Dissociation of the neural correlates of implicit and explicit memory

Abstract

One presentation of a word to a subject is enough to change the way in which the word is processed subsequently, even when there is no conscious (explicit) memory of the original presentation. This phenomenon is known as implicit memory1,2,3. The neural correlates of implicit memory have been studied previously4,5,6,7,8,9,10,11, but they have never been compared with the correlates of explicit memory while holding task conditions constant or while using a procedure that ensured that the neural correlates were not ‘contaminated’ by explicit memory. Here we use scalp-recorded event-related brain potentials to identify neural activity associated with implicit and explicit memory during the performance of a recognition memory task. Relative to new words, recently studied words produced activity in three neuroanatomically and functionally dissociable neural populations. One of these populations was activated whether or not the word was consciously recognized, and its activity therefore represents a neural correlate of implicit memory. Thus, when task and memory contamination effects are eliminated, the neural correlates of explicit and implicit memory differ qualitatively.

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Figure 1: ERP waveforms, averaged across subjects, from left and right frontal (F3, F4 of the 10–20 system26) and parietal (P3, P4) electrodes.
Figure 2: Scalp distributions27 of the differences between the ERPs to new words and different classes of studied word.
Figure 3: Magnitudes of ERP memory effects.
Figure 4: The semantic judgement task.

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Acknowledgements

This research was supported by the Wellcome Trust. P.W. was supported by the Austrian Research Foundation, and K.A. by the Biotechnology and Biological Sciences Research Council, UK.

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Correspondence to Michael D. Rugg.

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Rugg, M., Mark, R., Walla, P. et al. Dissociation of the neural correlates of implicit and explicit memory. Nature 392, 595–598 (1998) doi:10.1038/33396

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