A negative symptom of schizophrenia is an expressionless face.
Negative symptoms when it comes to psychological or mental disorders refers to symptoms that are absent or diminished once a person develops a condition such as schizophrenia. If a person showed a full range of facial expressions- smiling, laughter, anger, fear and pain- before they were diagnosed with schizophrenia,and then turned expressionless after being diagnosed with schizophrenia, it is a negative symptoms (absence or removal of a previous behavior or phenomenon).