THE SIMON EFFECT AND ATTENTION DEFICITS IN GILLES-DE-LA-TOURETTES SYNDROME AND HUNTINGTONS-DISEASE

Tourette's syndrome and Huntington's disease have long been clinically associated with attentional deficits. In this study, we aimed to dete rmine the nature and quantify the extent of such deficits. A technique was devised to ascertain the efficiency with which Tourette's syndrom e and Huntington's disease patients could shift and direct attention a way from naturally expected stimulus-response (S-R) linkages. This was done by varying the relationships formed between stimulus and respons e location. Attentional efficiency was indicated by relative speed of responding to relevant (congruent) and irrelevant (incongruent) stimul i, in a paradigm developed from the Simon effect. There were five cond itions progressively increasing in complexity. The stimuli consisted o f left and right pointing arrows and, in some cases, various condition ality manipulations were also employed, such that in the presence of a certain symbol (i.e. 'x') the nature of the response had to be revers ed, whereas in the presence of an alternative symbol (i.e. '='), the r esponse was compatible with the direction of the arrow. As predicted, Tourette's syndrome and Huntington's disease patients, regardless of m edication or depression status and unlike controls, were particularly disadvantaged in responding to various conflicting S-R configurations. Tourette's syndrome and Huntington's disease patients may experience difficulties in making attentional shifts, or in inhibiting inappropri ate responses; they may also be more susceptible (than controls) to th e conflict that can arise when the spatial code formed for the stimulu s is irrelevant for selecting the appropriate response. We conclude th at our findings support the notion that cognitive deficits in Tourette 's syndrome and Huntington's disease may stem from abnormalities of th e major pathways interconnecting the basal ganglia and the frontal lob es.