The brain at rest generates cycles of electrical activity that have been shown to be abnormal in people with schizophrenia. The alpha rhythm (~ 10 Hz) is the dominant resting state electrical cycle and each person has a propensity toward a particular frequency of oscillation for this rhythm. This individual alpha peak frequency (IAPF) is hypothesized to be central to visual perceptual processes and may have downstream influences on cognitive functions such as attention, working memory, or problem solving. In the current study we sought to determine whether IAPF was slower in schizophrenia, and whether lower IAPF predicted deficits in visual perception and cognition that are often observed in schizophrenia. Eyes-closed resting state EEG activity, visual attention, and global cognitive functioning were assessed in individuals with schizophrenia (N = 104) and a group of healthy controls (N = 101). Compared to controls, the schizophrenia group showed slower IAPF and was associated with poorer discrimination of visual targets and nontargets on a computerized attention task, as well as impaired global cognition measured using neuropsychological tests across groups. Notably, disruptions in visual attention fully mediated the relationship between IAPF and global cognition across groups. The current findings demonstrate that slower alpha oscillatory cycling accounts for global cognitive deficits in schizophrenia by way of impairments in perceptual discrimination measured during a visual attention task.
Prominent working memory (WM) deficits have been observed in people with schizophrenia (PSZ) across multiple sensory modalities, including the visuospatial realm. Electrophysiological abnormalities noted during early visual processing as well as later cognitive functions in PSZ may underlie deficiencies in WM ability, though the mechanisms linking behavior to neural responses are not well understood. WM dysfunction has also been observed in biological relatives of PSZ (REL) and therefore may be a manifestation of genetic liability for the disorder. We administered a delayed response visuospatial WM task to 23 PSZ, 30 of their REL, and 37 healthy controls (CTRL) to better understand the contributions of neural abnormalities to WM performance deficits associated with schizophrenia. PSZ performed more poorly on the WM task and failed to effectively process distractor stimuli as well as CTRL and REL. N1 electrophysiological responses to probes during retrieval differentiated the type and locations of stimuli presented during encoding in CTRL. Retrieval N1 responses in PSZ, however, failed to do so, while retrieval responses in REL showed more pronounced differentiation of stimulus features during encoding. Furthermore, neural responses during retrieval predicted behavioral performance in PSZ and REL, but not CTRL. These results suggest that retrieval processes are particularly important to efficient visuospatial WM function in PSZ and REL, and support further investigation of WM retrieval as a potential target for improving overall WM function through clinical intervention.
Working memory (WM) deficits have been repeatedly observed in people with schizophrenia (PSZ) and their unaffected biological relatives (REL). Given the apparent association with genetic liability for schizophrenia, WM deficits have been proposed as a potential endophenotype for the disorder. Abnormal neural responses during WM performance have likewise been observed in PSZ and REL and may reflect the expression of genetic liability for schizophrenia in brain function. Relatively recent investigations have examined the role of neural oscillatory activity during visuospatial WM function in healthy people, as well as dysfunction in psychopathology. This research was in part motivated by a neural model of WM proposed by Lisman and Idiart (Science 267:1512(Science 267: -1515(Science 267: , 1995 that delineated a mechanism for representing multiple stimuli within WM through systematic interactions between neural oscillations in the theta-and gamma-frequency ranges. Aberrant oscillatory activity in theta and gamma frequency ranges has since been proposed as a potential underlying factor in WM dysfunction in PSZ and REL. The experimental evidence derived from studies of healthy people that pertains to the theta-gamma model of WM is reviewed herein. Although scarce, direct examinations of theta-gamma interactions in PSZ and REL are likewise reviewed in addition to reports of separate deficits in theta and gamma frequencies observed in PSZ during WM. The implications of theta and gamma oscillatory deficits reported in PSZ are discussed in the context of the Lisman and Idiart (Science 267:1512(Science 267: -1515(Science 267: , 1995 model, as well as how these deficits may result in aberrant theta-gamma interactions that give rise to visuospatial WM dysfunction. Given evidence supporting the Lisman and Idiart (Science 267:1512(Science 267: -1515(Science 267: , 1995 model of theta-gamma interactions in WM and the lack of direct exploration of the model in schizophrenia, there is an imperative to carry out formal testing of theta-gamma interactions in PSZ and REL during WM.
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