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Biomedical subjects

Brian F O'Donnell

Publications and source records attributed to Brian F O'Donnell.

At least 19 recordsLinked to original sources
PubMed2006

Early stage vision in schizophrenia and schizotypal personality disorder.

Previous studies of visual perception have reported deficits in contrast sensitivity and dot motion discrimination in schizophrenia. We tested whether these deficits also appear in schizotypal personality disorder (SPD). SPD appears to be genetically and symptomatically related to schizophrenia, but without the marked psychosocial impairment associated with psychotic disorders. The present study investigated contrast sensitivity for moving and static gratings, form discrimination and dot motion discrimination in 24 patients with schizophrenia or schizoaffective disorder (SZ), 16 individuals with SPD, and 40 control subjects. SZ, but not SPD subjects, showed impairments on tests of contrast sensitivity for static and moving gratings, form discrimination in noise, and dot motion discrimination. Visual performance did not differ between medicated SZ patients and patients withdrawn from medication. These results confirm early stage visual deficits in schizophrenia regardless of medication status. SPD subjects, in contrast, show intact early stage visual processing despite the presence of marked schizotypal symptoms.

Adult↗
PubMed2006

Switch and maintenance of task set in schizophrenia.

Task set maintenance and switching deficits are robust in schizophrenia. However, little is known about how these constructs are related to one another. The development of an improved understanding of set switching and maintenance deficits in schizophrenia requires that these constructs be explicated in terms of elementary cognitive processes rather than grouped into broad psychological concepts like executive functioning. A relevant dichotomy has been proposed in which sensory and perceptual ("attentional") processes are distinguished from decisional ("intentional") processes in task maintenance and switching; however, the contributions these processes make to performance deficits in schizophrenia is not known. In the present study, 30 participants with schizophrenia and 27 healthy comparisons completed a cued attentional set switching task. In addition to analyses of mean response times, the contributions of attentional and intentional processes to task performance were estimated using an ex-Gaussian distributional analysis. Schizophrenia was associated with a set maintenance deficit that was accounted for by an attentional, rather than intentional, dysfunction. Both groups showed significant switch costs that could be attributed to attentional processes, but there was no evidence for an attentional set switching deficit in schizophrenia. The findings suggest that set switching and set maintenance may reflect distinct cognitive deficits in schizophrenia and that they may be associated with unique information processing mechanisms.

Adolescent↗
PubMed2006

Subjective perceptual distortions and visual dysfunction in children with autism.

Case reports and sensory inventories suggest that autism involves sensory processing anomalies. Behavioral tests indicate impaired motion and normal form perception in autism. The present study used first-person accounts to investigate perceptual anomalies and related subjective to psychophysical measures. Nine high-functioning children with autism and nine typically-developing children were given a questionnaire to assess the frequency of sensory anomalies, as well as psychophysical tests of visual perception. Results indicated that children with autism experience increased perceptual anomalies, deficits in trajectory discrimination consistent with dysfunction in the cortical dorsal pathway or in cerebellar midsagittal vermis, and high spatial frequency contrast impairments consistent with dysfunctional parvocellular processing. Subjective visual hypersensitivity was significantly related to greater deficits across vision tests.

Adolescent↗
PubMed2006

Psychophysiological evidence of altered neural synchronization in cannabis use: relationship to schizotypy.

OBJECTIVE: Cannabis use may produce neurophysiological disturbances similar to those observed in schizophrenia, particularly in relation to altered neural synchronization. Therefore, the current experiment examined the effect of cannabis use on EEG neural synchronization using the auditory steady-state evoked potential. METHOD: Auditory steady-state evoked potentials were assessed using varying rates of stimulation (auditory click-trains of 20, 30, 40 Hz) in current cannabis users (N=17) and drug-naive comparison subjects (N=16). EEG spectral power and signal-to-noise ratio at each stimulation frequency were compared between groups. RESULTS: Cannabis users showed decreased EEG power and signal-to-noise ratio at the stimulation frequency of 20 Hz. In addition, current cannabis users demonstrated increased schizotypal personality characteristics as assessed with the Schizotypal Personality Questionnaire, which positively correlated with total years of cannabis use. Finally, within the cannabis group, 20-Hz power values were negatively correlated with Schizotypal Personality Questionnaire scores. CONCLUSIONS: These data provide evidence for neural synchronization and early-stage sensory processing deficits in cannabis use. This finding, along with the observed increased rates of schizotypy in cannabis users, adds support for a cannabinoid link to schizophrenia spectrum disorders.

