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1.  Spatiotemporal dynamics of speech sound perception in chronic developmental stuttering 
Brain and language  2010;115(2):141-147.
High-density ERPs were recorded in eight adults with persistent developmental stuttering (PERS) and eight matched normally fluent (CONT) control volunteers while participants either repeatedly uttered the vowel ‘ah’ or listened to their own previously recorded vocalizations.
The frontocentral N1 auditory wave was reduced in response to spoken vowels relative to heard vowels (auditory-vocal gating), but no difference in the extent of such modulation was found in the PERS group. Abnormalities in the PERS group were restricted to the LISTEN condition, in the form of early N1 and late N3 amplitude changes. Voltage of the N1 wave was significantly reduced over right inferior temporo-occipital scalp in the PERS group. A laterality index derived from N1 voltage moderately correlated with the PERS group's assessed pre-experiment stuttering frequency. Source localization with sLORETA (Pascual-Marqui, 2002) revealed that at the peak of the N1 the PERS group displayed significantly greater current density in right primary motor cortex than the CONT group, suggesting abnormal early speech motor activation. Finally, the late N3 wave was reduced in amplitude over inferior temporo-occipital scalp, more so over the right hemisphere. SLORETA revealed that in the time window of the N3 the PERS group showed significantly less current density in right secondary auditory cortex than the CONT group, suggesting abnormal speech sound perception. These results point to a deficit in auditory processing of speech sounds in persistent developmental stuttering, stemming from early increased activation of right rolandic area and late reduced activation in right auditory cortex.
PMCID: PMC4334906  PMID: 20810160
chronic developmental stuttering; ERPs; speech perception; primary motor cortex; cortex; sLORETA; auditory-vocal gating
2.  Evidence for specificity of ERP abnormalities during response inhibition in ADHD children: A comparison with Reading Disorder children without ADHD 
Brain and cognition  2009;72(2):228-237.
Executive function and working memory deficits are not only present in ADHD, but also in Reading Disorder (RD). Here, high-density ERPs were recorded during the Stop Signal Task in 53 children and adolescents: An ADHD-combined type group, a group with RD, and a healthy control group. The ADHD-C group displayed unique abnormalities of the frontal N200. Both healthy controls and RD groups showed a success-related right frontal N200 modulation, which was absent in the ADHD group. Second, for Success Inhibition trials, the ADHD-C had smaller right frontal N200 waves relative to healthy controls, while the RD group didn't. In contrast, NoGo-P3 abnormalities were present both in the ADHD-C and RD groups. Impaired early response inhibition mechanisms, indexed by the frontal N200, appear to be limited to ADHD-C. In contrast, deficits in later cognitive control and error monitoring mechanisms, indexed by the NoGo-P3, appear to be present in both conditions.
PMCID: PMC4321824  PMID: 19850394
ADHD; Reading Disorder; Event-Related Potentials; Stop Signal Task; Inhibitory Control; N200; NoGo-P3
3.  High-Caloric and Chocolate Stimuli Processing in Healthy Humans: An Integration of Functional Imaging and Electrophysiological Findings 
Nutrients  2014;6(1):319-341.
There has been a great deal of interest in understanding how the human brain processes appetitive food cues, and knowing how such cues elicit craving responses is particularly relevant when current eating behavior trends within Westernized societies are considered. One substance that holds a special place with regard to food preference is chocolate, and studies that used functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs) have identified neural regions and electrical signatures that are elicited by chocolate cue presentations. This review will examine fMRI and ERP findings from studies that used high-caloric food and chocolate cues as stimuli, with a focus on responses observed in samples of healthy participants, as opposed to those with eating-related pathology. The utility of using high-caloric and chocolate stimuli as a means of understanding the human reward system will also be highlighted, as these findings may be particularly important for understanding processes related to pathological overeating and addiction to illicit substances. Finally, research from our own lab that focused on chocolate stimulus processing in chocolate cravers and non-cravers will be discussed, as the approach used may help bridge fMRI and ERP findings so that a more complete understanding of appetitive stimulus processing in the temporal and spatial domains may be established.
