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.

Subjective Sense of Memory Strength and the Objective Amount of Information Accurately Remembered Are Related to Distinct Neural Correlates at Encoding

“…In other words, although remembering the gist of a past event may lead to a strong subjective sense of remembrance, this is not necessarily correlated with verbatim details. For instance, patients with parietal lesions show reduced confidence in remembering their previous experiences, whereas their overall memory performance remains intact (Simons and Spiers, 2003;Simons et al, 2010). Therefore, a strong subjective sense of memory strength may be a consequence of frontal-parietal processes involved in top-down modulation of memory-and metamemory-related processes such as semantic processing, internal monitoring, and allocation of attentional resources that contribute to facilitating the reconstruction of visual scenes into general semantic categories.…”

“…One may speculate that arousal or acute stress might affect this balance and result in dissociation between subjective sense of remembrance and the objective memory content(s) remembered. A potent example of this is eyewitness misidentification, where a high subjective sense of confidence for correct recollection (i.e., the gist) occurs in the absence of objective veridicality of specific memory details (Loftus, 1979;Schacter, 2001;Sharot et al, 2007;Kensinger, 2008;Phelps and Sharot, 2008;Simons et al, 2010). It would be relevant for future research to address how the brain achieves an optimally adaptive balance between these distinct (sets of) processes when individuals are exposed to an acute stressor.…”

Item familiarity and controlled associative retrieval in Alzheimer's disease: An fMRI study

“…It has recently been proposed that the parietal lobe supports the subjective experience of recollection or a similar aspect of recollection, the feeling of confidence (Ally et al, 2008;Berryhill et al, 2007;Davidson et al, 2008;Hayes et al, 2011;Slotnick, 2010). Simons et al (2010) reported that patients with bilateral parietal lesions have impaired subjective recollection but preserved bottom-up attention processes during memory tasks. According to these authors, during memory retrieval, the parietal cortex is responsible for the subjective experience of richness, vividness and confidence in one's recollection that constitutes the sense of personal experience in the recollection function.…”

“…The design of our task does not allow an examination of how the retrieval of the associations is personally experienced by the participants and which region supports this process, since our task was designed to disentangle controlled retrieval of a pair from item familiarity. Intuitively, we can assume that healthy participants should feel that they have personally seen the association and, on the basis of current opinion regarding this process, one may assume this to be related to the inferior parietal cortex (Simons et al, 2010). According to the wide range of studies and reviews showing that the hippocampus plays a crucial role in retrieval of associated details, we should expect it to be involved in the recollection function.…”

Functional Heterogeneity in Posterior Parietal Cortex Across Attention and Episodic Memory Retrieval

“…Recently, memory researchers have also turned their attention to the role of PPC in cognition because human neuroimaging experiments have consistently revealed PPC activity during episodic retrieval (Wheeler and Buckner 2004;Wagner et al 2005;Cabeza et al 2008;Ciaramelli et al 2008;Vilberg and Rugg 2008b;Olson and Berryhill 2009). Moreover, studies of human patients with lesions to PPC have revealed subtle, but significant, memory impairments (Berryhill et al 2007;Davidson et al 2008;Berryhill et al 2010;Ciaramelli et al 2010;Drowos et al 2010; Simons et al 2010, cf. Ally et al 2008;Haramati et al 2008;Simons et al 2008).…”