Continuous theta burst stimulation of angular gyrus reduces subjective recollection

Abstract

The contribution of lateral parietal regions such as the angular gyrus to human episodic memory has been the subject of much debate following widespread observations of left parietal activity in healthy volunteers during functional neuroimaging studies of memory retrieval. Patients with lateral parietal lesions are not amnesic, but recent evidence indicates that their memory abilities may not be entirely preserved. Whereas recollection appears intact when objective measures such as source accuracy are used, patients often exhibit reduced subjective confidence in their accurate recollections. When asked to recall autobiographical memories, they may produce spontaneous narratives that lack richness and specificity, but can remember specific details when prompted. Two distinct theoretical accounts have been proposed to explain these results: that the patients have a deficit in the bottom-up capturing of attention by retrieval output, or that they have an impairment in the subjective experience of recollection. The present study aimed to differentiate between these accounts using continuous theta burst stimulation (cTBS) in healthy participants to disrupt function of specific left parietal subregions, including angular gyrus. Inconsistent with predictions of the attentional theory, angular gyrus cTBS did not result in greater impairment of free recall than cued recall. Supporting predictions of the subjective recollection account, temporary disruption of angular gyrus was associated with highly accurate source recollection accuracy but a selective reduction in participants' rated source confidence. The findings are consistent with a role for angular gyrus in the integration of memory features into a conscious representation that enables the subjective experience of remembering.

Figure 1. Schematic diagram illustrating the computerized memory tests.

Figure 2. cTBS target locations (blue circles) displayed on an inflated fiducial brain that illustrates parietal loci sensitive to recollection (small yellow spheres) and familiarity (small red spheres), derived from a meta-analysis of fMRI studies .

The centers of mass of these activation clusters (large spheres) were the targets for angular gyrus (AnG) and intraparietal sulcus (IPS) stimulation. Figure adapted from one kindly provided by Mick Rugg.

Figure 3. Performance of the groups who received cTBS targeting vertex and angular gyrus (AnG) on free and cued recall (left panel) and source recollection accuracy and confidence (right panel).

Error bars denote standard error of the mean.