Einladung zur öffentlichen Disputation

von Frau Neda Salari

Freitag, 24. August 2012 um 9:00 Uhr
Institut für Systemische Neurowissenschaften, Universitätsklinikum Hamburg- Eppendorf,
Martinistr. 52, Haus W34, Seminarraum (307)

"Functional Dissociation of Ongoing Oscillatory Brain States Revealed by a Custom-Developed Brain Computer Interface"

Abstract:

The state of a neural assembly in the human brain preceding an incoming stimulus is assumed to modu- late the processing of subsequently presented stimuli. The nature of this state can differ with respect to the frequency of ongoing oscillatory activity. Oscillatory activity of specific frequency range such as alpha (8-12 Hz) and gamma (30-45 Hz) band oscillations is hypothesized to play a functional role in visual object processing. However, the precise role of prestimulus alpha or gamma band oscillations for visual object processing is not completely understood. Therefore, a selective modulation of this prestimulus activity could clarify the functional role of these oscillations.

In contrast to previous studies in which oscillations of prestimulus activity were correlated with visual perfor- mance, we attempted to put the volunteers directly in control of the oscillatory brain activity. To this end, we designed and implemented a non-invasive brain com- puter interface (BCI) method to train volunteers to selectively increase their alpha or gamma band activity in the occipital cortex. During training, oscillatory brain activity was estimated online and fed back to the volunteers to enable a deliberate modulation of alpha or gamma band oscillations. During the testing phase which followed the training phase, alpha or gamma band activity was classified online and at predefined levels of activity, visual objects embedded in noise were presented in order to assess the influence of frequency modulation on subsequent visual object processing.

Our results demonstrated that volunteers learned to selectively modulate alpha or gamma band oscillations in the visual cortex with a high level of specificity regarding frequency range and localization. During phases of increased gamma band activity, visual object processing was improved.

Hence, the BCI method allows a selective manipula- tion of gamma band activity in the visual cortex and supports a prominent role of prestimulus gamma band activity for visual object processing.

 

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(Vortrag auf Englisch)

Kontakt:

Prof. Dr. Stefan Wermter
Vorsitzender des Promotionsprüfungsausschusses