thesis defense Esther Meeuwissen (Donders Series 100)
December 6, 2012
Pomotors: Prof. dr. P. Hagoort, Prof.dr. G. Fernández, copromotor: Dr. O. Jensen
Cortical oscillatory activity during memory formation
Cognition relies on the interplay between various brain regions. As many other cognitive functions, long-term memory (LTM) formation involves an extended network of brain areas; task-relevant brain areas which need to be engaged and task-irrelevant areas which need to be disengaged. We investigated oscillatory activity during memory formation using magnetoencephalography (MEG). Participants encoded word sequences, single words and single objects in LTM while MEG data was recorded. Brain activity recorded during successful encoding was compared to activity recorded during unsuccessful encoding.
The studies in this thesis show memory related effects in several brain areas depending on the type of stimuli participants encoded. Increased alpha activity over occipital and parietal areas was found to improve encoding of single words and word sequences in LTM. Strong alpha activity is commonly seen in areas not relevant for the task; therefore it is thought to reflect disengagement of the area. Low alpha activity is usually observed in areas involved in the task and thought to reflect engagement of the area. Encoding of objects seemed to benefit more from decreased alpha activity in the ventral stream. Low beta and high gamma activity in various central, frontal and temporal areas were found to improve encoding of word sequences, single words and objects. These effects are thought to be related to engagement of task-relevant areas. It is important to note that the size of the effects we observed correlated with the performance of participants on the memory tasks; the participants who remembered most of the stimuli produced the largest effects. This shows the importance of oscillatory activity for memory formation.