Person:
Khan, Usman

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Khan

First Name

Usman

Name

Khan, Usman
Author's Publications: search.filters.isAuthorOfPublication.0b1b083e-6084-4449-8d3d-c614d16bf51f

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Publication
    Corpus Callosum Abnormalities and Their Association with Psychotic Symptoms in Patients with Schizophrenia
    (Elsevier BV, 2010) Whitford, T; Kubicki, Marek; Schneiderman, Jason S.; O, Lauren J.; King, Rebecca; Alvarado, Jorge L.; Khan, Usman; Markant, Douglas; Nestor, Paul; Niznikiewicz, Margaret; McCarley, Robert William; Westin, Carl-Fredrik; Shenton, Martha
    Background—Whilst the neuroanatomical underpinnings of the functional brain disconnectivity observed in patients with schizophrenia remain elusive, white matter fiber bundles of the brain are a likely candidate given that they represent the infrastructure for long-distance neural communication. Methods—This study investigated for diffusion abnormalities in 19 patients with chronic schizophrenia (SZ), relative to 19 matched controls, across tractography-defined segments of the Corpus Callosum. Diffusion-weighted images were acquired with 51 non-collinear gradients on a 3T scanner (1.7mm isotropic voxels). The Corpus Callosum was extracted by means of whole-brain tractography and automated fiber-clustering, and was parcellated into six segments on the basis of fiber trajectories. The diffusion indices of Fractional Anisotropy (FA) and Mode were calculated for each segment. Results—Relative to the healthy controls, the SZ patients exhibited Mode increases in the Parietal fibers, suggesting a relative absence of crossing fibers. SZ patients also exhibited FA reductions in the Frontal fibers, which were underpinned by increased in Radial Diffusivity, consistent with myelin abnormalities. Significant correlations were observed between patients' degree of Reality Distortion and their FA and Radial Diffusivity, such that the most severely psychotic patients were the least abnormal in terms of their Frontal fiber diffusivity. Conclusions—The SZ patients exhibited a variety of diffusion abnormalities in the Corpus Callosum, which were related to the severity of their psychotic symptoms. To the extent that diffusion abnormalities influence axonal transmission velocities, these results provide support for those theories that emphasize neural timing abnormalities in the etiology of schizophrenia.
  • Thumbnail Image
    Publication
    Factors in sensory processing of prosody in schizotypal personality disorder: An fMRI experiment
    (Elsevier BV, 2010) Dickey, Chandlee; Morocz, Istvan Akos; Minney, Daniel; Niznikiewicz, Margaret; Voglmaier, Martina; Panych, Lawrence; Khan, Usman; Zacks, Rayna; Terry, Douglas P.; Shenton, Martha; McCarley, Robert William
    Introduction—Persons diagnosed with schizophrenia demonstrate deficits in prosody recognition. To examine prosody along the schizophrenia spectrum, antipsychotic-naïve schizotypal personality disorder (SPD) subjects and healthy control subjects were compared. It was hypothesized that SPD subjects would perform more poorly; with cognitive and demographic factors contributing to the poor performance. The superior temporal gyrus (STG) was selected as the region-of-interest (ROI) given its known abnormalities in SPD and its important role in the processing of prosody. Methods—SPD and healthy comparison (HC) subjects were matched on age, IQ, and parental social-economic status (PSES). Cognitive measures included the Speech Sound Perception Test (SSPT) to examine phonological processing (SPD= 68, HC = 74) and the Verbal Fluency task to examine executive functioning (SPD = 129, HC = 138). The main experiment was a novel fMRI task of prosody identification using semantically neutral sentences spoken with emotional prosody (SPD = 16, HC = 13). Finally, volumetric measurement of the superior temporal sulcus (STS), a key region for processing prosody, and partially overlapping with the STG, was performed (SPD = 30, HC = 30). Results—Phonological processing and executive functioning were both impaired in SPD subjects compared with HC subjects. Contrary to the prediction, SPD subjects, as a group, were similar to HC subjects in terms of correctly indentifying the emotion conveyed and reaction time. Within the SPD group, prosody identification accuracy was influenced by executive functioning, IQ and perhaps PSES, relationships not found with HC subjects. Phonological perception aided prosody identification in both diagnostic groups. As expected, both groups activated the STG while performing the prosody identification task. However, SPD subjects may have been less “efficient” in their recruitment of STG neurons. Finally, SPD subjects demonstrated a trend toward smaller STS volumes on the left, particularly the lower bank. Conclusions—These data suggest that subtle differences between SPD and controls in phonological processing, executive functioning, IQ, and possibly PSES, contributed to difficulty in processing prosody for some SPD subjects.
  • Thumbnail Image
    Publication
    Auditory processing abnormalities in schizotypal personality disorder: An fMRI experiment using tones of deviant pitch and duration
    (Elsevier BV, 2008) Dickey, Chandlee; Morocz, Istvan Akos; Niznikiewicz, Margaret; Voglmaier, Martina; Toner, Sarah; Khan, Usman; Dreusicke, Mark; Yoo, Seung-Schik; Shenton, Martha; McCarley, Robert William
    Background: One of the cardinal features of schizotypal personality disorder (SPD) is language abnormalities. The focus of this study was to determine whether or not there are also processing abnormalities of pure tones differing in pitch and duration in SPD. Methods: Thirteen neuroleptic-naïve male subjects met full criteria for SPD and were group-matched on age and parental socioeconomic status to 13 comparison subjects. Verbal learning was measured with the California Verbal Learning Test. Heschl’s gyrus volumes were measured using structural MRI. Whole-brain fMRI activation patterns in an auditory task of listening to tones including pitch and duration deviants were compared between SPD and control subjects. In a second and separate ROI analysis we found that peak activation in superior temporal gyrus (STG), Brodmann Areas 41 and 42, was correlated with verbal learning and clinical measures derived from the SCID-II interview. Results: In the region of the STG, SPD subjects demonstrated more activation to pitch deviants bilaterally (p<0.001); and to duration deviants in the left hemisphere (p=0.005) (two-sample t). SPD subjects also showed more bilateral parietal cortex activation to duration deviants. In no region did comparison subjects activate more than SPD subjects in either experiment. Exploratory correlations for SPD subjects suggest a relationship between peak activation on the right for deviant tones in the pitch experiment with odd speech and impaired verbal learning. There was no difference between groups on Heschl’s gyrus volume. Conclusions: These data suggest that SPD subjects have inefficient or hyper-responsive processing of pure tones both in terms of pitch and duration deviance that is not attributable to smaller Heschl’s gyrus volumes. Finally, these auditory processing abnormalities may have significance for the odd speech heard in some SPD subjects and downstream language and verbal learning deficits.