Schizophrenia
A psychotic disorder rooted in dysregulated dopaminergic signalling that produces positive symptoms through subcortical excess and negative/cognitive symptoms through cortical deficit, diagnosed on duration and function rather than any single test.
First principles
Psychosis is a failure of the brain's system for weighting what is real
Normal perception depends on the brain assigning appropriate 'salience' (significance) to sensory input and internal thought, filtering signal from noise via mesolimbic dopaminergic pathways. In schizophrenia, excess subcortical dopamine transmission causes aberrant salience: irrelevant stimuli and internally generated thoughts are tagged as intensely meaningful or externally real. The brain then constructs an explanation for these false salience signals: this is the origin of delusions (a rationalisation of aberrant experience) and hallucinations (internal events, such as one's own thoughts, misattributed to an external source). Positive symptoms are therefore not 'extra' abnormal contents but the downstream product of a single upstream dopaminergic fault.
Educational content pending clinical review. Not medical advice.