Non-verbal intelligence impairments decline over time in schizophrenia


12 December 2006

Cognitive function in patients with schizophrenia appears to decline over time, but only specific areas are affected, study findings show.

Gary Morrison (Crichton Royal Hospital, Dumfries, UK) and colleagues report that non-verbal intelligence declines significantly over time in patients with schizophrenia compared with mentally healthy individuals, whereas this differential change is not seen for verbal intelligence.

The researchers examined the course of cognitive impairment in 43 people with schizophrenia and 12 individuals free from psychosis, who were aged an average of 61 years, over a 33-year period.

Cognitive function assessments carried out at baseline showed that schizophrenia patients had impairment in both verbal and non-verbal intelligence at baseline compared with estimated premorbid scores, as measured using the Mill Hill Vocabulary Scale (MHVS) and the Raven's Standard Progressive Matrices (RSPM), respectively. This impairment was not found in the control group, however.

At follow-up, there was a significant decline in non-verbal intelligence over time in patients compared with controls, with RSPM scores changing each year from an average of 0 to almost –0.3 in patients and from 0 to just –0.05 in controls.

This differential change over time was not seen for verbal intelligence, however, with scores changing very little from 0 each year for both groups.

Commenting on the findings in the British Journal of Psychiatry, Morrison et al rule out the development of dementia, adverse medication effects, and normal cognitive aging as possible explanations for their findings. They believe the decline in non-verbal cognitive function is genuine.

"Our results also suggest that cognitive decline is not global, that is it does not resemble a true dementia, but instead affects specific areas of cognition and may thus reflect ongoing pathological changes in certain areas of the brain or brain systems involved in visuospatial problem-solving and the fluid components of intelligence," the team concludes.



Source: Br J Psychiatry 2006; 189: 556–557