Brain Dynamics Centre ~ gamma synchrony

Recently there has been a growing awareness amongst scientists that the reductionistic approach to characterizing brain function which has underpinned much previous research, whilst providing profoundly important insights regarding brain activity, nonetheless yields only an incomplete picture of how the brain operates as a system. The reductionistic approach involves examining brain processing activities by breaking them down into smaller and smaller sub-components, each of which is examined largely in isolation from other processes. Such an approach provides an incomplete account of brain function because it does not address the issue of how these spatially diffuse processing sub-components are integrated with each other. More specifically, given that the brain engages parallel distributed processes and does not function in a serial manner, different processes in the brain at any one time will be related to a greater or lesser extent to other processes occurring in different regions at the same time. The question arises how the brain keeps track of and operates on these relationships between different processes. This is known as the binding problem. Of central importance in this regard is a kind of high-frequency neuronal oscillation observed in the brain called gamma activity. It is thought that synchronization of gamma oscillations between different regions of the brain involved in related processing may be a mediator of binding. Evidence that spatially distributed synchronous gamma oscillations might play a role in binding originally emerged from animal experiments, particularly in visual processing during the early 1990s. Since then a considerable body of direct and indirect evidence has emerged linking these oscillations with cognitive binding in a wide range of contexts, primarily from animal experiments, but also from studies in humans. In addition, simulation studies and models of neuronal dynamics have increasingly pointed to synchrony as an important possible coding mechanism. These developments that have occurred during the last decade in the understanding of the importance of gamma synchrony for cognitive binding have important implications, which are beginning to be realized. One application of gamma synchrony concerns the neuropathological basis of schizophrenia. The idea that the core deficit in schizophrenia might relate to impaired coordination and integration of cognitive processes dates back to descriptions of the disorder by Stransky, Bleuler and Berze around the onset of World War I. There has recently been a renewed interest in this concept, including a modern reconceptualization in terms of the hypothesis that schizophrenia is a neurodevelopmental abnormality of connectivity, which results in a failure of the integration of spatially distributed parallel brain processing. This suggests that abnormalities of gamma synchrony might be a key feature of this disorder. Our group has undertaken a range of studies of gamma synchrony in normal cognition and in schizophrenia. This has involved the development of a new method of analyzing gamma synchrony at the whole brain level. Findings: Haig et al. (1999, Clinical Neurophysiology, 110, 158-165) found a relationship between gamma activity and speed of response in normal subjects. Haig et al. (2000, NeuroReport, 11, 669-675) introduced the new method of analyzing gamma synchrony and described two main synchronizations that occur in normals in processing task-relevant and -irrelevant information. Haig et al. (2000, Clinical Neurophysiology, 111, 1461-1468) described for the first time abnormalities of gamma related to brain processing in patients with schizophrenia. Lee et al. (2001, Clinical Neurophysiology, 112, 1499-1507, PDF [315K]) found that normal laterality of Gamma activity is specifically disturbed in schizophrenia in response to novel, but not routine (familiar) stimuli. Lee et al. (2001, submitted for publication) found that schizophrenia syndromes were differentiated by distinct patterns of Gamma disturbances: Psychomotor Poverty (deficit negative symptoms) showed decreased left hemisphere synchrony; Reality Distortion (delusions and hallucinations) was associated with increased right synchrony; Disorganization (defined primarily by thought disorder) showed a widespread enhancement with a delay in frontal gamma synchrony. Read news article on gamma discovery in schizophrenia: "Schizophrenia Discovery"

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