D.A. Parker CV



DAVID A. PARKER215 Hooper StreetThe University of GeorgiaAthens, GA 30602 HYPERLINK "mailto:daparker@uga.edu" daparker@uga.edu(678)-793-0326Fax: (706) 542-3275EDUCATION2013-2019 M.S., Ph.D. University of Georgia (in progress)Psychology, Behavior and Brain Sciences ProgramAdvisor: Brett A. Clementz, Ph.D.2008-2012B.A./B.A.University of GeorgiaPhilosophyCognitive Science PUBLICATONSHamm, J.P., Bobilev, A.E., Hayrynen, L.K., Hudgens-Haney, M.E, Oliver, W.T., Parker, D.A., McDowell, J.E., Buckley, P.A, Clementz, B.A. Stimulus train duration moderates gamma-band auditory neural entrainment abnormalities in schizophrenia. In Press at Schizophrenia ResearchMANUSCRIPTS IN PREPARATION Parker, D.A., Hamm J.P., McDowell, J.E., Clementz, B.A. Neural Investigations of Pre-stimulus activity during “GAP” paradigms. (Expected completion date: Summer 2016)Hudgens-Haney, M.E.*, Parker, D.A.*, Oliver, W.T., Hayrynen, L.K., Bobilev, A.M., Buckley, P.F., McDowell, J.E., Clementz, B.A. Simultaneous M/EEG recording of Pre-stimulus attention and cognitive control in SZ. (*=Co-first authors, expected completion date: Summer 2016)FUNDING AND AWARDS2016-2018 Franklin Foundation Neuroimaging Fellowship Award:-12 months of Graduate support (22% time)-$3500 in research funds (Annually)- $1000 travel funds (Annually)2016Franklin Foundation Travel Award ($1200)20161st Place Paper Presentation, UGA Psi Chi Annual Convention2015Michael H. Kernis Research Award: Best Presentation, Behavioral & Brain Sciences Program, Department of Psychology 2015Franklin Foundation Travel Award ($1200)2013Franklin Foundation Travel Award ($1500)2012Center for Undergraduate Research Opportunities Summer Research Fellowship ($3000) 2012Daniel?S.?Hart?Scholarship to Outstanding Undergraduate- UGA Philosophy Department ($1000)2008-12HOPE Scholarship (Full tuition Scholarship)PRESENTATIONS (Talks in italics)Huang, L.-Y., Parker,D.A, Hill, S.K., Sweeney, J.A., Pearlson, C.A.,Tamminga,C.A., Keshavan,M.S.,Clementz,B.A. (2016). Frontal Neural Dysfunction Implicated in Executive Inflexibility in Psychosis. Poster to be presented at Society for Neurosciences Annual conference.Parker, D.A., McDowell, J.E., Sabatinelli, D.,Keshavan, M.S., Tamminga, C.A., Pearlson, G.D, Clementz, B.A (2016). Auditory Steady-State Response in Bipolar Disorder with or without Psychosis: Findings from the Bipolar & Schizophrenia Network on Intermediate Phenotypes. Poster to be presented at Society of Psychophysiological Research Annual Meeting. Parker, D.A., Hudgens-Haney, M.E., McDowell, J.E., Sabatinelli, D.,Keshavan, M.S., Tamminga, C.A., Pearlson, G.D, Clementz, B.A (2016). Multivariate Discrimination of Neural Processing in Bipolar Disorder with or without Psychosis: Findings from the Bipolar & Schizophrenia Network on Intermediate Phenotypes. Talk presented at Society of Biological Psychiatry Annual Meeting. Parker, D.A., Hudgens-Haney, M.E., McDowell, J.E., Sabatinelli, D.,Keshavan, M.S., Tamminga, C.A., Pearlson, G.D, Clementz, B.A (2016). Divergent neural processing in Bipolar Disorder with or without psychosis. Talk presented at 39th Annual Psi Chi Convention at UGA. Hart, R., Bobilev, A., Oliver, W., Hudgens-Haney, M., Hayrynen, L., Parker, D.A., Buckley, P., McDowell, J. & Clementz, B.A. (2015). Resting state oscillatory activation associated with schizophrenia and high and low cognitive control. Poster presented at Society for Neuroscience annual conference.Parker, D.A., Hudgens-Haney, M.E., Oliver, W.T., Hayrynen, L.K., Kinght, J.B., Bobilev, A.M., Hamm, J.P, Arkin, S.C, Buckley, P.F., McDowell, J.E., Clementz, B.A. (2015). Reduced Steady-State Phase Synchronization during a Cognitive Control task. Talk presented at the 15th International Congress on Schizophrenia ResearchOliver, W., Hamm, J., Bobilev, A., Hudgens-Haney, M., Hayrynen, L., Parker, D.A, Hart, R., Buckley, P., Sweeney, J., McDowell, J., & Clementz, B. (2015) Neural oscillatory patterns during