Early Parietal Response in Episodic Retrieval Revealed with MEG
Introduction
The parietal lobe is active during episodic memory retrieval. Recent evidence from functional neuroimaging has led to models ascribing dissociable roles to superior and inferior subregions of the lateral parietal lobe during retrieval (Ciaramelli et al. 2008; Cabeza 2008; Vilberg & Rugg 2008). We use a novel pair-cued recall task to further describe the nature of parietal involvement in episodic memory recollection. Using magnetoencephalography (MEG) we investigate both spatial and temporal dynamics of the parietal response in the first 600 ms after subjects are prompted to initiate retrieval.
Section snippets
Methods
Eleven healthy young adults (mean age: 23.7, 6 male) studied 120 pairs of drawings of common objects and animals. After 45 minutes, subjects began the test phase while neural activity was recorded via a 306 channel MEG system at 1000 Hz. In all trials, a single stimulus was presented for 500 ms in one of two boxes followed by a 2750 ms response period. In ‘classify’ trials subjects indicated via finger response whether the presented stimulus was a living object. In ‘recall-classify’ trials they
Results
Occipital visual response to stimulus onset was similar for classify and recall-classify tasks. However, shortly after stimulus onset, MEG response in both the left superior and left inferior parietal lobules was increased for recall-classify trials relative to classify trials. This increased activity in the retrieval condition was sustained during the period of 100 ms to 300 ms after stimulus onset in both regions. While the retrieval effect was initially similar in the superior and inferior
Conclusions
The left parietal lobe shows an early response in episodic retrieval. This response is transient and likely precedes the actual recollection of target stimuli. The timing suggests that this left parietal response may be driven by directing attention to memory.