Impaired visual and odor recognition memory span in patients with hippocampal lesions

Abstract

In a recent study, rats with hippocampal lesions performed as well as did unoperated rats on an olfactory memory span task, performing approximately 80% correct even when the span length reached 24 odors. This finding seems potentially at odds with demonstrations that memory-impaired patients typically fail tasks in which large amounts of information must be retained. Accordingly, we have assessed recognition memory span performance for line drawings of objects, designs, and odors in amnesic patients with damage thought to be limited to the hippocampal region. The patients were impaired on all three tasks. We consider possible explanations for the difference between the findings for humans and rats, including the fact that olfactory function is particularly well-developed in rodents.

Figure 1

Mean visual span length for control volunteers (CON; n = 15) and for amnesic patients with damage thought to be limited to the hippocampal region (H; n = 5) on two visual span tasks. In one task (left two bars), the stimuli were line drawings of common objects. In the second task (right two bars), the stimuli were kaleidoscope-like colored designs. Brackets indicate standard error of the mean.

Figure 2

Olfactory span performance for control volunteers (CON; n = 16) and for amnesic patients with damage thought to be limited to the hippocampal region (H; n = 5). (A) Mean olfactory span length. (B) Percentage of trials performed correctly in the course of reaching a span length of 13 odors. (C) Mean number of errors accumulatedin the course of reaching a span length of 13 odors. Brackets indicate standard error of the mean.