Phase Locking in high gamma during a speech task

Abstract

A large topic of research within cognitive neuroscience is about how brain areas communicate and how the brain integrates different sensory signals into a unitary experience. High gamma frequencies in EEG and ECoG are thought to play a large role in ensemble formation and neuronal communication. High gamma up till now is treated as one large band, it is not yet clear if this band is composed of multiple smaller bands. Coherence is a relatively new solution to the binding problem, neuronal activity between different areas synchronizes to integrate different aspects of a stimulus. This has not yet been investigated in the high gamma frequency range. In this project five subjects that underwent surgical resection of an epileptic source in the brain due to intractable epilepsy, temporarily had an electrode grid implanted (for clinical purposes). These subjects participated in a language task. For each subject the phase locking value and phase locking statistics were used to find significant connections between electrodes for nine different frequency bands of which five in the high gamma range (between 80 and 385 Hz). A significant difference in number of connections between the speech and rest condition was found for the lower frequency bands, but not for the high gamma bands. This finding might be due to noise in the results above approximately 150 Hz. Because of this issue the high gamma bands could not reliably be compared. More research is needed to explore high gamma and the significance of phase locking in neuronal communication.