The cognitive and neural mechanisms underlying category-specific knowledge remain controversial. Here we report that, across multiple tasks (viewing, delayed match to sample, naming), pictures of animals and tools were associated with highly consistent, category-related patterns of activation in ventral (fusiform gyrus) and lateral (superior and middle temporal gyri) regions of the posterior temporal lobes. In addition, similar patterns of category-related activity occurred when subjects read the names of, and answered questions about, animals and tools. These findings suggest that semantic object information is represented in distributed networks that include sites for storing information about specific object attributes such as form (ventral temporal cortex) and motion (lateral temporal cortex).

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Event-related potentials and behavioral measures were obtained from young and elderly subjects while they performed two different auditory delayed match-to-sample tasks. In each experiment, subjects had to indicate whether an initial and a subsequent test sound were identical in two different conditions: one filled with distracting tone pips and one with no distractors. Electrophysiologically, elderly subjects had reduced attention-related activity over frontal regions. In addition, the distracting stimuli elicited an enhanced primary auditory evoked response in the elderly. The percentage of perseverative errors on the Wisconsin card sorting test, a putative measure of frontal lobe function, was positively correlated with the amplitude of the primary auditory evoked response in elderly subjects. Behaviorally, elderly subjects were impaired by distractors at long but not short delays. Taken together, these results suggest that increased distractibility and impaired sustained attention with aging may be due to altered prefrontal cortex function. These data support the loss of prefrontal suppression over the primary auditory regions with aging.

Naming pictures of objects from different categories (e.g. animals or tools) evokes maximal responses in different brain regions. However, these 'category-specific' regions typically respond to other object categories as well. Here we used stimulus familiarity to further investigate category representation. Naming pictures of animals and tools elicited category-related activity in a number of previously identified regions. This activity was reduced for familiar relative to novel stimuli. Reduced activation occurred in all object responsive areas in the ventral occipito-temporal cortex, regardless of which category initially produced the maximal response. This suggests that object representations in the ventral occipito-temporal cortex are not limited to a discrete area, but rather are widespread and overlapping. In other regions (e.g. the lateral temporal and left premotor cortices), experience-dependent reductions were category specific. Together, these findings suggest that category-related activations reflect the retrieval of information about category-specific features and attributes.

We compared the predictive value of cerebral perfusion as measured by arterial-spin labeling magnetic resonance imaging (ASL-MRI) with MRI-derived hippocampal volume for determining future cognitive and functional decline and subsequent conversion from mild cognitive impairment to dementia. Forty-eight mild cognitive impairment subjects received structural and ASL-MRI scans at baseline and clinical and neuropsychologic assessments annually. Thirteen subjects became demented during the period of longitudinal observation (2.7 ± 1.0 y). Cox regression analyses suggest that baseline hippocampal volume [relative risk (RR) = 0.99, P = 0.004], baseline right inferior parietal (RR = 0.64, P = 0.01) and right middle frontal (RR = 0.73, P = 0.01) perfusion were associated with conversion to dementia. Results from linear mixed effects modeling suggest that baseline perfusion from the right precuneus predicted subsequent declines in Clinical Dementia Rating Sum of Boxes (P = 0.002), Functional Activates Questionnaire (P = 0.01), and selective attention (ie, Stroop switching, P = 0.009) whereas baseline perfusion from the right middle frontal cortex predicted subsequent episodic memory decline (ie, total recognition discriminability score from the California Verbal Learning Test, P = 0.03). These results suggest that hypoperfusion as detected by ASL-MRI can predict subsequent clinical, functional, and cognitive decline and may be useful for identifying candidates for future Alzheimer disease treatment trials. Keywordsmild cognitive impairment; dementia; cognitive and functional decline; ASL perfusion MRI; hippocampal volume Mild cognitive impairment (MCI) is considered to be the transition between normal aging and Alzheimer disease (AD), the most prevalent dementing disorder in older adults. Studies with fluorodeoxyglucose (FDG) positron emission tomography (PET), which measures glucose metabolism, and technetium-99m hexamethylpropyleneamineoxime single photon emission NIH Public Access Author ManuscriptAlzheimer Dis Assoc Disord. Author manuscript; available in PMC 2010 May 6. Published in final edited form as:Alzheimer 7 ,8 and hippocampus, 6,9-11 are sensitive early markers of progression to AD. Using principal component analysis, Borroni et al 12 described a specific pattern of hypoperfusion in converters that involved the parietal and temporal lobes, precuneus and posterior cingulate cortex. Caroli et al 13 recently reported that compared with control subjects, amnestic MCI who converted to AD had hypoperfusion in the parahippocampal and inferior temporal cortices whereas amnestic MCI patients who did not convert to dementia had hypoperfusion in the retrosplenial cortex.To the extent that regional metabolism and perfusion are coupled, arterial spin-labeling magnetic resonance imaging (ASL-MRI), which labels arterial blood water as an endogenous diffusible tracer for perfusion, may be able to detect functional deficiencies in a way similar to FDG PET and SPECT. 14 In support of this, ASL-MRI studies of AD and...

The effects of age, subcortical vascular disease, apolipoprotein E (APOE) 4 allele and hypertension on entorhinal cortex (ERC) and hippocampal atrophy rates were explored in a longitudinal MRI study with 42 cognitively normal (CN) elderly subjects from 58 to 87 years old. The volumes of the ERC, hippocampus, and white matter hyperintensities (WMH) and the presence of lacunes were assessed on MR images. Age was significantly associated with increased atrophy rates of 0.04 ± 0.02% per year for ERC and 0.05 ± 0.02% per year for hippocampus. Atrophy rates of hippocampus, but not that of ERC increased with presence of lacunes, in addition to age. WMH, APOE 4 and hypertension had no significant effect on atrophy rates. In conclusion, age and presence of lacunes should be taken into consideration in imaging studies of CN subjects and AD patients to predict AD progression and assess the response to treatment trials.