Cannabis use is consistently linked to persistent cognitive deficits and an elevated risk of schizophrenia-like psychoses, with the degree of risk influenced by dose, duration, age of first use, and genetic factors, including a partially shared genetic predisposition with schizophrenia. In healthy humans, THC produces transient, dose-dependent psychotic symptoms and cognitive effects that can be reduced by cannabidiol. Rodent studies confirm these findings and show that adolescent exposure leads to structural brain changes and impaired synaptic plasticity in fronto-limbic systems. Over-activation of the endocannabinoid system during adolescence may alter brain maturation, causing long-lasting changes. The assessment of medical cannabis must consider populations at higher risk for psychiatric and cognitive complications.
Disturbances in the minimal Self—the basic, pre-reflective sense of embodied experience—are linked to episodic memory impairments in first-episode psychosis (FEP). In a pilot study using immersive virtual reality, 10 FEP patients and 35 matched healthy controls experienced a full-body illusion with either synchronous or asynchronous visuomotor stimulation to induce strong or weak embodiment. Under strong embodiment, FEP patients performed significantly worse than controls in recognizing contextual information, though their retrieval phenomenology ratings were similar. Under weak embodiment, FEP patients performed similarly to controls in contextual recognition but rated retrieval phenomenology significantly lower. Higher schizotypy in controls correlated with a diminished sense of Self and poorer episodic memory. The findings suggest that targeting minimal Self-disorders may improve episodic memory and psychosocial outcomes in schizophrenia spectrum disorders.
Cannabis use is associated with an increased risk of developing psychotic disorders among people already at clinical high risk for psychosis. In a prospective study of this population, cannabis use was linked to a higher incidence of psychotic disorders and to more persistent psychotic symptoms, as well as poorer functional outcomes. The findings strengthen evidence that cannabis acts as a risk factor for psychosis, though the direction of causality remains debated.
Error detection relies on two distinct brain systems: one tied to conscious awareness and another that operates without it. In people with schizophrenia, the conscious error-detection system is impaired, as shown by a reduced Error-Related Negativity (ERN) in EEG and MEG recordings during a speeded number comparison task. However, on trials where stimuli were presented unconsciously, both schizophrenia patients and healthy controls could still evaluate their own errors above chance levels. This dissociation indicates that non-conscious performance monitoring remains intact in schizophrenia, while conscious metacognition is specifically altered.