Line bisection and cerebellar damage

BACKGROUND: The cerebellum plays a role in higher-order cognitive processes, although the evidence concerning spatial cognition is not definite. OBJECTIVE: To investigate the role of the cerebellum in setting the midpoint of a horizontal line and to assess the role of visual monitoring of the movement of the upper limb. METHODS: Twelve patients, 6 with left-sided and 6 with right-sided cerebellar damage, and 12 control participants, marked the midpoint of horizontal lines with their left or right hand, under conditions of present versus absent visual control of the movement of the upper limb. RESULTS: When visual feedback was available, the patients' accuracy was comparable to that of control participants with a minor leftward bias. Without visual feedback, controls and right-sided cerebellar patients exhibited a rightward bias. Conversely, left-sided cerebellar patients still showed a leftward bias. CONCLUSIONS: The leftward bias may be related to the visual monitoring of the movement of the upper limb, being reversed when this is not available. Under these conditions, kinesthetic information becomes more relevant, and may contribute to the rightward bias. This effect is not shown by left cerebellar patients, possibly due to the disconnection between the left cerebellum and the right hemisphere, involved in spatial cognition.