Patterns of cortical activity and memory performance in Alzheimer's disease.

BACKGROUND: Declarative memory changes are the hallmark of Alzheimer's disease, although their functional neuroanatomy is not restricted to a single structure. Factor analysis provides statistical methods for evaluating patterns of cerebral changes in regional glucose uptake. METHODS: Thirty-three Alzheimer's patients and 33 age- and gender-matched control subjects were studied with magnetic resonance imaging and positron emission tomography with [(18)F] deoxyglucose. During the tracer-uptake period, subjects performed a serial verbal learning task. Cortical activity was measured in 32 regions of interest, four in each lobe on both hemispheres. RESULTS: Factor analysis with varimax rotation identified seven factors explaining 80% of the variance ("parietal cortex," "occipital cortex," "right temporo-prefrontal areas," "frontal cortex," "motor strip," "left temporal cortex," and "posterior temporal cortex"). Relative to control subjects, Alzheimer's patients showed significantly reduced values on the factors occipital cortex, right temporo-prefrontal areas, frontal cortex, and left temporal cortex. The factor temporo-prefrontal areas showed large differences between patients with good and poor performance, but little difference when control subjects were similarly divided. CONCLUSIONS: Findings suggest that Alzheimer's disease is characterized by altered patterns of cortical activity, rather than deficits in a single location, and emphasize the importance of right temporo-prefrontal circuitry for understanding memory deficits.

Dorsal striatal size, shape, and metabolic rate in never-medicated and previously medicated schizophrenics performing a verbal learning task.

BACKGROUND: Magnetic resonance imaging and positron emission tomography were used to study the size and metabolic rate of the caudate and the putamen in 18 patients with schizophrenia (n=16) or schizo-affective disorder (n=2) and 24 age- and sex-matched control subjects. METHODS: The patients were either never medicated (n=7) or drug free (n=11) for a median of 3 weeks. During uptake of fludeoxyglucose F 18, all patients performed a serial verbal learning test. Positron emission tomographic and magnetic resonance imaging scans were coregistered, and the caudate and the putamen were traced on the magnetic resonance image. RESULTS: The striatum had a significantly lower relative metabolic rate in schizophrenics than in controls. Never-medicated patients had lower metabolic rates in the right putamen (ventral part of the dorsal striatum) than previously medicated patients. The caudate was significantly smaller in never-medicated patients than in controls and largest in previously medicated patients. Patients with higher relative metabolic rates in the putamen scored higher on the Abnormal Involuntary Movements Scale. CONCLUSIONS: The findings are consistent with reports of striatal enlargement in previously medicated patients and size increases after neuroleptic treatment. Never-medicated patients, in contrast, had ventral striatal structures that were smaller and less active than those observed in controls and previously medicated patients.