Determinants of Benton Facial Recognition Test performance in normal adults.

Clinical investigations have found that lesions of the right cerebral hemisphere can disrupt face perception. Much less is known about the determinants of facial discrimination in healthy adults, although age-related differences in many cognitive abilities have been shown to correlate with simple processing speed and variation in regional brain volumes. In this study, 174 healthy adults between the ages of 20 and 92 were asked to match pictures of unfamiliar faces. After their performance was regressed on age, sex, education, and perceptual comparison speed, adding terms for frontal lobe volume, nonfrontal volume, and ventricle-to-brain ratio (VBR) derived from magnetic resonance imaging improved the model and accounted for 35% of the variance in facial discrimination. VBR and processing speed alone accounted for nearly 34% of the variance. These findings suggest that both normal atrophic brain changes and decreases in processing speed contribute to individual differences in facial discrimination.

MRI volumes of amygdala and hippocampus in non-mentally retarded autistic adolescents and adults.

OBJECTIVE: To determine whether volumes of hippocampus and amygdala are abnormal in people with autism. BACKGROUND: Neuropathologic studies of the limbic system in autism have found decreased neuronal size, increased neuronal packing density, and decreased complexity of dendritic arbors in hippocampus, amygdala, and other limbic structures. These findings are suggestive of a developmental curtailment in the maturation of the neurons and neuropil. METHODS: Measurement of hippocampus, amygdala, and total brain volumes from 1.5-mm coronal, spoiled gradient-recalled echo MRI scans in 14 non-mentally retarded autistic male adolescents and young adults and 14 individually matched, healthy community volunteers. RESULTS: Amygdala volume was significantly smaller in the autistic subjects, both with (p = 0.006) and without (p = 0.01) correcting for total brain volume. Total brain volume and absolute hippocampal volume did not differ significantly between groups, but hippocampal volume, when corrected for total brain volume, was significantly reduced (p = 0.04) in the autistic subjects. CONCLUSIONS: There is a reduction in the volume of amygdala and hippocampus in people with autism, particularly in relation to total brain volume. The histopathology of autism suggests that these volume reductions are related to a reduction in dendritic tree and neuropil development, and likely reflect the underdevelopment of the neural connections of limbic structures with other parts of the brain, particularly cerebral cortex.