PMCID: PMC3916864  PMID: 24434747
chocolate; fMRI; ERPs; high-caloric
4.  Is conflict monitoring supramodal? Spatiotemporal dynamics of cognitive control processes in an auditory Stroop task 
The electrophysiological correlates of conflict processing and cognitive control have been well characterized for the visual modality in paradigms such as the Stroop task. Much less is known about corresponding processes in the auditory modality. Here, electroencephalographic recordings of brain activity were measured during an auditory Stroop task, using three different forms of behavioral response (Overt verbal, Covert verbal, and Manual), that closely paralleled our previous visual-Stroop study. As expected, behavioral responses were slower and less accurate for incongruent compared to congruent trials. Neurally, incongruent trials showed an enhanced fronto-central negative-polarity wave (Ninc), similar to the N450 in visual-Stroop tasks, with similar variations as a function of behavioral response mode, but peaking ~150 ms earlier, followed by an enhanced positive posterior wave. In addition, sequential behavioral and neural effects were observed that supported the conflict-monitoring and cognitive-adjustment hypothesis. Thus, while some aspects of the conflict detection processes, such as timing, may be modality-dependent, the general mechanisms would appear to be supramodal.
PMCID: PMC3422637  PMID: 21964643
Auditory; Stroop; Conflict; EEG; Incongruency
5.  Long-range synchronization and local desynchronization of alpha oscillations during visual short-term memory retention in children 
Local alpha-band synchronization has been associated with both cortical idling and active inhibition. Recent evidence, however, suggests that long-range alpha synchronization increases functional coupling between cortical regions. We demonstrate increased long-range alpha and beta band phase synchronization during short-term memory retention in children 6–10 years of age. Furthermore, whereas alpha-band synchronization between posterior cortex and other regions is increased during retention, local alpha-band synchronization over posterior cortex is reduced. This constitutes a functional dissociation for alpha synchronization across local and long-range cortical scales. We interpret long-range synchronization as reflecting functional integration within a network of frontal and visual cortical regions. Local desynchronization of alpha rhythms over posterior cortex, conversely, likely arises because of increased engagement of visual cortex during retention.
PMCID: PMC2840055  PMID: 19943040
Child development; Functional integration; Connectivity; MEG; Neural synchrony; Oscillatory network dynamics; Alpha
6.  Altered Long-Range Phase Synchronization and Cortical Activation in Children Born Very Preterm 
IFMBE proceedings  2010;29(9):250-253.
Children born very preterm, even with broadly normal IQ, commonly show selective difficulties in visuospatial processing and executive functioning. Very little, however, is known what alterations in cortical processing underlie these deficits. We recorded MEG while eight children born very preterm (≤32 weeks gestational age) and eight full-term controls performed a visual short-term memory task at mean age 7.5 years (range 6.4 – 8.4). Previously, we demonstrated increased long-range alpha and beta band phase synchronization between MEG sensors during STM retention in a group of 17 full-term children age 6–10 years. Here we present preliminary evidence that long-range phase synchronization in very preterm children, relative to controls, is reduced in the alpha-band but increased in the theta-band. In addition, we investigated cortical activation during STM retention employing synthetic aperture magnetometry (SAM) beamformer to localize changes in gamma-band power. Preliminary results indicate sequential activation of occipital, parietal and frontal cortex in control children, as well as reduced activation in very preterm children relative to controls. These preliminary results suggest that children born very preterm exhibit altered inter-regional functional connectivity and cortical activation during cognitive processing.
PMCID: PMC3039420  PMID: 21331353
preterm birth; beamformer; short-term memory; neural synchrony; functional connectivity
7.  The somatotopy of speech: Phonation and articulation in the human motor cortex 
Brain and cognition  2009;70(1):31-41.
