Todd K Stevens

Robarts Research Institute, London, Ontario, Canada

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Publications (17)52.82 Total impact

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    ABSTRACT: The Tm(3+) chelate of DOTAM [1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane] possessing sterically demanding t-butyl amide substitution favors TSAP geometry. This chelate displayed a paraCEST signal associated with the highly shifted amide proton signal at approximately -100 ppm that was beyond the frequency of macromolecule magnetization transfer. This signal also displayed high temperature dependence (0.57 ppm °C(-1) ) in the range of 35-42 °C and at neutral pH. Copyright © 2013 John Wiley & Sons, Ltd.
    Contrast Media & Molecular Imaging 05/2013; 8(3):289-92. · 2.87 Impact Factor
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    ABSTRACT: Negative self-referential processing and identity disturbance are not uncommon clinical outcomes in adults who were significantly maltreated as children. In this study a novel cognitive paradigm, akin to mirror viewing while experiencing negative versus positive thoughts, was developed to investigate verbal and visual self-referential processing disturbances in women with maltreatment-related posttraumatic stress disorder (PTSD). Relative to women without PTSD, women with PTSD endorsed more negative and less positive trait-adjectives as self-descriptive, and experienced more negative and less positive affect in response to viewing pictures of themselves while listening to both negative and positive trait adjectives. In an fMRI study, women without PTSD demonstrated increased blood oxygenation level dependent (BOLD) response within the perigenual region of the anterior cingulate cortex during self-referential processing while listening to positive trait adjectives relative to neutral words. Positively valenced self-descriptiveness and affective response ratings predicted BOLD response within the right amygdala during self-referential processing within women with PTSD. The theoretical and clinical significance of abnormal self-referential processing in trauma-related psychiatric disorders is discussed. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
    Psychological Trauma Theory Research Practice and Policy 11/2011; 3(4):318-328. · 0.89 Impact Factor
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    ABSTRACT: To explore the functional neural correlates of emotional numbing symptoms in individuals with posttraumatic stress disorder (PTSD). The study was conducted between September 2006 and June 2008 at the University of Western Ontario. Women with (n = 14) and without (n = 16) PTSD (based on DSM-IV criteria) completed a standardized emotional imagery task while undergoing functional magnetic resonance imaging, in addition to an assessment for emotional numbing symptoms. The study design was correlational, with primary outcome measures being blood oxygenation level-dependent (BOLD) response to emotional imagery task and self-reported severity of emotional numbing symptoms. Women without PTSD were not trauma exposed. In women with PTSD, emotional numbing symptoms predicted less positive affect in response to positive-valence scripts (P < .05) and less BOLD response within the dorsomedial prefrontal cortex during imagery of positive and negative scripts that were explicitly socially relevant (P < .001). In contrast, in women without PTSD, emotional numbing symptoms, while unrelated to subjective emotional responses, predicted greater response within the ventromedial prefrontal cortex during positive and negative scripts, in addition to scripts that elicited fear anxiety by nonsocial means (all P values < .001). The findings could not be attributed to dysphoria. These findings are consistent with previous research regarding emotional numbing and emotional awareness. Less response within the medial prefrontal cortex during emotional imagery in individuals with high emotional numbing may indicate deficient conscious and reflective emotional processing. Further study is required to elucidate associations between state and trait emotional numbing and the neural correlates of psychological treatments specific to emotional numbing.
    The Journal of Clinical Psychiatry 11/2011; 73(4):431-6. · 5.81 Impact Factor
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    ABSTRACT: Emotion theory emphasizes the distinction between social vs non-social emotional-processing (E-P) although few functional neuroimaging studies have examined whether the neural systems that mediate social vs non-social E-P are similar or distinct. The present fMRI study of script-driven imagery in 20 women demonstrates that social E-P, independent of valence, more strongly recruits brain regions involved in social- and self-referential processing, specifically the dorsomedial prefrontal cortex, posterior cingulate/precuneus, bilateral temporal poles, bilateral temporoparietal junction and right amygdala. Functional response within brain regions involved in E-P was also significantly more pronounced during negatively relative to positively valenced E-P. Finally, the effect for social E-P was increased for positive relative to negative stimuli in many of these same regions. Future research directions for social and affective neuroscience are discussed.
    Social Cognitive and Affective Neuroscience 06/2011; 6(3):375-92. · 5.04 Impact Factor
