Functional-anatomic correlates of memory retrieval that suggest nontraditional processing roles for multiple distinct regions within posterior parietal cortex - PubMed (original) (raw)

Functional-anatomic correlates of memory retrieval that suggest nontraditional processing roles for multiple distinct regions within posterior parietal cortex

Benjamin J Shannon et al. J Neurosci. 2004.

Abstract

Current theories of posterior parietal cortex (PPC) function emphasize space-based attention and motor intention. Imaging studies of long-term memory have demonstrated PPC activation during successful memory retrieval. Here, we explored the relationship between memory processes and classical notions of PPC function. Study 1 investigated old-new recognition using picture and sound stimuli to test whether PPC memory effects were dependent on visuospatial attention. A region lateral to the intraparietal sulcus [inferior parietal lobule complex (IPLC)] and two regions in the medial PPC [precuneus complex (PCC) and posterior cingulate/retrosplenial cortex (pC/Rsp)] showed strong retrieval success effects for both picture and sound stimuli. Study 2 explored a recognition task with varied response contingencies to investigate whether these retrieval success effects are dependent on motor intentions. In one condition, subjects responded to both old and new items. In two other conditions, subjects responded only to old or only to new items. IPLC, PCC, and pC/Rsp continued to show retrieval success effects with similar magnitudes for all response contingencies, including a condition in which no responses were made to old items. In a third study, IPLC and PCC activity was modulated at retrieval based on levels of processing at study, suggesting sensitivity to memory demands. These studies demonstrate that retrieval success effects in lateral and medial PPC regions are not affected by manipulations predicted by classical theories of PPC function but can be modulated by memory-related manipulations. PPC regions thus have prominent response properties associated with memory, which may arise through interactions with medial temporal cortex.

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Figures

Figure 1.

Figure 1.

Behavioral results for study 1. a, Corrected recognition performance: the percentage of incorrectly identified new items (FA) was subtracted from the percentage of correctly identified old items (HIT) to evaluate performance for each modality. b, Response time. Mean response times for HIT and CR trial types are shown for each modality. For all figures, error bars represent SEM.

Figure 2.

Figure 2.

Conjunctions of whole-brain activation maps reveal regions associated with retrieval success. a, Conjunction maps generated from HIT>CR for pictures and HIT>CR for sounds reveal regions showing retrieval success effects for pictures (red), sounds (blue), and both (yellow). b, Conjunction maps generated from HIT>CR and PIC>SND (CR trials only) contrasts show regions that exhibit retrieval success effects with (HIT>CR; green) and without (HIT>CR SELECTIVE; yellow) effects of modality. For all maps, images represent transverse sections with the approximate level taken from the atlas of Talairach and Tournoux (1988). The left hemisphere is displayed on the left. The anatomic backdrop represents the average anatomic image from the subjects included in the study.

Figure 3.

Figure 3.

Anatomical location of parietal regions relative to landmarks. Medial (M) and lateral (L) views of PPC show regions IPLC (red), PCC (green), and pC/Rsp (yellow) along with estimates of LIP (blue; based on the study by Sereno et al., 2001) [a spherical region was generated about a peak coordinate exactly contralateral to a reported peak (-32, -68, 46)]. Images were created using Caret software (Van Essen et al., 2001; Van Essen, 2002). A, Anterior; P, posterior; D, dorsal; V, ventral.

Figure 4.

Figure 4.

PPC retrieval success effects occur for both picture and sound stimuli. Regional analyses were conducted for IPLC, PCC, and an extrastriate visual region as a control (VIS CTRL). The difference in signal change between correctly identified old (HIT) and new (CR) items is plotted for PIC and SND items for each region. Inferential statistics are not presented forth is experiment, because IPLC and PCC were defined based on data from this experiment (Fig. 2_b_).

Figure 5.

Figure 5.

Behavioral results for study 2. a, Corrected recognition performance. b, Response time. Mean response times for HIT and CR trial types are shown for each trial type that required a response. c, The proportion of items identified by subjects as old in each condition. O/N, Response Old/New condition.

Figure 6.

Figure 6.

PPC retrieval success effects are independent of response contingencies. Regional analyses were conducted for IPLC, PCC, and a motor region as a control (MTR CTRL). The difference in signal change between correctly identified old (HIT) and new (CR) items is plotted for Respond Old/New (O/N), Respond Old (O), and Respond New (N) conditions for each region. IPLC and PCC showed retrieval success effects for all conditions; motor cortex was more active when responses were made, but did not modulate based on the mnemonic status of an item. For all inferential comparisons, asterisks and bars represent different levels of significance: *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 7.

Figure 7.

Conjunctions of whole-brain activation maps reveal PPC regions showing retrieval success effects for all response contingencies. Note the similarity between these regions and those shown in Figure 2.

Figure 8.

Figure 8.

Behavioral results for study 3. a, Corrected recognition performance. b, Response time. Mean response times are shown for each trial type [DH, HIT following deep study (DEEP); SH, HIT following shallow study(SHAL)].

Figure 9.

Figure 9.

PPC retrieval success effects are influenced by retrieval demands. Regional analyses were conducted for IPLC and PCC. The difference in signal change between correctly recognized old items following deep study (DEEP), following shallow study (SHAL), and correctly rejected new items (CR) is plotted for each region. Both IPLC and PCC showed significant HIT>CR effects, the magnitudes of which were significantly modulated at retrieval dependent on levels of processing at encoding.

Figure 10.

Figure 10.

Whole-brain activation maps reveal PPC regions modulating by retrieval demands. Maps show voxels that demonstrate significantly greater activity for deeply studied HIT items versus shallowly studied HIT items.

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