TY - JOUR T1 - Encoding of Multiple Reward-Related Computations in Transient and Sustained High-Frequency Activity in Human OFC JF - Current Biology Y1 - 2018 A1 - Ignacio Saez A1 - Jack Lin A1 - Arjen Stolk A1 - Edward Chang A1 - Josef Parvizi A1 - Gerwin Schalk A1 - Robert T. Knight A1 - Ming Hsu KW - ECoC KW - Electrocorticography KW - ERP KW - event-related potential KW - field potential KW - FP KW - HFA KW - high-frequency activity KW - OFC KW - orbitofrontal cortex KW - reward-prediction error KW - RPE AB - Summary Human orbitofrontal cortex (OFC) has long been implicated in value-based decision making. In recent years, convergent evidence from human and model organisms has further elucidated its role in representing reward-related computations underlying decision making. However, a detailed description of these processes remains elusive due in part to (1) limitations in our ability to observe human OFC neural dynamics at the timescale of decision processes and (2) methodological and interspecies differences that make it challenging to connect human and animal findings or to resolve discrepancies when they arise. Here, we sought to address these challenges by conducting multi-electrode electrocorticography (ECoG) recordings in neurosurgical patients during economic decision making to elucidate the electrophysiological signature, sub-second temporal profile, and anatomical distribution of reward-related computations within human OFC. We found that high-frequency activity (HFA) (70–200 Hz) reflected multiple valuation components grouped in two classes of valuation signals that were dissociable in temporal profile and information content: (1) fast, transient responses reflecting signals associated with choice and outcome processing, including anticipated risk and outcome regret, and (2) sustained responses explicitly encoding what happened in the immediately preceding trial. Anatomically, these responses were widely distributed in partially overlapping networks, including regions in the central OFC (Brodmann areas 11 and 13), which have been consistently implicated in reward processing in animal single-unit studies. Together, these results integrate insights drawn from human and animal studies and provide evidence for a role of human OFC in representing multiple reward computations. VL - 28 UR - http://www.sciencedirect.com/science/article/pii/S0960982218309758 ER - TY - JOUR T1 - Spatiotemporal dynamics of word retrieval in speech production revealed by cortical high-frequency band activity. JF - Proceedings of the National Academy of Sciences of the United States of America Y1 - 2017 A1 - Riès, Stephanie K. A1 - Dhillon, Rummit K. A1 - Clarke, Alex A1 - King-Stephens, David A1 - Laxer, Kenneth D. A1 - Weber, Peter B. A1 - Kuperman, Rachel A. A1 - Auguste, Kurtis I. A1 - Peter Brunner A1 - Gerwin Schalk A1 - Lin, Jack J. A1 - Parvizi, Josef A1 - Crone, Nathan E. A1 - Dronkers, Nina F. A1 - Robert T. Knight AB - Word retrieval is core to language production and relies on complementary processes: the rapid activation of lexical and conceptual representations and word selection, which chooses the correct word among semantically related competitors. Lexical and conceptual activation is measured by semantic priming. In contrast, word selection is indexed by semantic interference and is hampered in semantically homogeneous (HOM) contexts. We examined the spatiotemporal dynamics of these complementary processes in a picture naming task with blocks of semantically heterogeneous (HET) or HOM stimuli. We used electrocorticography data obtained from frontal and temporal cortices, permitting detailed spatiotemporal analysis of word retrieval processes. A semantic interference effect was observed with naming latencies longer in HOM versus HET blocks. Cortical response strength as indexed by high-frequency band (HFB) activity (70-150 Hz) amplitude revealed effects linked to lexical-semantic activation and word selection observed in widespread regions of the cortical mantle. Depending on the subsecond timing and cortical region, HFB indexed semantic interference (i.e., more activity in HOM than HET blocks) or semantic priming effects (i.e., more activity in HET than HOM blocks). These effects overlapped in time and space in the left posterior inferior temporal gyrus and the left prefrontal cortex. The data do not support a modular view of word retrieval in speech production but rather support substantial overlap of lexical-semantic activation and word selection mechanisms in the brain. UR - http://www.ncbi.nlm.nih.gov/pubmed/28533406 ER - TY - JOUR T1 - Word pair classification during imagined speech using direct brain recordings. JF - Scientific reports Y1 - 2016 A1 - Martin, Stéphanie A1 - Peter Brunner A1 - Iturrate, Iñaki A1 - Millán, José Del R. A1 - Gerwin Schalk A1 - Robert T. Knight A1 - Pasley, Brian N. AB - People that cannot communicate due to neurological disorders would benefit from an internal speech decoder. Here, we showed the ability to classify individual words during imagined speech from electrocorticographic signals. In a word imagery task, we used