sustained visual attention task in schizophrenia and high/low cognitive control. Poster presented at the Society for Psychophysiological Research Annual Meeting. Parker, D.A., Hudgens-Haney, M.E., Oliver, W.T., Hayrynen, L.K., Kinght, J.B., Bobilev, A.M., Hamm, J.P, Arkin, S.C, Buckley, P.F., McDowell, J.E., Clementz, B.A. (2014). Alpha band dynamics in Schizophrenia during an ocular motor inhibition task. Poster presented at Society for Psychophysiological Research Annual Conference.Arkin, S., Bobilev, A., Rodrigue, A., Oliver, W., Hudgens-Haney, M., Schaeffer, D., Hayrynen, L., Hamm, J., Parker, D.A., Weinberger, A., McDowell, J., & Clementz, B.A. (2014) Resting state neural activity analysis between schizophrenia patients and high and low working memory capacity controls via EEG and fMR techniques. Poster presented at BIRC SEC mini-conference, Athens, GA. Parker, D.A., Hamm J.P., McDowell, J.E., Clementz, B.A. (2013) Pre-trial alpha band dynamics affect saccadic reaction times as a function of temporal expectancy. Talk presented at the nanosymposum on Functional Mechanisms of Attention at the Society for Neurosciences Annual Conference.UNDERGRADUATE PRESENTATIONS (Talks in italics)Parker, D.A., Hamm J.P., Clementz, B.A. McDowell, JE. (2013) Investigating the GAP effect in the Generation of Express Saccades. Talk presented at the Center for Undergraduate Research Opportunities Symposium at the University of Georgia.?Parker, D.A., Schaefer, D. J., McDowell, JE. (2012)The effects of Volume Removal on Fractional Anisotropy. Talk and Poster presented at the Center for Undergraduate Research Opportunities Symposium at the University of Georgia.?Parker, D.A. (2011) Is Embodied Cognition an Alternative Theory of Cognition? Talk Presented at the Classic City Undergraduate Philosophy Conference at University of Georgia.?EXPERIENCEResearch2013-PresentGraduate Student, Clinical and Cognitive Neuroscience Laboratory (Brett Clementz, Ph.D. and Jennifer McDowell, Ph.D.)-Department of Psychology, University of Georgia.2011-2013Research Assistant/Co-Lab Manager, Clinical and Cognitive Neuroscience Laboratory (Brett Clementz, Ph.D. and Jennifer McDowell Ph.D.)- Department of Psychology, University of Georgia.Summer 2011Independent Researcher, Investigating the philosophical implications of dynamic system theory and embodied cognition under the direction of Sarah Wright, Ph.D.-Department of Philosophy, University of GeorgiaWorkshop2016Advanced M/EEG Statistical Parametric Mapping (SPM) Workshop at Wellcome Trust Centre for Neuroimaging at the University City of London May 14-16thFusion M/EEG Pre-processing and AnalysisAdvanced M/EEG Source AnalysisDynamic Causal Modeling and Bayesian InferenceERPSteady-StatePhase-CouplingLFPAdvanced Model testingTeaching2016Guest Lecturer, University of GeorgiaPsych 4300-EEG and MEG methods and Demonstration (4 Lectures) (Spring)2015Graduate Teaching Assistant, University of GeorgiaPsych 3890-Research Methods (Fall 2015)2015Guest Lecturer, University of GeorgiaPsych 4300-EEG methods and Demonstration (2 Lectures) (Spring)2014Graduate Teaching Assistant, University of GeorgiaPsych 1101- Introduction to Psychology (Fall 2014)2014Guest Lecturer, University of GeorgiaPsych 4300-EEG/MEG methods and Demonstration (4 Lectures) (Spring)2013Graduate Teaching Assistant, University of GeorgiaPsych 4100- Cognitive Psychology (Fall 2013)PROFESSIONAL ACTIVITIESProfessional Organizations:2014-PresentSociety for Psychophysiological Research2013-PresentSociety for Neuroscience2010-PresentPhi Sigma Tau, UGA Chapter President 2010-11Service:2013-PresentMaintained Liquid Helium Levels in MEG system at BIRC2013-PresentUndergraduate Mentoring CCNL: Meagan Buford, Zoe Shneider,Tiffany Javadi, Mitra Kumareswaran, Ian Berger.Abstracts (In most recent to oldest order):1) POSTER to be presented at Society for Neuroscience Annual Meeting 2016.Frontal Neural Dysfunction Implicated in Executive Inflexibility in PsychosisL.