Differentiation between deviant trajectory planning, action planning, and reduced psychomotor speed in schizophrenia

Abstract

Introduction. Abnormal psychomotor behaviour in schizophrenia might be based on separate deficits. Here we studied the relationship between trajectory planning, action planning, psychomotor speed, and indices of cognitive functioning in a large group of stabilised patients with schizophrenia.

Method. Sixty-one patients and 30 controls were tested. Trajectory planning was assessed in a graphic task in which sequences of single lines, gradually changing in direction, had to be drawn. Shifts to a comfortable drawing direction reflect anticipatory trajectory planning. Action planning was evaluated in a task in which figures varying in complexity and familiarity had to be copied. Psychomotor speed was measured by use of a simple line copying task. Measures of information processing speed, attention, working memory, and problem solving were derived from neuropsychological tests.

Results. Patients much more often opted for the unusual bottom-to-top direction to draw the vertical lines in the drawing task. They changed the line orientation less often than the controls did. In the patient group, these trajectory planning indices did not correlate with measures of action planning, psychomotor speed, or neuropsychological test scores.

Conclusion. Deviant trajectory planning strongly characterises schizophrenia, and is independent from action planning deficits and reduced psychomotor speed.

Keywords:

• Action planning
• Psychomotor speed
• Schizophrenia
• Trajectory planning

Acknowledgments

This research was partly financially supported by an unrestricted grant from Janssen-Cilag Belgium. Janssen-Cilag did not have any role in the study design; in the conduction, collection, analysis, or interpretation of the data; in the writing of the manuscript; or in the (decision of) publication of this paper. The authors would like to thank Leen Gielen and Sara Vermeylen for their help in the administration of the tests/tasks, and Lianne Vermeeren for her help in the analysis of the Line-Sequencing Task. The authors would also kindly like to thank all the participants of the study.