high gamma (70-150þinspaceHz) time features with a support vector machine model to classify individual words from a pair of words. To account for temporal irregularities during speech production, we introduced a non-linear time alignment into the SVM kernel. Classification accuracy reached 88% in a two-class classification framework (50% chance level), and average classification accuracy across fifteen word-pairs was significant across five subjects (meanþinspace=þinspace58%; pþinspace<þinspace0.05). We also compared classification accuracy between imagined speech, overt speech and listening. As predicted, higher classification accuracy was obtained in the listening and overt speech conditions (meanþinspace=þinspace89% and 86%, respectively; pþinspace<þinspace0.0001), where speech stimuli were directly presented. The results provide evidence for a neural representation for imagined words in the temporal lobe, frontal lobe and sensorimotor cortex, consistent with previous findings in speech perception and production. These data represent a proof of concept study for basic decoding of speech imagery, and delineate a number of key challenges to usage of speech imagery neural representations for clinical applications. VL - 6 UR - http://www.ncbi.nlm.nih.gov/pubmed/27165452 ER - TY - JOUR T1 - Decoding spectrotemporal features of overt and covert speech from the human cortex. JF - Frontiers in Neuroengineering Y1 - 2014 A1 - Martin, Stéphanie A1 - Peter Brunner A1 - Holdgraf, Chris A1 - Heinze, Hans-Jochen A1 - Nathan E. Crone A1 - Rieger, Jochem A1 - Gerwin Schalk A1 - Robert T. Knight A1 - Pasley, Brian N. KW - covert speech KW - decoding model KW - Electrocorticography KW - pattern recognition KW - speech production AB - Auditory perception and auditory imagery have been shown to activate overlapping brain regions. We hypothesized that these phenomena also share a common underlying neural representation. To assess this, we used electrocorticography intracranial recordings from epileptic patients performing an out loud or a silent reading task. In these tasks, short stories scrolled across a video screen in two conditions: subjects read the same stories both aloud (overt) and silently (covert). In a control condition the subject remained in a resting state. We first built a high gamma (70–150 Hz) neural decoding model to reconstruct spectrotemporal auditory features of self-generated overt speech. We then evaluated whether this same model could reconstruct auditory speech features in the covert speech condition. Two speech models were tested: a spectrogram and a modulation-based feature space. For the overt condition, reconstruction accuracy was evaluated as the correlation between original and predicted speech features, and was significant in each subject (p < 0.00001; paired two-sample t-test). For the covert speech condition, dynamic time warping was first used to realign the covert speech reconstruction with the corresponding original speech from the overt condition. Reconstruction accuracy was then evaluated as the correlation between original and reconstructed speech features. Covert reconstruction accuracy was compared to the accuracy obtained from reconstructions in the baseline control condition. Reconstruction accuracy for the covert condition was significantly better than for the control condition (p < 0.005; paired two-sample t-test). The superior temporal gyrus, pre- and post-central gyrus provided the highest reconstruction information. The relationship between overt and covert speech reconstruction depended on anatomy. These results provide evidence that auditory representations of covert speech can be reconstructed from models that are built from an overt speech data set, supporting a partially shared neural substrate. VL - 7 UR - http://www.ncbi.nlm.nih.gov/pubmed/24904404 IS - 14 ER - TY - JOUR T1 - Proceedings of the Fifth International Workshop on Advances in Electrocorticography. JF - Epilepsy Behav Y1 - 2014 A1 - A L Ritaccio A1 - Peter Brunner A1 - Gunduz, Aysegul A1 - Hermes, Dora A1 - Hirsch, Lawrence J A1 - Jacobs, Joshua A1 - Kamada, Kyousuke A1 - Kastner, Sabine A1 - Robert T. Knight A1 - Lesser, Ronald P A1 - Miller, Kai A1 - Sejnowski, Terrence A1 - Worrell, Gregory A1 - Gerwin Schalk KW - Brain Mapping KW - brain-computer interface KW - electrical stimulation mapping KW - Electrocorticography KW - functional mapping KW - Gamma-frequency electroencephalography KW - High-frequency oscillations KW - Neuroprosthetics KW - Seizure detection KW - Subdural grid AB -

The Fifth International Workshop on Advances in Electrocorticography convened in San Diego, CA, on November 7-8, 2013. Advancements in methodology, implementation, and commercialization across both research and in the interval year since the last workshop were the focus of the gathering. Electrocorticography (ECoG) is now firmly established as a preferred signal source for advanced research in functional, cognitive, and neuroprosthetic domains. Published output in ECoG fields has increased tenfold in the past decade. These proceedings attempt to summarize the state of the art.