-Y. HUANG1, D. A. PARKER1, S. K. HILL2, J. A. SWEENEY3, G. D. PEARLSON4, C. A. TAMMINGA3, M. S. KESHAVAN5, B. A. CLEMENTZ1;?Abstract:Difficulty to switch from an existing response set to a new one is called perseverative errors, which can be measured using the Wisconsin Card Sorting Test (WCST). Perseverative errors are consistently seen in animals with prefrontal lesions, indicating the critical role of the region in attention control, task switching and context updating. Using electroencephalogram simultaneously administered with WCST, studies with healthy human subjects captured weaker P300 evoked potential around the prefrontal area during error trials. This finding confirmed P300 as an endogenous task-switching marker in addition to its modality-independent salience detection properties, making it a powerful ERP component to assess the neural correlates of cognitive response in different populations. Psychosis cases are known to have elevated perseverative errors, but the electrophysiological profiles of psychotic probands in relation to task-switching are less understood. In the present study, 628 clinically stable subjects from the Bipolar and Schizophrenia Network on Intermediate Phenotypes consortium (B-SNIP) underwent Penn Conditional Exclusion Test (PCET), a computerized analog to WCST. These participants were divided into high, medium, and low-performing groups based on their perseverative error rates in PCET, then each group’s ERP components to an auditory oddball task, a standard paradigm to consistently evoke P300, were examined. Principle component analysis of the pooled ERP recordings condensed the data into two components, accounting for about 90% of P300 variability in the sample; 1-way ANOVA showed marked difference in P300 and N200 amplitudes between high, medium, and low performance groups (p=0.0047 and p=0.01, respectively). This analysis provided direct evidence that perseverative error rates are associated with strength of prefrontal response to novel information, regardless of disease load.2) POSTER to be presented at Society for Psychophysiology Annual Meeting 2016.REDUCED BETA-BAND AUDITORY STEADY-STATE RESPONSE IN BIPOLAR DISORDER WITH OR WITHOUT PSYCHOSIS: Findings from the Bipolar & Schizophrenia Network on Intermediate PhenotypesDavid A. Parker1, Jennifer E. McDowell1, Matcheri S. Keshavan2, Carol A. Tamminga3, Godfrey D. Pearlson4,5, Brett A. Clementz11Psychology/Neuroscience, University of Georgia, Athens, GA,2Psychiatry, Harvard Medical School, Boston, MA,3Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX,4Psychiatry and Neurobiology, Yale University School of Medicine, New Haven, CT,5The Institute of Living, Hartford Hospital, Hartford, CTAbstract:Background: Psychotic symptomatology occurs in about half of persons with bipolar I disorder (BD). The presence of psychotic symptoms could indicate important and unique neurobiological distinctions between BD disease states. This study measured brain activity using EEG during auditory steady-state (aSSR) to probe beta-, gamma- and high gamma-band (20-hz, 40-hz, 80-hz) oscillatory network capability between BD disorder persons with (BD-P) and without psychosis (BD-NP). Methods: 136 individuals (Healthy=68, BD-P=41, BD-NP=27) participated. Stimuli were 1500ms binaural broadband noise sequences modulated at 20, 40, or 80-hz. Grand average ERPs for each frequency was used in a spatial PCA on the 64-sensor EEG data to comprehensively and accurately capture the spatial topographies of ERPs. Two components for each frequency were identified; these components were used to reduce the multi-sensor data to one waveform per component for each subject. FFTs with 1-hz resolution were calculated on each component waveform resulting in time-frequency plots ranging from 5 to 90-hz and -500 pre to 2000ms post-stimulus onset for each frequency and subject. ANOVA’s were calculated for each component for each frequency of