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The Journal of Neuroscience, May 24, 2006, 26(21):5835-5839; doi:10.1523/JNEUROSCI.0258-06.2006
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Brief Communications
The Medial Temporal Lobe Distinguishes Old from New Independently of Consciousness
Sander M. Daselaar,1,2 Mathias S. Fleck,2,3 Steven E. Prince,2,3 andRoberto Cabeza2,3 1University of Amsterdam, Faculty of Science, Swammerdam Institute for Life Sciences, 1098 SM Amsterdam, The Netherlands, and 2Duke University, Center for Cognitive Neuroscience and 3Department of Psychological and Brain Sciences, Durham, North Carolina 27708
Correspondence should be addressed to Sander M. Daselaar, University of Amsterdam, Faculty of Science, Swammerdam Institute for Life Sciences, Kruislaan 320, 1098 SM Amsterdam, The Netherlands. Email: s.m.daselaar{at}uva.nl
Although it is widely accepted that the medial temporal lobes (MTLs) are critical for becoming aware that something happened in the past, there is virtually no evidence whether MTL sensitivity to event oldness also depends on conscious awareness. Using event-related functional magnetic resonance imaging, we show that activity in posterior MTL tracks whether an item is actually old (true oldness), regardless of participants' awareness of oldness (perceived oldness). Confirming its sensitivity to the objective nature of the stimulus, activity in this region was strongly correlated with individual memory performance (r = 0.74). At the same time, we found that memory errors (misses) were associated with activity in an anterior MTL region, which signaled whether an item was consciously experienced as new (perceived novelty). Logistic regression analyses based on individual trial activity indicated that the two MTL regions showed opposing relationships with behavior, and that memory performance was determined by their joint activity. Furthermore, functional connectivity analyses showed that perceived novelty activity in the posterior MTL inhibited true oldness activity in the anterior MTL. These findings indicate that participants' behavior reflected the combined effects of multiple MTL regions. More generally, our results show that parts of MTL can distinguish old from new independently of consciousness.
Key words: behavior; cognition; memory; recognition; human; hippocampus; parahippocampal
Received Sept. 28, 2005; revised March 20, 2006; accepted April 18, 2006.
Correspondence should be addressed to Sander M. Daselaar, University of Amsterdam, Faculty of Science, Swammerdam Institute for Life Sciences, Kruislaan 320, 1098 SM Amsterdam, The Netherlands. Email: s.m.daselaar{at}uva.nl
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