Soft neurological signs and schizophrenia - a looking glass into core pathology?

Cvetić et al (2009) raise extremely interesting points in chosing to investigate soft neurological signs, which have arguably been forgotten by many psychiatrists. These abnormalities are found in 50-65% of patients with schizophrenia, and yet neurological examinations seem to be so rarely performed clinically (Heinrichs & Buchanan 1988). Perhaps it is time for us to consider again how important these signs might be as a diagnostic marker. In support of this suggestion is evidence showing that neurological abnormalities of motor function might actually be quite central to the disease process. Ridler et al. (Ridler 2006) have recently found that people with schizophrenia showed both delayed motor development in early childhood (implying abnormalities of development of motor systems) and impaired adult executive function. Additionally, normal subjects showed a positive correlation between motor development and executive function (Ridler 2006). This seems to imply that infant motor function and adult executive function are closely linked, and that developmental abnormalities of motor function might be extremely important to the pathogenesis of schizophrenia, rather than an idiosyncracy of these patients. Indeed, the idea that deficits in early formation of motor systems might actually cause schizophrenia has received some support Evidence from neuroimaging further supports the idea that abnormalities of motor cortical and subcortical regions of the brain are central to schizophrenia. Ridler et al. (2006) examined schizophrenic patients and showed a discontinuity between Infant Motor Development (IMD) and both premotor gray matter volume and fronto-parietal white matter volumes in adulthood. They argue that, since neuronal connectivity deficits are known to be important in the pathogenesis of schizophrenia, this implies that the premotor cortex is essentially disconnected in these patients, and cannot play its normal role in motor function (Ridler 2006). It is also argued that, since the motor cortex (with its links to the cerebellum) is important in adult executive function, this disconnectivity might also explain executive deficits in schizophrenic adults (Heyder 2004, Erlenmeyer-Kimling 2000). This evidence strongly suggests that abnormal motor development plays a central role in causing some of the main deficits observed in adult schizophrenia. Importantly, it is fairly easy to see how underlying deficits in motor function might produce not only executive deficits, but also Soft Neurological Signs, which we observe in schizophrenia. For example, premotor cortical disconnection might account for deficiencies in sensorimotor integration – for example in the " opposition index finger-thumb " test, dysdia-dochokinesia, and finger-nose test, and …