Predictive knowledge of stimulus relevance does not influence top-down suppression of irrelevant information in older adults

Zanto, Theodore P.; Hennigan, Kelly; Östberg, Mattias; Clapp, Wesley C.; Gazzaley, Adam

doi:10.1016/j.cortex.2009.08.003

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Volume 46, Issue 4 , Pages 564-574, April 2010

Predictive knowledge of stimulus relevance does not influence top-down suppression of irrelevant information in older adults

Theodore P. Zanto
- Department of Neurology, University of California San Francisco, CA, USA
- Department Physiology, University of California San Francisco, CA, USA
Kelly Hennigan
- Department of Neurology, University of California San Francisco, CA, USA
- Department Physiology, University of California San Francisco, CA, USA
Mattias Östberg
- Department of Neurology, University of California San Francisco, CA, USA
- Department Physiology, University of California San Francisco, CA, USA
Wesley C. Clapp
- Department of Neurology, University of California San Francisco, CA, USA
- Department Physiology, University of California San Francisco, CA, USA
Adam Gazzaley
- Department of Neurology, University of California San Francisco, CA, USA
- Department Physiology, University of California San Francisco, CA, USA
- Corresponding author. UCSF – MC2240, 600 16th St, Genentech Hall, Room N472J, San Francisco, CA 94158-2517, USA.

Received 6 December 2008; received in revised form 9 April 2009 and 2 May 2009; accepted 5 August 2009. published online 11 September 2009.

Abstract

Our ability to focus attention on task-relevant stimuli and ignore irrelevant distractions is reflected by differential enhancement and suppression of neural activity in sensory cortices. Previous research has shown that older adults exhibit a deficit in suppressing task-irrelevant information, the magnitude of which is associated with a decline in working memory performance. However, it remains unclear if a failure to suppress is a reflection of an inability of older adults to rapidly assess the relevance of information upon stimulus presentation when they are not aware of the relevance beforehand. To address this, we recorded the electroencephalogram (EEG) in healthy older participants (aged 60—80 years) while they performed two different versions of a selective face/scene working memory task, both with and without prior knowledge as to when relevant and irrelevant stimuli would appear. Each trial contained two faces and two scenes presented sequentially followed by a 9sec delay and a probe stimulus. Participants were given the following instructions: remember faces (ignore scenes), remember scenes (ignore faces), remember the xth and yth stimuli (where x and y could be 1st, 2nd, 3rd or 4th), or passively view all stimuli. Working memory performance remained consistent regardless of task instructions. Enhanced neural activity was observed at posterior electrodes to attended stimuli, while neural responses that reflected the suppression of irrelevant stimuli was absent for both tasks. The lack of significant suppression at early stages of visual processing was revealed by P1 amplitude and N1 latency modulation indices. These results reveal that prior knowledge of stimulus relevance does not modify early neural processing during stimulus encoding and does not improve working memory performance in older adults. These results suggest that the inability to suppress irrelevant information early in the visual processing stream by older adults is related to mechanisms specific to top-down suppression.