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

Abstract

Pathological brain regions generate proportionately less high-frequency (beta) activity than non-pathological regions, a phenomenon accentuated by barbiturate administration. Previously, we reported a loss of high-frequency brain electrical response to thiopental in dementia of the Alzheimer's type (DAT). The current study examines whether this phenomenon may be detected in early stages of the illness. Using quantitative electroencephalography, we examined power in the 20-28 Hz band in patients with early DAT (n=7, age 71.0+/-3.2 years, Folstein Mini Mental State 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). No significant group differences in beta power were detectable at baseline. In response to thiopental, early DAT subjects compared to controls showed a significantly smaller beta power response in the frontal region at 1-3 min postinjection. Losses were smaller than those of subjects with moderately severe DAT and demonstrated a non-linear correlation with decreases in cognitive function as assessed by the MMSE score (r2=0.75). In early stages of DAT, a barbiturate challenge may unmask abnormalities in brain electrical activity not seen at baseline. Such changes may reflect underlying cortical deafferentation.