Theta synchronization during episodic retrieval: Neural correlates of conscious awareness

In a past study, Klimesch and colleagues examined whether the conscious experience of remembering and knowing are associated with neural synchronization in the theta bandwidth.  These investigators first presented participants with a series of words (through both auditory and visual means) and then tested participants’ memory for these words using a recognition test and the “Remember-Know” task. 

During the recognition test, participants were shown a series of words (the participants saw some of these words earlier during the experiment, whereas other words were not seen before) and were asked to judge whether these same words were presented to them earlier.  For those words that were judged as “old” (previously presented), participants also performed the Remember-Know task. 

The Remember-Know task is widely used in memory research to study one’s state of consciousness during a recognition decision.  “Remember” judgments are made when an “old” decision on the recognition test is accompanied by awareness of details of the previous occurrence of the stimulus in question.  “Know” judgments are made when an “old” decision is not accompanied by such awareness.

Among other interesting results, Klimesch and colleagues found that theta power was larger for Know judgments early during the recognition period of a word (300 – 450 ms) and larger for Remember judgments during a later period (450 – 625 ms). The investigators concluded that these patterns of theta associated with Remember and Know judgments demonstrate that the temporal dynamics of the neural synchronization plays an important role in the experiential characteristics associated with memory retrieval.