A large literature has demonstrated an abnormal sense ofagency (SOA) in schizophrenic individuals. One limitation ofsuch studies is that they focus exclusively on cognitive orperceptual judgments, thus failing to address affective aspectsof SOA. In our recent work, we have used instrumentaldivergence – the distance between outcome probabilitydistributions associated with available actions – as a formalmeasure of agency, demonstrating an influence of this noveldecision variable on behavioral choice preferences andassociated neural computations in neurotypical adults. Here,we show that the preference for high instrumental divergence(i.e., for high-agency environments) is significantlymodulated by individual differences in positive and negativeschizotypy dimensions. Implications for future assessmentsof clinical populations are discussed.

Cerebellar mutism is a rare finding associated with resection of posterior fossa tumors or cerebellar hemorrhages. We reviewed the medical records of six children, aged 6 to 12 years, who developed cerebellar mutism after resection of a posterior fossa mass or as a result of posterior fossa trauma. From 1989 to 1994, 210 children underwent posterior fossa resection at our institution, and four developed mutism (an incidence of 1.6%). All four patients had primitive neuroectodermal tumors. The fifth patient experienced trauma, and another patient had an arteriovenous malformation (AVM). In four children, hydrocephalus developed as a result of their tumor or AVM. Four developed cerebellar mutism 24 to 48 hours after surgery or trauma, and one developed cerebellar mutism 5 days after surgery, coincident with hydrocephalus. In one, mutism occurred after a second resection was performed for a recurrence of his posterior fossa tumor. Cerebellar mutism lasted 10 days in one patient and 2 to 8 weeks in the other four. Dysarthria was apparent in four patients during the recovery phase. We suggest trauma to the dentate nucleus and/or its outflow tract, the superior cerebellar peduncle, as a cause of reversible mutism. Because posterior fossa tumors are common in children, mutism should be recognized as an important side effect of surgery.