Episodic memory refers to our memory of specific events in our lives, so it contains information about time and space, such as when and where the event occurred. Because of its various components, episodic memory is seriously impaired in the case of ...
Episodic memory refers to our memory of specific events in our lives, so it contains information about time and space, such as when and where the event occurred. Because of its various components, episodic memory is seriously impaired in the case of memory disorder. However, previous research on episodic memory has not sufficiently considered its various aspects, as mentioned above. Brilliant progress in the realm of virtual reality can enable us to substantially approach unique characteristics of episodic memory. There are three advantages to using virtual reality in research on episodic memory. First, researchers can easily control information about time and space. Second, the self-reference effect is maximized by active navigation in a freely explorable environment. Third, a high-quality virtual reality guarantees high validity of results owing to its close resemblance to real life. For these reasons, using virtual reality allows us to effectively study episodic memory. We sought to understand the brain mechanism related to episodic memory from multiple views, by measuring EEGs (electroencephalograms, the neural oscillation electrically recorded from the scalp) of both healthy people and patients with episodic memory deficits, and analyzing their biosignals through various methods.
In the first year, we set up a 3D virtual environment laboratory and assessed the new laboratory system. We compared user experiences from an existing HMD (head-mounted display, providing a large field of view by projecting images in front of the user’s eyes) method with those from a method utilizing newly introduced polarization glasses (using different polarizing filters so that each eye sees a different image). It was confirmed that the latter elicited a higher sense of reality and immersion from users, but lower cybersickness (i.e., symptoms similar to car sickness due to the virtual environment). Then, we conducted research on human factors affecting perception in virtual reality. The results revealed that immersion tendency and hypnotic susceptibility were important human factors in a given task. Additionally, we examined differences between memories about items (what) and memories about the context of those items (where). Results confirmed the old/new effect of ERPs (event-related potentials, analysis to identify the neural oscillation related to specific events, averaging a number of EEG epochs for same conditions), which meant that there was a larger positive voltage when participants recognized the old items than when they saw the new items. We also found a difference in brain activity between the memories about items and those about contexts. Then, we adopted neurofeedback training (system inducing trainees to control their neural activities) to depression patients. After the training, their cognitive function improved with changes in brain activity pattern. For the following research, we reviewed previous studies on the EEG characteristics of schizophrenia. We found abnormalities in gamma oscillations in patients with schizophrenia, and realized that we need to pay attention to the relationship between memory deficits and gamma oscillation.
In the second year, we focused on the old/new effect during episodic memory recognition. We examined the phase synchronization (temporal similarity of the EEG/ERP amplitude pattern from among the many electrode sites on the scalp) in healthy adults during memory recognition. It was found that the phase synchronization in the theta band was most powerful, and connectivity was strongest between the right frontal lobe and left parietal lobe. As preliminary research on mild cognitive impairment (MCI: a brain function syndrome involving the onset and evolution of cognitive impairments beyond those expected based on the age and education of the individual), we examined the memory recall of healthy elderly people by using a neuropsychological test (a battery of tests to diagnose dementia) and the virtual reality-based episodic memory test. We found a positive correlation between the word list recollection test scores of the CERAD-K neuropsychological test and the percentage of correct answers on the virtual reality-based episodic memory test. This result suggests that the virtual reality-based episodic memory test can be a useful alternative. Then, we examined the episodic memory of both young adults and elderly people. We observed the old/new effect in both the young adult and elderly groups; however, the magnitude of the effect was lower and its duration was shorter in the latter. Furthermore, we examined the episodic memory of patients with schizophrenia. Compared to healthy individuals, schizophrenia patients showed lower theta power on the frontal area, weaker alpha power suppression on the posterior area, and exaggerated beta power.
In the third year, we developed a social cognition training program for schizophrenia patients. Social cognition here refers to comprehensive cognitive ability for successful social interaction with other people. According to recent studies, emotion perception deficits of schizophrenia patients come from a deficit in multisensory integration ability combining various modalities of perception, not just a problem on a single modality. Therefore, we developed emotion recognition enhancement program using emotional faces and emotional vocalizations. After the training, the patients’ emotion recognition was improved to the levels shown by healthy individuals. We also reviewed numerous recent studies to identify EEG indices to facilitate diagnoses of MCI and Alzheimer's dementia. We confirmed that these diseases can be identified by various EEG analysis methods, such as source localization, coherence, phase synchronization, and brain connectivity.
Our three-year research demonstrated that research on memory using virtual reality was effective for both healthy people and patients. Our findings are meaningful to the fields of cognitive neuroscience, neuropsychology, physiological psychology, and psychiatry. Furthermore, our emotion recognition enhancement program is a new type of training program, which has not been developed before in our country or elsewhere.