This question is basically asking for the differential diagnosis of symptoms of ' sadness of mood, talking less and staying on the bed" in a patient of schizophrenia who has been staed on antipsychotics. 1. The sadness of mood and decreased interaction can be of course due to depression 2. Negative symptoms of schizophrenia have a similar presentation where avolition can result in 'staying on the bed' and asociality and alogia may result in decrease interaction 3. Fuher, the use of antipsychotics can cause drug-induced parkinsonism which again looks quite similar to negative symptoms. The fouh option 'responding to external stimuli' doesn't explain the symptoms and hence is the answer