Functional brain asymmetry, attentional modulation, and interhemispheric transfer in boys with Tourette syndrome

Abstract

We tested the hypothesis that children with Tourette syndrome (TS) would exhibit aberrant brain lateralization compared to a healthy control (HC) group in an attention-modulation version of a verbal dichotic listening task using consonant-vowel syllables. The modulation of attention to focus on the right ear stimulus in the dichotic listening situation is thought to involve the same prefrontal attentional and executive functions that are involved in the suppression of tics, whereas, performance when focusing attention on the left ear stimulus additionally involves a callosal transfer of information. In light of presumed disturbances in transfer of information across the corpus callosum, we hypothesized that children with TS would, however, have difficulty modulating the functional lateralization that ensues through a shift of attention to the left side. This hypothesis was tested by exploring the correlations between CC size and left ear score in the forced-left condition. Twenty boys with TS were compared with 20 age- and handedness-matched healthy boys. Results indicated similar performance in the TS and HC groups for lateralization of hemispheric function. TS subjects were also able to shift attention normally when instructed to focus on the right ear stimulus. When instructed to focus attention on the left ear stimulus, however, performance deteriorated in the TS group. Correlations with CC area further supported the hypothesized presence of deviant callosal functioning in the TS group.

Fig. 1

Mean correct reports for the right and the left ear split for attentional condition and for the Tourette syndrome (TS) and the healthy control (HC) groups.

Fig. 2

Scatter plots of individual performance for the three attention conditions. The diagonal line is a symmetry line=45°. All individuals falling below the line have a right ear advantage (REA) and all individuals falling above the line have a left ear advantage (LEA).

Fig. 3

Residuals for left ear performance and CC size (controlled for whole brain volume), showing separate fit lines for the TS only and the HC group.

Fig. 4

Mean correct reports for the right and the left ear in the forced-left condition for the Tourette syndrome (TS) and the healthy control (HC) groups.