Attenuation of brain high frequency electrocortical response after thiopental in early stages of Alzheimer's dementia

Rationale. Pathological brain regions generate proportionately less high fr equency (beta) activity than non-pathological regions, a phenomenon accentu ated by barbiturate administration. Objectives: Previously, we reported a l oss of high-frequency brain electrical response to thiopental in dementia o f the Alzheimer's type (DAT). The current study examines whether this pheno menon may be detected in early stages of the illness. Methods, Using quanti tative electroencephalography, we examined power in the 20-28 Hz band in pa tients with early DAT (n=7, age 71.0 +/- 3.2 years, Folstein Mini Mental St ate Score, MMSE 26.2 +/- 0.8). normal controls (n=8, age 74.3 +/- 3.2 years , MMSE 29.0 +/- 0.3) and subjects with moderately severe DAT (n=6, age 76.6 +/- 3.0 years, MMSE=12.5 +/- 3.7) at baseline and following an intravenous bolus of thiopental (0.5 mg/kg). Results: No significant group differences in beta power were detectable at baseline. In response to thiopental, earl y DAT subjects compared to controls showed a significantly smaller beta pow er response in the frontal region at 1-3 min postinjection. Losses were sma ller than those of subjects with moderately severe DAT and demonstrated a n on-linear correlation with decreases in cognitive function as assessed by t he MMSE score (r(2)=0.75). Conclusion: In early stages of DAT, a barbiturat e challenge may unmask abnormalities in brain electrical activity not seen at base-line. Such changes may reflect underlying cortical deafferentation.