Interhemispheric theta coherence in the hippocampus for successful object-location memory in human intracranial encephalography.

Our knowledge concerning visual-spatial memory related phase synchronization within the ipsilateral hippocampus or between contralateral hippocampi during memory encoding in humans is currently limited. The present study examines the relationship between phase synchronization within the hippocampus and memory performance during virtual navigation in an object-location memory navigation task using intracranial depth electrodes in human subjects. Specifically, we focus on the phase synchronization ratio between periods when the target object was in and out of visual focus. Our findings indicate that there is a significant relationship between this phase synchronization ratio and object-location memory performance in the theta band (p = 0.015, R = -0.71), but not in the delta or alpha bands. Importantly, this theta coherence has a significant linear relationship with memory performance between contralateral hippocampus electrode pairs (p = 0.006, R = -0.77), but not ipsilateral electrode pairs (p = 0.79, R = -0.09). In addition, this theta coherence has a significant linear relationship with memory performance during stationary periods (p = 0.002, R = -0.82), but not movement periods (p = 0.10, R = -0.51). These findings suggest that, during navigation, interhemispheric hippocampal theta coherence when stationary and focusing on the target object may be a critical determinant of successful object-location memory.

A thin film polyimide mesh microelectrode for chronic epidural electrocorticography recording with enhanced contactability.

OBJECTIVE: Epidural electrocorticography (ECoG) activity may be more reliable and stable than single-unit-activity or local field potential. Invasive brain computer interface (BCI) devices are limited by mechanical mismatching and cellular reactive responses due to differences in the elastic modulus and the motion of stiff electrodes. We propose a mesh-shaped electrode to enhance the contactability between surface of dura and electrode. APPROACH: We designed a polyimide (PI) electrode with a mesh pattern for more conformal contact with a curved surface. We compared the contact capability of mesh PI electrodes with conventionally used sheet PI electrode. The electrical properties of the mesh PI electrode were evaluated for four weeks. We recorded the epidural ECoG (eECoG) activity on the surface of rhesus monkey brains while they performed a saccadic task for four months. MAIN RESULTS: The mesh PI electrode showed good contact with the agarose brain surface, as evaluated by visual inspection and signal measurement. It was about 87% accurate in predicting the direction of saccade eye movement. SIGNIFICANCE: Our results indicate that the mesh PI electrode was flexible and good contact on the curved surface and can record eECoG activity maintaining close contact to dura, which was proved by in vivo and in vitro test.