The role of the hippocampus in retaining relational information across short delays: The importance of memory load
- 1Department of Psychology, University of California, San Diego, California 92093, USA
- 2Department of Psychiatry, University of California, San Diego, California 92093, USA
- 3Department of Psychology and Neuroscience Center, Brigham Young University, Provo, Utah 84602, USA
- 4Department of Medicine, Pulmonary and Critical Care Division, Intermountain Medical Center, Murray, Utah 84143, USA
- 5Veterans Affairs Medical Center 116A, San Diego, California 92161, USA
- 6Department of Neurosciences, University of California, San Diego, California 92093, USA
Abstract
Patients with hippocampal damage are sometimes impaired at remembering information across delays as short as a few seconds. How are these impairments to be understood? One possibility is that retention of some kinds of information is critically dependent on the hippocampus, regardless of the retention interval and regardless of whether the task depends on working memory or long-term memory. Alternatively, retention may be dependent on the hippocampus only when the task involves a memory load large enough to exceed working memory capacity. To explore these possibilities, we assessed the performance of patients with hippocampal lesions on two tasks requiring retention of the same object-in-scene information across a brief delay. The tasks placed different demands on memory. In one task, which used a continuous recognition format, participants needed to try to hold up to nine scenes in mind, even when no scene intervened between the study scene and the corresponding test scene. Patients were impaired in this condition. In a second task, using a conventional study-test format, participants needed to hold in mind only one scene at a time for either 3 or 14 sec. With this procedure, patients performed as well as controls after a 3-sec delay but were impaired after a 14-sec delay. We suggest that retention of object-in-scene information is dependent on the hippocampus only when working memory is insufficient to support performance (because memory load is high or the retention interval is long). In these circumstances performance depends, at least in part, on long-term memory.
Footnotes
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↵7 Corresponding author.
E-mail lsquire{at}ucsd.edu; fax (858) 552-7457.
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[Supplemental material is available for this article.]
- Received September 10, 2010.
- Accepted February 23, 2011.
