%0 Journal Article %J Front Hum Neurosci %D 2012 %T Temporal evolution of gamma activity in human cortex during an overt and covert word repetition task. %A Leuthardt, E C %A Pei, Xiao-Mei %A Breshears, Jonathan %A Charles M Gaona %A Sharma, Mohit %A Zachary V. Freudenberg %A Barbour, Dennis L %A Gerwin Schalk %K cortex %K Electrocorticography %K gamma rhythms %K human %K Speech %X

Several scientists have proposed different models for cortical processing of speech. Classically, the regions participating in language were thought to be modular with a linear sequence of activations. More recently, modern theoretical models have posited a more hierarchical and distributed interaction of anatomic areas for the various stages of speech processing. Traditional imaging techniques can only define the location or time of cortical activation, which impedes the further evaluation and refinement of these models. In this study, we take advantage of recordings from the surface of the brain [electrocorticography (ECoG)], which can accurately detect the location and timing of cortical activations, to study the time course of ECoG high gamma (HG) modulations during an overt and covert word repetition task for different cortical areas. For overt word production, our results show substantial perisylvian cortical activations early in the perceptual phase of the task that were maintained through word articulation. However, this broad activation is attenuated during the expressive phase of covert word repetition. Across the different repetition tasks, the utilization of the different cortical sites within the perisylvian region varied in the degree of activation dependent on which stimulus was provided (auditoryor visual cue) and whether the word was to be spoken or imagined. Taken together, the data support current models of speech that have been previously described with functional imaging. Moreover, this study demonstrates that the broad perisylvian speech network activates early and maintains suprathreshold activation throughout the word repetition task that appears to be modulated by the demands of different conditions.

%B Front Hum Neurosci %V 6 %P 99 %8 05/2012 %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/22563311 %R 10.3389/fnhum.2012.00099 %0 Journal Article %J J Neural Eng %D 2011 %T Decoding vowels and consonants in spoken and imagined words using electrocorticographic signals in humans. %A Pei, Xiao-Mei %A Barbour, Dennis L %A Leuthardt, E C %A Gerwin Schalk %K Adolescent %K Adult %K Brain %K Brain Mapping %K Cerebral Cortex %K Communication Aids for Disabled %K Data Interpretation, Statistical %K Discrimination (Psychology) %K Electrodes, Implanted %K Electroencephalography %K Epilepsy %K Female %K Functional Laterality %K Humans %K Male %K Middle Aged %K Movement %K Speech Perception %K User-Computer Interface %X

Several stories in the popular media have speculated that it may be possible to infer from the brain which word a person is speaking or even thinking. While recent studies have demonstrated that brain signals can give detailed information about actual and imagined actions, such as different types of limb movements or spoken words, concrete experimental evidence for the possibility to 'read the mind', i.e. to interpret internally-generated speech, has been scarce. In this study, we found that it is possible to use signals recorded from the surface of the brain (electrocorticography) to discriminate the vowels and consonants embedded in spoken and in imagined words, and we defined the cortical areas that held the most information about discrimination of vowels and consonants. The results shed light on the distinct mechanisms associated with production of vowels and consonants, and could provide the basis for brain-based communication using imagined speech.

%B J Neural Eng %V 8 %P 046028 %8 08/2011 %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/21750369 %N 4 %R 10.1088/1741-2560/8/4/046028 %0 Journal Article %J J Neurosci %D 2011 %T Nonuniform high-gamma (60-500 Hz) power changes dissociate cognitive task and anatomy in human cortex. %A Charles M Gaona %A Sharma, Mohit %A Zachary V. Freudenberg %A Breshears, Jonathan %A Bundy, David T %A Roland, Jarod %A Barbour, Dennis L %A Gerwin Schalk %A Leuthardt, E C %K Acoustic Stimulation %K Adolescent %K Adult %K Analysis of Variance %K Brain Mapping %K Brain Waves %K Cerebral Cortex %K Cognition Disorders %K Electroencephalography %K Epilepsy %K Evoked Potentials %K Female %K Humans %K Male %K Middle Aged %K Neuropsychological Tests %K Nonlinear Dynamics %K Photic Stimulation %K Reaction Time %K Spectrum Analysis %K Time Factors %K Vocabulary %X

High-gamma-band (>60 Hz) power changes in cortical electrophysiology are a reliable indicator of focal, event-related cortical activity. Despite discoveries of oscillatory subthreshold and synchronous suprathreshold activity at the cellular level, there is an increasingly popular view that high-gamma-band amplitude changes recorded from cellular ensembles are the result of asynchronous firing activity that yields wideband and uniform power increases. Others have demonstrated independence of power changes in the low- and high-gamma bands, but to date, no studies have shown evidence of any such independence above 60 Hz. Based on nonuniformities in time-frequency analyses of electrocorticographic (ECoG) signals, we hypothesized that induced high-gamma-band (60-500 Hz) power changes are more heterogeneous than currently understood. Using single-word repetition tasks in six human subjects, we showed that functional responsiveness of different ECoG high-gamma sub-bands can discriminate cognitive task (e.g., hearing, reading, speaking) and cortical locations. Power changes in these sub-bands of the high-gamma range are consistently present within single trials and have statistically different time courses within the trial structure. Moreover, when consolidated across all subjects within three task-relevant anatomic regions (sensorimotor, Broca's area, and superior temporal gyrus), these behavior- and location-dependent power changes evidenced nonuniform trends across the population. Together, the independence and nonuniformity of power changes across a broad range of frequencies suggest that a new approach to evaluating high-gamma-band cortical activity is necessary. These findings show that in addition to time and location, frequency is another fundamental dimension of high-gamma dynamics.

%B J Neurosci %V 31 %P 2091-100 %8 02/2011 %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/21307246 %N 6 %R 10.1523/JNEUROSCI.4722-10.2011