Showing papers by "Gregory McCarthy published in 2007"

Perception of dynamic changes in facial affect and identity in autism

Abstract: Despite elegant behavioral descriptions of abnormalities for processing emotional facial expressions and biological motion in autism, identification of the neural mechanisms underlying these abnormalities remains a critical and largely unmet challenge. We compared brain activity with dynamic and static facial expressions in participants with and without high-functioning autism using event-related functional magnetic resonance imaging (fMRI) and three classes of face stimuli—emotion morphs (fearful and angry), identity morphs and static images (fearful, angry and neutral). We observed reduced activity in the amygdala (AMY) and fusiform gyrus (FFG) to dynamic emotional expressions in people with autism. There was also a lack of modulation by dynamic compared with static emotional expressions of social brain regions including the AMY, posterior superior temporal sulcus (STS) region and FFG. We observed equivalent emotion and identity morph-evoked activity in participants with and without autism in a region corresponding to the expected location of the more generally motion-sensitive area MT or V5. We conclude that dysfunctions in key components of the human face processing system including the AMY, FFG and posterior STS region are present in individuals with high-functioning autism, and this dysfunction might contribute to the deficits in processing emotional facial expressions.

Effect of bupropion extended release on negative emotion processing in major depressive disorder: a pilot functional magnetic resonance imaging study.

Abstract: BACKGROUND: Prior imaging studies suggest that patients with major depressive disorder have abnormalities in frontal and limbic neural circuitry including the amygdala, which is relatively more activated at rest and in response to negative emotional stimuli (sadness, fear, etc.) in depressed patients than in controls. Concurrently, patients with depression may have decreased activation of attentional executive regions in response to attentional stimuli. This study examined the effect of bupropion XL, an extended release formulation of the nonserotonergic antidepressant agent bupropion, using a paradigm that investigated both negative emotional response and attentional processing. METHOD: Functional magnetic resonance imaging (fMRI) scans and clinical ratings were obtained for 10 patients with DSM-IV-TR-defined major depressive disorder (mean [SD] age = 41 [+/- 7] years, mean [SD] Hamilton Rating Scale for Depression [HAM-D] score = 21 [+/- 4]) before and after 8 weeks of treatment with bupropion XL. The fMRI sessions were conducted during administration of the Emotional Oddball Task; scans were obtained while subjects viewed emotional distracters and performed an attentional executive function task. The primary outcome was fMRI activations evoked by the emotional distracters. The first baseline fMRI scan was performed in December 2004, and the last posttreatment scan was in March 2005. RESULTS: Treatment with bupropion XL was associated with improvements in HAM-D and Clinical Global Impressions scale ratings (p < .05). Treatment reduced fMRI activation during emotional distracters in several regions including right orbital frontal cortex, left dorsomedial prefrontal cortex, right ventromedial prefrontal cortex, right anterior cingulate cortex, right inferior frontal cortex, right amygdala/parahippocampal area, right caudate, right fusiform gyrus, and left posterior cingulate. In addition, changes in fMRI activation in the amygdala correlated with improvements on the HAM-D (p < .05). Treatment increased activation to attentional targets in the following regions: right middle and inferior frontal gyri, right caudate, and bilateral precuneus. CONCLUSION: Despite the limitations of a small sample size and the lack of a placebo control group, this study demonstrated that bupropion XL therapy for 8 weeks may attenuate emotion-induced, blood-oxygen-level-dependent (BOLD) activation responses in the amygdala and related brain regions. Such attenuation may be associated with a positive clinical response in depression. Bupropion XL also improved activation in the executive-function neural network. These fMRI surrogate markers offer promise for studying antidepressant and neurocognitive effects of existing and novel therapies.

Unconscious word processing engages a distributed network of brain regions

Abstract: A briefly exposed visual stimulus may not be consciously perceived if it is preceded and followed by a dissimilar visual pattern or mask. Despite the subject's lack of awareness, prior behavioral studies have shown that such masked stimuli, nevertheless, engage domain-specific processes [Dehaene, S., Naccache, L., Cohen, L., Le Bihan, D., Mangin, J.-F., Poline, J.-B., et al. Cerebral mechanisms of word masking and unconscious repetition priming. Nature Neuroscience, 4, 752--758, 2001; Bar, M., & Biederman, I. Subliminal visual priming. Psychological Science, 9, 464--469, 1998; Dehaene, S., Naccache, L., Le Clec'H, G., Koechlin, E., Mueller, M., Dehaene-Lambertz, G., et al. Imaging unconscious semantic priming. Nature, 395, 597--600, 1998; Whalen, P. J., Rauch, S. L., Etcoff, N. L., McInerney, S. C., Lee, M. B., & Jenike, M. A. Masked presentations of emotional facial expressions modulate amygdala activity without explicit knowledge. Journal of Neuroscience, 18, 411--418, 1998; Marcel, A. J. Conscious and unconscious perception: Experiments on visual masking and word recognition. Cognitive Psychology, 15, 197--237, 1983]. Masking thus provides a method for identifying language processes that are preattentive and automatic. Functional magnetic resonance imaging used in concert with masking may identify brain regions engaged by these unconscious language processes. In an adaptation design, subjects viewed a continuous stream of masked words and masked nonwords while performing an unrelated detection task, in which they were asked to make a response to a visible colored nonword stimulus (i.e., ampersands in red or blue font). Most trials were masked nonwords and masked words were presented once every 12--15 sec. The task ensured participant engagement, while the masked nonword baseline controlled for perceptual and orthographic processing. Participants were naive to the purpose of the experiment and testing indicated that they did not consciously perceive either the words or nonwords. Masked words, but not masked nonwords, strongly activated left hemisphere language regions, including Broca's area, the angular gyrus, and the lateral temporal lobe. Differential activation of the posterior corpus callosum was also observed.

