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Thomas J. Whitford, Department of Psychiatry Brigham and Women's Hospital Harvard School of Medicine Boston, MA, USA and Department of Psychiatry Melbourne Neuropsychiatry Centre University of Melbourne Melbourne, Australia,
Marek Kubicki, Department of Psychiatry VA Boston Healthcare System and Department of Psychiatry Brigham and Women's Hospital Harvard Medical School Boston, MA, USA,
Martha E. Shenton, VA Boston Healthcare System and Department of Psychiatry Brigham and Women's Hospital Harvard Medical School Boston, MA, USA
Emil Kraepelin, one of the founding fathers of the diagnostic concept of schizophrenia, argued that the disorder was underpinned by abnormalities in brain structure. In his 1899 textbook, Kraepelin wrote: “in dementia praecox [schizophrenia], partial damage to, or destruction of, cells of the cerebral cortex must probably occur” (Kraepelin,1907). Since that time, an enormous amount of research has been undertaken with an eye to determining whether or not Kraepelin was correct. Until recently, the question of whether patients with schizophrenia (SZ) exhibit abnormalities in brain structure was more or less synonymous with the question of whether they exhibit abnormalities in gray matter (GM). The GM, so-called because of its grayish appearance in post-mortem tissue sections, is thought to consist primarily of neuron bodies, dendrites, axon terminals and other synaptic infrastructure and certain classes of neuroglia. Until recently, the vast majority of research aimed at investigating the neuroanatomical underpinnings of SZ has focused on GM. This is perhaps understandable, given that GM comprises both the brain's fundamental units of information processing (neurons) and the sites-of-action for most psychotropic medications (synapses). In recent years, however, a growing proportion of contemporary research has begun to focus on the “other half of the brain” (as wryly denoted by Fields, 2004), i.e. the white matter. The white matter (WM) is primarily constituted of myelinated axon sheaths, which form the infrastructure for signal transmission between spatially discrete populations of neurons.
Patients with schizophrenia (SZ) characteristically exhibit supranormal levels of cortical activity to self-induced sensory stimuli, ostensibly because of abnormalities in the neural signals (corollary discharges, CDs) normatively involved in suppressing the sensory consequences of self-generated actions. The nature of these abnormalities is unknown. This study investigated whether SZ patients experience CDs that are abnormally delayed in their arrival at the sensory cortex.
Twenty-one patients with SZ and 25 matched control participants underwent electroencephalography (EEG). Participants' level of cortical suppression was calculated as the amplitude of the N1 component evoked by a button press-elicited auditory stimulus, subtracted from the N1 amplitude evoked by the same stimulus presented passively. In the three experimental conditions, the auditory stimulus was delivered 0, 50 or 100 ms subsequent to the button-press. Fifteen SZ patients and 17 healthy controls (HCs) also underwent diffusion tensor imaging (DTI), and the fractional anisotropy (FA) of participants' arcuate fasciculus was used to predict their level of cortical suppression in the three conditions.
While the SZ patients exhibited subnormal N1 suppression to undelayed, self-generated auditory stimuli, these deficits were eliminated by imposing a 50-ms, but not a 100-ms, delay between the button-press and the evoked stimulus. Furthermore, the extent to which the 50-ms delay normalized a patient's level of N1 suppression was linearly related to the FA of their arcuate fasciculus.
These data suggest that SZ patients experience temporally delayed CDs to self-generated auditory stimuli, putatively because of structural damage to the white-matter (WM) fasciculus connecting the sites of discharge initiation and destination.
This paper presents the multigigawatt single-beam CO2 laser system and the configuration and the main subsystems of the 0.5 TW four-beam CO2 laser system being built at the IPPLM. Selected construction details and early test results are given.
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