A sizable literature on the neuroimaging of speech production has reliably shown activations in the orofacial region of the primary motor cortex. These activations have invariably been interpreted as reflecting “mouth” functioning and thus articulation. We used functional magnetic resonance imaging to compare an overt speech task with tongue movement, lip movement, and vowel phonation. The results showed that the strongest motor activation for speech was the somatotopic larynx area of the motor cortex, thus reflecting the significant contribution of phonation to speech production. In order to analyze further the phonatory component of speech, we performed a voxel-based meta-analysis of neuroimaging studies of syllable-singing (11 studies) and compared the results with a previously-published meta-analysis of oral reading (11 studies), showing again a strong overlap in the larynx motor area. Overall, these findings highlight the under-recognized presence of phonation in imaging studies of speech production, and support the role of the larynx motor cortex in mediating the “melodicity” of speech.
PMCID: PMC2873785  PMID: 19162389
Speech; Vocalization; Phonation; Larynx; Articulation; Brain; fMRI; Neuroimaging; Meta-analysis; ALE
8.  A Non-Invasive Imaging Approach to Understanding Speech Changes following Deep Brain Stimulation in Parkinson’s Disease 
To explore the use of non-invasive functional imaging and “virtual” lesion techniques to study the neural mechanisms underlying motor speech disorders in Parkinson’s disease. Here, we report the use of Positron Emission Tomography (PET) and transcranial magnetic stimulation (TMS) to explain exacerbated speech impairment following subthalamic nucleus deep brain stimulation (STN-DBS) in a patient with Parkinson’s disease.
Perceptual and acoustic speech measures as well as cerebral blood flow (CBF) during speech as measured by PET were obtained with STN-DBS on and off. TMS was applied to a region in the speech motor network found to be abnormally active during DBS. Speech disruption by TMS was compared both perceptually and acoustically with that resulting from DBS on.
Speech production was perceptually inferior and acoustically less contrastive during left STN stimulation compared to no stimulation. Increased neural activity in left dorsal premotor cortex (PMd) was observed during DBS on. “Virtual” lesioning of this region resulted in speech characterized by decreased speech segment duration, increased pause duration, and decreased intelligibility.
This case report provides evidence that impaired speech production accompanying STN-DBS may be resulting from unintended activation of PMd. Clinical application of functional imaging and TMS may lead to optimizing the delivery of STN-DBS to improve outcomes for speech production as well as general motor abilities.
PMCID: PMC2779712  PMID: 19029533
9.  Effects of Motivation and Medication on Electrophysiological Markers of Response Inhibition in Children with Attention-Deficit/Hyperactivity Disorder 
Biological Psychiatry  2010;67(7):624-631.
Theories of attention-deficit/hyperactivity disorder (ADHD) posit either executive deficits and/or alterations in motivational style and reward processing as core to the disorder. Effects of motivational incentives on electrophysiological correlates of inhibitory control and relationships between motivation and stimulant medication have not been explicitly tested.
Children (9–15 years) with combined-type ADHD (n = 28) and matched typically developing children (CTRL) (n = 28) performed a go/no-go task. Electroencephalogram data were recorded. Amplitude of two event-related potentials, the N2 and P3 (markers of response conflict and attention), were measured. The ADHD children were all stimulant responders tested on and off their usual dose of methylphenidate; CTRLs were never medicated. All children performed the task under three motivational conditions: reward; response cost; and baseline, in which points awarded/deducted for inhibitory performance varied.
There were effects of diagnosis (CTRL > ADHD unmedicated), medication (on > off), and motivation (reward and/or response cost > baseline) on N2 and P3 amplitude, although the N2 diagnosis effect did not reach statistical significance (p = .1). Interactions between motivation and diagnosis/medication were nonsignificant (p > .1).
Motivational incentives increased amplitudes of electrophysiological correlates of response conflict and attention in children with ADHD, towards the baseline (low motivation) amplitudes of control subjects. These results suggest that, on these measures, motivational incentives have similar effects in children with ADHD as typically developing CTRLs and have additive effects with stimulant medication, enhancing stimulus salience and allocation of attentional resources during response inhibition.