Acoustic Stimulation↗
PubMed2005

The effect of cannabis use and gender on the visual steady state evoked potential.

OBJECTIVE: Cannabis use often induces subjective distortions of perception. However, little work has been done examining the electroencephalographic (EEG) correlates of early sensory processing in cannabis users. The present study therefore examined visual function in cannabis users as assessed via the steady state visual evoked potential. (SSVEP). METHODS: SSVEPs were examined in current cannabis users (n = 17; 59% male; mean age = 23.2 (S.D. = 5.3)) and drug-naive controls (n = 16; 38% male; mean age = 21.3 (S.D. = 3.1)) to periodic photic stimulation presented at 18 and 25 Hz. The visual SSVEP was quantified via spectral power and the phase-locking factor (PLF) at each frequency of stimulation. The transient N160 event-related potential (ERP) was also evaluated at stimulus onset. RESULTS: The results showed that for both frequencies, female subjects in general displayed larger visual SSVEPs. A significant gender X group interaction also occurred at 18 Hz of stimulation, and age of onset of cannabis use positively correlated with 18 Hz spectral power values. Finally, the transient N160 component was shown to be reduced in cannabis users, regardless of gender. CONCLUSIONS: The present study was the first to demonstrate altered visual SSVEPs in cannabis users, and extends previous research demonstrating increased steady state responses in female subjects. While decreased SSVEPs provide initial evidence of altered oscillatory properties in primary visual circuits, reduction of the transient N160 component suggests disruption of later-stage visual processing in cannabis users. SIGNIFICANCE: These data provide evidence of cannabinoid modulation of sensory/perceptual function in the visual system, and indicates that cannabis use may affect the oscillatory properties of sensory cortical circuits.

Adolescent↗
PubMed2005

Contributions of subtype and spectral frequency analyses to the study of P50 ERP amplitude and suppression in schizophrenia.

BACKGROUND: Poor suppression of P50 event-related potential (ERP) amplitudes to paired-click stimuli may indicate genetic liability for schizophrenia and weak "sensory gating." Evidence suggests, however, that P50 amplitude is selectively impaired in nonparanoid, but not paranoid, schizophrenia subtypes. Furthermore, paired-click suppression can appear deficient in schizophrenia due to smaller evoked responses to the first stimulus (S1), rather than larger, less effectively "gated" responses to the second (S2). Finally, the P50 ERP is comprised of activity from at least two frequency components that may be distinctly impaired: the gamma band, associated with sensory registration, and the low frequency response, associated with attention/encoding processes. P50 and related frequency subcomponents were examined as a function of illness subtype to further integrate these concepts. METHOD: The standard paired-click paradigm was administered to 38 schizophrenia (27 paranoid, 11 nonparanoid) and 38 age-matched healthy control participants. P50 amplitudes and spectral power of gamma band (GBR; 20-50 Hz) and low frequency (LFR; 1-20 Hz) responses were analyzed. RESULTS: P50 analyses revealed smaller S1 amplitude and normal S2 in schizophrenia participants collectively, but no differentiation of schizophrenia subtypes. Spectral analyses revealed smaller magnitude S1 and normal S2 responses in schizophrenia across both the GBR and LFR. The LFR, but not GBR, was found to distinguish nonparanoid from control groups, while paranoid participants evidenced no impairment in either frequency domain. LFR amplitude values correlated with clinical ratings of cognitive symptomatology. CONCLUSIONS: ERP deficits in the dual-click paradigm were specific to S1 amplitudes and most prominent in the low frequency response. These results replicate previous findings and extend their relevance to schizophrenia subtype distinctions. Implications for the recurrent inhibition model of sensory gating are discussed.

