the hope of providing an insight into their behavioural effects.
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