Short-term episodic memory encoding in the human brain: a magnetoencephalography and electroencephalography study

The short-term memory encoding of visual patterns in the human brain refers to the formation of neural codes which can be used further in a wide range of working memory processes. In the present study, episodic encoding of pictorial stimuli in short-term memory were assessed using noninvasive electromagnetic measurements in human subjects as they performed continuous 1-back comparison short-term memory tasks . Estimation of the temporal dynamics of this process and source localization of the involved cortical generators was based on distributed inverse algorithms applied to multichannel magnetoencephalographic (MEG ) and electroencephalographic (EEG ) data. Results show average response times of 495 ± 110 ms and 270 ± 8.5 ms for memory and control conditions, respectively. The major time-domain electromagnetic responses related to the short-term episodic memory encoding of the presented single stimuli in the continuous 1-back comparison task were estimated to start after 320 ms to stimulus onset and continued until the disappearance of the stimuli. Distributed current estimates during this interval showed a significant activation in the left inferior medial temporal lobe in memory condition compared to control. This area could be significantly involved at least in intentional encoding processes.