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    ABSTRACT: Imaging studies of pain processing in primary psychiatric disorders are just emerging. This study explored the neural correlates of stress-induced analgesia in individuals with posttraumatic stress disorder (PTSD). It combined functional magnetic resonance imaging (fMRI) and the traumatic script-driven imagery symptom provocation paradigm to examine the effects of trauma-related cues on pain perception in individuals with PTSD. The study included 17 patients with PTSD and 26 healthy, trauma-exposed controls. Participants received warm (nonpainful) or hot (painful) thermal stimuli after listening to a neutral or a traumatic script while they were undergoing an fMRI scan at a 4.0 T field strength. Between-group analyses revealed that after exposure to the traumatic scripts, the blood oxygen level-dependent (BOLD) signal during pain perception was greater in the PTSD group than the control group in the head of the caudate. In the PTSD group, strong positive correlations resulted between BOLD signal and symptom severity in a number of brain regions previously implicated in stress-induced analgesia, such as the thalamus and the head of the caudate nucleus. Trait dissociation as measured by the Dissociative Experiences Scale correlated negatively with the right amygdala and the left putamen. Limitations: This study included heterogeneous traumatic experiences, a different proportion of military trauma in the PTSD versus the control group and medicated patients with PTSD. These data indicate that in patients with PTSD trauma recall will lead in a state-dependent manner to greater activation in brain regions implicated in stress-induced analgesia. Correlational analyses lend support to cortical hyperinhibition of the amygdala as a function of dissociation.
    Journal of psychiatry & neuroscience: JPN 11/2010; 36(1):6-14. · 6.24 Impact Factor
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    ABSTRACT: Research has investigated responses to script-driven imagery of traumatic events personally experienced by individuals with posttraumatic stress disorder (PTSD), although less is known about responses to imagery of standardized nonidiographic emotional events. This study investigated self-report and functional neural responses to imagery of interpersonal (social) versus intrapersonal (nonsocial) negative and positive events in women with versus without PTSD. Women with PTSD reported decreased positive affect in response to imagery of positive events, and increased negative affect and emotional avoidance in response to imagery of both negative and positive events. BOLD responses within the dorsomedial prefrontal cortex, temporal poles, insula, and amygdala differed between groups primarily in response to imagery of positive events. Future research directions and clinical implications for social and emotional functioning in trauma-related disorders are discussed. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
    Psychological Trauma Theory Research Practice and Policy 05/2010; 2(2):145-157. · 0.89 Impact Factor
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    ABSTRACT: The Eastern concept of ‘mindfulness’ is intended to represent a particular quality of attentional processing and awareness of events. The present study demonstrated in 19 healthy women that individual differences in trait mindful ‘observing’ positively predict fMRI-BOLD response during emotional imagery within the dorsomedial prefrontal cortex (DMPFC) and left amygdala. Mindful ‘acting with awareness’ positively predicted DMPFC response only during relaxation imagery.
    Personality and Individual Differences. 01/2010;
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    ABSTRACT: The "default network" consists of a number of brain regions that exhibit correlated low-frequency activity at rest and that have been suggested to be involved in the processing of self-relevant stimuli. Activity in many of these areas has also been shown to be altered in individuals with posttraumatic stress disorder (PTSD). We hypothesized that the posterior cingulate cortex (PCC)/precuneus, part of the default network, would exhibit altered connectivity at rest with other areas of the default network and regions associated with PTSD. Seventeen medicated and unmedicated female patients with chronic posttraumatic stress disorder (PTSD) related to early-life trauma and 15 healthy female controls underwent a 5.5-minute functional magnetic resonance imaging scan with their eyes closed. We assessed areas of the brain whose activity positively and negatively correlated with that of the PCC/precuneus in both groups. At rest, spontaneous low-frequency activity in the PCC/precuneus was more strongly correlated with activity in other areas of the default network in healthy controls than in patients with PTSD. Direct comparison of the 2 groups showed that PCC/ precuneus connectivity was also greater in healthy controls than in patients with PTSD in a number of areas previously associated with PTSD, including the right amygdala and the hippocampus/parahippocampal gyrus. Because our PTSD sample comprised only women with chronic early-life trauma exposure, our results may not be generalizeable to male patients, to a population with single trauma exposure or to those who were adults when the trauma occurred. In addition, our sample included patients taking medication and it is not yet clear how altered connectivity is affected by medication. Spontaneous activity in the default network during rest, as measured using PCC correlations, is altered in patients with PTSD. The potential effects of psychotropic medications on default network connectivity in the present sample remain unknown. In this patient population, the observed alterations may be associated with the disturbances in self-referential processing often observed in patients with chronic PTSD related to early-life trauma.
    Journal of psychiatry & neuroscience: JPN 06/2009; 34(3):187-94. · 6.24 Impact Factor
