Tardive dyskinesia and associated cognitive disorders: a convergent neuropsychological and neurophysiological...

This study sought to assess whether tardive dyskinesia (TD) related differentially to two types of cognitive functioning in schizophrenia. Thirteen schizophrenics with severe formal thought disorders (+FTD) were matched for age, sex, education, chronicity, dosage, hospital care, with 13 schizophrenics selected for absence of or minimal formal thought disorders (-FTD). TD and neuroleptic dosage were analyzed in relation to cognitive and motor tests of the Luria-Nebraska (L-N) battery and to attentional evoked potentials (EPs). EPs were recorded at electrodes Fz, Cz, and Pz, in a dichotic signal detection task (oddball paradigm), during attention and inattention conditions. Group differences on attentional EPs replicated published results with flatter and smaller positive waves in +FTD patients and larger late negative waves (FzN4-N7) in -FTD patients. Controlling for dosage, the following were the best groups discriminators. +FTD schizophrenics presented more severe dyskinesia in the orofacial area and poorer verbal scores on L-N. Severe TD correlated with smaller N1 amplitudes. +FTDs also presented distinct attentional EP deficits with abnormally small P3a, a correlate of deficient categorization and orienting. Neuroleptic dosage was not directly correlated to any single motor or cognitive measure, nor to TD indices. The hypothesis of a differential association of TD with distinct attentional/cognitive disorders was generally supported.