Parietal contributions to recollection: electrophysiological evidence from aging and patients with parietal lesions

Abstract

There has been much recent investigation into the role of parietal cortex in memory retrieval. Proposed hypotheses include attention to internal memorial representations, an episodic working memory-type buffer, and an accumulator of retrieved memorial information. The current investigation used event-related potentials (ERPs) to test the episodic buffer hypothesis, and to assess the memorial contribution of parietal cortex in younger and older adults, and in patients with circumscribed lateral parietal lesions. In a standard recognition memory paradigm, subjects studied color pictures of common objects. One-third of the test items were presented in the same viewpoint as the study phase, one-third were presented in a 90 degrees rotated viewpoint, and one-third were presented in a noncanonical viewpoint. Conflicting with the episodic buffer hypothesis, results revealed that the duration of the parietal old/new effect was longest for the canonical condition and shortest for the noncanonical condition. Results also revealed that older adults demonstrated a diminished parietal old/new effect relative to younger adults. Consistent with previous data reported by Simons et al., patients with lateral parietal lesions showed no behavioral impairment compared to controls. Behavioral and ERP data from parietal lesion patients are presented and discussed. From these results, the authors speculate that the parietal old/new effect may be the neural correlate of an individual's subjective recollective experience.

Figure 1

Example of study and test stimuli

Figure 2

Lesion diagrams for the patients with parietal lobe lesions. Each patient's lesion was manually traced on a structural MRI of their brain, normalized to MNI space, and displayed on axial slices of a canonical structural image (slice positions indicated on sagittal section at foot of figure). Patient L2's lesion affected BA 5 and 7, with some extension into BA 40. Patient L3's lesion involved BA 7 and 39, as well as BA 17–19. Patient L4’s lesion is predominantly in BA 5, with some extension into BA 18 and 19. Patient R1's lesion involved BA 7 and 39, in addition to BA 1–3.

Figure 3

Younger Adult old/new scalp topography maps for the three conditions. Topographies are presented in 50 ms averages going forward.

Figure 4

Younger Adult topographic p-value maps created by the nonparametric permutation test. Topographies are presented in 50 ms averages going forward.

Figure 5

Older Adult old/new scalp topography maps for the three conditions. Topographies are presented in 50 ms averages going forward.

Figure 6

Topographic p-value maps created by the nonparametric permutation test between the younger and older adults. Topographies are presented in 50 ms averages going forward.

Figure 7

Mean amplitudes of the parietal old/new effect for the older and younger adults on all three conditions.

Figure 8

Boxplots showing the accuracy data for the parietal lesion patients and the younger and older adults for the three conditions. Lesion patient data are plotted individually. (YA – Younger Adults; OA – Older Adults; LC – Lesion Controls; PL – Lesion Patients).

Figure 9

Old/new scalp topography maps for parietal lesion patient R1, collapsed across the three conditions. Topographies are presented in 50 ms averages going forward Supplementary Table 1. Neuropsychological test data for the parietal lesion patients and controls.