The Inverse Relationship Between Nonverbal Intelligence and the Latency of the Hoffmann Reflex from the Right and Left Thenar Muscles in Right- and Left-Handed Subjects

Abstract

The relationship between nonverbal reasoning ability and the latency of the Hoffmann (H) reflex was studied in right- and left-handed subjects. The nonverbal reasoning ability was assessed by the Cattell's Culture Fair Intelligence test. Hand preference was assessed by the Edinburgh Handedness Inventory. Hoffmann reflex was recorded from thenar muscles of the right and left thumbs. In left-handers (total sample), IQ was found to be significantly and negatively linearly related to the H-reflex latency from the left side. In strong left-handers, there was a significant negative linear relationship between IQ and the H-reflex latency from right and left sides, but with a higher correlation for the left side. In weak lefthanders, IQ did not show any significant relation to the H-reflex latencies from the right and left sides. In right-handers (total sample), there was a significant negative linear correlation between IQ and the H-reflex latency from the right side. In right-handed women without familial sinistrality (FS -), IQ was found to be inversely related to the H-reflex latency from the right and left side, but with a higher correlation for the right side. In right-handed women with FS, IQ did not show any significant relation to the H-reflex latency from the right and left sides. In right-handed men with right eye preference and FS-, IQ was found to be negatively linearly related to the H-reflex latency from the right and left sides equally. In right-handed men with right eye FS +, mixed eye FS -, +, mixed eye-right foot (FS -), mixed eye-mixed foot, and left eye preference there was no significant relationship between IQ and the H-reflex latency from the right and left sides. Only in strong left-handers there was a significant, positive linear correlation between IQ and the right minus left (R-L) difference of latencies. The H-reflex latency from the right and left sides was not significantly correlated with the R-L difference of latencies in left-handers. In right-handed women with right eye preference FS -, and in right-handed men with right eye preferences FS -, The H-reflex latency from the right side was found to be positively linearly correlated with the R-L difference of latencies. In right-handed women FS +, and in right-handed men FS +, and mixed or left eye preference, the H-reflex latency from the left side was found to be negatively linearly related to the R-L difference of latencies. The results of this work support the speed concept of cerebral information-processing with regard to intelligence, even at the spinal cord level The exceptions from this rule concerning FS+ and nonright eye preference were discussed. It was suggested that the factors such as handedness, FS, eye and foot preferences should be taken into consideration in studies related to the biological basis of intelligence.

Key Words:

• Hoffmann reflex
• nonverbal intelligence
• spinal cord
• handedness
• human