The original dopamine hypothesis began being questioned, as many were unsure of the association between schizophrenic symptoms and dopamine activity. The positive symptoms of schizophrenia involve hallucinations and delusions, which is done by increased subcortical release of dopamine (and augments D2 receptor activation). The negative symptoms of schizophrenia involve lack of motivation, impaired speech (caused from reduced dopamine receptor activation), etc. Dopaminergic and serotonergic deviations have bee known to be major contributors of the positive and negative schizophrenic symptoms.