QUANTITATIVE-ANALYSIS OF HEMISPATIAL NEGLECT IN THE INTRACAROTID SODIUM AMOBARBITAL (ISA) TEST

There are dramatic changes in the electroencephalogram of the inactiva ted hemisphere in the intracarotid sodium amobarbital test. One of the more profound behavioral changes during this procedure is left hemisp atial neglect accompanying right hemisphere inactivation. The present study was designed to ascertain whether there was a clear relationship between the degree of hemispheric inactivation (as measured by the el ectroencephalogram) and the degree of left hemispatial neglect during this procedure. Sixty-nine participants undergoing right hemisphere in tracarotid sodium amobarbital testing were presented with a random let ter cancellation test at various points during the procedure. Neglect was quantified as significant, moderate, minimal, or none, based on ho w many target letters the patients missed. The simultaneous electroenc ephalogram from each of these testing points was spectrally analyzed a nd topographic maps were generated. The degree of neglect was then com pared with the comparable topographic map. It was found that as the am obarbital-induced right hemispheric dysfunction regressed, the degree of neglect lessened in a systematic fashion, as did the profound elect roencephalographic changes induced by the drug. Thus, there is a clear relation between the degree of hemispheric inactivation induced by th e amobarbital and the degree of left hemispatial neglect. This relatio nship held regardless of side of hemispheric language dominance or epi leptic focus. These results replicate previous findings that right hem isphere inactivation during the intracarotid sodium amobarbital test r esults in left hemispatial neglect. They extend these findings by clea rly showing that neglect changes in a quantitative fashion (rather tha n being an all-or-none phenomenon) and further, show that there is a c lear relationship between the severity of neglect and the degree of he mispheric dysfunction.