Mean signal and response time influences on multivoxel signals of contextual retrieval in the medial temporal lobe

Abstract

Introduction: The medial temporal lobe supports integrating the "what," "where," and "when" of an experience into a unified memory. However, it remains unclear how representations of these contextual features are neurally encoded and distributed across medial temporal lobe subregions. Methods: This study conducted functional magnetic resonance imaging of the medial temporal lobe, while participants retrieved pair, spatial, and temporal source memories. Multivoxel classifiers were trained to distinguish between retrieval conditions before and after correction for mean signal and response times, to more thoroughly characterize the multivoxel signal associated with memory context. Results: Activity in perirhinal and parahippocampal cortex dissociated between memory for associated items and memory for their spatiotemporal context, and hippocampal activity was linked to memory for spatial context. However, perirhinal and hippocampal classifiers were, respectively, driven by effects of mean signal amplitude and task difficulty, whereas the parahippocampal classifier survived correction for these effects. Conclusion: These findings demonstrate dissociable coding mechanisms for episodic memory context across the medial temporal lobe, and further highlight a critical distinction between multivoxel representations driven by spatially distributed activity patterns, and those driven by the regional signal. In this study, multivoxel analysis of medial temporal lobe activation patterns was conducted to distinguish between item, spatial and temporal contextual memory retrieval. Hippocampal activity, related to response times, was linked to spatial retrieval, whereas perirhinal cortex activity, related to the mean signal, and parahippocampal cortex activity patterns, were both linked to item retrieval.