Reduced multimodal integration of memory features following continuous theta burst stimulation of angular gyrus

Abstract

Background: Lesions of the angular gyrus (AnG) region of human parietal cortex do not cause amnesia, but appear to be associated with reduction in the ability to consciously experience the reliving of previous events.

Objectives/hypothesis: We used continuous theta burst stimulation to test the hypothesis that the cognitive mechanism implicated in this memory deficit might be the integration of retrieved sensory event features into a coherent multimodal memory representation.

Methods: Healthy volunteers received stimulation to AnG or a vertex control site after studying stimuli that each comprised a visual object embedded in a scene, with the name of the object presented auditorily. Participants were then asked to make memory judgments about the studied stimuli that involved recollection of single event features (visual or auditory), or required integration of event features within the same modality, or across modalities.

Results: Participants' ability to retrieve context features from across multiple modalities was significantly reduced after AnG stimulation compared to stimulation of the vertex. This effect was observed only for the integration of cross-modal context features but not for integration of features within the same modality, and could not be accounted for by task difficulty as performance was matched across integration conditions following vertex stimulation.

Conclusion: These results support the hypothesis that AnG is necessary for the multimodal integration of distributed cortical episodic features into a unified conscious representation that enables the experience of remembering.

Keywords: Brain stimulation; Memory; Parietal lobe; Recollection; Source monitoring.

Fig. 1

Schematic representation of the experiment. In each study phase trial, an object (in this case, a ball) was presented on the left or right of a scene, on top of or underneath another salient object. Concurrently, the name of the object was presented auditorily in a male or female voice, spoken in a Scottish or English accent. Following cTBS targeting vertex or angular gyrus, the test phase was administered. Examples of the three source memory conditions are displayed (top: single source, middle: within-modal source, bottom: cross-modal source). See text for further details.

Fig. 2

Source memory accuracy of participants after cTBS targeting vertex or angular gyrus (AnG) in conditions that required the integration of event features either within the same modality, or across modalities. A selective impairment was observed in cross-modal source accuracy following AnG stimulation.