Robert Patrick McMahon

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OBJECTIVE Electroencephalographic (EEG) synchronization in the gamma band is thought to represent a neuronal mechanism by which the brain integrates information processed in different cortical areas to build a coherent internal representation. Previous studies have reported abnormal gamma range ( approximately 40 Hz) synchronization in schizophrenic(More)
BACKGROUND Impairments in working memory have been proposed to underlie a broad range of cognitive deficits seen in schizophrenia. Visual working memory impairments are frequently reported in schizophrenia. Investigations of visual working memory generally assume intact visual information processing, despite evidence of visual perceptual impairments in(More)
OBJECTIVE The study was designed to assess the predictive relationship between brain structure volume and positive and negative symptom response to clozapine and haloperidol. METHOD Partially responsive outpatients with schizophrenia who participated in a 10-week, parallel-group, double-blind comparison of clozapine and haloperidol and who had an(More)
Sensory gating can be measured by the suppression of auditory evoked potentials in a paired-click paradigm. The normal gating of the P50 response to the second stimulus (S2) is impaired in many schizophrenic patients. Various in vitro and in vivo evoked potential paradigms have shown that a stimulus evokes early gamma frequency oscillation, which is(More)
BACKGROUND It is well known that individuals with schizophrenia have dopaminergic abnormalities as well as memory-related difficulties, both of which are associated with impulsive decision making. We used a delay discounting measure to test the degree to which patients make future-oriented decisions. METHODS 42 patients with schizophrenia and 29 healthy(More)
OBJECTIVE The heteromodal association cortex has been hypothesized to be selectively involved in the pathophysiology of schizophrenia. To test this hypothesis, the authors measured prefrontal, inferior parietal, and superior temporal gyrus volumes and examined the pattern of connections among these regions. METHOD Forty-four patients with schizophrenia or(More)
BACKGROUND In a previous pilot study, MK-0777--a γ-aminobutyric acid (GABA)(A) α2/α3 partial agonist--was reported to improve delayed memory and cognitive measures of prefrontal cortical function in people with schizophrenia. The current study was designed to further examine the efficacy and safety of MK-0777 for the treatment of cognitive impairments in(More)
BACKGROUND Impairments of executive functioning, such as set-shifting ability, are seen as core deficits of schizophrenia and are of interest as candidate intermediate phenotype markers. The Intradimensional/Extradimensional (ID/ED) shift task offers a differentiated assessment of shifting from previously reinforced stimuli as well as shifting from(More)
We report on the correlations between whole brain rCBF and the positive and negative symptoms of schizophrenia in two cohorts of patients who were scanned while free of antipsychotic medication. We hypothesized that positive symptoms would correlate with rCBF in limbic and paralimbic regions, and that negative symptoms would correlate with rCBF in frontal(More)
This study reports evidence that patients with schizophrenia demonstrate a slowing of working memory (WM) consolidation, which is the process of transforming transient perceptual representations into durable WM representations. Sixteen schizophrenia patients and 16 healthy control participants performed a task measuring the visual WM consolidation rate in a(More)