interest to test for group differences.Results: Both BD-P and BD-NP showed significantly weaker entrainment at 20-hz than the healthy comparison group (P<.0012). Conclusions: Deficits at 20-hz suggest dysregulation of long-range neural communication between the primary sensory cortices and higher order cortical regions and is related to the core pathology of BD. 3) TALK Presented at Society for Biological Psychiatry Annual Meeting 2016.Multivariate Discrimination of Neural Processing in Bipolar Disorder with or without Psychosis: Findings from the Bipolar & Schizophrenia Network on Intermediate Phenotypes.David A. Parker1, Matt E. Hudgins-Haney1, Jennifer E. McDowell1, Dean Sabatinelli1, Matcheri S. Keshavan2, Carol A. Tamminga3, Godfrey D. Pearlson4,5, Brett A. Clementz11Psychology/Neuroscience, University of Georgia, Athens, GA,2Psychiatry, Harvard Medical School, Boston, MA,3Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX,4Psychiatry and Neurobiology, Yale University School of Medicine, New Haven, CT,5The Institute of Living, Hartford Hospital, Hartford, CTAbstract:Background:Psychotic symptomatology occurs in up to half of patients diagnosed with bipolar I disorder (BD). The presentation or absence of psychotic symptoms could indicate important biologically based divergent disease properties of BD. This project leveraged multiple electroencephalography (EEG) tasks to find key components of differentiation between BD with psychosis (BD-P) or without (BD-NP).Methods:108 individuals (Healthy Controls=53, BD-P=33, BD-NP=22) completed three EEG tasks selected because they discriminate between healthy and patient groups: two measuring auditory neural processing (Oddball and Paired Stimulus) and one measuring visual-emotional neural processing (International Affective Picture System, IAPS). After spatial Principle Components Analysis identified key ERP components for each task, univariate ANOVAs identified time-bin variables with significant group differences for each task (FWE<.01). Post hoc linear discriminant analysis identified variables that best discriminated groups.Results:Each task provided significant group differences, with 22 variables in total. Post hoc analysis identified 6 variables that significantly discriminated between groups (p<.03). Each task had a neural variable that discriminated healthy controls from BD patients (1 IAPS, 1 Paired Stimulus, 1 Oddball). 3 variables discriminated based on the presence or absence of psychosis and were all from the visual-emotional processing task (3 IAPS).Conclusions:This project used multiple EEG measures to identify key variables of biologically based divergences between healthy and BD-NP and BD-P groups. Visual-emotional neural divergences were found based on the presence of psychosis. This has critical implications for biologically based classification of BD, as well as attempts at genotyping and treatment development.4) Poster presented at Society for Neuroscience Annual Meeting 2015.Investigating resting state oscillatory dynamics associated with schizophrenia and high and low working memory capacityRachael V Hart1, Anastasia M. Bobilev1, William T Oliver1, Matthew E. Hudgens-Haney1, Lauren K Hayrynen1, David A. Parker1, Jennifer E. McDowell1, and Brett A. Clementz1.1. Departments of Psychology and Neuroscience, BioImaging Research Center, University of Georgia, Athens, GA; 2. Department of Psychiatry, Georgia Health Sciences University, Medical College of Georgia, Augusta, GA.Patients with schizophrenia (SZ) have general cognitive deficits that manifest in poor performance on tests of executive function compared to healthy persons. Levels of executive function are associated with performance on working memory capacity (WMC) tasks. Performance on these tasks varies greatly within the healthy population and, similarly to persons with schizophrenia, those with low WMC perform poorly compared to high WMC individuals. This study sought to examine