VL - 41 UR - http://www.ncbi.nlm.nih.gov/pubmed/25461213 ER - TY - JOUR T1 - Spatial and temporal relationships of electrocorticographic alpha and gamma activity during auditory processing. JF - NeuroImage Y1 - 2014 A1 - Potes, Cristhian A1 - Peter Brunner A1 - Gunduz, Aysegul A1 - Robert T. Knight A1 - Gerwin Schalk KW - alpha and high gamma activity KW - auditory processing KW - electrocorticography (ECoG) KW - functional connectivity KW - granger causality KW - thalamo-cortical interactions AB - Neuroimaging approaches have implicated multiple brain sites in musical perception, including the posterior part of the superior temporal gyrus and adjacent perisylvian areas. However, the detailed spatial and temporal relationship of neural signals that support auditory processing is largely unknown. In this study, we applied a novel inter-subject analysis approach to electrophysiological signals recorded from the surface of the brain (electrocorticography (ECoG)) in ten human subjects. This approach allowed us to reliably identify those ECoG features that were related to the processing of a complex auditory stimulus (i.e., continuous piece of music) and to investigate their spatial, temporal, and causal relationships. Our results identified stimulus-related modulations in the alpha (8-12 Hz) and high gamma (70-110 Hz) bands at neuroanatomical locations implicated in auditory processing. Specifically, we identified stimulus-related ECoG modulations in the alpha band in areas adjacent to primary auditory cortex, which are known to receive afferent auditory projections from the thalamus (80 of a total of 15,107 tested sites). In contrast, we identified stimulus-related ECoG modulations in the high gamma band not only in areas close to primary auditory cortex but also in other perisylvian areas known to be involved in higher-order auditory processing, and in superior premotor cortex (412/15,107 sites). Across all implicated areas, modulations in the high gamma band preceded those in the alpha band by 280 ms, and activity in the high gamma band causally predicted alpha activity, but not vice versa (Granger causality, p<1e(-8)). Additionally, detailed analyses using Granger causality identified causal relationships of high gamma activity between distinct locations in early auditory pathways within superior temporal gyrus (STG) and posterior STG, between posterior STG and inferior frontal cortex, and between STG and premotor cortex. Evidence suggests that these relationships reflect direct cortico-cortical connections rather than common driving input from subcortical structures such as the thalamus. In summary, our inter-subject analyses defined the spatial and temporal relationships between music-related brain activity in the alpha and high gamma bands. They provide experimental evidence supporting current theories about the putative mechanisms of alpha and gamma activity, i.e., reflections of thalamo-cortical interactions and local cortical neural activity, respectively, and the results are also in agreement with existing functional models of auditory processing. VL - 97 UR - http://www.ncbi.nlm.nih.gov/pubmed/24768933 ER - TY - JOUR T1 - Proceedings of the Third International Workshop on Advances in Electrocorticography. JF - Epilepsy Behav Y1 - 2012 A1 - A L Ritaccio A1 - Beauchamp, Michael A1 - Bosman, Conrado A1 - Peter Brunner A1 - Chang, Edward A1 - Nathan E. Crone A1 - Gunduz, Aysegul A1 - Disha Gupta A1 - Robert T. Knight A1 - Leuthardt, Eric A1 - Litt, Brian A1 - Moran, Daniel A1 - Ojemann, Jeffrey A1 - Parvizi, Josef A1 - Ramsey, Nick A1 - Rieger, Jochem A1 - Viventi, Jonathan A1 - Voytek, Bradley A1 - Williams, Justin A1 - Gerwin Schalk KW - Brain Mapping KW - brain-computer interface KW - Electrocorticography KW - Gamma-frequency electroencephalography KW - high-frequency oscillation KW - Neuroprosthetics KW - Seizure detection KW - Subdural grid AB - The Third International Workshop on Advances in Electrocorticography (ECoG) was convened in Washington, DC, on November 10-11, 2011. As in prior meetings, a true multidisciplinary fusion of clinicians, scientists, and engineers from many disciplines gathered to summarize contemporary experiences in brain surface recordings. The proceedings of this meeting serve as evidence of a very robust and transformative field but will yet again require revision to incorporate the advances that the following year will surely bring. VL - 25 UR - http://www.ncbi.nlm.nih.gov/pubmed/23160096 IS - 4 ER -