Controlled scanpath variation alters fusiform face activation

Abstract: We investigated the influence of experimentally guided saccades and fixations on fMRI activation in brain regions specialized for face and object processing. Subjects viewed a static image of a face while a small fixation cross made a discrete jump within the image every 500 ms. Subjects were required to make a saccade and fixate the cross at its new location. Each run consisted of alternating blocks in which the subject was guided to make a series of saccades and fixations that constituted either a Typical or an Atypical face scanpath. Typical scanpaths were defined as a scanpath in which the fixation cross landed on the eyes or the mouth in 90% of all trials. Atypical scanpaths were defined as scanpaths in which the fixation cross landed on the eyes or mouth on 12% of all trials. The average saccade length was identical in both typical and atypical blocks, and both were preceded by a baseline block where the fixation cross made much smaller jumps in the middle of the screen. Within the functionally predefined face area of the ventral occipitotemporal cortex (VOTC), typical scanpaths evoked significantly more activity when compared to atypical scanpaths. A voxel-based analysis revealed a similar pattern in clusters of voxels located within VOTC, frontal eye fields, superior colliculi, intraparietal sulcus, and inferior frontal gyrus. These results demonstrate that fMRI activation is highly sensitive to the pattern of eye movements employed during face processing, and thus illustrates the potential confounding influence of uncontrolled eye movements for neuroimaging studies of face and object perception in normal and clinical populations.

Guided saccades modulate object and face-specific activity in the fusiform gyrus.

Abstract: We investigated the influence of saccadic eye movements on the magnitude of functional MRI (fMRI) activation in brain regions known to participate in object and face perception. In separate runs, subjects viewed a static image of a uniform gray field, a face, or a flower. Every 500 ms a small fixation cross made a discrete jump within the image and subjects were required to make a saccade and fixate the cross at its new location. Each run consisted of alternating blocks in which the subject was guided to make small and large saccades. A comparison of large vs. small saccade blocks revealed robust activity in the oculomotor system, particularly within the frontal eye fields (FEF), intraparietal sulcus (IPS), and superior colliculi regardless of the background image. Activity within portions of the ventral occipitotemporal cortex (VOTC) including the lingual and fusiform gyri was also modulated by saccades, but here saccade-related activity was strongly influenced by the background image. Activity within the VOTC was strongest when large saccadic eye movements were made over an image of a face or a flower compared to a uniform gray image. Of most interest was activity in the functionally predefined face-specific region of the fusiform gyrus, where large saccades made over a face increased activity, but where similar large saccades made over a flower or a uniform gray field did not increase activity. These results demonstrate the potentially confounding influence of uncontrolled eye movements for neuroimaging studies of face and object perception.

Neuroimaging for the Diagnosis and Study of Psychiatric Disorders

Abstract: One out of every four families has a family member with a serious neuropsychiatric illness. Because such an illness is often disabling, it is no surprise that four out of the five major causes of disability world-wide for individuals between 15 and 45 years of age (clinical depression, alcohol related disorders, schizophrenia, iron deficiency anemia, and bipolar illness) are neuropsychiatric disorders. The disability they create exceeds that caused by HIV, cancer, cardiovascular disease, and road accidents [1]. Motivated by such a strong impact, significant research efforts have been directed toward understanding, analyzing, and diagnosing neuropsychiatric disorders. In what follows we first discuss the need for neuroimaging methods in the diagnostic assessment process. Next we summarize the neuroimaging methods that have been applied to neuropsychiatric studies. Then, we outline the signal processing challenges in functional neuroimaging methods and discuss the specific difficulties in multisite data analysis for the diagnosis of neuropsychiatric disorders.

Neuroimaging for the Diagnosis and Study of Psychiatric Disorders [Life Sciences]

Abstract: This paper summarizes the neuroimaging methods in the diagnostic assessment process that have been applied to neuropsychiatric studies. Here, we outline the signal processing challenges in structural and functional neuroimaging methods and discuss the specific difficulties in multisite data analysis for the diagnosis of neuropsychiatric disorders. Currently, fMRI and other brain imaging methods are used to aid in diagnosis primarily by revealing various types of pathology; e.g., evidence of brain tumors or multiple strokes. Significant research efforts have been directed toward understanding, analyzing, and diagnosing neuropsychiatric disorders.