Adult↗
PubMed2005

Relationship between steady-state and induced gamma activity to motion.

When a moving stimulus is presented at a specific temporal frequency, both steady-state responses and induced gamma activity may be elicited in the electroencephalogram. The electroencephalogram was recorded when study participants viewed random dot kinematograms under three conditions: coherent motion, incoherent motion and stationary. Dot position was changed at a rate of 9.3 Hz in the coherent and incoherent conditions. Induced power at 40 Hz was increased during coherent motion compared with the other conditions. In contrast, the steady-state response at 9.3 Hz showed a trend for increased power during the incoherent condition. These results suggest that steady-state responses to moving stimuli reflect sensory activation, while the induced gamma activity indexes perceptual processes.

Adult↗
PubMed2005

Auditory P3 indexes personality traits and cognitive function in healthy men and women.

The relationship of the auditory P3 event-related potential to major personality dimensions and neuropsychological performance was examined in psychiatrically healthy men and women (28 male, 15 female) recruited from the community. An auditory oddball paradigm was used to collect P3 amplitude and latency data. Personality traits were measured with the NEO Five-Factor Inventory. Several Wechsler Adult Intelligence Scale-Revised (WAIS-R) subtests, the Digit Symbol Test, and the Trail Making Test comprised the neuropsychological tests. A multivariate statistical procedure (Partial Least Squares) was used to quantify the relationships between P3 variables and personality and neuropsychological performance variables. P3 amplitude was negatively related to Neuroticism and positively related to Extraversion, Openness, Agreeableness and Conscientiousness. Better neuropsychological performance was associated with greater P3 amplitude and earlier latency. Thus, greater P3 amplitude was associated with less deviant personality scores and better neuropsychological performance in healthy subjects. Earlier P3 latency was also associated with better neuropsychological performance. The physiological significance of these relationships is not yet clear, but these results suggest that neural assemblies indexed by P3 may subserve both elemental cognition and healthy personality function.

Adolescent↗
PubMed2005

Personality traits in schizophrenia and related personality disorders.

We investigated whether schizophrenia spectrum disorders share common personality characteristics or traits. Participants with a diagnosis of schizophrenia or schizoaffective disorder (SZ) or with a schizophrenia spectrum personality disorder (schizophrenia spectrum PD: schizoid, paranoid, and schizotypal personality disorder) were compared with non-psychiatric control subjects on the five-factor model of personality and the psychosis-proneness scales. On the five-factor personality scales, SZ subjects showed higher levels of neuroticism, and lower levels of openness, agreeableness, extraversion, and conscientiousness than control subjects. Higher scores on openness and lower scores on neuroticism distinguished schizophrenia spectrum PD from SZ. On the psychosis-proneness scales, both PD and SZ participants scored high relative to non-psychiatric control participants on magical ideation and perceptual aberration, while PD participants scored intermediate between non-psychiatric control participants and SZ on social anhedonia. Discriminant analysis indicated that schizophrenia spectrum patients could be distinguished from PDs by more severe social withdrawal and maladjustment, while subjects with PDs could be best distinguished from control subjects on the basis of odd or novel ideation and decreased conscientiousness.

Adult↗
PubMed2005

Steady state visual evoked potential abnormalities in schizophrenia.

OBJECTIVE: The steady state visual evoked potential (SSVEP) can be used to test the frequency response function of neural circuits. Previous studies have shown reduced SSVEPs to alpha and lower frequencies of stimulation in schizophrenia. We investigated SSVEPs in schizophrenia at frequencies spanning the theta (4Hz) to gamma (40Hz) range. METHODS: The SSVEPs to seven different frequencies of stimulation (4, 8, 17, 20, 23, 30 and 40Hz) were obtained from 18 schizophrenia subjects and 33 healthy control subjects. Power at stimulating frequency (signal power) and power at frequencies above and below the stimulating frequency (noise power) were used to quantify the SSVEP responses. RESULTS: Both groups showed an inverse relationship between power and frequency of stimulation. Schizophrenia subjects showed reduced signal power compared to healthy control subjects at higher frequencies (above 17Hz), but not at 4 and 8Hz at occipital region. Noise power was higher in schizophrenia subjects at frequencies between 4 and 20Hz over occipital region and at 4, 17 and 20Hz over frontal region. CONCLUSIONS: SSVEP signal power at beta and gamma frequencies of stimulation were reduced in schizophrenia. Schizophrenia subjects showed higher levels of EEG noise during photic stimulation at beta and lower frequencies. SIGNIFICANCE: Inability to generate or maintain oscillations in neural networks may contribute to deficits in visual processing in schizophrenia.

