Dissociation between memory accuracy and memory confidence following bilateral parietal lesions

Abstract

Numerous functional neuroimaging studies have observed lateral parietal lobe activation during memory tasks: a surprise to clinicians who have traditionally associated the parietal lobe with spatial attention rather than memory. Recent neuropsychological studies examining episodic recollection after parietal lobe lesions have reported differing results. Performance was preserved in unilateral lesion patients on source memory tasks involving recollecting the context in which stimuli were encountered, and impaired in patients with bilateral parietal lesions on tasks assessing free recall of autobiographical memories. Here, we investigated a number of possible accounts for these differing results. In 3 experiments, patients with bilateral parietal lesions performed as well as controls at source recollection, confirming the previous unilateral lesion results and arguing against an explanation for those results in terms of contralesional compensation. Reducing the behavioral relevance of mnemonic information critical to the source recollection task did not affect performance of the bilateral lesion patients, indicating that the previously observed reduced autobiographical free recall might not be due to impaired bottom-up attention. The bilateral patients did, however, exhibit reduced confidence in their source recollection abilities across the 3 experiments, consistent with a suggestion that parietal lobe lesions might lead to impaired subjective experience of rich episodic recollection.

Figure 1.

Lesion overlay diagrams of the patients with unilateral and bilateral parietal lobe lesions, manually traced on a structural MRI scan of their brain, normalized to MNI space, and displayed on axial slices of a canonical structural image.

Figure 2.

Performance of the patients with unilateral and bilateral parietal lobe lesions and the combined matched control participants on (a) the recognition and recognition confidence, and (b) the recollection and recollection confidence, components of the auditory source memory task in Experiment 1. Error bars indicate standard error of the mean.

Figure 3.

Standardized Z-scores enabling comparison between the differently aged unilateral and bilateral patients on (a) recollection, and (b) recollection confidence, in Experiment 1. The dashed line indicates 2 standard deviations below the patients’ control group mean.

Figure 4.

Performance of the patients with bilateral parietal lesions and matched control participants on the recollection and recollection confidence components of (a) the auditory source task with reduced behavioral relevance in Experiment 2, and (b) the visual source task in Experiment 3. Error bars indicate standard error of the mean.