Individuals with 22q11.2 deletion syndrome show intact prediction but reduced adaptation in responses to repeated sounds: Evidence from Bayesian mapping.

One of the most common copy number variants, the 22q11.2 microdeletion, confers an increased risk for schizophrenia. Since schizophrenia has been associated with an aberrant neural response to repeated stimuli through both reduced adaptation and prediction, we here hypothesized that this may also be the case in nonpsychotic individuals with a 22q11.2 deletion. We recorded high-density EEG from 19 individuals with 22q11.2 deletion syndrome (12-25 years), as well as 27 healthy volunteers with comparable age and sex distribution, while they listened to a sequence of sounds arranged in a roving oddball paradigm. Using posterior probability maps and dynamic causal modelling we tested three different models accounting for repetition dependent changes in cortical responses as well as in effective connectivity; namely an adaptation model, a prediction model, and a model including both adaptation and prediction. Repetition-dependent changes were parametrically modulated by a combination of adaptation and prediction and were apparent in both cortical responses and in the underlying effective connectivity. This effect was reduced in individuals with a 22q11.2 deletion and was negatively correlated with negative symptom severity. Follow-up analysis showed that the reduced effect of the combined adaptation and prediction model seen in individuals with 22q11.2 deletion was driven by reduced adaptation rather than prediction failure. Our findings suggest that adaptation is reduced in individuals with a 22q11.2 deletion, which can be interpreted in light of the framework of predictive coding as a failure to suppress prediction errors.

Alteration of functional brain architecture in 22q11.2 deletion syndrome - Insights into susceptibility for psychosis.

The 22q11.2 deletion is one of the most common copy number variants in humans. Carriers of the deletion have a markedly increased risk for neurodevelopmental brain disorders, including schizophrenia, autism spectrum disorders, and attention deficit hyperactivity disorder. The high risk of psychiatric disorders associated with 22q11.2 deletion syndrome offers a unique possibility to identify the functional abnormalities that precede the emergence of psychosis. Carriers of a 22q11.2 deletion show a broad range of sensory processing and cognitive abnormalities similar as in schizophrenia, such as auditory and visual sensory processing, response inhibition, working memory, social cognition, reward processing and arithmetic processing. All these processes have a significant negative impact on daily life if impaired and have been studied extensively in schizophrenia using task-based functional neuroimaging. Here, we review task-related functional brain mapping studies that have used electroencephalography or functional magnetic resonance imaging to identify functional alterations in carriers with 22q11.2 deletion syndrome within the above mentioned cognitive and sensory domains. We discuss how the identification of functional changes at the brain system level can advance the general understanding of which neurobiological alterations set the frame for the emergence of neurodevelopmental disorders in the human brain. The task-based functional neuroimaging literature shows conflicting results in many domains. Nevertheless, consistent similarities between 22q11.2 deletion syndrome and schizophrenia have been found for sensory processing, social cognition and working memory. We discuss these functional brain alterations in terms of potential biomarkers of increased risk for psychosis in the general population.

Surprise responses in the human brain demonstrate statistical learning under high concurrent cognitive demand.

The ability to learn about regularities in the environment and to make predictions about future events is fundamental for adaptive behaviour. We have previously shown that people can implicitly encode statistical regularities and detect violations therein, as reflected in neuronal responses to unpredictable events that carry a unique prediction error signature. In the real world, however, learning about regularities will often occur in the context of competing cognitive demands. Here we asked whether learning of statistical regularities is modulated by concurrent cognitive load. We compared electroencephalographic metrics associated with responses to pure-tone sounds with frequencies sampled from narrow or wide Gaussian distributions. We showed that outliers evoked a larger response than those in the centre of the stimulus distribution (i.e., an effect of surprise) and that this difference was greater for physically identical outliers in the narrow than in the broad distribution. These results demonstrate an early neurophysiological marker of the brain's ability to implicitly encode complex statistical structure in the environment. Moreover, we manipulated concurrent cognitive load by having participants perform a visual working memory task while listening to these streams of sounds. We again observed greater prediction error responses in the narrower distribution under both low and high cognitive load. Furthermore, there was no reliable reduction in prediction error magnitude under high-relative to low-cognitive load. Our findings suggest that statistical learning is not a capacity limited process, and that it proceeds automatically even when cognitive resources are taxed by concurrent demands.

Brain connectivity in disorders of consciousness.

The last 10 years witnessed a considerable increase in our knowledge of brain function in survivors to severe brain injuries with disorders of consciousness (DOC). At the same time, a growing interest developed for the use of functional neuroimaging as a new diagnostic tool in these patients. In this context, particular attention has been devoted to connectivity studies-as these, more than measures of brain metabolism, may be more appropriate to capture the dynamics of large populations of neurons. Here, we will review the pros and cons of various connectivity methods as potential diagnostic tools in brain-damaged patients with DOC. We will also discuss the relevance of the study of the level versus the contents of consciousness in this context.

Preserved feedforward but impaired top-down processes in the vegetative state.

Frontoparietal cortex is involved in the explicit processing (awareness) of stimuli. Frontoparietal activation has also been found in studies of subliminal stimulus processing. We hypothesized that an impairment of top-down processes, involved in recurrent neuronal message-passing and the generation of long-latency electrophysiological responses, might provide a more reliable correlate of consciousness in severely brain-damaged patients, than frontoparietal responses. We measured effective connectivity during a mismatch negativity paradigm and found that the only significant difference between patients in a vegetative state and controls was an impairment of backward connectivity from frontal to temporal cortices. This result emphasizes the importance of top-down projections in recurrent processing that involve high-order associative cortices for conscious perception.