55 More recently, Engel and Fries56 have suggested that synchronized beta-band activity serves the maintenance of the actual sensorimotor or cognitive states. In contrast to gamma-band activity, the role of beta-band oscillations has been less explored in SCZ. Uhlhaas et al45 showed a pronounced impairment in long-range synchronization deficits in chronic SCZ

patients Inhibitors,research,lifescience,medical during perceptual organization This is consistent with evidence highlighting the role of beta-band oscillations in establishing transient patterns of interactions across larger distances in oscillatory networks.14 Further evidence for an involvement of disturbed betaband oscillations in cognitive deficits in SCZ was reported by Ford and colleagues.57 The authors hypothesized that SCZ patients may fail to adequately predict the causes of sensory perception which Inhibitors,research,lifescience,medical could, for example, lead to learn more self-generated speech acts being assigned to an external source as the result of a failure in the efference copy.58

To investigate this hypothesis, Inhibitors,research,lifescience,medical Ford et al recorded EEG activity prior to self-generated speech vs a perception condition during which self-generated utterances were played back to the participants. Results showed that the phase-locking of beta-band oscillations was larger in the prespeech than in the prelistening interval. In SCZ patients, however, beta-band synchrony in the prespeech condition was

reduced relative to controls and this reduction was particularly pronounced in patients with a history of auditory hallucinations. Inhibitors,research,lifescience,medical The authors suggest that the synchronized beta-band activity reflects a forward model which dampens auditory responsiveness to selfgenerated speech. In SCZ patients, this forward model is impaired and, as a result, self-generated Inhibitors,research,lifescience,medical speech acts may be experienced as an externally generated percept. This hypothesis is consistent with recent evidence that beta-band oscillations mediate mainly top-down activity, and hence are critically involved in the prediction of upcoming of sensory events while gamma-band oscillations, at least in sensory cortices, are involved in feedforward signaling.59 This distinction is supported by the differential laminar expression of beta and gamma-band oscillations, respectively.60 In vitro and in vivo recordings show that gamma-band activity is prominently generated in superficial layers 2/3 of the cortex,61 the main origin of feed forward connections, whereas beta oscillations are mainly found in infragranular layers,62 from which feedback projections originate preferentially.