Intact visual perceptual discrimination in humans in the absence of perirhinal cortex - PubMed (original) (raw)

Intact visual perceptual discrimination in humans in the absence of perirhinal cortex

C E Stark et al. Learn Mem. 2000 Sep-Oct.

Abstract

While the role of the perirhinal cortex in declarative memory has been well established, it has been unclear whether the perirhinal cortex might serve an additional nonmnemonic role in visual perception. Evidence that the perirhinal cortex might be important for visual perception comes from a recent report that monkeys with perirhinal cortical lesions are impaired on difficult (but not on simple) visual discrimination tasks. We administered these same tasks to nine amnesic patients, including three severely impaired patients with complete damage to perirhinal cortex bilaterally (E.P., G.P., and G.T.). The patients performed all tasks as well as controls. We suggest that the function of perirhinal cortex as well as antero-lateral temporal cortex may differ between humans and monkeys.

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Figures

Figure 1

Figure 1

Examples of trials from three of the difficult tasks. (a) Visually degraded object discrimination with a 30%–40% white-noise mask (Task 4). (b) Visually degraded object discrimination (the same trial) with a 70%–80% white-noise mask (Task 6). (c) Face discrimination (Task 7). Although performance on each of these tasks has been reported to be impaired in monkeys with perirhinal damage (Buckley et al. 1998; Buckley and Gaffan, in press), patients with complete damage to perirhinal cortex bilaterally performed normally. The correct choice in each of these examples is the lower left corner.

Figure 2

Figure 2

T2-weighted magnetic resonance images showing the extent of bilateral temporal lobe damage in each of the patients in the encephalitic group. The left side of the brain is on the left side of the image, and the top of the image is anterior. Damaged tissue is indicated by bright signal. In patient E.P (left) the damage extends 7 cm caudally from the temporal pole bilaterally and includes the amygdala, the hippocampal region (dentate gyrus, cell fields of the hippocampus proper, and subicular complex), entorhinal cortex, perirhinal cortex, and the rostral parahippocampal cortex (∼ 20% on the left and 60% on the right). The lesion also extends laterally to include the rostral portion of the fusiform gyrus. In patient G.P. (center) the damage extends through the anterior 7 cm of the left temporal lobe and the anterior 6 cm of the right temporal lobe. The damage includes bilaterally the amygdala and the hippocampal region and the entorhinal, perirhinal, and parahippocampal cortices. Lateral damage is most severe in the anterior 1 cm of the temporal lobe, where it includes the fusiform gyrus as well as the inferior, middle, and superior temporal gyri. From 1 to 4.5 cm caudally, the lateral damage is restricted to the fusiform gyrus and the inferior temporal gyrus. The insular cortex is also damaged, with the lesion extending further caudally on the left side (3cm) than on the right side (2.5 cm). In patient G.T. (right) the damage extends through the anterior 7 cm of the left temporal lobe and the anterior 5 cm of the right temporal lobe. The damage includes bilaterally the amygdala and the hippocampal region and the entorhinal, perirhinal, and parahippocampal cortices. Lateral cortical regions (fusiform gyrus and inferior, middle, and superior temporal gyri) are also damaged bilaterally at the level of the temporal pole. The damage to the fusiform gyrus continues caudally from the temporal pole for 6.0 cm on the left and for 4.5 cm on the right. The damage to the inferior, middle, and superior temporal gyri extends caudally from the temporal pole for 4.5 cm on the left and for 2.5 cm on the right. There is also bilateral damage to insular cortex, more extensive on the left than on the right.

Figure 3

Figure 3

Results from the three easy perceptual tasks (size, color, polygon discrimination) and four more difficult tasks (the face discrimination task and the three visually degraded object–discrimination tasks with a “snow mask” covering 30%–80% of each object). Performance on the three easy tasks has been reported to be unimpaired in monkeys with perirhinal damage, and performance on the difficult tasks has been reported to be impaired (Buckley et al. 1998; Buckley and Gaffan, in press). Performance is shown both for five control volunteers (CON) and for three amnesic patients with large medial temporal lobe lesions resulting from herpes simplex encephalitis (ENC). Error bars indicate the standard error of the mean.

Figure 4

Figure 4

Results from all seven tests for all four groups of participants averaged across the three test sessions (CON, five controls; ENC, three amnesic patients with large medial temporal lobe lesions due to encephalitis; H, three amnesic patients with damage limited to the hippocampal formation; and KOR, three amnesic patients with diencephalic damage due to Korsakoff's syndrome). None of the amnesic groups were impaired relative to controls on any test. Average scores for individual participants are shown (black dots) along with the standard error of the mean for each group (error bars). The tests are ordered according to how difficult they were for the controls (CON).

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