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Working memory, long-term memory, and medial temporal lobe function

  • Author(s): Jeneson, Annette
  • et al.

Working memory has traditionally been viewed as independent of the hippocampus and related medial temporal lobe (MTL) structures. Yet, memory-impaired patients with MTL damage are sometimes impaired at remembering visual or relational information across delays as short as a few seconds. The challenge has been to understand the nature of these impairments. Discussion of the possible contribution of MTL structures to working memory has often focused on a distinction between tasks with short retention intervals (a few seconds) and tasks with longer retention intervals. Yet, questions about the possible role of the MTL in working memory do not turn on any particular retention interval. Instead, the important distinction is between tasks where the material to be learned and maintained is within the capacity of working memory and tasks where what is to be learned exceeds capacity. When capacity is exceeded, or when material must be retrieved following the redirection of attention, performance depends in part on long-term memory, even if the retention interval is brief. In three experiments, we assessed the ability of patients with MTL damage to retain relational information (object-location associations and object-in-scene information) or visual information (colored squares) across brief delays. In all experiments, patients performed as well as controls when working memory was sufficient to support performance and they were impaired only when the task requirements exceeded working memory capacity. This pattern of results supports the idea that maintenance of relational or visual information in working memory is intact after MTL damage and that damage to the MTL structures impairs performance only when the task depends, in part, on long-term memory

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