research


Prodrome

prodrome

A prodromal phase is characterized by subthreshold or attenuated psychotic symptoms and deterioration in social, academic, and occupational functioning. This period precedes the onset of psychosis by less than a year to several years.

Research in this area and period of the disorder has gained considerable interest as electophysiological and functional magentic resonance imaging has shown that measures of neurocognitive dysfunction in schizophrenia has been observed in first-episode psychotic patients. These measures of neurocognitive dysfunction are assumed to have been present before the onset of psychosis suggesting a genetic vulnerability and/or neurodevelopmental condition associated with the disorder.[Murray, 1992; Waddington, 1993; Weinberger, 1996]. An aim of this research study is to examine whether event-related potential (ERP) and functional magnetic resonance imaging (fMRI) measures of three established domians of neruocognitive dysfunction in schizophrenia (auditory processing, attention, and working memeory) are abnormal in prodromal patients relative to healthy comparison subjects. We also plan to examine whether these neurophysiological abnormalities are predictive of conversion to psychosis in prodromal patients during a 24-month follow-up period.

Efferent Copy/Corollary Discharge

corollary discharge

Schizophrenia is a pan-cerebral illness, affecting almost every modality, function, and brain region studied. While each symptom and function might have its own failed mechanism, parsimony encourages us to find an elemental mechanism that could be at the root of at least some of the dysfunctions observed. Our studies have focused on how dysfunction of the efference copy/corollary discharge mechanism might explain auditory verbal hallucination. We have found that dysfunction of the crollary discharge can also be observed in the somaosensory system

An efference copy or corollary discharge acts to surpress cortical responses to self produced actions such as sounds. This mechanism has shown to be dysfunctional in schizophrenia. The syncronization of neural activity preceding self-generated actions may reflect the operation of a forward model, which acts to dampen sensation from those actions.

methods


Electroencephalography (EEG)

ERP plot

Electroencephalography (EEG) based event-related potentials are time-locked to an action. The wave form elicited from a sensory stimulation is comprised of different components depending on the sensory input and the location site that the ERP is associated with. A few components are described below.

The N1 is a negative directed component that occurs approximately 100ms after the stimulus is presented. The N1 caputures processing associated with attention.

The P3 component is a positive directed element that is associated with novely detection in recognition and discrimination tasks. The P3 occurs 300ms after onset of a stimulus.

The N400 is related to processing related to semantic and grammatical processing and is a negative directed component that occurs 400ms after the onset of the stimulus.

Functional Magnetic Resonance Imaging fMRI

Comp2 fig

Functional Margentic Resonance Imaging (fMRI)is a type of MRI scan that uses a strong magnet to take pictures of the brain. fMRI shows activation that is localized to a certain region.

The use of fMRI provides insight into the structural of the brain and also which structures are activated while performing specific tasks related to certain cogntiive functions. The neural activity that takes place while undergoing a task is reflected in the blood-oxygen levels of the brain that is detected by the fMRI technique. The use of fMRI is a non-invasive procedure.