Is the posterior parietal lobe involved in working memory retrieval? Evidence from patients with bilateral parietal lobe damage

Abstract

Neuroimaging evidence suggests that the parietal lobe has an important role in memory retrieval, yet neuropsychology is largely silent on this topic. Recently, we reported that unilateral parietal lobe damage impairs various forms of visual working memory when tested by old/new recognition. Here, we investigate whether parietal lobe working memory deficits are linked to problems at retrieval. We tested two patients with bilateral parietal lobe damage in a series of visual working memory tasks that probed recall and old/new recognition. Stimuli were presented sequentially and several stimulus categories were tested. The results of these experiments show that parietal lobe damage disproportionately impairs old/new recognition as compared to cued recall across stimulus categories. The observed performance dissociation suggests that the posterior parietal lobe plays a particularly vital role in working memory retrieval.

Figure 1

Patient Lesion Traces. Lesions are shown on T2 fluid-attenuated inversion recovery (FLAIR) images in which the lesions appear as white higher intensity patches in parietal regions. Anatomical landmarks are marked in red and blue. Red lines mark the central sulcus, blue lines mark the intraparietal sulcus. Radiological convention is followed (left is on the right). Abbreviations: AG = angular gyrus, MOG = middle occipital gyrus, SPG = superior parietal gyrus.

Figure 2

Trial design of Experiment 1a. On each trial, four colors, abstract shapes, or tools were presented sequentially (1000 ms each) and after a brief delay of 1000 ms, a probe image was presented and remained on the computer screen until subjects responded as to which temporal position the probe item had previously occupied. In this example, the correct response would be 3.

Figure 3

Order recall and recognition performance (Experiments 1a and 1b) as a function of stimulus category. The order recall performance is measured by accuracy (left axis), and the order recognition is measured by corrected recognition (right axis). Error bars indicate the standard error of the mean (SEM).

Figure 4

Object recall and recognition performance (Experiments 2a and 2b). The pattern of behavior observed for tools was also observed with color and shape stimulus categories in the object recognition experiment (data not shown). Error bars indicate SEM.

Figure 5

Recall and recognition performance. Patients’ scores are in standardized units (z-scores) with regards to control subject performance. By convention, impaired performance is when z > 1.96.

Figure 6

Results of Experiment 3, non-repeating stimuli recognition. Corrected recognition performance as a function of group membership. Error bars indicate SEM.