Relationship between memantine serum levels and COG shift. Memantine serum levels are plotted against the shift of the y coordinate of the COG after training. Positive values indicate a shift in a medial, negative values a shift in a lateral direction. Linear correlation analysis reveals no significant correlation. Subjects who participated in the single dosage experiment are red-labelled, subjects who participated in the ascending dosage experiment are blue-labelled, and subjects who participated in the control experiment (repeated low dosage) are green-labelled. Memantine serum levels of the single dosage experiment refer to the values obtained 5 hours after drug administration.