differences in resting state neural activity between persons with schizophrenia and healthy subjects with high and low WMC. In the current study, WMC was determined by a conglomerate score based on performance on computerized operation span, symmetry span and reading span tasks. Persons with schizophrenia, as well as healthy individuals with high and low WMC scores completed a five-minute eyes-open resting state paradigm while 142 Superconducting quantum interference device (SQUID) Magnetoencephalography (MEG) data were collected.Time-frequency analysis of resting state activity demonstrated differences in activation between all three groups (SZ, high WMC, and low WMC) across frequency bands. The low WMC group exhibited some commonalities with both the high WMC and SZ groups. Notably, activity in the alpha frequency band was unique in that high WMC demonstrated regionalized power differences compared to both low WMC and SZ groups. Future analyses will employ additional statistical tools to further elucidate differences in oscillatory dynamics across these groups. Results from this study suggest that frequency-specific intrinsic activity may markedly contribute to individual differences in working memory capacity in both healthy persons and those with schizophrenia, while other features of intrinsic activity may be distinctly characteristic of schizophrenia. 5) TALK Presented at the International Congress on Schizophrenia Research Annual Meeting 2015.Reduced Steady-State Phase Synchronization during a Cognitive Control taskDavid Alan Parker1, Matthew Hudgens-Haney2, William Oliver2, Lauren Hayrynen2, Anastasia Bobilev2, Justin Knight1, 2, Rachael Hart1, 2, Peter F Buckley3, Jennifer McDowell1, 2, Brett A Clementz?1, 2INSTITUTIONS (ALL):?1. Psychology, University of Georgia , Athens, GA, United States.?2. Neuroscience, University of Georgia , Athens, GA, United States.?3. Department of Psychiatry, Georgia Health Sciences University, Augusta, GA, United States.?Abstract:Background: Individuals with schizophrenia (SZ) have documented evidence of cognitive control abnormalities. This study investigated neural activity of those with SZ in comparison to healthy groups with high (HCC) and low cognitive control (LCC), the latter of which exhibit similar behavioral abnormalities on cognitive control tasks without exhibiting symptoms of schizophrenia. By using a flickering checkerboard, a steady-state (SS) neural response is induced and overall levels of neural entrainment can be measured and compared between groups. SZ have been shown to have marked impairments at different frequency bands. By using a steady-state response we investigated the overall neural entrainment using dense array whole-head EEG (64 sensors).Methods: Participants completed a saccade task with increasing levels of difficulty (split by block) in order to place sufficient demands on cognitive control. Trials consisted of flickering checkerboards in central (15 Hz) and both peripheral visual fields (12 Hz), followed by brightening of one peripheral checkerboard (target) while all kept flickering. The three blocks were: (1) pro-saccade and NoGo randomly interleaved; (2) Anti-saccade and NoGo randomly interleaved; and (3) pro, anti, and NoGo randomly interleaved. Single trial power and inter-trial phase coherence (ITC) was and compared across groups and conditions.Results: Group by Task ANOVA showed reduced ITC at 15 Hz for SZ (p<.01) during the Pro/Nogo and Pro/Anti/Nogo task that was significantly different from HCC and LCC (p<.01, p<.01). For Pro/Nogo block: the initial 15 Hz ITC response and 15 Hz ITC during the 1000ms leading up to the saccade cue correlated with likelihood of making a correct response. For Pro/Anti/Nogo: the first 1000ms 15 Hz ITC response correlated with the likelihood of making a correct response during the anti-saccade task. The 15 Hz ITC at 1000ms to 2500ms after onset of steady-state correlated with the likelihood