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    ABSTRACT: Although the posterior oral cavity and oropharynx play a major role in swallowing, their central representation is poorly understood. High-field functional magnetic resonance imaging of the brain was used to study the central processing of brief air-pulses, delivered to the peritonsillar region of the lateral oropharynx, in six healthy adults. Bilateral air-pulse stimulation was associated with the activation of a bilateral network including the primary somatosensory cortex and the thalamus, classic motor areas (primary motor cortex, supplementary motor area, cingulate motor areas), and polymodal areas (including the insula and frontal cortex). These results suggest that oropharyngeal stimulation can activate a bilaterally distributed cortical network that overlaps cortical regions previously implicated in oral and pharyngeal sensorimotor functions such as tongue movement, mastication, and swallowing. The present study also demonstrates the utility of air-pulse stimulation in investigating oropharyngeal sensorimotor processing in functional brain imaging experiments.
    Neuroscience 07/2008; 153(4):1300-8. · 3.12 Impact Factor
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    ABSTRACT: Individuals with posttraumatic stress disorder (PTSD) often exhibit deficits in emotional experience and expression, which suggests that certain individuals with PTSD may be alexithymic. In this study, in a sample of 105 individuals with PTSD, clinical correlates of alexithymia included reexperiencing, hyperarousal, numbing, dissociative symptoms, and retrospectively reported experiences of childhood emotional neglect. In a subsample of 26 individuals with PTSD related to a motor vehicle accident, functional neural responses to trauma-script imagery were associated with severity of alexithymia, including increased right posterior-insula and ventral posterior-cingulate activation and decreased bilateral ventral anterior-cingulate, ventromedial prefrontal, anterior-insula, and right inferior frontal cortex activation. Clinical and theoretical implications and future research directions are discussed.
    Journal of Abnormal Psychology 03/2008; 117(1):171-81. · 4.86 Impact Factor
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    ABSTRACT: To examine individual differences in levels of emotional awareness as a predictor of the blood oxygenation level dependent (BOLD) response to trauma script-driven imagery in trauma-exposed individuals with (n = 25) and without (n = 16) posttraumatic stress disorder (PTSD). Participants completed the Levels of Emotional Awareness Scale (LEAS) and a functional magnetic resonance imaging trauma script-driven imagery paradigm. Patients with PTSD exhibited lower LEAS scores in comparison with the control group. LEAS scores correlated positively with BOLD activity during trauma script-imagery in the ventral anterior cingulate cortex (vACC) in healthy controls, whereas LEAS scores correlated negatively with activation of vACC in individuals with PTSD. Patients with PTSD exhibit lower than average levels of emotional awareness. Levels of emotional awareness are differentially associated with vACC response during trauma script-driven imagery in healthy controls versus individuals with PTSD.
    Psychosomatic Medicine 02/2008; 70(1):27-31. · 4.08 Impact Factor
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    ABSTRACT: The goal of this study was to compare neural activation patterns in patients with PTSD with and without current comorbid major depression. Traumatized subjects with PTSD (n=11), PTSD+major depression (MDD, n=15), and subjects (n=16) who met criterion A for PTSD but never developed the disorder were studied using the script-driven symptom-provocation paradigm adapted to functional magnetic resonance imaging (fMRI) at a 4-Tesla field strength. Both the PTSD+MDD and PTSD-MDD groups revealed decreased brain activation in the anterior cingulate gyrus (BA 24) and the right ventrolateral prefrontal cortex (BA 47). After covariation for differences in PTSD severity between these groups, the left insula (BA 13) remained more significantly activated in the PTSD-MDD group than in the PTSD+MDD group. In contrast, the PTSD+MDD group showed greater activation than the PTSD-MDD group in the bilateral anterior cingulate gyrus (BA 24) and posterior cingulate cortices (BA 23, 31). These results suggest different patterns of brain activation related to comorbid major depression occurring in the context of PTSD.
    Psychiatry Research 06/2007; 155(1):45-56. · 2.46 Impact Factor
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    ABSTRACT: To design and apply a method to quantitatively evaluate the MR compatibility of electroencephalographic (EEG) scalp electrodes based on pulse sequence-independent metrics. Three types of electrodes (constructed primarily of brass, silver, and conductive plastic, respectively) were tested. B0 field distortions, B1 shielding, and heat induction was measured in adjacent agarose and oil phantoms at 4 T. B0 field maps were corrected for distortions caused by the measurement apparatus and passive shim heating, and projections perpendicular to the surfaces of the electrodes were fit, generating cubic coefficients representing the electrode distortion severity. Signal loss in T2-weighted images was used to determine B1 shielding by the electrodes. Temperature measurements were recorded during the application of a high-power pulse sequence. Significantly different B0 distortions were observed in the three types of electrodes. The B1 shielding detected in all three electrodes is minimal for most human MRI, and no significant heating was detected in the electrodes or adjacent phantom. The three types of electrodes were successfully differentiated in terms of MR compatibility based on pulse sequence-independent B0 field distortions.
