Basic MEG : Cognitive function ( 4 ) 1 - 5 - 25 : Cerebral oscillatory

Introduction: Several studies have reported a relationship between neural activity in the parietal cortex and episodic memory retrieval. While positron emission tomography has revealed that the left parietal cortex shows greater activity in retrieving auditory information than visual information during word recognition, the temporal characteristics of such parietal activities remain unclear. In the present study, by using magnetoencephalography (MEG), we examined the neural dynamics of the parietal cortex during episodic memory retrieval in which memories were encoded with either visual or auditory associative information. Methods: Participants were 9 right-handed young adults (5 females, 4 males). In the learning phase, participants were instructed to memorize (i) 40 words without associates (word condition), (ii) 40 words with relevant sounds (auditory condition), and (iii) 40 words with relevant pictures (visual condition). MEG signals were measured during the test phase in which subjects were randomly presented with 120 study words and 40 distracter words, and were required to discern if the presented word was involved in the study words. Data from test phase was analyzed within the 4 conditions including correctly rejected distracter. Results and Conclusion: Behavioral data showed that recognition performance in the auditory condition was significantly higher than the word condition. MEG waveforms showed increased neural activity in the left parietal cortex in the auditory condition compared to the visual condition in the latency range between 200 and 300ms after the onset of the stimuli. In contrast, the right parietal cortex showed no significant differences. These findings suggest that changes in neural activity in the left parietal cortex during episodic memory retrieval may therefore depend on modality-specific information associated with the encoding process.