As part of the normal ageing process, some older people show an impairment in their ability to ignore information that is irrelevant to the task at hand, but their ability to enhance processing of relative stimuli remains intact. Adam Gazzaley (pictured) at the University of California, Berkeley and colleagues presented 17 healthy younger participants (aged 19 to 30) and 16 healthy older participants (aged 60 to 77 years) with alternating photos of faces and outdoor scenes. The participants were instructed to either remember the faces, the scenes or to passively observe both. Their brains were scanned by fMRI throughout.
When instructed to remember the outdoor scenes, all the participants, young and old, showed enhanced activity in the left parahippocampal/lingual gyrus – a brain area associated with processing scenes – as they viewed the photos. However, when instructed to remember the faces (and ignore the scenes), 88 per cent of the younger participants showed suppressed activity in the brain area that processes scenes compared with only 44 per cent of the older participants. Crucially, this suppression deficit was linked to actual memory performance. When the older participants’ memory for the faces was tested seconds later, those whose memory was poorer than the younger controls showed the suppression deficit, whereas those whose memory was equal to the controls did not.
“These data suggest that [some] older individuals are able to focus on pertinent information but are overwhelmed by interference from failure to ignore distracting information, resulting in memory impairment for the relevant information”, the researchers said.
The researchers drew encouragement from the fact that not all the older participants showed the suppression deficit. “Future studies should seek to elucidate the factors contributing to successful ageing and preserved top-down modulation…”, they said.
Gazzaley, A., Cooney, J.W., Rissman, J. & D’Esposito, M. (2005). Top-down suppression deficit underlies working memory impairment in normal ageing. Nature Neuroscience. Advance Online Publication. DOI: 10.11038/nn1543.