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Disrupted conscious access linked to altered brain connectivity in psychosis

The Journal of Neuroscience
Reuters Health - 25/11/2020 - People with schizophrenia have a higher threshold for conscious perception, which correlates with altered cerebral connectivity, new findings show.

Individuals who had bipolar disorder with psychotic features also had deficits in conscious access compared with those with bipolar disorder but no psychosis and with healthy controls, Dr. Josselin Houenou of APHP, Hopitaux Universitaires Mondor in Creteil, France, and colleagues report in The Journal of Neuroscience.

The findings support the global neuronal workspace (GNW) theory, which posits that conscious access requires global activation of long-distance neuronal networks.

"The GNW theory assumes that conscious perception arises from the stabilization of neuronal activity within a distributed network, rendering a specific piece of information reportable to others," Dr. Houenou and his colleagues explain.

Increased threshold for conscious perception and altered cerebral connectivity occur in schizophrenia and bipolar disorder, the authors note, but it's unclear whether these deficits are related to one another, or how they relate to psychosis.

To investigate, they compared consciousness threshold to cerebral structural connectivity in 97 people, including 46 healthy controls, 25 schizophrenia patients, 17 bipolar disorder patients with a history of psychosis, and nine bipolar disorder patients with no psychosis history.

They measured consciousness threshold with visual masking and cerebral connectivity with diffusion magnetic resonance imaging (MRI) tractography. They looked specifically at bundles of fibers involved in consciousness based on the GNW theory: the inferior-fronto-occipital fasciculus (IFOF), cingulum long fibers (CLF) and corpus callosum. Two non-consciousness-related bundles served as controls.

The masking threshold was 53 ms for study participants without psychosis and 63 ms for those who had psychosis (P<0.001). Among bipolar patients, average threshold was 49 ms for those without psychotic symptoms and 63 ms for those with psychotic symptoms (P=0.02).

The masking threshold was similar for the bipolar disorder patients without psychosis and the controls (49 ms vs. 54 ms).

For patients and controls, masking threshold negatively correlated with mean generalized fractional anisotropy in the IFOF, CLF and corpus callosum, but not in the control bundles.

The findings support the theory, in schizophrenia research and psychiatry at large, that people with psychosis rely too much on "prayer" - their beliefs - and not enough on visual and other sensory information, Dr. Houenou told Reuters Health in a phone interview.

"Patients do not have a good enough conscious access to external stimuli," he said. "That's why they do not use enough of that external stimulation."

If confirmed, findings could help guide therapy for patients with psychosis, he added, by showing them that they should rely more on their senses and less on their own beliefs.

SOURCE: https://bit.ly/3pUMjDL The Journal of Neuroscience, online November 23, 2020.

By Anne Harding

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