of making a correct pro-saccade. SZ also showed reduced Theta ITC (4-7 Hz) that was significantly different from the HCC (p<.01) and LCC (p<.01 at first 500ms, and p<.05 at 1000ms to onset of cue). Conclusion: SZ shows reduced neural phase synchrony in response to a steady-state cue and reduced Theta ITC during a cognitive control task. Reduced phase synchronization could be indicative of underlying psychopathology of SZ. Acknowledgements: Funding for this study was provided by NIH Grant MH094172.6) POSTER presented at Society for Psychophysiology Annual Meeting 2014.NEURONAL OSCILLATORY PATTERNS DURING SUSTAINED VISUAL ATTENTION TASK IN SCHIZOPHRENIA AND HIGH/LOW COGNITIVE CONTROLWilliam T Oliver1, Jordan P Hamm2, Anastasia M Bobilev1, Matt E Hudgens-Haney1, Lauren K Hayrynen1, David A Parker1, Peter F Buckley3, John A Sweeney4, Jennifer E McDowell1, & Brett A Clementz11University of Georgia,?2Columbia University,?3Georgia Regents University,?4University of Texas-SouthwesternDescriptors: schizophrenia, attention, cognitionCognitive control (CC) is an extensively tested top-down process that can be utilized in multiple sensory domains. CC can distinguish psychological pathologies and even be used to detect significant heterogeneity within diagnostic criteria. Persons with schizophrenia (SZ) exhibit deficits in early visual processing and this nuanced dysfunctional processing can be elucidated by imposing control over covertly attended locations. This project sought to determine how neuronal oscillatory activations in early visual processing varied as a function of CC in healthy individuals and those with SZ. Healthy participants were divided into the top and bottom quartiles for performance on a working memory SPAN task and compared to those with SZ during a sustained visual attention and target detection task. Dense array EEG (211 channels) data were recorded during the task. Visual stimuli were presented as a grating of vertical bars, each flickering at a different frequency (6.67, 7.14Hz, etc.) and across three optical densities (.5, 1, 2 deg of visual angle). A fast Fourier Transform at .01Hz resolution was utilized to compare stimulus specific oscillatory activity, as well as non-specific cortical activities across groups. Results indicate that non-specific activity is increased in SZ patients, and to a lesser degree in non-pathological low cognitive control individuals. An interaction was found between optical stimulus density and attended location for non-specific brain activity, suggesting a difference in overall gain as a function of task difficulty.NIH Grant MH094172.7) POSTER presented at Society for Psychophysiology Annual Meeting 2014.ALPHA BAND DYNAMICS IN SCHIZOPHRENIA DURING AN OCULAR MOTOR INHIBITION TASKDavid A. Parker 1, Matthew E. Hudgens-Haney1, William T. Oliver1, Lauren Hayrynen1, Justin B. Knight1, Anastasia M. Bobilev1, Jordan P. Hamm1, Sophie C. Arkin1, Peter F. Buckley2, Jennifer E. McDowell1, Brett A. Clementz11. Departments of Psychology and Neuroscience, BioImaging Research Center, University of Georgia, Athens, GA; 2. Department of Psychiatry, Georgia Health Sciences University, Medical College of Georgia, Augusta, GA.Individuals with schizophrenia (SZ) have documented evidence of cognitive control abnormalities. This study investigated neural activity of those with SZ in comparison to healthy groups with high (HCC) and low cognitive control (LCC), the latter of which exhibit similar behavioral abnormalities on cognitive control tasks without exhibiting symptoms of schizophrenia. Participants completed a saccade task with increasing levels of difficulty (split by block) in order to place sufficient demands on cognitive control. Trials consisted of flickering checkerboards in central (15 Hz) and both peripheral visual fields (12 Hz), followed by brightening of one peripheral checkerboard (target) while all kept flickering. The three blocks were: (1) prosaccade and NoGo