Dr. Halgren was recruited to UCSD in 2005 by the Department of Radiology. He co-directs the Multimodal Imaging Laboratory with his longtime collaborator Dr. Anders Dale, helping to facilitate research integrating hemodynamic, electromagnetic, and structural imaging.
His own research projects combine functional magnetic resonance imaging (MRI), magnetoencephalography, and electroencephalography, within the context of structural MRI, for high-resolution spatiotemporal mapping of brain activity during cognition. He validates these measures using intracranial recordings from microelectrode arrays in patients with epilepsy.
Dr. Halgren received his PhD in Neurosciences from UCLA in 1974, studying memory using single-unit recordings and electrical stimulation in the human medial temporal lobe. Following postdoctoral fellowship and research appointments in cognitive neurophysiology at the UCLA Brain Research Institute, in 1981 he joined the UCLA faculty in Psychiatry and Biobehavioral Sciences.
Dr. Halgren is a licensed psychologist and served as Director of Neuropsychology at the VA Regional Epilepsy Center and California Comprehensive Epilepsy Program in Los Angeles. From 1990 to 1997, he was also a Director of Research at the Institut National de la Santé et de la Recherche Médicale (INSERM) in France, where he worked with the group of Talairach. In 1997, he joined the faculty of the Department of Radiology at the University of Utah School of Medicine, where he also was a member of the Neurosciences Program. In 1999, he joined the Martinos Center, a joint effort of Massachusetts General Hospital, Massachusetts Institute of Technology, and Harvard Medical School, where he was the founding director of the Magnetoencephalography Laboratory.
In his research, Dr. Halgren attempts to identify, locate, and characterize the neurocognitive stages used to encode and interpret events. Of particular interest are middle latency focal processes that encode faces and words, and later distributed processes that organize attention, or integrate semantic stimuli with the ongoing cognitive context. In which cortical areas are they generated, which cells are involved, how are they modulated, and what is the effect of that modulation on information processing? The overall goal is to understand fundamental integrative cognitive processes at the synaptic and system levels.
Dr. Halgren has an active teaching role in the Graduate Program in Neurosciences. He also provides instruction to postgraduate fellows and serves as a mentor to junior faculty. Dr. Halgren serves on the Editorial Board of the journal Human Brain Mapping and is the Chair of the International Advisory Board for Biomag.
Multimodal Imaging Laboratory
Overall, I am interested in large-scale neurophysiological processes in humans, with 4 broad themes:
Methodological: We described methods for source localization from MEG and EEG (~126, ~133), simultaneous hemodynamic and microneurophysiological cortical recordings in humans (~134); we quantified the degree of cancellation at EEG and MEG sensors when multiple sources are active (~141), and demonstrated experimentally that it is necessary to include the anisotropy of the white matter (~146) and possibly extracellular filtering (~154), in calculating EEG propagation. We described a method for consistently and automatically labeling the gyri and sulci of the brain using standard anatomical nomenclature (~153), and validated tract tracing methods by comparing diffusion tensor imaging (DTI) collected before vs after anterior temporal lobectomy (~156).
Epilepsy: We used novel multi-microelectrode technology to describe neuronal firing and laminar transmembrane currents underlying human interictal spikes (~127, ~151), and MRI-constrained distributed MEG inverse solutions to describe the spatiotemporal evolution of interictal discharges (~143). We used automated white matter tract segmentation and quantification from DTI (~129, ~132, ~137, ~139), automated subcortical volumetry from MRI (~130), and automated cortical reconstruction and thickness/volumetry from MRI (~131), to describe the structural basis of human temporal lobe epilepsy.
Sleep: We made fundamental contributions to understanding the neural basis of the most common EEG elements present during non-REM sleep, including the K complex (~135), slow oscillation (~148), and sleep spindle (~149, ~150, ~155).
Cognition: We used MEG to determine the spatiotemporal pattern of brain activation during phonological segmentation (~128), auditory pattern monitoring (~152), word processing in the first and second language of bilinguals (~144), and verbal memory (~138), where the relationship to intracranial recordings was described (~157). Using intracranial recordings, we identified the sequential stages used by Broca’s area to attach morphosyntactic markers to words (~140), and described theta and gamma oscillations in the hippocampal system during remote declarative memory (~142). We described a relationship between local cortical thickness and spelling (~145), and the influence of a microcephalin gene on cortical thickness (~147).
I am principal investigator of grants from NIH (R01: Neural Basis of Endogenous Potentials in Humans) and from NSF (Spatiotemporal dynamics of word processing in bilingual brain). I am co-PI with Terry Sejnowski on another R01 (Integrated empirical and multiscale modeling of human sleep spindles). I also actively participate in other grants, notably those concerned with brain development (led by Doris Trauner- PCND, or in collaboration with Jeff Elman).