    Journal of Magnetic Resonance Imaging 05/2007; 25(4):872-7. · 2.57 Impact Factor
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    ABSTRACT: While brain-imaging studies in young adults have implicated multiple cortical regions in swallowing, investigations in older subjects are lacking. This study examined the neural representations of voluntary saliva swallowing and water swallowing in older adults. Nine healthy females were examined with event-related functional magnetic resonance imaging (fMRI) while laryngeal swallow-related movements were recorded. Swallowing in the older adults, like young adults, activated multiple cortical regions, most prominently the lateral pericentral, perisylvian, and anterior cingulate cortex. Activation of the postcentral gyrus was lateralized to the left hemisphere for saliva and water swallowing, consistent with our findings in young female subjects. Comparison of saliva and water swallowing revealed a fourfold increase in the brain volume activated by the water swallow compared to the saliva swallow, particularly within the right premotor and prefrontal cortex. This task-specific activation pattern may represent a compensatory response to the demands of the water swallow in the face of age-related diminution of oral sensorimotor function.
    Experimental Brain Research 02/2007; 176(1):12-22. · 2.22 Impact Factor
  • Todd K Stevens
    Advances in neurology 02/2006; 97:285-92.
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    ABSTRACT: Brain-imaging studies have shown that visually-cued, voluntary swallowing activates a distributed network of cortical regions including the precentral and postcentral gyri, anterior cingulate cortex (ACC), insula, frontoparietal operculum, cuneus and precuneus. To elucidate the functional contributions of these discrete activation foci for swallowing, a "Go, No-Go" functional magnetic resonance imaging (fMRI) paradigm was designed. Brain activation associated with visually-cued swallowing was compared with brain activation evoked by a comparable visual cue instructing the subject not to swallow. Region-of-interest analyses performed on data from eight healthy subjects showed a significantly greater number of activated voxels within the precentral gyrus, postcentral gyrus, and ACC during the "Go" condition compared to the "No-Go" condition. This finding suggests that the precentral gyrus, postcentral gyrus, and ACC contribute primarily to the act of swallowing. In contrast, the numbers of activated voxels within the cuneus and precuneus were not significantly different for the "Go" and "No-Go" conditions, suggesting that these regions mediate processing of the cue to swallow. Together these findings support the view that the discrete cortical foci previously implicated in swallowing mediate functionally distinct components of the swallowing act.
    Experimental Brain Research 02/2005; 161(1):81-90. · 2.22 Impact Factor
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    ABSTRACT: Although multiple regions of the cerebral cortex have been implicated in swallowing, the functional contributions of each brain area remain unclear. The present study sought to clarify the roles of these cortical foci in swallowing by comparing brain activation associated with voluntary saliva swallowing and voluntary tongue elevation. Fourteen healthy right-handed subjects were examined with single-event-related functional magnetic resonance imaging (fMRI) while laryngeal movements associated with swallowing and tongue movement were simultaneously recorded. Both swallowing and tongue elevation activated 1) the left lateral pericentral and anterior parietal cortex, and 2) the anterior cingulate cortex (ACC) and adjacent supplementary motor area (SMA), suggesting that these brain regions mediate processes shared by swallowing and tongue movement. Tongue elevation activated a larger total volume of cortex than swallowing, with significantly greater activation within the ACC, SMA, right precentral and postcentral gyri, premotor cortex, right putamen, and thalamus. Although a contrast analysis failed to identify activation foci specific to swallowing, superimposed activation maps suggested that the most lateral extent of the left pericentral and anterior parietal cortex, rostral ACC, precuneus, and right parietal operculum/insula were preferentially activated by swallowing. This finding suggests that these brain areas may mediate processes specific to swallowing. Approximately 60% of the subjects showed a strong functional lateralization of the postcentral gyrus toward the left hemisphere for swallowing, whereas 40% showed a similar activation bias for the tongue elevation task. This finding supports the view that the oral sensorimotor cortices within the left and right hemispheres are functionally nonequivalent.
    Journal of Neurophysiology 11/2004; 92(4):2428-43. · 3.30 Impact Factor

Publication Stats

390 Citations
52.82 Total Impact Points

Institutions

  • 2011–2013
    • Robarts Research Institute
      • • Centre for Functional and Metabolic Mapping (CFMM)
      • • Imaging Research Laboratories
      London, Ontario, Canada
  • 2006–2011
    • The University of Western Ontario
      • • Department of Psychology
      • • Department of Medical Biophysics
      London, Ontario, Canada
  • 2010
    • University of British Columbia - Vancouver
      Vancouver, British Columbia, Canada
  • 2009
    • Old Dominion University
      • Department of Philosophy and Religious Studies
      Norfolk, Virginia, United States