randomly interleaved; (2) antisaccade and NoGo randomly interleaved; and (3) pro, anti, and NoGo randomly interleaved. Single trial power and inter-trial phase coherence (ITC) was calculated from whole-head EEG (64 sensor) and compared across groups and conditions. During the pre-target entrainment period for the prosaccade and antisaccade trials, SZ exhibited significantly reduced alpha (8-12 Hz) ITC relative to HCC but not LCC. After the target onset in both prosaccade and antisaccade trials, HCC displayed increased theta/alpha (4-12 Hz) power in comparison to both the SZ and LCC groups. These findings suggest that decreased phase coherence during the pre-target period might be due to the etiology of SZ, while theta/alpha power modulations might contribute to the behavioral similarities between SZ and LCC groups.Acknowledgements: Funding for this study was provided by NIH Grant MH094172.8) Talk presented at the nanosymposum on Functional Mechanisms of Attention at the Society for Neurosciences Annual Conference 2013.Pre-trial alpha band dynamics affect saccadic reaction times as a function of temporal expectancy*D. A. PARKER1,2, J. P. HAMM3,2, J. E. MCDOWELL4,2, B. A. CLEMENTZ4,2; 1Psychology, 3Neurosci., 4Psychology and Neurosci., 2Univ. of Georgia, Athens, GAAbstract:Pre-stimulus alpha band (8-14 hz) fluctuations in cortical regions involved in early visual registration influence saccadic reaction times. Reaction time distributions are sometimes bimodal in humans when a brief gap is introduced between fixation offset and peripheral cue onset. This results in separate populations of so-called express and regular latency saccades. Saccadic response type on a given trial may be influenced by dynamic fluctuations (phase vs power) of excitability in the alpha band. It is currently unknown what aspects of these fluctuations are influenced by temporal expectancy (i.e. knowing when a trial will begin) and how they interact with discrete cortical preparatory processes and neural manifestations of target processing. This study characterizes the mechanistic role of alpha dynamics in saccadic activity.Neurologically healthy subjects (30) completed pro-saccade gap tasks. The blocked condition (n=15) completed the task with a predictable gap period of 200 ms and the interleaved condition (n=15) completed an equal number of trials with a 200 ms gap, but embedded within trials of unpredictable gaps (ranging from 0-400 ms). Dense array electroencephalography was used to examine brain oscillations across a wide frequency bandwidth in the period before peripheral cue onset. Morlet wavelet-based time-frequency decomposition on single trials was used to quantify oscillatory phase, inter-trial phase locking, response-type phase bifurcation, and power in the time-frequency domain. Trials were segregated for each subject into regular and express saccades following skewness adjusted mixture modeling.Global pre-trial alpha power was greater for regular saccades than express saccades regardless of condition. The blocked condition showed 2 effects not observed in the interleaved condition: 1) greater frontal relative to parietal alpha power over all trials and 2) an alpha band phase bifurcation 200 ms prior to trial onset with distinct phase differences for the regular vs express trials.These results indicate a differential involvement of frontal vs parietal eye field circuitry in the generation of saccades when there is a temporal expectation of target onset. When trial onset time was blocked, alpha oscillations appeared to influence reactions times following the ‘pulsed inhibition model’, wherein alpha alternates between different phases of excitability and suppression. When the target onset was temporally unpredictable, pre-trial alpha phase did not vary with reaction times, suggesting that different cortical mechanisms and/or alpha-generating circuits are engaged. ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download