PMCID: PMC2845810  PMID: 19914599
ADHD; electrophysiology; motivation; response inhibition; stimulant medication
10.  Cortical Gray Matter in Attention-Deficit/Hyperactivity Disorder: A Structural Magnetic Resonance Imaging Study 
Previous studies have shown smaller brain volume and less gray matter in children with attention-deficit/hyperactivity disorder (ADHD). Relatively few morphological studies have examined structures thought to subserve inhibitory control, one of the diagnostic features of ADHD. We examined one such region, the pars opercularis, predicting a thinner cortex of the inferior frontal gyrus (IFG) in children with ADHD.
Structural images were obtained from 49 children (24 control; 25 ADHD combined subtype) aged 9 though 15 years. Images were processed using a volumetric pipeline to provide a fully automated estimate of regional volumes of gray and white matter. A further analysis using FreeSurfer provided measures of cortical thickness for each lobe, and for 13 regions in the frontal lobe.
Relative to controls, children with ADHD had smaller whole brain volume and lower gray matter, but not white matter, volumes in all lobes. An analysis of frontal regions showed a significant interaction of group by region. Planned contrasts showed bilateral thinner cortex in the pars opercularis in children with ADHD.
Children with ADHD showed both diffuse and regional gray matter abnormalities. Consistent with its putative role in response inhibition, the cortex of the pars opercularis was thinner in children with ADHD who, as expected, had significantly poorer inhibitory performance on a Go/No-go task. These differences held for both hemispheres raising the possibility that a developmental abnormality of IFG might drive development of inhibition difficulties.
PMCID: PMC2829134  PMID: 20410712
Attention-deficit/hyperactivity disorder; MRI; Cortical thickness; Inferior frontal gyrus; Gray matter
11.  Looking before you leap: A theory of motivated control of action 
Cognition  2009;112(1):141-158.
The acquisition of volitional control depends, in part, on developing the ability to countermand a planned action. Many tasks have been used to tap the efficiency of this process, but few studies have investigated how it may be modulated by participants’ motivation. Multiple mechanisms may be involved in the deliberate exercise of caution when incentives are provided. For example, control may involve modulation of the efficiency of the countermanding process, and/or inhibitory modulation of the impulse to go. One of the most commonly used paradigms to assess control of action is the Stop Signal Task, in which a primary Go stimulus is occasionally followed by a countermanding Stop signal, allowing a Stop Signal Reaction Time (SSRT) to be inferred as the outcome of a “horse race” between the go and countermanding processes. Here, we present a computational model in which high task motivation modulates proactive pre-stimulus inhibition of the go response. This allows responses to be calibrated so as to fall within a time-window that maximizes the probability of success, regardless of trial type, but does not decrease the observed SSRT. We report empirical support for the model from a sample of typically developing children, and discuss the broader implications for operationalizing measures of volitional control.
PMCID: PMC2706947  PMID: 19409540
Inhibition; Motivation; Stop Signal Reaction Time; Restraint; Control of action
12.  The Temporal Dynamics of Implicit Processing of Non-Letter, Letter, and Word-Forms in the Human Visual Cortex 
The decoding of visually presented line segments into letters, and letters into words, is critical to fluent reading abilities. Here we investigate the temporal dynamics of visual orthographic processes, focusing specifically on right hemisphere contributions and interactions between the hemispheres involved in the implicit processing of visually presented words, consonants, false fonts, and symbolic strings. High-density EEG was recorded while participants detected infrequent, simple, perceptual targets (dot strings) embedded amongst a of character strings. Beginning at 130 ms, orthographic and non-orthographic stimuli were distinguished by a sequence of ERP effects over occipital recording sites. These early latency occipital effects were dominated by enhanced right-sided negative-polarity activation for non-orthographic stimuli that peaked at around 180 ms. This right-sided effect was followed by bilateral positive occipital activity for false-fonts, but not symbol strings. Moreover the size of components of this later positive occipital wave was inversely correlated with the right-sided ROcc180 wave, suggesting that subjects who had larger early right-sided activation for non-orthographic stimuli had less need for more extended bilateral (e.g., interhemispheric) processing of those stimuli shortly later. Additional early (130–150 ms) negative-polarity activity over left occipital cortex and longer-latency centrally distributed responses (>300 ms) were present, likely reflecting implicit activation of the previously reported ‘visual-word-form’ area and N400-related responses, respectively. Collectively, these results provide a close look at some relatively unexplored portions of the temporal flow of information processing in the brain related to the implicit processing of potentially linguistic information and provide valuable information about the interactions between hemispheres supporting visual orthographic processing.