Adult↗
PubMed2005

Personality differences in schizophrenia are related to performance on neuropsychological tasks.

Altered cognition and personality appear to emerge in tandem and adversely affect outcome in schizophrenia, yet little research has been done to determine whether these are related or independent domains. In this study, the relationship between the Big Five personality traits--neuroticism, extraversion, openness, agreeableness, conscientiousness--and cognitive and motor performance in outpatients with chronic, clinically stable schizophrenia (N = 30) and age-matched healthy comparison subjects (N = 45) was examined. Subjects completed tests of attention, executive and motor functions, and the NEO-Five Factor Personality Inventory. Patients scored significantly higher on neuroticism and lower on extraversion and agreeableness, but after variance due to neuropsychological performance was statistically removed from NEO scale scores, personality dimensions and profiles no longer differed between groups. Neuropsychological performance and demographic variables, but not diagnosis, uniquely accounted for statistically significant amounts of personality variance, and neuropsychological task performance was correlated with personality dimensions in both patients and comparison subjects. These cross-sectional data provide preliminary evidence that personality dysfunction in schizophrenia may be mediated by disease-related changes in cognitive operations, or the neural processes underlying them. Longitudinal studies utilizing more comprehensive measures of neurocognitive performance are needed to define further the relationship between neuropsychological function and personality in schizophrenia.

Adult↗
PubMed2004

Neural synchronization deficits to auditory stimulation in bipolar disorder.

Patients with bipolar disorder show cognitive deficits and disorganized behavior, which may reflect a disturbance in neural synchronization. We tested whether EEG measures of auditory neural synchronization were abnormal in bipolar disorder. Nineteen symptomatic patients with bipolar disorder and 32 non-psychiatric control subjects were evaluated. Click trains (500 ms duration) presented at 20, 30, 40 and 50 Hz were used to evoke EEG synchronization. Patients with bipolar disorder showed reduced power across the frequencies of stimulation. Phase-locking across trials was also disturbed in bipolar disorder, consistent with poor phase synchronization between the stimulus and EEG. Abnormal high frequency neural synchronization may contribute to cognitive deficits in bipolar disorder.

Acoustic Stimulation↗
PubMed2003

The startle reflex in schizophrenia: habituation and personality correlates.

Schizophrenia has long been associated with abnormal patterns of arousal that are thought to reflect disturbances in the reticular-activating system of the brain. Psychophysiological investigations of sensory responsivity have repeatedly demonstrated reduced reactivity and habituation to moderately intense stimuli in patients with schizophrenia. While not traditionally used as a measure of physiological arousal, the startle reflex represents an alternative method for studying reactivity and habituation in schizophrenia. This study examined eye blink responsivity to a repeatedly presented intense acoustic startle probe in men with chronic schizophrenia and healthy normal controls. Subjects' personality profiles were also measured, as increased reactivity and arousal have been traditionally implicated as a physiological component to the personality trait of neuroticism. Results indicated that schizophrenic subjects did demonstrate significantly reduced rates of habituation to the acoustic startle probe and higher scores on measures of neuroticism in comparison to normal controls. However, no correlation between habituation rate and neuroticism emerged. These studies replicate previous findings of habituation in schizophrenia and provide further evidence for sensory reactivity disturbances in schizophrenia. The relationship of these findings to cognitive disturbances in schizophrenia is considered and directions for future research are discussed.

