The N100 reduction might be the result of an overlapping component, the processing negativity, which is elicited during selective attention paradigms and appears to be reduced in schizophrenia patients. A reduction in processing negativity is consistent with the deficits in selective attention that have been proposed
to account for some schizophrenic symptomatology. Inhibitors,research,lifescience,medical To date, the only endophenotype whose linkage analysis has pointed to a specific candidate mechanism for neuronal dysfunction in schizophrenia comes from the work on the sensory gating dysfunction by the group led by Freedman.5 The paradigm used was to present to the subject pairs of identical stimuli. Normal subjects diminish the amplitudes of the P50 wave response to Inhibitors,research,lifescience,medical the second stimulus, whereas schizophrenic
patients consistently have a deficit in P50 inhibition.79 This deficit is present in the unaffected parents of schizophrenic probands, who have themselves an ancestral family history of schizophrenia, but not in parents without such histories.80 Furthermore, the families of early-onset schizophrenia show bilineal inheritance of the P50 inhibitory deficit, ie, both parents are affected.81 Thus, bilineal inheritance may be related to more severe and earlier illness onset. Animal studies Inhibitors,research,lifescience,medical showed that the inhibition of the second stimulus is mediated through cholinergic activation Inhibitors,research,lifescience,medical of hippocampal interneurons mediated via α7 nicotinic receptors. In schizophrenics and their relatives, nicotine transiently normalizes the deficit in P50 inhibition,82 as predicted from the animal model. The gene encoding the α7 nicotinic receptor is localized in the region 15q14, a region of chromosome 15 found Inhibitors,research,lifescience,medical to be linked to schizophrenia in several genome scans. Freedman et al37 showed that the P50 defect maps to the site of the α7 nicotinic receptor gene with a lod score of 5.3 under an autosomal find protocol dominant model. Replication of these data, identification of the molecular
abnormality, and determination of the role of and the abnormality in the pathogenesis of schizophrenia are necessary as the next steps. Eye movement Hundreds of studies have described the characteristic eye-movement dysfunction (HMD) in schizophrenic patients (for a review, see reference 83). This smooth pursuit dysfunction is stable over time,84 present during symptom remission,85 and familial, as it is found in almost 50% of unaffected relatives.85 Schizophrenic patients and their relatives also demonstrate a deficiency in their ability to inhibit reflex saccades to the target.86 Antisaccades EMD is found only in relatives of schizophrenic patients who themselves have increased rates of errors. These data suggest that abnormal smooth pursuit and saccade dysfunction are familial.