PMCID: PMC2796900  PMID: 20046826
word reading; ERPs; visual cortex; visual orthography
13.  A Bias Against Disconfirmatory Evidence Is Associated With Delusion Proneness in a Nonclinical Sample 
Schizophrenia Bulletin  2007;33(4):1023-1028.
Previous work has suggested that a bias against disconfirmatory evidence (BADE) may be associated with the schizophrenia spectrum. The current investigation focused on whether a BADE (1) overlaps with traditional measures of memory and executive functions or selectively taps into a unique aspect of cognition and (2) is correlated with delusional ideation but not with other aspects of schizotypy. Sixty-eight undergraduate students were administered the Schizotypal Personality Questionnaire (SPQ), the BADE test, the Rey Auditory Verbal Learning Test (RAVLT), the Wisconsin Card Sorting Test (WCST), the Trail Making Tests A and B (TMT), and tests used to estimate IQ. Factor analysis of all cognition measures resulted in a 6-factor solution, 4 of which reflected the 4 domains of neuropsychological tests (WCST, RAVLT, TMT, and IQ), and 2 of which reflected different aspects of the BADE test: Initial Belief and Integration of Disconfirmatory Evidence. This solution suggests that BADE measures were independent from the other cognitive domains measured. Integration of Disconfirmatory Evidence was the only factor that correlated with delusion-content subscales of the SPQ, providing support for the contribution of a BADE to delusional ideation.
PMCID: PMC2632321  PMID: 17347526
schizotypy; delusions; cognition; decision making; reasoning
14.  Motivational incentives and methylphenidate enhance electrophysiological correlates of error monitoring in children with attention deficit/hyperactivity disorder 
Background Children with attention deficit hyperactivity disorder (ADHD) are characterised by developmentally inappropriate levels of hyperactivity, impulsivity and/or inattention and are particularly impaired when performing tasks that require a high level of cognitive control. Methylphenidate (MPH) and motivational incentives may help improve cognitive control by enhancing the ability to monitor response accuracy and regulate performance accordingly.
Methods Twenty-eight children with DSM-IV ADHD (combined type) aged 9–15 years and pairwise-matched typically developing children (CTRL) performed a go/no-go task in which the incentives attached to performance on no-go trials were manipulated. The ADHD group performed the task off and on their usual dose of MPH. CTRL children performed the task twice but were never medicated. EEG data were recorded simultaneously and two electrophysiological indices of error monitoring, the error-related negativity (ERN) and error positivity (Pe) were measured. Amplitudes of each ERP were compared between diagnostic groups (CTRL, ADHD), medication days (Off MPH, On MPH) and motivational conditions (baseline – low incentive, reward, response cost).
Results Error rates were lower in the reward and response cost conditions compared with baseline across diagnostic groups and medication days. ERN and Pe amplitudes were significantly reduced in ADHD compared with CTRL, and were significantly enhanced by MPH. Incentives significantly increased ERN and Pe amplitudes in the ADHD group but had no effect in CTRL. The effects of incentives did not interact with the effects of MPH on either ERP. Effect sizes were computed and revealed larger effects of MPH than incentives on ERN and Pe amplitudes.
Conclusions The findings reveal independent effects of motivational incentives and MPH on two electrophysiological markers of error monitoring in children with ADHD, suggesting that each may be important tools for enhancing or restoring cognitive control in these children.
PMCID: PMC3807603  PMID: 23662815
ADHD; electrophysiology; error monitoring; motivation; methylphenidate; stimulant medication

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