Acoustic Stimulation↗
PubMed2003

Visual function in Huntington's disease patients and presymptomatic gene carriers.

Disturbances of visual cognition, visuomotor performance, and visual memory have been described frequently in Huntington's disease (HD). Early stage visual abnormalities could contribute to these deficits. We evaluated visual processing in 20 control subjects who were non-gene carriers at risk for HD, nine presymptomatic gene-positive subjects, and eight subjects with a recent diagnosis of Huntington's disease. Visual perceptual tests of contrast sensitivity and motion discrimination were used to probe early stage visual processing. Extraocular movements were evaluated in a neurologic examination, and the Digit Symbol test was used to test visual motor performance. Contrast sensitivity did not differ among the three groups. Motion discrimination was impaired in HD subjects but not in the presymptomatic gene carriers when compared to gene noncarriers. Among gene carriers, impaired motion discrimination performance was associated with poorer Digit Symbol performance and extraocular abnormalities. These findings suggest that the early stages of HD are associated with disturbances of motion perception as well as disruptions of visual motor and ocular motor performance.

Adult↗
PubMed2003

N400 abnormalities in unmedicated patients with schizophrenia during a lexical decision task.

A lexical decision task was used to investigate semantic processing in schizophrenia. Eighteen unmedicated schizophrenics and 18 gender/age-matched controls were tested. Subjects were visually presented with pairs of words. The target word (S2) was either a non-word, semantically related, or unrelated to preceding word (S1). Subjects decided whether the S2 was a word or non-word. Event related potentials (ERPs) elicited by the S2, including N350, and the late positive component (LPC) were measured. The latency of the N350 was prolonged in schizophrenia. The N400 effect, measured by the mean amplitude (300-500 ms) from difference waves (unrelated word-related word, non-word-related word), was smaller in patients. Peak amplitude of the LPC was reduced and latency of the LPC was delayed in the schizophrenics. Behaviorally, control subjects responded much faster to related words compared to unrelated or non-words, while patients showed little difference in processing speed between word categories. A reduced N400 effect suggested inefficient utilization of the context, while prolonged latency of the ERP components suggested a general delay of semantic information processing in schizophrenia.

Adult↗
PubMed2003

EEG synchronization to modulated auditory tones in schizophrenia, schizoaffective disorder, and schizotypal personality disorder.

OBJECTIVE: The authors tested whether neural synchronization deficits were present in subjects with schizophrenia and schizotypal personality disorder. METHOD: Amplitude-modulated tones were used to evaluate auditory steady-state evoked potential entrainment in a combined group of 21 subjects with schizophrenia or schizoaffective disorder, 11 subjects with schizotypal personality disorder, and 22 nonpsychiatric comparison subjects. RESULTS: The schizophrenia or schizoaffective disorder group exhibited decreased power compared to the schizotypal personality disorder and nonpsychiatric comparison groups. There were no differences between groups in N100 amplitude. CONCLUSIONS: Subjects with schizophrenia but not subjects with schizotypal personality disorder have deficits in steady-state responses to periodic stimuli, despite an intact response to sensory-evoked potentials (N100). These deficits reflect aberrant neural synchronization or resolution and may contribute to disturbed perceptual and cognitive integration in schizophrenia.

Acoustic Stimulation↗
PubMed2003

Psychometrically matched visual-processing tasks in schizophrenia spectrum disorders.

Patients with schizophrenia show deficits in visual perception and working memory, but the relationship between these deficits has not been characterized with psychometrically matched tasks. The authors administered 2 visual discrimination and 6 recognition tasks to 43 schizophrenia spectrum patients and 22 nonpsychiatric subjects. When performing difficulty-matched tasks, spectrum subjects showed more severe impairments for motion compared with form processing. When tasks were matched on true score variance, spectrum subjects exhibited worse performance on both form and motion discrimination, and a differential deficit in motion recognition with a short display duration and long interstimulus interval. These results provide evidence of differential deficits in visual processing in schizophrenia that appear to be dependent on the temporal characteristics of the tasks.

Adult↗