Michael S. Mega, Ivo D. Dinov, Linda Lee, Roger P. Woods, Paul M. Thompson, Colin J. Holmes, Carla L. Back, D. Louis Collins, Alan C. Evans and Arthur W. Toga
Laboratory of Neuro Imaging and Alzheimer's Disease Center, Department of Neurology, Division of Brain Mapping, UCLA School of Medicine, Los Angeles, California 90095
Montreal Neurological Institute, McGill University, Montreal, Canada
Background: Memory impaired patients with a retrieval deficit (RT) have been thought to spare Papez's circuit compared to those with an amnestic disorder (AM) regardless of the pathophysiology underlying their deficit. It is unknown if additional network dysfunction subserves these two memory disorders.
Methods: Eighteen patients who presented to the UCLA Memory Disorders Clinic, evaluated with neuropsychological testing and resting [99mTc]-HMPAO single photon emission computed tomography (SPECT), were matched across all cognitive tasks and divided equally into those with an AM and those with an RT based on Rey Auditory Verbal Learning Test performance. SPECT studies, registered to a probabilistic anatomic atlas, normalized across group mean and variance intensity levels, were subjected to a voxel-by-voxel subtraction of the RT minus AM groups. Sub-Volume Thresholding (SVT) corrected random lobar noise to produce a 3D cortical significance map.
Results: Bilateral anterior cingulate cortex and left medial temporal cortex showed the most profoundly increased perfusion followed by right dorsolateral prefrontal cortex for the RT minus AM comparison.
Conclusion: Compared to patients with an AM, regardless of the underlying pathophysiology, patients with a RT have preserved medial temporal encoding, and cingulate/dorsolateral prefrontal cognitive-executive circuit activity.
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