Laminar analysis of intracortical electrical activity in humans

Ulbert, I.1, Halgren, E.2, and Karmos, G.1
1Institute for Psychology of the Hungarian Academy of Sciences, Budapest, Hungary; 2Martinos Center for Biomedical Imaging, HMS/MGH/MIT, Charlestown, MA

The human brain is dominated by the neocortex, a large folded surface, whose cellular and synaptic elements are arranged in layers. Since cortical structure is relatively constant across its surface, local information processing can be inferred from multiple laminar recordings of its electrical activity along a line perpendicular to its surface. Such recordings need to be spaced close together, and need to be wideband in order to sample both synaptic currents and action potentials. Current source density analysis can identify the synaptic generators of the intracortical field-potentials. Simultaneous multiple- and single-unit activity records lends convergent information to the definition of these processes, and provides insight into local cellular responses to the field-potential being analyzed. Until recently, laminar multiple microelectrode recordings have been performed only in animals. Cognitive event-related potential (ERP) studies are difficult or impossible to be performed adequately in animals because of the complexity of the tasks where they are evoked and manipulated. Furthermore, it is obviously superior to characterize in detail the pathophysiology of an actual human disease epilepsy - as opposed to an animal model of that disease. Additional information from human studies could help improve diagnostic techniques for the surgical resection of epilepsy by better defining tissue for resection, and regions of eloquent cortex, through increased knowledge of local ERP generators and the represented cognitive function.